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* [RFC PATCH v2 00/20] fscrypt: key management improvements
@ 2019-02-11 17:27 Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 01/20] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
                   ` (19 more replies)
  0 siblings, 20 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

Hello,

This patchset makes major improvements to how keys are added, removed,
and derived in fscrypt, aka ext4/f2fs/ubifs encryption.  It does this by
adding new ioctls that add and remove encryption keys directly to/from
the filesystem, and by adding a new encryption policy version ("v2")
where the user-provided keys are only used as input to HKDF-SHA512 and
are identified by their cryptographic hash.

All new APIs and all cryptosystem changes are documented in
Documentation/filesystems/fscrypt.rst.  Userspace can use the new key
management ioctls with existing encrypted directories, but migrating to
v2 encryption policies is needed for the full benefits.

These changes solve four interrelated problems:

(1) Providing fscrypt keys via process-subscribed keyrings is abusing
    encryption as an OS-level access control mechanism, causing many
    bugs where processes don't get access to the keys they need -- e.g.,
    when a 'sudo' command or a system service needs to access encrypted
    files.  It's also inconsistent with the filesystem/VFS "view" of
    encrypted files which is global, so sometimes things randomly happen
    to work anyway due to caching.  Regardless, currently almost all
    fscrypt users actually do need global keys, so they're having to use
    workarounds that heavily abuse the session or user keyrings, e.g.
    Android and Chromium OS both use a systemwide "session keyring" and
    the 'fscrypt' tool links all user keyrings into root's user keyring.

(2) Currently there's no way to securely and efficiently remove a
    fscrypt key such that not only is the original key wiped, but also
    all files and directories protected by that key are "locked" and
    their per-file keys wiped.  Many users want this and are using
    'echo 2 > /proc/sys/vm/drop_caches' as a workaround, but this is
    root-only, and also is overkill so can be a performance disaster.

(3) The key derivation function (KDF) that fscrypt uses to derive
    per-file keys is nonstandard, inflexible, and has some weaknesses
    such as being reversible and not evenly distributing the entropy
    from the user-provided keys.

(4) fscrypt doesn't check that the correct key was supplied.  This can
    be a security vulnerability, since it allows malicious local users
    to associate the wrong key with files to which they have read-only
    access, causing other users' processes to read/write the wrong data.

Ultimately, the solutions to these problems all tie into each other.  By
adding a filesystem-level encryption keyring with ioctls to add/remove
keys to/from it, the keys are made usable filesystem-wide (solves
problem #1).  It also becomes easy to track the inodes that were
"unlocked" with each key, so they can be evicted when the key is removed
(solves problem #2).  Moreover, the filesystem-level keyring is a
natural place to store an HMAC transform keyed by each key, thus making
it easy and efficient to switch the KDF to HKDF (solves problem #3).

Finally, to check that the correct key was supplied, I use HKDF to
derive a cryptographically secure key_identifier for each key (solves
problem #4).  This in combination with key quotas and other careful
precautions also makes it safe to allow non-root users to add and remove
keys to/from the filesystem-level keyring.  Thus, all problems are
solved without having to restrict the fscrypt API to root only.

The patchset is organized as follows:

- Patches 1-12 add new ioctls FS_IOC_ADD_ENCRYPTION_KEY,
  FS_IOC_REMOVE_ENCRYPTION_KEY, and FS_IOC_GET_ENCRYPTION_KEY_STATUS.
  Adding a key logically "unlocks" all files on the filesystem that are
  protected by that key; removing a key "locks" them again.

- Patches 13-16 add support for v2 encryption policies.

- Patches 17-19 wire up the new ioctls to ext4, f2fs, and ubifs.

- Patch 20 updates the fscrypt documentation for all the changes.

v1 of this patchset was sent in October 2017 with title "fscrypt:
filesystem-level keyring and v2 policy support".  This revived version
follows the same basic design but incorporates numerous improvements,
such as splitting keyinfo.c into multiple files for much better
understandability, and introducing "per-mode" encryption keys to
implement the semantics of the DIRECT_KEY encryption policy flag.

This applies to the fscrypt.git tree.  You can also get it from git at:

	Repository:   https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git
	Branch:       fscrypt-key-mgmt-improvements-v2

I've started writing xfstests for the new APIs.  So far they cover basic
functionality.  They can be found at:

	Repository:   https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/xfstests-dev.git
	Branch:       fscrypt-key-mgmt-improvements

The xfstests depend on new xfs_io commands which can be found at:

	Repository:   https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/xfsprogs-dev.git
	Branch:       fscrypt-key-mgmt-improvements

I've also made proof-of-concept changes to the 'fscrypt' userspace
program (https://github.com/google/fscrypt) to make it support v2
encryption policies.  You can find these changes in git at:

	Repository:   https://github.com/ebiggers/fscrypt.git
	Branch:       fscrypt-key-mgmt-improvements

To make the 'fscrypt' userspace program experimentally use v2 encryption
policies on new encrypted directories, add the following to
/etc/fscrypt.conf within the "options" section:

	"policy_version": "2"

It's also planned for Android and Chromium OS to switch to the new
ioctls and eventually to v2 encryption policies.  Work-in-progress,
proof-of-concept changes by Satya Tangirala for AOSP can be found at
https://android-review.googlesource.com/q/topic:fscrypt-key-mgmt-improvements

Eric Biggers (20):
  fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h>
  fscrypt: use FSCRYPT_ prefix for uapi constants
  fscrypt: use FSCRYPT_* definitions, not FS_*
  fs: add ->s_master_keys to struct super_block
  fscrypt: add ->ci_inode to fscrypt_info
  fscrypt: refactor v1 policy key setup into keysetup_legacy.c
  fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl
  fs/inode.c: export inode_lru_list_del()
  fs/inode.c: rename and export dispose_list()
  fs/dcache.c: add shrink_dcache_inode()
  fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl
  fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl
  fscrypt: add an HKDF-SHA512 implementation
  fscrypt: v2 encryption policy support
  fscrypt: allow unprivileged users to add/remove keys for v2 policies
  fscrypt: require that key be added when setting a v2 encryption policy
  ext4: wire up new fscrypt ioctls
  f2fs: wire up new fscrypt ioctls
  ubifs: wire up new fscrypt ioctls
  fscrypt: document the new ioctls and policy version

 Documentation/filesystems/fscrypt.rst | 668 ++++++++++++++----
 MAINTAINERS                           |   1 +
 fs/crypto/Kconfig                     |   2 +
 fs/crypto/Makefile                    |  10 +-
 fs/crypto/crypto.c                    |  14 +-
 fs/crypto/fname.c                     |   5 +-
 fs/crypto/fscrypt_private.h           | 357 ++++++++--
 fs/crypto/hkdf.c                      | 188 +++++
 fs/crypto/keyinfo.c                   | 592 ----------------
 fs/crypto/keyring.c                   | 950 ++++++++++++++++++++++++++
 fs/crypto/keysetup.c                  | 504 ++++++++++++++
 fs/crypto/keysetup_legacy.c           | 342 ++++++++++
 fs/crypto/policy.c                    | 388 ++++++++---
 fs/dcache.c                           |  32 +
 fs/ext4/ioctl.c                       |  24 +
 fs/f2fs/file.c                        |  46 ++
 fs/inode.c                            |  22 +-
 fs/super.c                            |   3 +
 fs/ubifs/ioctl.c                      |  24 +-
 include/linux/dcache.h                |   1 +
 include/linux/fs.h                    |   3 +
 include/linux/fscrypt.h               |  37 +-
 include/uapi/linux/fs.h               |  54 +-
 include/uapi/linux/fscrypt.h          | 163 +++++
 24 files changed, 3490 insertions(+), 940 deletions(-)
 create mode 100644 fs/crypto/hkdf.c
 delete mode 100644 fs/crypto/keyinfo.c
 create mode 100644 fs/crypto/keyring.c
 create mode 100644 fs/crypto/keysetup.c
 create mode 100644 fs/crypto/keysetup_legacy.c
 create mode 100644 include/uapi/linux/fscrypt.h

-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 01/20] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h>
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 02/20] fscrypt: use FSCRYPT_ prefix for uapi constants Eric Biggers
                   ` (18 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

More fscrypt definitions are being added, and we shouldn't use a
disproportionate amount of space in <linux/fs.h> for fscrypt stuff.
So move the fscrypt definitions to a new header <linux/fscrypt.h>.

For source compatibility with existing userspace programs, <linux/fs.h>
still includes the new header.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 MAINTAINERS                  |  1 +
 include/linux/fscrypt.h      |  1 +
 include/uapi/linux/fs.h      | 54 ++-------------------------------
 include/uapi/linux/fscrypt.h | 58 ++++++++++++++++++++++++++++++++++++
 4 files changed, 63 insertions(+), 51 deletions(-)
 create mode 100644 include/uapi/linux/fscrypt.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 51029a425dbe..f3c60ca897cc 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6199,6 +6199,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tytso/fscrypt.git
 S:	Supported
 F:	fs/crypto/
 F:	include/linux/fscrypt*.h
+F:	include/uapi/linux/fscrypt.h
 F:	Documentation/filesystems/fscrypt.rst
 
 FSI-ATTACHED I2C DRIVER
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index e5194fc3983e..8b1e44421497 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -16,6 +16,7 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
+#include <uapi/linux/fscrypt.h>
 
 #define FS_CRYPTO_BLOCK_SIZE		16
 
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 121e82ce296b..0f4e66b1bcd0 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -13,6 +13,9 @@
 #include <linux/limits.h>
 #include <linux/ioctl.h>
 #include <linux/types.h>
+#ifndef __KERNEL__
+#include <linux/fscrypt.h>
+#endif
 
 /* Use of MS_* flags within the kernel is restricted to core mount(2) code. */
 #if !defined(__KERNEL__)
@@ -212,57 +215,6 @@ struct fsxattr {
 #define FS_IOC_GETFSLABEL		_IOR(0x94, 49, char[FSLABEL_MAX])
 #define FS_IOC_SETFSLABEL		_IOW(0x94, 50, char[FSLABEL_MAX])
 
-/*
- * File system encryption support
- */
-/* Policy provided via an ioctl on the topmost directory */
-#define FS_KEY_DESCRIPTOR_SIZE	8
-
-#define FS_POLICY_FLAGS_PAD_4		0x00
-#define FS_POLICY_FLAGS_PAD_8		0x01
-#define FS_POLICY_FLAGS_PAD_16		0x02
-#define FS_POLICY_FLAGS_PAD_32		0x03
-#define FS_POLICY_FLAGS_PAD_MASK	0x03
-#define FS_POLICY_FLAG_DIRECT_KEY	0x04	/* use master key directly */
-#define FS_POLICY_FLAGS_VALID		0x07
-
-/* Encryption algorithms */
-#define FS_ENCRYPTION_MODE_INVALID		0
-#define FS_ENCRYPTION_MODE_AES_256_XTS		1
-#define FS_ENCRYPTION_MODE_AES_256_GCM		2
-#define FS_ENCRYPTION_MODE_AES_256_CBC		3
-#define FS_ENCRYPTION_MODE_AES_256_CTS		4
-#define FS_ENCRYPTION_MODE_AES_128_CBC		5
-#define FS_ENCRYPTION_MODE_AES_128_CTS		6
-#define FS_ENCRYPTION_MODE_SPECK128_256_XTS	7 /* Removed, do not use. */
-#define FS_ENCRYPTION_MODE_SPECK128_256_CTS	8 /* Removed, do not use. */
-#define FS_ENCRYPTION_MODE_ADIANTUM		9
-
-struct fscrypt_policy {
-	__u8 version;
-	__u8 contents_encryption_mode;
-	__u8 filenames_encryption_mode;
-	__u8 flags;
-	__u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
-};
-
-#define FS_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct fscrypt_policy)
-#define FS_IOC_GET_ENCRYPTION_PWSALT	_IOW('f', 20, __u8[16])
-#define FS_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct fscrypt_policy)
-
-/* Parameters for passing an encryption key into the kernel keyring */
-#define FS_KEY_DESC_PREFIX		"fscrypt:"
-#define FS_KEY_DESC_PREFIX_SIZE		8
-
-/* Structure that userspace passes to the kernel keyring */
-#define FS_MAX_KEY_SIZE			64
-
-struct fscrypt_key {
-	__u32 mode;
-	__u8 raw[FS_MAX_KEY_SIZE];
-	__u32 size;
-};
-
 /*
  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
  *
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
new file mode 100644
index 000000000000..193339cb53fd
--- /dev/null
+++ b/include/uapi/linux/fscrypt.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_FSCRYPT_H
+#define _UAPI_LINUX_FSCRYPT_H
+
+#include <linux/types.h>
+
+/*
+ * File system encryption support
+ */
+/* Policy provided via an ioctl on the topmost directory */
+#define FS_KEY_DESCRIPTOR_SIZE	8
+
+#define FS_POLICY_FLAGS_PAD_4		0x00
+#define FS_POLICY_FLAGS_PAD_8		0x01
+#define FS_POLICY_FLAGS_PAD_16		0x02
+#define FS_POLICY_FLAGS_PAD_32		0x03
+#define FS_POLICY_FLAGS_PAD_MASK	0x03
+#define FS_POLICY_FLAG_DIRECT_KEY	0x04	/* use master key directly */
+#define FS_POLICY_FLAGS_VALID		0x07
+
+/* Encryption algorithms */
+#define FS_ENCRYPTION_MODE_INVALID		0
+#define FS_ENCRYPTION_MODE_AES_256_XTS		1
+#define FS_ENCRYPTION_MODE_AES_256_GCM		2
+#define FS_ENCRYPTION_MODE_AES_256_CBC		3
+#define FS_ENCRYPTION_MODE_AES_256_CTS		4
+#define FS_ENCRYPTION_MODE_AES_128_CBC		5
+#define FS_ENCRYPTION_MODE_AES_128_CTS		6
+#define FS_ENCRYPTION_MODE_SPECK128_256_XTS	7 /* Removed, do not use. */
+#define FS_ENCRYPTION_MODE_SPECK128_256_CTS	8 /* Removed, do not use. */
+#define FS_ENCRYPTION_MODE_ADIANTUM		9
+
+struct fscrypt_policy {
+	__u8 version;
+	__u8 contents_encryption_mode;
+	__u8 filenames_encryption_mode;
+	__u8 flags;
+	__u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+};
+
+#define FS_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct fscrypt_policy)
+#define FS_IOC_GET_ENCRYPTION_PWSALT	_IOW('f', 20, __u8[16])
+#define FS_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct fscrypt_policy)
+
+/* Parameters for passing an encryption key into the kernel keyring */
+#define FS_KEY_DESC_PREFIX		"fscrypt:"
+#define FS_KEY_DESC_PREFIX_SIZE		8
+
+/* Structure that userspace passes to the kernel keyring */
+#define FS_MAX_KEY_SIZE			64
+
+struct fscrypt_key {
+	__u32 mode;
+	__u8 raw[FS_MAX_KEY_SIZE];
+	__u32 size;
+};
+
+#endif /* _UAPI_LINUX_FSCRYPT_H */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 02/20] fscrypt: use FSCRYPT_ prefix for uapi constants
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 01/20] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 03/20] fscrypt: use FSCRYPT_* definitions, not FS_* Eric Biggers
                   ` (17 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Prefix all filesystem encryption UAPI constants except the ioctl numbers
with "FSCRYPT_" rather than with "FS_".  This namespaces the constants
more appropriately and makes it clear that they are related specifically
to the filesystem encryption feature, and to the 'fscrypt_*' structures.
With some of the old names like "FS_POLICY_FLAGS_VALID", it was not
immediately clear that the constant had anything to do with encryption.

This is also useful because we'll be adding more encryption-related
constants, e.g. for the policy version, and we'd otherwise have to
choose whether to use unclear names like FS_POLICY_V1 or inconsistent
names like FS_ENCRYPTION_POLICY_V1.

For source compatibility with existing userspace programs, keep the old
names defined as aliases to the new names.

Finally, as long as new names are being defined anyway, I skipped
defining new names for the fscrypt mode numbers that aren't actually
used: INVALID (0), AES_256_GCM (2), AES_256_CBC (3), SPECK128_256_XTS
(7), and SPECK128_256_CTS (8).

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/filesystems/fscrypt.rst | 36 +++++++--------
 include/uapi/linux/fscrypt.h          | 66 +++++++++++++++++----------
 2 files changed, 61 insertions(+), 41 deletions(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 08c23b60e016..4f9df6ba669e 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -223,9 +223,10 @@ a little endian number, except that:
   is encrypted with AES-256 where the AES-256 key is the SHA-256 hash
   of the file's data encryption key.
 
-- In the "direct key" configuration (FS_POLICY_FLAG_DIRECT_KEY set in
-  the fscrypt_policy), the file's nonce is also appended to the IV.
-  Currently this is only allowed with the Adiantum encryption mode.
+- In the "direct key" configuration (FSCRYPT_POLICY_FLAG_DIRECT_KEY
+  set in the fscrypt_policy), the file's nonce is also appended to the
+  IV.  Currently this is only allowed with the Adiantum encryption
+  mode.
 
 Filenames encryption
 --------------------
@@ -272,14 +273,14 @@ empty directory or verifies that a directory or regular file already
 has the specified encryption policy.  It takes in a pointer to a
 :c:type:`struct fscrypt_policy`, defined as follows::
 
-    #define FS_KEY_DESCRIPTOR_SIZE  8
+    #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
 
     struct fscrypt_policy {
             __u8 version;
             __u8 contents_encryption_mode;
             __u8 filenames_encryption_mode;
             __u8 flags;
-            __u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+            __u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
     };
 
 This structure must be initialized as follows:
@@ -288,18 +289,17 @@ This structure must be initialized as follows:
 
 - ``contents_encryption_mode`` and ``filenames_encryption_mode`` must
   be set to constants from ``<linux/fs.h>`` which identify the
-  encryption modes to use.  If unsure, use
-  FS_ENCRYPTION_MODE_AES_256_XTS (1) for ``contents_encryption_mode``
-  and FS_ENCRYPTION_MODE_AES_256_CTS (4) for
-  ``filenames_encryption_mode``.
+  encryption modes to use.  If unsure, use FSCRYPT_MODE_AES_256_XTS
+  (1) for ``contents_encryption_mode`` and FSCRYPT_MODE_AES_256_CTS
+  (4) for ``filenames_encryption_mode``.
 
 - ``flags`` must contain a value from ``<linux/fs.h>`` which
   identifies the amount of NUL-padding to use when encrypting
-  filenames.  If unsure, use FS_POLICY_FLAGS_PAD_32 (0x3).
-  In addition, if the chosen encryption modes are both
-  FS_ENCRYPTION_MODE_ADIANTUM, this can contain
-  FS_POLICY_FLAG_DIRECT_KEY to specify that the master key should be
-  used directly, without key derivation.
+  filenames.  If unsure, use FSCRYPT_POLICY_FLAGS_PAD_32 (0x3).  In
+  addition, if the chosen encryption modes are both
+  FSCRYPT_MODE_ADIANTUM, this can contain
+  FSCRYPT_POLICY_FLAG_DIRECT_KEY to specify that the master key should
+  be used directly, without key derivation.
 
 - ``master_key_descriptor`` specifies how to find the master key in
   the keyring; see `Adding keys`_.  It is up to userspace to choose a
@@ -399,11 +399,11 @@ followed by the 16-character lower case hex representation of the
 ``master_key_descriptor`` that was set in the encryption policy.  The
 key payload must conform to the following structure::
 
-    #define FS_MAX_KEY_SIZE 64
+    #define FSCRYPT_MAX_KEY_SIZE 64
 
     struct fscrypt_key {
             u32 mode;
-            u8 raw[FS_MAX_KEY_SIZE];
+            u8 raw[FSCRYPT_MAX_KEY_SIZE];
             u32 size;
     };
 
@@ -572,7 +572,7 @@ much confusion if an encryption policy were to be added to or removed
 from anything other than an empty directory.)  The struct is defined
 as follows::
 
-    #define FS_KEY_DESCRIPTOR_SIZE  8
+    #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
     #define FS_KEY_DERIVATION_NONCE_SIZE 16
 
     struct fscrypt_context {
@@ -580,7 +580,7 @@ as follows::
             u8 contents_encryption_mode;
             u8 filenames_encryption_mode;
             u8 flags;
-            u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+            u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
             u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
     };
 
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 193339cb53fd..f9b99cc028bc 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -8,34 +8,30 @@
  * File system encryption support
  */
 /* Policy provided via an ioctl on the topmost directory */
-#define FS_KEY_DESCRIPTOR_SIZE	8
+#define FSCRYPT_KEY_DESCRIPTOR_SIZE	8
 
-#define FS_POLICY_FLAGS_PAD_4		0x00
-#define FS_POLICY_FLAGS_PAD_8		0x01
-#define FS_POLICY_FLAGS_PAD_16		0x02
-#define FS_POLICY_FLAGS_PAD_32		0x03
-#define FS_POLICY_FLAGS_PAD_MASK	0x03
-#define FS_POLICY_FLAG_DIRECT_KEY	0x04	/* use master key directly */
-#define FS_POLICY_FLAGS_VALID		0x07
+/* Encryption policy flags */
+#define FSCRYPT_POLICY_FLAGS_PAD_4		0x00
+#define FSCRYPT_POLICY_FLAGS_PAD_8		0x01
+#define FSCRYPT_POLICY_FLAGS_PAD_16		0x02
+#define FSCRYPT_POLICY_FLAGS_PAD_32		0x03
+#define FSCRYPT_POLICY_FLAGS_PAD_MASK		0x03
+#define FSCRYPT_POLICY_FLAG_DIRECT_KEY		0x04	/* use master key directly */
+#define FSCRYPT_POLICY_FLAGS_VALID		0x07
 
 /* Encryption algorithms */
-#define FS_ENCRYPTION_MODE_INVALID		0
-#define FS_ENCRYPTION_MODE_AES_256_XTS		1
-#define FS_ENCRYPTION_MODE_AES_256_GCM		2
-#define FS_ENCRYPTION_MODE_AES_256_CBC		3
-#define FS_ENCRYPTION_MODE_AES_256_CTS		4
-#define FS_ENCRYPTION_MODE_AES_128_CBC		5
-#define FS_ENCRYPTION_MODE_AES_128_CTS		6
-#define FS_ENCRYPTION_MODE_SPECK128_256_XTS	7 /* Removed, do not use. */
-#define FS_ENCRYPTION_MODE_SPECK128_256_CTS	8 /* Removed, do not use. */
-#define FS_ENCRYPTION_MODE_ADIANTUM		9
+#define FSCRYPT_MODE_AES_256_XTS		1
+#define FSCRYPT_MODE_AES_256_CTS		4
+#define FSCRYPT_MODE_AES_128_CBC		5
+#define FSCRYPT_MODE_AES_128_CTS		6
+#define FSCRYPT_MODE_ADIANTUM			9
 
 struct fscrypt_policy {
 	__u8 version;
 	__u8 contents_encryption_mode;
 	__u8 filenames_encryption_mode;
 	__u8 flags;
-	__u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+	__u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 };
 
 #define FS_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct fscrypt_policy)
@@ -43,16 +39,40 @@ struct fscrypt_policy {
 #define FS_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct fscrypt_policy)
 
 /* Parameters for passing an encryption key into the kernel keyring */
-#define FS_KEY_DESC_PREFIX		"fscrypt:"
-#define FS_KEY_DESC_PREFIX_SIZE		8
+#define FSCRYPT_KEY_DESC_PREFIX		"fscrypt:"
+#define FSCRYPT_KEY_DESC_PREFIX_SIZE		8
 
 /* Structure that userspace passes to the kernel keyring */
-#define FS_MAX_KEY_SIZE			64
+#define FSCRYPT_MAX_KEY_SIZE			64
 
 struct fscrypt_key {
 	__u32 mode;
-	__u8 raw[FS_MAX_KEY_SIZE];
+	__u8 raw[FSCRYPT_MAX_KEY_SIZE];
 	__u32 size;
 };
+/**********************************************************************/
+
+/* old names; don't add anything new here! */
+#define FS_KEY_DESCRIPTOR_SIZE		FSCRYPT_KEY_DESCRIPTOR_SIZE
+#define FS_POLICY_FLAGS_PAD_4		FSCRYPT_POLICY_FLAGS_PAD_4
+#define FS_POLICY_FLAGS_PAD_8		FSCRYPT_POLICY_FLAGS_PAD_8
+#define FS_POLICY_FLAGS_PAD_16		FSCRYPT_POLICY_FLAGS_PAD_16
+#define FS_POLICY_FLAGS_PAD_32		FSCRYPT_POLICY_FLAGS_PAD_32
+#define FS_POLICY_FLAGS_PAD_MASK	FSCRYPT_POLICY_FLAGS_PAD_MASK
+#define FS_POLICY_FLAG_DIRECT_KEY	FSCRYPT_POLICY_FLAG_DIRECT_KEY
+#define FS_POLICY_FLAGS_VALID		FSCRYPT_POLICY_FLAGS_VALID
+#define FS_ENCRYPTION_MODE_INVALID	0	/* never used */
+#define FS_ENCRYPTION_MODE_AES_256_XTS	FSCRYPT_MODE_AES_256_XTS
+#define FS_ENCRYPTION_MODE_AES_256_GCM	2	/* never used */
+#define FS_ENCRYPTION_MODE_AES_256_CBC	3	/* never used */
+#define FS_ENCRYPTION_MODE_AES_256_CTS	FSCRYPT_MODE_AES_256_CTS
+#define FS_ENCRYPTION_MODE_AES_128_CBC	FSCRYPT_MODE_AES_128_CBC
+#define FS_ENCRYPTION_MODE_AES_128_CTS	FSCRYPT_MODE_AES_128_CTS
+#define FS_ENCRYPTION_MODE_SPECK128_256_XTS	7	/* removed */
+#define FS_ENCRYPTION_MODE_SPECK128_256_CTS	8	/* removed */
+#define FS_ENCRYPTION_MODE_ADIANTUM	FSCRYPT_MODE_ADIANTUM
+#define FS_KEY_DESC_PREFIX		FSCRYPT_KEY_DESC_PREFIX
+#define FS_KEY_DESC_PREFIX_SIZE		FSCRYPT_KEY_DESC_PREFIX_SIZE
+#define FS_MAX_KEY_SIZE			FSCRYPT_MAX_KEY_SIZE
 
 #endif /* _UAPI_LINUX_FSCRYPT_H */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 03/20] fscrypt: use FSCRYPT_* definitions, not FS_*
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 01/20] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 02/20] fscrypt: use FSCRYPT_ prefix for uapi constants Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 04/20] fs: add ->s_master_keys to struct super_block Eric Biggers
                   ` (16 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Update fs/crypto/ to use the new names for the UAPI constants rather
than the old names, then make the old definitions conditional on
!__KERNEL__.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/crypto.c           |  2 +-
 fs/crypto/fname.c            |  2 +-
 fs/crypto/fscrypt_private.h  | 16 +++++------
 fs/crypto/keyinfo.c          | 53 ++++++++++++++++++------------------
 fs/crypto/policy.c           | 14 +++++-----
 include/uapi/linux/fscrypt.h |  2 ++
 6 files changed, 46 insertions(+), 43 deletions(-)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 4dc788e3bc96..8217a4434621 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -139,7 +139,7 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 	memset(iv, 0, ci->ci_mode->ivsize);
 	iv->lblk_num = cpu_to_le64(lblk_num);
 
-	if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY)
+	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
 		memcpy(iv->nonce, ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 
 	if (ci->ci_essiv_tfm != NULL)
diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 7ff40a73dbec..37c26ad36d0e 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -187,7 +187,7 @@ bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 				  u32 max_len, u32 *encrypted_len_ret)
 {
 	int padding = 4 << (inode->i_crypt_info->ci_flags &
-			    FS_POLICY_FLAGS_PAD_MASK);
+			    FSCRYPT_POLICY_FLAGS_PAD_MASK);
 	u32 encrypted_len;
 
 	if (orig_len > max_len)
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 7da276159593..52e09ef40bfa 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -34,7 +34,7 @@ struct fscrypt_context {
 	u8 contents_encryption_mode;
 	u8 filenames_encryption_mode;
 	u8 flags;
-	u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+	u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 	u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 } __packed;
 
@@ -84,7 +84,7 @@ struct fscrypt_info {
 	u8 ci_data_mode;
 	u8 ci_filename_mode;
 	u8 ci_flags;
-	u8 ci_master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+	u8 ci_master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 	u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 };
 
@@ -99,16 +99,16 @@ typedef enum {
 static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
 					   u32 filenames_mode)
 {
-	if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC &&
-	    filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS)
+	if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
+	    filenames_mode == FSCRYPT_MODE_AES_128_CTS)
 		return true;
 
-	if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS &&
-	    filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)
+	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
+	    filenames_mode == FSCRYPT_MODE_AES_256_CTS)
 		return true;
 
-	if (contents_mode == FS_ENCRYPTION_MODE_ADIANTUM &&
-	    filenames_mode == FS_ENCRYPTION_MODE_ADIANTUM)
+	if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
+	    filenames_mode == FSCRYPT_MODE_ADIANTUM)
 		return true;
 
 	return false;
diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
index 1e11a683f63d..a8c1e886b0bc 100644
--- a/fs/crypto/keyinfo.c
+++ b/fs/crypto/keyinfo.c
@@ -21,7 +21,7 @@
 
 static struct crypto_shash *essiv_hash_tfm;
 
-/* Table of keys referenced by FS_POLICY_FLAG_DIRECT_KEY policies */
+/* Table of keys referenced by DIRECT_KEY policies */
 static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */
 static DEFINE_SPINLOCK(fscrypt_master_keys_lock);
 
@@ -78,7 +78,7 @@ static int derive_key_aes(const u8 *master_key,
  */
 static struct key *
 find_and_lock_process_key(const char *prefix,
-			  const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE],
+			  const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
 			  unsigned int min_keysize,
 			  const struct fscrypt_key **payload_ret)
 {
@@ -88,7 +88,7 @@ find_and_lock_process_key(const char *prefix,
 	const struct fscrypt_key *payload;
 
 	description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
-				FS_KEY_DESCRIPTOR_SIZE, descriptor);
+				FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
 	if (!description)
 		return ERR_PTR(-ENOMEM);
 
@@ -106,7 +106,7 @@ find_and_lock_process_key(const char *prefix,
 	payload = (const struct fscrypt_key *)ukp->data;
 
 	if (ukp->datalen != sizeof(struct fscrypt_key) ||
-	    payload->size < 1 || payload->size > FS_MAX_KEY_SIZE) {
+	    payload->size < 1 || payload->size > FSCRYPT_MAX_KEY_SIZE) {
 		fscrypt_warn(NULL,
 			     "key with description '%s' has invalid payload",
 			     key->description);
@@ -130,32 +130,32 @@ find_and_lock_process_key(const char *prefix,
 }
 
 static struct fscrypt_mode available_modes[] = {
-	[FS_ENCRYPTION_MODE_AES_256_XTS] = {
+	[FSCRYPT_MODE_AES_256_XTS] = {
 		.friendly_name = "AES-256-XTS",
 		.cipher_str = "xts(aes)",
 		.keysize = 64,
 		.ivsize = 16,
 	},
-	[FS_ENCRYPTION_MODE_AES_256_CTS] = {
+	[FSCRYPT_MODE_AES_256_CTS] = {
 		.friendly_name = "AES-256-CTS-CBC",
 		.cipher_str = "cts(cbc(aes))",
 		.keysize = 32,
 		.ivsize = 16,
 	},
-	[FS_ENCRYPTION_MODE_AES_128_CBC] = {
+	[FSCRYPT_MODE_AES_128_CBC] = {
 		.friendly_name = "AES-128-CBC",
 		.cipher_str = "cbc(aes)",
 		.keysize = 16,
 		.ivsize = 16,
 		.needs_essiv = true,
 	},
-	[FS_ENCRYPTION_MODE_AES_128_CTS] = {
+	[FSCRYPT_MODE_AES_128_CTS] = {
 		.friendly_name = "AES-128-CTS-CBC",
 		.cipher_str = "cts(cbc(aes))",
 		.keysize = 16,
 		.ivsize = 16,
 	},
-	[FS_ENCRYPTION_MODE_ADIANTUM] = {
+	[FSCRYPT_MODE_ADIANTUM] = {
 		.friendly_name = "Adiantum",
 		.cipher_str = "adiantum(xchacha12,aes)",
 		.keysize = 32,
@@ -194,7 +194,7 @@ static int find_and_derive_key(const struct inode *inode,
 	const struct fscrypt_key *payload;
 	int err;
 
-	key = find_and_lock_process_key(FS_KEY_DESC_PREFIX,
+	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
 					ctx->master_key_descriptor,
 					mode->keysize, &payload);
 	if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
@@ -205,7 +205,7 @@ static int find_and_derive_key(const struct inode *inode,
 	if (IS_ERR(key))
 		return PTR_ERR(key);
 
-	if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) {
+	if (ctx->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
 		if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
 			fscrypt_warn(inode->i_sb,
 				     "direct key mode not allowed with %s",
@@ -269,14 +269,14 @@ allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
 	return ERR_PTR(err);
 }
 
-/* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */
+/* Master key referenced by DIRECT_KEY policy */
 struct fscrypt_master_key {
 	struct hlist_node mk_node;
 	refcount_t mk_refcount;
 	const struct fscrypt_mode *mk_mode;
 	struct crypto_skcipher *mk_ctfm;
-	u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE];
-	u8 mk_raw[FS_MAX_KEY_SIZE];
+	u8 mk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+	u8 mk_raw[FSCRYPT_MAX_KEY_SIZE];
 };
 
 static void free_master_key(struct fscrypt_master_key *mk)
@@ -317,13 +317,13 @@ find_or_insert_master_key(struct fscrypt_master_key *to_insert,
 	 * raw key, and use crypto_memneq() when comparing raw keys.
 	 */
 
-	BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE);
+	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
 
 	spin_lock(&fscrypt_master_keys_lock);
 	hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
 		if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
-			   FS_KEY_DESCRIPTOR_SIZE) != 0)
+			   FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
 			continue;
 		if (mode != mk->mk_mode)
 			continue;
@@ -367,7 +367,7 @@ fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
 		goto err_free_mk;
 	}
 	memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
-	       FS_KEY_DESCRIPTOR_SIZE);
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(mk->mk_raw, raw_key, mode->keysize);
 
 	return find_or_insert_master_key(mk, raw_key, mode, ci);
@@ -446,8 +446,8 @@ void __exit fscrypt_essiv_cleanup(void)
 
 /*
  * Given the encryption mode and key (normally the derived key, but for
- * FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's
- * symmetric cipher transform object(s).
+ * DIRECT_KEY mode it's the master key), set up the inode's symmetric cipher
+ * transform object(s).
  */
 static int setup_crypto_transform(struct fscrypt_info *ci,
 				  struct fscrypt_mode *mode,
@@ -457,7 +457,7 @@ static int setup_crypto_transform(struct fscrypt_info *ci,
 	struct crypto_skcipher *ctfm;
 	int err;
 
-	if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) {
+	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
 		mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
 		if (IS_ERR(mk))
 			return PTR_ERR(mk);
@@ -474,7 +474,7 @@ static int setup_crypto_transform(struct fscrypt_info *ci,
 	if (mode->needs_essiv) {
 		/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
 		WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
-		WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY);
+		WARN_ON(ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
 
 		err = init_essiv_generator(ci, raw_key, mode->keysize);
 		if (err) {
@@ -524,9 +524,10 @@ int fscrypt_get_encryption_info(struct inode *inode)
 		/* Fake up a context for an unencrypted directory */
 		memset(&ctx, 0, sizeof(ctx));
 		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
-		ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
-		ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
-		memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
+		ctx.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
+		ctx.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
+		memset(ctx.master_key_descriptor, 0x42,
+		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	} else if (res != sizeof(ctx)) {
 		return -EINVAL;
 	}
@@ -534,7 +535,7 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 		return -EINVAL;
 
-	if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
+	if (ctx.flags & ~FSCRYPT_POLICY_FLAGS_VALID)
 		return -EINVAL;
 
 	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
@@ -545,7 +546,7 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 	memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
-	       FS_KEY_DESCRIPTOR_SIZE);
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 
 	mode = select_encryption_mode(crypt_info, inode);
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index bd7eaf9b3f00..1e0563cea1a5 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -22,7 +22,7 @@ static bool is_encryption_context_consistent_with_policy(
 				const struct fscrypt_policy *policy)
 {
 	return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
-		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
+		      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
 		(ctx->flags == policy->flags) &&
 		(ctx->contents_encryption_mode ==
 		 policy->contents_encryption_mode) &&
@@ -37,13 +37,13 @@ static int create_encryption_context_from_policy(struct inode *inode,
 
 	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
-					FS_KEY_DESCRIPTOR_SIZE);
+					FSCRYPT_KEY_DESCRIPTOR_SIZE);
 
 	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
 				     policy->filenames_encryption_mode))
 		return -EINVAL;
 
-	if (policy->flags & ~FS_POLICY_FLAGS_VALID)
+	if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID)
 		return -EINVAL;
 
 	ctx.contents_encryption_mode = policy->contents_encryption_mode;
@@ -126,7 +126,7 @@ int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 	policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
 	policy.flags = ctx.flags;
 	memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
-				FS_KEY_DESCRIPTOR_SIZE);
+				FSCRYPT_KEY_DESCRIPTOR_SIZE);
 
 	if (copy_to_user(arg, &policy, sizeof(policy)))
 		return -EFAULT;
@@ -200,7 +200,7 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 	if (parent_ci && child_ci) {
 		return memcmp(parent_ci->ci_master_key_descriptor,
 			      child_ci->ci_master_key_descriptor,
-			      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
+			      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
 			(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 			(parent_ci->ci_filename_mode ==
 			 child_ci->ci_filename_mode) &&
@@ -217,7 +217,7 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 
 	return memcmp(parent_ctx.master_key_descriptor,
 		      child_ctx.master_key_descriptor,
-		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
+		      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
 		(parent_ctx.contents_encryption_mode ==
 		 child_ctx.contents_encryption_mode) &&
 		(parent_ctx.filenames_encryption_mode ==
@@ -255,7 +255,7 @@ int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 	ctx.filenames_encryption_mode = ci->ci_filename_mode;
 	ctx.flags = ci->ci_flags;
 	memcpy(ctx.master_key_descriptor, ci->ci_master_key_descriptor,
-	       FS_KEY_DESCRIPTOR_SIZE);
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
 	res = parent->i_sb->s_cop->set_context(child, &ctx,
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index f9b99cc028bc..3bbc5dfbde21 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -53,6 +53,7 @@ struct fscrypt_key {
 /**********************************************************************/
 
 /* old names; don't add anything new here! */
+#ifndef __KERNEL__
 #define FS_KEY_DESCRIPTOR_SIZE		FSCRYPT_KEY_DESCRIPTOR_SIZE
 #define FS_POLICY_FLAGS_PAD_4		FSCRYPT_POLICY_FLAGS_PAD_4
 #define FS_POLICY_FLAGS_PAD_8		FSCRYPT_POLICY_FLAGS_PAD_8
@@ -74,5 +75,6 @@ struct fscrypt_key {
 #define FS_KEY_DESC_PREFIX		FSCRYPT_KEY_DESC_PREFIX
 #define FS_KEY_DESC_PREFIX_SIZE		FSCRYPT_KEY_DESC_PREFIX_SIZE
 #define FS_MAX_KEY_SIZE			FSCRYPT_MAX_KEY_SIZE
+#endif /* !__KERNEL__ */
 
 #endif /* _UAPI_LINUX_FSCRYPT_H */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 04/20] fs: add ->s_master_keys to struct super_block
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (2 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 03/20] fscrypt: use FSCRYPT_* definitions, not FS_* Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 05/20] fscrypt: add ->ci_inode to fscrypt_info Eric Biggers
                   ` (15 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add an ->s_master_keys keyring to 'struct super_block'.  New fscrypt
ioctls will allow adding and removing encryption keys from this keyring.
This will enable solving multiple interrelated problems with how fscrypt
keys are provided and managed currently, including:

- Making the key status (which is currently per-process) match the
  filesystem-level status of which encrypted files are "unlocked".

- Supporting a proper API to remove encryption keys, "locking" the
  corresponding encrypted files.

- Caching an HMAC transform for each master key, allowing the use of
  HKDF while still retaining good performance.

- Preventing denial of service via keyctl_invalidate().

Similar to the existing ->s_cop, the keyring is added to the VFS-level
superblock struct rather than separately to the ext4, f2fs, and ubifs
superblock structs so that it can be used by the shared code in
fs/crypto/.  To minimize overhead, the keyring will only be allocated if
userspace actually adds a key; otherwise will stay NULL.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/super.c         | 3 +++
 include/linux/fs.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 48e25eba8465..7ca05dda905c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -291,6 +291,9 @@ static void __put_super(struct super_block *s)
 		security_sb_free(s);
 		put_user_ns(s->s_user_ns);
 		kfree(s->s_subtype);
+#ifdef CONFIG_FS_ENCRYPTION
+		key_put(s->s_master_keys);
+#endif
 		call_rcu(&s->rcu, destroy_super_rcu);
 	}
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ba7889bb9ef6..70d929ac89f9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1405,6 +1405,7 @@ struct super_block {
 	const struct xattr_handler **s_xattr;
 #ifdef CONFIG_FS_ENCRYPTION
 	const struct fscrypt_operations	*s_cop;
+	struct key		*s_master_keys; /* master crypto keys in use */
 #endif
 	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 05/20] fscrypt: add ->ci_inode to fscrypt_info
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (3 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 04/20] fs: add ->s_master_keys to struct super_block Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 06/20] fscrypt: refactor v1 policy key setup into keysetup_legacy.c Eric Biggers
                   ` (14 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add an inode back-pointer to 'struct fscrypt_info', such that
inode->i_crypt_info->ci_inode == inode.

This will be useful for:

1. Evicting the inodes when a fscrypt key is removed, since we'll track
   the inodes using a given key by linking their fscrypt_infos together,
   rather than the inodes directly.  This avoids bloating 'struct inode'
   with a new list_head.

2. Simplifying the per-file key setup, since the inode pointer won't
   have to be passed around everywhere just in case something goes wrong
   and it's needed for fscrypt_warn().

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h | 3 +++
 fs/crypto/keyinfo.c         | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 52e09ef40bfa..ac24edfc297f 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -73,6 +73,9 @@ struct fscrypt_info {
 	 */
 	struct fscrypt_mode *ci_mode;
 
+	/* Back-pointer to the inode */
+	struct inode *ci_inode;
+
 	/*
 	 * If non-NULL, then this inode uses a master key directly rather than a
 	 * derived key, and ci_ctfm will equal ci_master_key->mk_ctfm.
diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
index a8c1e886b0bc..6c1e675d4eef 100644
--- a/fs/crypto/keyinfo.c
+++ b/fs/crypto/keyinfo.c
@@ -542,6 +542,8 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	if (!crypt_info)
 		return -ENOMEM;
 
+	crypt_info->ci_inode = inode;
+
 	crypt_info->ci_flags = ctx.flags;
 	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 06/20] fscrypt: refactor v1 policy key setup into keysetup_legacy.c
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (4 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 05/20] fscrypt: add ->ci_inode to fscrypt_info Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 07/20] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl Eric Biggers
                   ` (13 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

In preparation for introducing v2 encryption policies which will find
and derive encryption keys differently from the current v1 encryption
policies, refactor the v1 policy-specific key setup code from keyinfo.c
into keysetup_legacy.c.  Then rename keyinfo.c to keysetup.c.

Note: the code moved into keysetup_legacy.c includes the table of master
keys referenced by v1 DIRECT_KEY policies.  I've chosen to keep this
table as-is rather than trying to replace it with using the
filesystem-level keyring, since the latter would add more complexity
than it would save especially given the requirement to continue to
support the keys actually being provided in a process-subscribed
keyring.  However, to distinguish the structures in this table from the
structures that will go in the filesystem-level keyring, I renamed them
from 'struct fscrypt_master_key' to 'struct fscrypt_direct_key'.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/Makefile          |   8 +-
 fs/crypto/fscrypt_private.h |  37 ++-
 fs/crypto/keyinfo.c         | 595 ------------------------------------
 fs/crypto/keysetup.c        | 309 +++++++++++++++++++
 fs/crypto/keysetup_legacy.c | 340 +++++++++++++++++++++
 include/linux/fscrypt.h     |   4 +-
 6 files changed, 687 insertions(+), 606 deletions(-)
 delete mode 100644 fs/crypto/keyinfo.c
 create mode 100644 fs/crypto/keysetup.c
 create mode 100644 fs/crypto/keysetup_legacy.c

diff --git a/fs/crypto/Makefile b/fs/crypto/Makefile
index cb496989a6b6..75c0c29fcc62 100644
--- a/fs/crypto/Makefile
+++ b/fs/crypto/Makefile
@@ -1,4 +1,10 @@
 obj-$(CONFIG_FS_ENCRYPTION)	+= fscrypto.o
 
-fscrypto-y := crypto.o fname.o hooks.o keyinfo.o policy.o
+fscrypto-y := crypto.o \
+	      fname.o \
+	      hooks.o \
+	      keysetup.o \
+	      keysetup_legacy.o \
+	      policy.o
+
 fscrypto-$(CONFIG_BLOCK) += bio.o
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index ac24edfc297f..c5a8181fc26c 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -4,9 +4,8 @@
  *
  * Copyright (C) 2015, Google, Inc.
  *
- * This contains encryption key functions.
- *
- * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
+ * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
+ * Heavily modified since then.
  */
 
 #ifndef _FSCRYPT_PRIVATE_H
@@ -77,11 +76,10 @@ struct fscrypt_info {
 	struct inode *ci_inode;
 
 	/*
-	 * If non-NULL, then this inode uses a master key directly rather than a
-	 * derived key, and ci_ctfm will equal ci_master_key->mk_ctfm.
-	 * Otherwise, this inode uses a derived key.
+	 * If non-NULL, then encryption is done using the master key directly
+	 * and ci_ctfm will equal ci_direct_key->dk_ctfm.
 	 */
-	struct fscrypt_master_key *ci_master_key;
+	struct fscrypt_direct_key *ci_direct_key;
 
 	/* fields from the fscrypt_context */
 	u8 ci_data_mode;
@@ -161,7 +159,7 @@ extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
 					 u32 orig_len, u32 max_len,
 					 u32 *encrypted_len_ret);
 
-/* keyinfo.c */
+/* keysetup.c */
 
 struct fscrypt_mode {
 	const char *friendly_name;
@@ -172,6 +170,29 @@ struct fscrypt_mode {
 	bool needs_essiv;
 };
 
+static inline bool
+fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
+{
+	return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
+}
+
+extern struct crypto_skcipher *
+fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
+			  const struct inode *inode);
+
+extern int fscrypt_set_derived_key(struct fscrypt_info *ci,
+				   const u8 *derived_key);
+
 extern void __exit fscrypt_essiv_cleanup(void);
 
+/* keysetup_legacy.c */
+
+extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
+
+extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
+				     const u8 *raw_master_key);
+
+extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
+					struct fscrypt_info *ci);
+
 #endif /* _FSCRYPT_PRIVATE_H */
diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
deleted file mode 100644
index 6c1e675d4eef..000000000000
--- a/fs/crypto/keyinfo.c
+++ /dev/null
@@ -1,595 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * key management facility for FS encryption support.
- *
- * Copyright (C) 2015, Google, Inc.
- *
- * This contains encryption key functions.
- *
- * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
- */
-
-#include <keys/user-type.h>
-#include <linux/hashtable.h>
-#include <linux/scatterlist.h>
-#include <linux/ratelimit.h>
-#include <crypto/aes.h>
-#include <crypto/algapi.h>
-#include <crypto/sha.h>
-#include <crypto/skcipher.h>
-#include "fscrypt_private.h"
-
-static struct crypto_shash *essiv_hash_tfm;
-
-/* Table of keys referenced by DIRECT_KEY policies */
-static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */
-static DEFINE_SPINLOCK(fscrypt_master_keys_lock);
-
-/*
- * Key derivation function.  This generates the derived key by encrypting the
- * master key with AES-128-ECB using the inode's nonce as the AES key.
- *
- * The master key must be at least as long as the derived key.  If the master
- * key is longer, then only the first 'derived_keysize' bytes are used.
- */
-static int derive_key_aes(const u8 *master_key,
-			  const struct fscrypt_context *ctx,
-			  u8 *derived_key, unsigned int derived_keysize)
-{
-	int res = 0;
-	struct skcipher_request *req = NULL;
-	DECLARE_CRYPTO_WAIT(wait);
-	struct scatterlist src_sg, dst_sg;
-	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
-
-	if (IS_ERR(tfm)) {
-		res = PTR_ERR(tfm);
-		tfm = NULL;
-		goto out;
-	}
-	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
-	req = skcipher_request_alloc(tfm, GFP_NOFS);
-	if (!req) {
-		res = -ENOMEM;
-		goto out;
-	}
-	skcipher_request_set_callback(req,
-			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
-			crypto_req_done, &wait);
-	res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
-	if (res < 0)
-		goto out;
-
-	sg_init_one(&src_sg, master_key, derived_keysize);
-	sg_init_one(&dst_sg, derived_key, derived_keysize);
-	skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize,
-				   NULL);
-	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
-out:
-	skcipher_request_free(req);
-	crypto_free_skcipher(tfm);
-	return res;
-}
-
-/*
- * Search the current task's subscribed keyrings for a "logon" key with
- * description prefix:descriptor, and if found acquire a read lock on it and
- * return a pointer to its validated payload in *payload_ret.
- */
-static struct key *
-find_and_lock_process_key(const char *prefix,
-			  const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
-			  unsigned int min_keysize,
-			  const struct fscrypt_key **payload_ret)
-{
-	char *description;
-	struct key *key;
-	const struct user_key_payload *ukp;
-	const struct fscrypt_key *payload;
-
-	description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
-				FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
-	if (!description)
-		return ERR_PTR(-ENOMEM);
-
-	key = request_key(&key_type_logon, description, NULL);
-	kfree(description);
-	if (IS_ERR(key))
-		return key;
-
-	down_read(&key->sem);
-	ukp = user_key_payload_locked(key);
-
-	if (!ukp) /* was the key revoked before we acquired its semaphore? */
-		goto invalid;
-
-	payload = (const struct fscrypt_key *)ukp->data;
-
-	if (ukp->datalen != sizeof(struct fscrypt_key) ||
-	    payload->size < 1 || payload->size > FSCRYPT_MAX_KEY_SIZE) {
-		fscrypt_warn(NULL,
-			     "key with description '%s' has invalid payload",
-			     key->description);
-		goto invalid;
-	}
-
-	if (payload->size < min_keysize) {
-		fscrypt_warn(NULL,
-			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
-			     key->description, payload->size, min_keysize);
-		goto invalid;
-	}
-
-	*payload_ret = payload;
-	return key;
-
-invalid:
-	up_read(&key->sem);
-	key_put(key);
-	return ERR_PTR(-ENOKEY);
-}
-
-static struct fscrypt_mode available_modes[] = {
-	[FSCRYPT_MODE_AES_256_XTS] = {
-		.friendly_name = "AES-256-XTS",
-		.cipher_str = "xts(aes)",
-		.keysize = 64,
-		.ivsize = 16,
-	},
-	[FSCRYPT_MODE_AES_256_CTS] = {
-		.friendly_name = "AES-256-CTS-CBC",
-		.cipher_str = "cts(cbc(aes))",
-		.keysize = 32,
-		.ivsize = 16,
-	},
-	[FSCRYPT_MODE_AES_128_CBC] = {
-		.friendly_name = "AES-128-CBC",
-		.cipher_str = "cbc(aes)",
-		.keysize = 16,
-		.ivsize = 16,
-		.needs_essiv = true,
-	},
-	[FSCRYPT_MODE_AES_128_CTS] = {
-		.friendly_name = "AES-128-CTS-CBC",
-		.cipher_str = "cts(cbc(aes))",
-		.keysize = 16,
-		.ivsize = 16,
-	},
-	[FSCRYPT_MODE_ADIANTUM] = {
-		.friendly_name = "Adiantum",
-		.cipher_str = "adiantum(xchacha12,aes)",
-		.keysize = 32,
-		.ivsize = 32,
-	},
-};
-
-static struct fscrypt_mode *
-select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
-{
-	if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
-		fscrypt_warn(inode->i_sb,
-			     "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
-			     inode->i_ino, ci->ci_data_mode,
-			     ci->ci_filename_mode);
-		return ERR_PTR(-EINVAL);
-	}
-
-	if (S_ISREG(inode->i_mode))
-		return &available_modes[ci->ci_data_mode];
-
-	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
-		return &available_modes[ci->ci_filename_mode];
-
-	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
-		  inode->i_ino, (inode->i_mode & S_IFMT));
-	return ERR_PTR(-EINVAL);
-}
-
-/* Find the master key, then derive the inode's actual encryption key */
-static int find_and_derive_key(const struct inode *inode,
-			       const struct fscrypt_context *ctx,
-			       u8 *derived_key, const struct fscrypt_mode *mode)
-{
-	struct key *key;
-	const struct fscrypt_key *payload;
-	int err;
-
-	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
-					ctx->master_key_descriptor,
-					mode->keysize, &payload);
-	if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
-		key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
-						ctx->master_key_descriptor,
-						mode->keysize, &payload);
-	}
-	if (IS_ERR(key))
-		return PTR_ERR(key);
-
-	if (ctx->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
-		if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
-			fscrypt_warn(inode->i_sb,
-				     "direct key mode not allowed with %s",
-				     mode->friendly_name);
-			err = -EINVAL;
-		} else if (ctx->contents_encryption_mode !=
-			   ctx->filenames_encryption_mode) {
-			fscrypt_warn(inode->i_sb,
-				     "direct key mode not allowed with different contents and filenames modes");
-			err = -EINVAL;
-		} else {
-			memcpy(derived_key, payload->raw, mode->keysize);
-			err = 0;
-		}
-	} else {
-		err = derive_key_aes(payload->raw, ctx, derived_key,
-				     mode->keysize);
-	}
-	up_read(&key->sem);
-	key_put(key);
-	return err;
-}
-
-/* Allocate and key a symmetric cipher object for the given encryption mode */
-static struct crypto_skcipher *
-allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
-			   const struct inode *inode)
-{
-	struct crypto_skcipher *tfm;
-	int err;
-
-	tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
-	if (IS_ERR(tfm)) {
-		fscrypt_warn(inode->i_sb,
-			     "error allocating '%s' transform for inode %lu: %ld",
-			     mode->cipher_str, inode->i_ino, PTR_ERR(tfm));
-		return tfm;
-	}
-	if (unlikely(!mode->logged_impl_name)) {
-		/*
-		 * fscrypt performance can vary greatly depending on which
-		 * crypto algorithm implementation is used.  Help people debug
-		 * performance problems by logging the ->cra_driver_name the
-		 * first time a mode is used.  Note that multiple threads can
-		 * race here, but it doesn't really matter.
-		 */
-		mode->logged_impl_name = true;
-		pr_info("fscrypt: %s using implementation \"%s\"\n",
-			mode->friendly_name,
-			crypto_skcipher_alg(tfm)->base.cra_driver_name);
-	}
-	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
-	err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
-	if (err)
-		goto err_free_tfm;
-
-	return tfm;
-
-err_free_tfm:
-	crypto_free_skcipher(tfm);
-	return ERR_PTR(err);
-}
-
-/* Master key referenced by DIRECT_KEY policy */
-struct fscrypt_master_key {
-	struct hlist_node mk_node;
-	refcount_t mk_refcount;
-	const struct fscrypt_mode *mk_mode;
-	struct crypto_skcipher *mk_ctfm;
-	u8 mk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
-	u8 mk_raw[FSCRYPT_MAX_KEY_SIZE];
-};
-
-static void free_master_key(struct fscrypt_master_key *mk)
-{
-	if (mk) {
-		crypto_free_skcipher(mk->mk_ctfm);
-		kzfree(mk);
-	}
-}
-
-static void put_master_key(struct fscrypt_master_key *mk)
-{
-	if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock))
-		return;
-	hash_del(&mk->mk_node);
-	spin_unlock(&fscrypt_master_keys_lock);
-
-	free_master_key(mk);
-}
-
-/*
- * Find/insert the given master key into the fscrypt_master_keys table.  If
- * found, it is returned with elevated refcount, and 'to_insert' is freed if
- * non-NULL.  If not found, 'to_insert' is inserted and returned if it's
- * non-NULL; otherwise NULL is returned.
- */
-static struct fscrypt_master_key *
-find_or_insert_master_key(struct fscrypt_master_key *to_insert,
-			  const u8 *raw_key, const struct fscrypt_mode *mode,
-			  const struct fscrypt_info *ci)
-{
-	unsigned long hash_key;
-	struct fscrypt_master_key *mk;
-
-	/*
-	 * Careful: to avoid potentially leaking secret key bytes via timing
-	 * information, we must key the hash table by descriptor rather than by
-	 * raw key, and use crypto_memneq() when comparing raw keys.
-	 */
-
-	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
-
-	spin_lock(&fscrypt_master_keys_lock);
-	hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
-		if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
-			   FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
-			continue;
-		if (mode != mk->mk_mode)
-			continue;
-		if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize))
-			continue;
-		/* using existing tfm with same (descriptor, mode, raw_key) */
-		refcount_inc(&mk->mk_refcount);
-		spin_unlock(&fscrypt_master_keys_lock);
-		free_master_key(to_insert);
-		return mk;
-	}
-	if (to_insert)
-		hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key);
-	spin_unlock(&fscrypt_master_keys_lock);
-	return to_insert;
-}
-
-/* Prepare to encrypt directly using the master key in the given mode */
-static struct fscrypt_master_key *
-fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
-		       const u8 *raw_key, const struct inode *inode)
-{
-	struct fscrypt_master_key *mk;
-	int err;
-
-	/* Is there already a tfm for this key? */
-	mk = find_or_insert_master_key(NULL, raw_key, mode, ci);
-	if (mk)
-		return mk;
-
-	/* Nope, allocate one. */
-	mk = kzalloc(sizeof(*mk), GFP_NOFS);
-	if (!mk)
-		return ERR_PTR(-ENOMEM);
-	refcount_set(&mk->mk_refcount, 1);
-	mk->mk_mode = mode;
-	mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
-	if (IS_ERR(mk->mk_ctfm)) {
-		err = PTR_ERR(mk->mk_ctfm);
-		mk->mk_ctfm = NULL;
-		goto err_free_mk;
-	}
-	memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
-	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	memcpy(mk->mk_raw, raw_key, mode->keysize);
-
-	return find_or_insert_master_key(mk, raw_key, mode, ci);
-
-err_free_mk:
-	free_master_key(mk);
-	return ERR_PTR(err);
-}
-
-static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
-{
-	struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
-
-	/* init hash transform on demand */
-	if (unlikely(!tfm)) {
-		struct crypto_shash *prev_tfm;
-
-		tfm = crypto_alloc_shash("sha256", 0, 0);
-		if (IS_ERR(tfm)) {
-			fscrypt_warn(NULL,
-				     "error allocating SHA-256 transform: %ld",
-				     PTR_ERR(tfm));
-			return PTR_ERR(tfm);
-		}
-		prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
-		if (prev_tfm) {
-			crypto_free_shash(tfm);
-			tfm = prev_tfm;
-		}
-	}
-
-	{
-		SHASH_DESC_ON_STACK(desc, tfm);
-		desc->tfm = tfm;
-		desc->flags = 0;
-
-		return crypto_shash_digest(desc, key, keysize, salt);
-	}
-}
-
-static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
-				int keysize)
-{
-	int err;
-	struct crypto_cipher *essiv_tfm;
-	u8 salt[SHA256_DIGEST_SIZE];
-
-	essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
-	if (IS_ERR(essiv_tfm))
-		return PTR_ERR(essiv_tfm);
-
-	ci->ci_essiv_tfm = essiv_tfm;
-
-	err = derive_essiv_salt(raw_key, keysize, salt);
-	if (err)
-		goto out;
-
-	/*
-	 * Using SHA256 to derive the salt/key will result in AES-256 being
-	 * used for IV generation. File contents encryption will still use the
-	 * configured keysize (AES-128) nevertheless.
-	 */
-	err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
-	if (err)
-		goto out;
-
-out:
-	memzero_explicit(salt, sizeof(salt));
-	return err;
-}
-
-void __exit fscrypt_essiv_cleanup(void)
-{
-	crypto_free_shash(essiv_hash_tfm);
-}
-
-/*
- * Given the encryption mode and key (normally the derived key, but for
- * DIRECT_KEY mode it's the master key), set up the inode's symmetric cipher
- * transform object(s).
- */
-static int setup_crypto_transform(struct fscrypt_info *ci,
-				  struct fscrypt_mode *mode,
-				  const u8 *raw_key, const struct inode *inode)
-{
-	struct fscrypt_master_key *mk;
-	struct crypto_skcipher *ctfm;
-	int err;
-
-	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
-		mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
-		if (IS_ERR(mk))
-			return PTR_ERR(mk);
-		ctfm = mk->mk_ctfm;
-	} else {
-		mk = NULL;
-		ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
-		if (IS_ERR(ctfm))
-			return PTR_ERR(ctfm);
-	}
-	ci->ci_master_key = mk;
-	ci->ci_ctfm = ctfm;
-
-	if (mode->needs_essiv) {
-		/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
-		WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
-		WARN_ON(ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
-
-		err = init_essiv_generator(ci, raw_key, mode->keysize);
-		if (err) {
-			fscrypt_warn(inode->i_sb,
-				     "error initializing ESSIV generator for inode %lu: %d",
-				     inode->i_ino, err);
-			return err;
-		}
-	}
-	return 0;
-}
-
-static void put_crypt_info(struct fscrypt_info *ci)
-{
-	if (!ci)
-		return;
-
-	if (ci->ci_master_key) {
-		put_master_key(ci->ci_master_key);
-	} else {
-		crypto_free_skcipher(ci->ci_ctfm);
-		crypto_free_cipher(ci->ci_essiv_tfm);
-	}
-	kmem_cache_free(fscrypt_info_cachep, ci);
-}
-
-int fscrypt_get_encryption_info(struct inode *inode)
-{
-	struct fscrypt_info *crypt_info;
-	struct fscrypt_context ctx;
-	struct fscrypt_mode *mode;
-	u8 *raw_key = NULL;
-	int res;
-
-	if (inode->i_crypt_info)
-		return 0;
-
-	res = fscrypt_initialize(inode->i_sb->s_cop->flags);
-	if (res)
-		return res;
-
-	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
-	if (res < 0) {
-		if (!fscrypt_dummy_context_enabled(inode) ||
-		    IS_ENCRYPTED(inode))
-			return res;
-		/* Fake up a context for an unencrypted directory */
-		memset(&ctx, 0, sizeof(ctx));
-		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
-		ctx.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
-		ctx.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
-		memset(ctx.master_key_descriptor, 0x42,
-		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	} else if (res != sizeof(ctx)) {
-		return -EINVAL;
-	}
-
-	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
-		return -EINVAL;
-
-	if (ctx.flags & ~FSCRYPT_POLICY_FLAGS_VALID)
-		return -EINVAL;
-
-	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
-	if (!crypt_info)
-		return -ENOMEM;
-
-	crypt_info->ci_inode = inode;
-
-	crypt_info->ci_flags = ctx.flags;
-	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
-	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
-	memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
-	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
-
-	mode = select_encryption_mode(crypt_info, inode);
-	if (IS_ERR(mode)) {
-		res = PTR_ERR(mode);
-		goto out;
-	}
-	WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
-	crypt_info->ci_mode = mode;
-
-	/*
-	 * This cannot be a stack buffer because it may be passed to the
-	 * scatterlist crypto API as part of key derivation.
-	 */
-	res = -ENOMEM;
-	raw_key = kmalloc(mode->keysize, GFP_NOFS);
-	if (!raw_key)
-		goto out;
-
-	res = find_and_derive_key(inode, &ctx, raw_key, mode);
-	if (res)
-		goto out;
-
-	res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
-	if (res)
-		goto out;
-
-	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
-		crypt_info = NULL;
-out:
-	if (res == -ENOKEY)
-		res = 0;
-	put_crypt_info(crypt_info);
-	kzfree(raw_key);
-	return res;
-}
-EXPORT_SYMBOL(fscrypt_get_encryption_info);
-
-void fscrypt_put_encryption_info(struct inode *inode)
-{
-	put_crypt_info(inode->i_crypt_info);
-	inode->i_crypt_info = NULL;
-}
-EXPORT_SYMBOL(fscrypt_put_encryption_info);
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
new file mode 100644
index 000000000000..898a82d5ff3c
--- /dev/null
+++ b/fs/crypto/keysetup.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Key setup facility for FS encryption support.
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
+ * Heavily modified since then.
+ */
+
+#include <crypto/aes.h>
+#include <crypto/sha.h>
+#include <crypto/skcipher.h>
+#include <linux/key.h>
+
+#include "fscrypt_private.h"
+
+static struct crypto_shash *essiv_hash_tfm;
+
+static struct fscrypt_mode available_modes[] = {
+	[FSCRYPT_MODE_AES_256_XTS] = {
+		.friendly_name = "AES-256-XTS",
+		.cipher_str = "xts(aes)",
+		.keysize = 64,
+		.ivsize = 16,
+	},
+	[FSCRYPT_MODE_AES_256_CTS] = {
+		.friendly_name = "AES-256-CTS-CBC",
+		.cipher_str = "cts(cbc(aes))",
+		.keysize = 32,
+		.ivsize = 16,
+	},
+	[FSCRYPT_MODE_AES_128_CBC] = {
+		.friendly_name = "AES-128-CBC",
+		.cipher_str = "cbc(aes)",
+		.keysize = 16,
+		.ivsize = 16,
+		.needs_essiv = true,
+	},
+	[FSCRYPT_MODE_AES_128_CTS] = {
+		.friendly_name = "AES-128-CTS-CBC",
+		.cipher_str = "cts(cbc(aes))",
+		.keysize = 16,
+		.ivsize = 16,
+	},
+	[FSCRYPT_MODE_ADIANTUM] = {
+		.friendly_name = "Adiantum",
+		.cipher_str = "adiantum(xchacha12,aes)",
+		.keysize = 32,
+		.ivsize = 32,
+	},
+};
+
+static struct fscrypt_mode *
+select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
+{
+	if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
+		fscrypt_warn(inode->i_sb,
+			     "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
+			     inode->i_ino, ci->ci_data_mode,
+			     ci->ci_filename_mode);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (S_ISREG(inode->i_mode))
+		return &available_modes[ci->ci_data_mode];
+
+	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
+		return &available_modes[ci->ci_filename_mode];
+
+	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
+		  inode->i_ino, (inode->i_mode & S_IFMT));
+	return ERR_PTR(-EINVAL);
+}
+
+/* Create a symmetric cipher object for the given encryption mode and key */
+struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
+						  const u8 *raw_key,
+						  const struct inode *inode)
+{
+	struct crypto_skcipher *tfm;
+	int err;
+
+	tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
+	if (IS_ERR(tfm)) {
+		fscrypt_warn(inode->i_sb,
+			     "error allocating '%s' transform for inode %lu: %ld",
+			     mode->cipher_str, inode->i_ino, PTR_ERR(tfm));
+		return tfm;
+	}
+	if (unlikely(!mode->logged_impl_name)) {
+		/*
+		 * fscrypt performance can vary greatly depending on which
+		 * crypto algorithm implementation is used.  Help people debug
+		 * performance problems by logging the ->cra_driver_name the
+		 * first time a mode is used.  Note that multiple threads can
+		 * race here, but it doesn't really matter.
+		 */
+		mode->logged_impl_name = true;
+		pr_info("fscrypt: %s using implementation \"%s\"\n",
+			mode->friendly_name,
+			crypto_skcipher_alg(tfm)->base.cra_driver_name);
+	}
+	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
+	err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
+	if (err)
+		goto err_free_tfm;
+
+	return tfm;
+
+err_free_tfm:
+	crypto_free_skcipher(tfm);
+	return ERR_PTR(err);
+}
+
+static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
+{
+	struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
+
+	/* init hash transform on demand */
+	if (unlikely(!tfm)) {
+		struct crypto_shash *prev_tfm;
+
+		tfm = crypto_alloc_shash("sha256", 0, 0);
+		if (IS_ERR(tfm)) {
+			fscrypt_warn(NULL,
+				     "error allocating SHA-256 transform: %ld",
+				     PTR_ERR(tfm));
+			return PTR_ERR(tfm);
+		}
+		prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
+		if (prev_tfm) {
+			crypto_free_shash(tfm);
+			tfm = prev_tfm;
+		}
+	}
+
+	{
+		SHASH_DESC_ON_STACK(desc, tfm);
+		desc->tfm = tfm;
+		desc->flags = 0;
+
+		return crypto_shash_digest(desc, key, keysize, salt);
+	}
+}
+
+static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
+				int keysize)
+{
+	int err;
+	struct crypto_cipher *essiv_tfm;
+	u8 salt[SHA256_DIGEST_SIZE];
+
+	if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
+		return -EINVAL;
+
+	essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
+	if (IS_ERR(essiv_tfm))
+		return PTR_ERR(essiv_tfm);
+
+	ci->ci_essiv_tfm = essiv_tfm;
+
+	err = derive_essiv_salt(raw_key, keysize, salt);
+	if (err)
+		goto out;
+
+	/*
+	 * Using SHA256 to derive the salt/key will result in AES-256 being
+	 * used for IV generation. File contents encryption will still use the
+	 * configured keysize (AES-128) nevertheless.
+	 */
+	err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
+	if (err)
+		goto out;
+
+out:
+	memzero_explicit(salt, sizeof(salt));
+	return err;
+}
+
+void __exit fscrypt_essiv_cleanup(void)
+{
+	crypto_free_shash(essiv_hash_tfm);
+}
+
+/* Given the per-file key, set up the file's crypto transform object(s) */
+int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
+{
+	struct fscrypt_mode *mode = ci->ci_mode;
+	struct crypto_skcipher *ctfm;
+	int err;
+
+	ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
+	if (IS_ERR(ctfm))
+		return PTR_ERR(ctfm);
+
+	ci->ci_ctfm = ctfm;
+
+	if (mode->needs_essiv) {
+		err = init_essiv_generator(ci, derived_key, mode->keysize);
+		if (err) {
+			fscrypt_warn(ci->ci_inode->i_sb,
+				     "error initializing ESSIV generator for inode %lu: %d",
+				     ci->ci_inode->i_ino, err);
+			return err;
+		}
+	}
+	return 0;
+}
+
+/*
+ * Find the master key, then set up the inode's actual encryption key.
+ */
+static int setup_file_encryption_key(struct fscrypt_info *ci)
+{
+	return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
+}
+
+static void put_crypt_info(struct fscrypt_info *ci)
+{
+	if (!ci)
+		return;
+
+	if (ci->ci_direct_key) {
+		fscrypt_put_direct_key(ci->ci_direct_key);
+	} else {
+		crypto_free_skcipher(ci->ci_ctfm);
+		crypto_free_cipher(ci->ci_essiv_tfm);
+	}
+	kmem_cache_free(fscrypt_info_cachep, ci);
+}
+
+int fscrypt_get_encryption_info(struct inode *inode)
+{
+	struct fscrypt_info *crypt_info;
+	struct fscrypt_context ctx;
+	struct fscrypt_mode *mode;
+	int res;
+
+	if (inode->i_crypt_info)
+		return 0;
+
+	res = fscrypt_initialize(inode->i_sb->s_cop->flags);
+	if (res)
+		return res;
+
+	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
+	if (res < 0) {
+		if (!fscrypt_dummy_context_enabled(inode) ||
+		    IS_ENCRYPTED(inode))
+			return res;
+		/* Fake up a context for an unencrypted directory */
+		memset(&ctx, 0, sizeof(ctx));
+		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
+		ctx.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
+		ctx.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
+		memset(ctx.master_key_descriptor, 0x42,
+		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	} else if (res != sizeof(ctx)) {
+		return -EINVAL;
+	}
+
+	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
+		return -EINVAL;
+
+	if (ctx.flags & ~FSCRYPT_POLICY_FLAGS_VALID)
+		return -EINVAL;
+
+	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
+	if (!crypt_info)
+		return -ENOMEM;
+
+	crypt_info->ci_inode = inode;
+
+	crypt_info->ci_flags = ctx.flags;
+	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
+	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
+	memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
+
+	mode = select_encryption_mode(crypt_info, inode);
+	if (IS_ERR(mode)) {
+		res = PTR_ERR(mode);
+		goto out;
+	}
+	WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
+	crypt_info->ci_mode = mode;
+
+	res = setup_file_encryption_key(crypt_info);
+	if (res)
+		goto out;
+
+	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
+		crypt_info = NULL;
+out:
+	if (res == -ENOKEY)
+		res = 0;
+	put_crypt_info(crypt_info);
+	return res;
+}
+EXPORT_SYMBOL(fscrypt_get_encryption_info);
+
+void fscrypt_put_encryption_info(struct inode *inode)
+{
+	put_crypt_info(inode->i_crypt_info);
+	inode->i_crypt_info = NULL;
+}
+EXPORT_SYMBOL(fscrypt_put_encryption_info);
diff --git a/fs/crypto/keysetup_legacy.c b/fs/crypto/keysetup_legacy.c
new file mode 100644
index 000000000000..a48588458f07
--- /dev/null
+++ b/fs/crypto/keysetup_legacy.c
@@ -0,0 +1,340 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Key setup for v1 encryption policies
+ *
+ * Copyright 2015, 2019 Google LLC
+ */
+
+/*
+ * This file implements compatibility functions for the original encryption
+ * policy version ("v1"), including:
+ *
+ * - Deriving per-file keys using the AES-128-ECB based KDF
+ *   (rather than the new method of using HKDF-SHA512)
+ *
+ * - Retrieving fscrypt master keys from process-subscribed keyrings
+ *   (rather than the new method of using a filesystem-level keyring)
+ *
+ * - Handling policies with the DIRECT_KEY flag set using a master key table
+ *   (rather than the new method of implementing DIRECT_KEY with per-mode keys
+ *    managed alongside the master keys in the filesystem-level keyring)
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/skcipher.h>
+#include <keys/user-type.h>
+#include <linux/hashtable.h>
+#include <linux/scatterlist.h>
+
+#include "fscrypt_private.h"
+
+/* Table of keys referenced by DIRECT_KEY policies */
+static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */
+static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);
+
+/*
+ * Legacy key derivation function.  This generates the derived key by encrypting
+ * the master key with AES-128-ECB using the nonce as the AES key.  This
+ * provides a unique derived key with sufficient entropy for each inode.
+ * However, it's nonstandard, non-extensible, doesn't evenly distribute the
+ * entropy from the master key, and is trivially reversible: an attacker who
+ * compromises a derived key can "decrypt" it to get back to the master key,
+ * then derive any other key.  For all new code, use HKDF instead.
+ *
+ * The master key must be at least as long as the derived key.  If the master
+ * key is longer, then only the first 'derived_keysize' bytes are used.
+ */
+static int derive_key_aes(const u8 *master_key,
+			  const u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE],
+			  u8 *derived_key, unsigned int derived_keysize)
+{
+	int res = 0;
+	struct skcipher_request *req = NULL;
+	DECLARE_CRYPTO_WAIT(wait);
+	struct scatterlist src_sg, dst_sg;
+	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
+
+	if (IS_ERR(tfm)) {
+		res = PTR_ERR(tfm);
+		tfm = NULL;
+		goto out;
+	}
+	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
+	req = skcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req) {
+		res = -ENOMEM;
+		goto out;
+	}
+	skcipher_request_set_callback(req,
+			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+			crypto_req_done, &wait);
+	res = crypto_skcipher_setkey(tfm, nonce, FS_KEY_DERIVATION_NONCE_SIZE);
+	if (res < 0)
+		goto out;
+
+	sg_init_one(&src_sg, master_key, derived_keysize);
+	sg_init_one(&dst_sg, derived_key, derived_keysize);
+	skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize,
+				   NULL);
+	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+out:
+	skcipher_request_free(req);
+	crypto_free_skcipher(tfm);
+	return res;
+}
+
+/*
+ * Search the current task's subscribed keyrings for a "logon" key with
+ * description prefix:descriptor, and if found acquire a read lock on it and
+ * return a pointer to its validated payload in *payload_ret.
+ */
+static struct key *
+find_and_lock_process_key(const char *prefix,
+			  const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
+			  unsigned int min_keysize,
+			  const struct fscrypt_key **payload_ret)
+{
+	char *description;
+	struct key *key;
+	const struct user_key_payload *ukp;
+	const struct fscrypt_key *payload;
+
+	description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
+				FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
+	if (!description)
+		return ERR_PTR(-ENOMEM);
+
+	key = request_key(&key_type_logon, description, NULL);
+	kfree(description);
+	if (IS_ERR(key))
+		return key;
+
+	down_read(&key->sem);
+	ukp = user_key_payload_locked(key);
+
+	if (!ukp) /* was the key revoked before we acquired its semaphore? */
+		goto invalid;
+
+	payload = (const struct fscrypt_key *)ukp->data;
+
+	if (ukp->datalen != sizeof(struct fscrypt_key) ||
+	    payload->size < 1 || payload->size > FSCRYPT_MAX_KEY_SIZE) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' has invalid payload",
+			     key->description);
+		goto invalid;
+	}
+
+	if (payload->size < min_keysize) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
+			     key->description, payload->size, min_keysize);
+		goto invalid;
+	}
+
+	*payload_ret = payload;
+	return key;
+
+invalid:
+	up_read(&key->sem);
+	key_put(key);
+	return ERR_PTR(-ENOKEY);
+}
+
+/* Master key referenced by DIRECT_KEY policy */
+struct fscrypt_direct_key {
+	struct hlist_node		dk_node;
+	refcount_t			dk_refcount;
+	const struct fscrypt_mode	*dk_mode;
+	struct crypto_skcipher		*dk_ctfm;
+	u8				dk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+	u8				dk_raw[FSCRYPT_MAX_KEY_SIZE];
+};
+
+static void free_direct_key(struct fscrypt_direct_key *dk)
+{
+	if (dk) {
+		crypto_free_skcipher(dk->dk_ctfm);
+		kzfree(dk);
+	}
+}
+
+void fscrypt_put_direct_key(struct fscrypt_direct_key *dk)
+{
+	if (!refcount_dec_and_lock(&dk->dk_refcount, &fscrypt_direct_keys_lock))
+		return;
+	hash_del(&dk->dk_node);
+	spin_unlock(&fscrypt_direct_keys_lock);
+
+	free_direct_key(dk);
+}
+
+/*
+ * Find/insert the given key into the fscrypt_direct_keys table.  If found, it
+ * is returned with elevated refcount, and 'to_insert' is freed if non-NULL.  If
+ * not found, 'to_insert' is inserted and returned if it's non-NULL; otherwise
+ * NULL is returned.
+ */
+static struct fscrypt_direct_key *
+find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
+			  const u8 *raw_key, const struct fscrypt_info *ci)
+{
+	unsigned long hash_key;
+	struct fscrypt_direct_key *dk;
+
+	/*
+	 * Careful: to avoid potentially leaking secret key bytes via timing
+	 * information, we must key the hash table by descriptor rather than by
+	 * raw key, and use crypto_memneq() when comparing raw keys.
+	 */
+
+	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
+
+	spin_lock(&fscrypt_direct_keys_lock);
+	hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) {
+		if (memcmp(ci->ci_master_key_descriptor, dk->dk_descriptor,
+			   FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
+			continue;
+		if (ci->ci_mode != dk->dk_mode)
+			continue;
+		if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
+			continue;
+		/* using existing tfm with same (descriptor, mode, raw_key) */
+		refcount_inc(&dk->dk_refcount);
+		spin_unlock(&fscrypt_direct_keys_lock);
+		free_direct_key(to_insert);
+		return dk;
+	}
+	if (to_insert)
+		hash_add(fscrypt_direct_keys, &to_insert->dk_node, hash_key);
+	spin_unlock(&fscrypt_direct_keys_lock);
+	return to_insert;
+}
+
+/* Prepare to encrypt directly using the master key in the given mode */
+static struct fscrypt_direct_key *
+fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key)
+{
+	struct fscrypt_direct_key *dk;
+	int err;
+
+	/* Is there already a tfm for this key? */
+	dk = find_or_insert_direct_key(NULL, raw_key, ci);
+	if (dk)
+		return dk;
+
+	/* Nope, allocate one. */
+	dk = kzalloc(sizeof(*dk), GFP_NOFS);
+	if (!dk)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&dk->dk_refcount, 1);
+	dk->dk_mode = ci->ci_mode;
+	dk->dk_ctfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key,
+						ci->ci_inode);
+	if (IS_ERR(dk->dk_ctfm)) {
+		err = PTR_ERR(dk->dk_ctfm);
+		dk->dk_ctfm = NULL;
+		goto err_free_dk;
+	}
+	memcpy(dk->dk_descriptor, ci->ci_master_key_descriptor,
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);
+
+	return find_or_insert_direct_key(dk, raw_key, ci);
+
+err_free_dk:
+	free_direct_key(dk);
+	return ERR_PTR(err);
+}
+
+/* v1 policy, DIRECT_KEY: use the master key directly */
+static int setup_v1_file_key_direct(struct fscrypt_info *ci,
+				    const u8 *raw_master_key)
+{
+	const struct fscrypt_mode *mode = ci->ci_mode;
+	struct fscrypt_direct_key *dk;
+
+	if (!fscrypt_mode_supports_direct_key(mode)) {
+		fscrypt_warn(ci->ci_inode->i_sb,
+			     "direct key flag not allowed with %s",
+			     mode->friendly_name);
+		return -EINVAL;
+	}
+
+	if (ci->ci_data_mode != ci->ci_filename_mode) {
+		fscrypt_warn(ci->ci_inode->i_sb,
+			     "direct key flag not allowed with different contents and filenames modes");
+		return -EINVAL;
+	}
+
+	/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
+	if (WARN_ON(mode->needs_essiv))
+		return -EINVAL;
+
+	dk = fscrypt_get_direct_key(ci, raw_master_key);
+	if (IS_ERR(dk))
+		return PTR_ERR(dk);
+	ci->ci_direct_key = dk;
+	ci->ci_ctfm = dk->dk_ctfm;
+	return 0;
+}
+
+/* v1 policy, !DIRECT_KEY: derive the file's encryption key */
+static int setup_v1_file_key_derived(struct fscrypt_info *ci,
+				     const u8 *raw_master_key)
+{
+	const int keysize = ci->ci_mode->keysize;
+	u8 *derived_key;
+	int err;
+
+	/*
+	 * This cannot be a stack buffer because it will be passed to the
+	 * scatterlist crypto API during derive_key_aes().
+	 */
+	derived_key = kmalloc(keysize, GFP_NOFS);
+	if (!derived_key)
+		return -ENOMEM;
+
+	err = derive_key_aes(raw_master_key, ci->ci_nonce,
+			     derived_key, keysize);
+	if (err)
+		goto out;
+
+	err = fscrypt_set_derived_key(ci, derived_key);
+out:
+	kzfree(derived_key);
+	return err;
+}
+
+int fscrypt_setup_v1_file_key(struct fscrypt_info *ci, const u8 *raw_master_key)
+{
+	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
+		return setup_v1_file_key_direct(ci, raw_master_key);
+	else
+		return setup_v1_file_key_derived(ci, raw_master_key);
+}
+
+int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci)
+{
+	struct key *key;
+	const struct fscrypt_key *payload;
+	int err;
+
+	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
+					ci->ci_master_key_descriptor,
+					ci->ci_mode->keysize, &payload);
+	if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
+		key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
+						ci->ci_master_key_descriptor,
+						ci->ci_mode->keysize, &payload);
+	}
+
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	err = fscrypt_setup_v1_file_key(ci, payload->raw);
+	up_read(&key->sem);
+	key_put(key);
+	return err;
+}
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 8b1e44421497..5afb9fc13ef4 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -112,7 +112,7 @@ extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
 extern int fscrypt_inherit_context(struct inode *, struct inode *,
 					void *, bool);
-/* keyinfo.c */
+/* keysetup.c */
 extern int fscrypt_get_encryption_info(struct inode *);
 extern void fscrypt_put_encryption_info(struct inode *);
 
@@ -312,7 +312,7 @@ static inline int fscrypt_inherit_context(struct inode *parent,
 	return -EOPNOTSUPP;
 }
 
-/* keyinfo.c */
+/* keysetup.c */
 static inline int fscrypt_get_encryption_info(struct inode *inode)
 {
 	return -EOPNOTSUPP;
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 07/20] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (5 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 06/20] fscrypt: refactor v1 policy key setup into keysetup_legacy.c Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 08/20] fs/inode.c: export inode_lru_list_del() Eric Biggers
                   ` (12 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add a new fscrypt ioctl, FS_IOC_ADD_ENCRYPTION_KEY.  This ioctl adds an
encryption key to the filesystem's fscrypt keyring ->s_master_keys,
making any files encrypted with that key appear "unlocked".

Why we need this
~~~~~~~~~~~~~~~~

The main problem is that the "locked/unlocked" (ciphertext/plaintext)
status of encrypted files is global, but the fscrypt keys are not.
fscrypt only looks for keys in the keyring(s) the process accessing the
filesystem is subscribed to: the thread keyring, process keyring, and
session keyring, where the session keyring may contain the user keyring.

Therefore, userspace has to put fscrypt keys in the keyrings for
individual users or sessions.  But this means that when a process with a
different keyring tries to access encrypted files, whether they appear
"unlocked" or not is nondeterministic.  This is because it depends on
whether the files are currently present in the inode cache.

Fixing this by consistently providing each process its own view of the
filesystem depending on whether it has the key or not isn't feasible due
to how the VFS caches work.  Furthermore, while sometimes users expect
this behavior, it is misguided for two reasons.  First, it would be an
OS-level access control mechanism largely redundant with existing access
control mechanisms such as UNIX file permissions, ACLs, LSMs, etc.
Encryption is actually for protecting the data at rest.

Second, almost all users of fscrypt actually do need the keys to be
global.  The largest users of fscrypt, Android and Chromium OS, achieve
this by having PID 1 create a "session keyring" that is inherited by
every process.  This works, but it isn't scalable because it prevents
session keyrings from being used for any other purpose.

On general-purpose Linux distros, the 'fscrypt' userspace tool [1] can't
similarly abuse the session keyring, so to make 'sudo' work on all
systems it has to link all the user keyrings into root's user keyring
[2].  This is ugly and raises security concerns.  Moreover it can't make
the keys available to system services, such as sshd trying to access the
user's '~/.ssh' directory (see [3], [4]) or NetworkManager trying to
read certificates from the user's home directory (see [5]).

By having an API to add a key to the *filesystem* we'll be able to fix
the above bugs, remove userspace workarounds, and clearly express the
intended semantics: the locked/unlocked status of an encrypted directory
is global, and encryption is orthogonal to OS-level access control.

Why not use the add_key() syscall
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We use an ioctl for this API rather than the existing add_key() system
call because the ioctl gives us the flexibility needed to implement
fscrypt-specific semantics that will be introduced in later patches:

- Supporting key removal with the semantics such that the secret is
  removed immediately and any unused inodes using the key are evicted;
  also, the eviction of any in-use inodes can be retried.

- Calculating a key-dependent cryptographic identifier and returning it
  to userspace.

- Allowing keys to be added and removed by non-root users, but only keys
  for v2 encryption policies; and to prevent denial-of-service attacks,
  users can only remove keys they themselves have added, and a key is
  only really removed after all users who added it have removed it.

Trying to shoehorn these semantics into the keyrings syscalls would be
very difficult, whereas the ioctls make things much easier.

However, to reuse code the implementation still uses the keyrings
service internally.  Thus we get lockless RCU-mode key lookups without
having to re-implement it, and the keys automatically show up in
/proc/keys for debugging purposes.

References:

    [1] https://github.com/google/fscrypt
    [2] https://goo.gl/55cCrI#heading=h.vf09isp98isb
    [3] https://github.com/google/fscrypt/issues/111#issuecomment-444347939
    [4] https://github.com/google/fscrypt/issues/116
    [5] https://bugs.launchpad.net/ubuntu/+source/fscrypt/+bug/1770715

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/Makefile           |   1 +
 fs/crypto/crypto.c           |  11 +-
 fs/crypto/fscrypt_private.h  |  44 +++++-
 fs/crypto/keyring.c          | 288 +++++++++++++++++++++++++++++++++++
 fs/crypto/keysetup.c         |  34 ++++-
 include/linux/fscrypt.h      |   9 ++
 include/uapi/linux/fscrypt.h |  40 +++--
 7 files changed, 414 insertions(+), 13 deletions(-)
 create mode 100644 fs/crypto/keyring.c

diff --git a/fs/crypto/Makefile b/fs/crypto/Makefile
index 75c0c29fcc62..accdd622c908 100644
--- a/fs/crypto/Makefile
+++ b/fs/crypto/Makefile
@@ -3,6 +3,7 @@ obj-$(CONFIG_FS_ENCRYPTION)	+= fscrypto.o
 fscrypto-y := crypto.o \
 	      fname.o \
 	      hooks.o \
+	      keyring.o \
 	      keysetup.o \
 	      keysetup_legacy.o \
 	      policy.o
diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 8217a4434621..8726c4e94077 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -451,6 +451,8 @@ void fscrypt_msg(struct super_block *sb, const char *level,
  */
 static int __init fscrypt_init(void)
 {
+	int err = -ENOMEM;
+
 	/*
 	 * Use an unbound workqueue to allow bios to be decrypted in parallel
 	 * even when they happen to complete on the same CPU.  This sacrifices
@@ -473,14 +475,20 @@ static int __init fscrypt_init(void)
 	if (!fscrypt_info_cachep)
 		goto fail_free_ctx;
 
+	err = fscrypt_init_keyring();
+	if (err)
+		goto fail_free_info;
+
 	return 0;
 
+fail_free_info:
+	kmem_cache_destroy(fscrypt_info_cachep);
 fail_free_ctx:
 	kmem_cache_destroy(fscrypt_ctx_cachep);
 fail_free_queue:
 	destroy_workqueue(fscrypt_read_workqueue);
 fail:
-	return -ENOMEM;
+	return err;
 }
 module_init(fscrypt_init)
 
@@ -497,6 +505,7 @@ static void __exit fscrypt_exit(void)
 	kmem_cache_destroy(fscrypt_info_cachep);
 
 	fscrypt_essiv_cleanup();
+	fscrypt_exit_keyring();
 }
 module_exit(fscrypt_exit);
 
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index c5a8181fc26c..b4c431208555 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -14,9 +14,12 @@
 #include <linux/fscrypt.h>
 #include <crypto/hash.h>
 
-/* Encryption parameters */
+#define CONST_STRLEN(str)	(sizeof(str) - 1)
+
 #define FS_KEY_DERIVATION_NONCE_SIZE	16
 
+#define FSCRYPT_MIN_KEY_SIZE		16
+
 /**
  * Encryption context for inode
  *
@@ -159,6 +162,45 @@ extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
 					 u32 orig_len, u32 max_len,
 					 u32 *encrypted_len_ret);
 
+/* keyring.c */
+
+/*
+ * fscrypt_master_key_secret - secret key material of an in-use master key
+ */
+struct fscrypt_master_key_secret {
+
+	/* Size of the raw key in bytes */
+	u32			size;
+
+	/* The raw key */
+	u8			raw[FSCRYPT_MAX_KEY_SIZE];
+
+} __randomize_layout;
+
+/*
+ * fscrypt_master_key - an in-use master key
+ *
+ * This represents a master encryption key which has been added to the
+ * filesystem and can be used to "unlock" the encrypted files which were
+ * encrypted with it.
+ */
+struct fscrypt_master_key {
+
+	/* The secret key material */
+	struct fscrypt_master_key_secret	mk_secret;
+
+	/* Arbitrary key descriptor which was assigned by userspace */
+	struct fscrypt_key_specifier		mk_spec;
+
+} __randomize_layout;
+
+extern struct key *
+fscrypt_find_master_key(struct super_block *sb,
+			const struct fscrypt_key_specifier *mk_spec);
+
+extern int __init fscrypt_init_keyring(void);
+extern void fscrypt_exit_keyring(void);
+
 /* keysetup.c */
 
 struct fscrypt_mode {
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
new file mode 100644
index 000000000000..252e863d681d
--- /dev/null
+++ b/fs/crypto/keyring.c
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Filesystem-level keyring for fscrypt
+ *
+ * Copyright 2019 Google LLC
+ */
+
+/*
+ * This file implements management of fscrypt master keys in the
+ * filesystem-level keyring, including the ioctls:
+ *
+ * - FS_IOC_ADD_ENCRYPTION_KEY: add a key
+ */
+
+#include <linux/key-type.h>
+#include <linux/seq_file.h>
+
+#include "fscrypt_private.h"
+
+static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
+{
+	memzero_explicit(secret, sizeof(*secret));
+}
+
+static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
+				   struct fscrypt_master_key_secret *src)
+{
+	memcpy(dst, src, sizeof(*dst));
+	memzero_explicit(src, sizeof(*src));
+}
+
+static void free_master_key(struct fscrypt_master_key *mk)
+{
+	wipe_master_key_secret(&mk->mk_secret);
+	kzfree(mk);
+}
+
+static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
+{
+	switch (spec->type) {
+	case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
+		return FSCRYPT_KEY_DESCRIPTOR_SIZE;
+	}
+	return 0;
+}
+
+static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
+{
+	if (spec->__reserved)
+		return false;
+	return master_key_spec_len(spec) != 0;
+}
+
+static int fscrypt_key_instantiate(struct key *key,
+				   struct key_preparsed_payload *prep)
+{
+	key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
+	return 0;
+}
+
+static void fscrypt_key_destroy(struct key *key)
+{
+	free_master_key(key->payload.data[0]);
+}
+
+static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
+{
+	seq_puts(m, key->description);
+}
+
+/*
+ * Type of key in ->s_master_keys.  Each key of this type represents a master
+ * key which has been added to the filesystem.  Its payload is a
+ * 'struct fscrypt_master_key'.  The "." prefix in the key type name prevents
+ * users from adding keys of this type via the keyrings syscalls rather than via
+ * the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
+ */
+static struct key_type key_type_fscrypt = {
+	.name			= "._fscrypt",
+	.instantiate		= fscrypt_key_instantiate,
+	.destroy		= fscrypt_key_destroy,
+	.describe		= fscrypt_key_describe,
+};
+
+/* Search ->s_master_keys */
+static struct key *search_fscrypt_keyring(struct key *keyring,
+					  struct key_type *type,
+					  const char *description)
+{
+	/*
+	 * We need to mark the keyring reference as "possessed" so that we
+	 * acquire permission to search it, via the KEY_POS_SEARCH permission.
+	 */
+	key_ref_t keyref = make_key_ref(keyring, true);
+
+	keyref = keyring_search(keyref, type, description);
+	if (IS_ERR(keyref)) {
+		if (PTR_ERR(keyref) == -EAGAIN || /* not found */
+		    PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
+			keyref = ERR_PTR(-ENOKEY);
+		return ERR_CAST(keyref);
+	}
+	return key_ref_to_ptr(keyref);
+}
+
+#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE	\
+	(CONST_STRLEN("fscrypt-") + FIELD_SIZEOF(struct super_block, s_id))
+
+#define FSCRYPT_MK_DESCRIPTION_SIZE	(2 * FSCRYPT_KEY_DESCRIPTOR_SIZE + 1)
+
+static void format_fs_keyring_description(
+			char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
+			const struct super_block *sb)
+{
+	sprintf(description, "fscrypt-%s", sb->s_id);
+}
+
+static void format_mk_description(
+			char description[FSCRYPT_MK_DESCRIPTION_SIZE],
+			const struct fscrypt_key_specifier *mk_spec)
+{
+	sprintf(description, "%*phN",
+		master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
+}
+
+/* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
+static int allocate_filesystem_keyring(struct super_block *sb)
+{
+	char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
+	struct key *keyring;
+
+	if (sb->s_master_keys)
+		return 0;
+
+	format_fs_keyring_description(description, sb);
+	keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+				current_cred(), KEY_POS_SEARCH |
+				  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
+				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
+	if (IS_ERR(keyring))
+		return PTR_ERR(keyring);
+
+	/* Pairs with smp_load_acquire() in fscrypt_find_master_key() */
+	smp_store_release(&sb->s_master_keys, keyring);
+	return 0;
+}
+
+/*
+ * Find the specified master key in ->s_master_keys.
+ * Returns ERR_PTR(-ENOKEY) if not found.
+ */
+struct key *fscrypt_find_master_key(struct super_block *sb,
+				    const struct fscrypt_key_specifier *mk_spec)
+{
+	struct key *keyring;
+	char description[FSCRYPT_MK_DESCRIPTION_SIZE];
+
+	/* pairs with smp_store_release() in allocate_filesystem_keyring() */
+	keyring = smp_load_acquire(&sb->s_master_keys);
+	if (keyring == NULL)
+		return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */
+
+	format_mk_description(description, mk_spec);
+	return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
+}
+
+/*
+ * Allocate a new fscrypt_master_key which contains the given secret, set it as
+ * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
+ * into the given keyring.  Synchronized by fscrypt_add_key_mutex.
+ */
+static int add_new_master_key(struct fscrypt_master_key_secret *secret,
+			      const struct fscrypt_key_specifier *mk_spec,
+			      struct key *keyring)
+{
+	struct fscrypt_master_key *mk;
+	char description[FSCRYPT_MK_DESCRIPTION_SIZE];
+	struct key *key;
+	int err;
+
+	mk = kzalloc(sizeof(*mk), GFP_NOFS);
+	if (!mk)
+		return -ENOMEM;
+
+	mk->mk_spec = *mk_spec;
+
+	move_master_key_secret(&mk->mk_secret, secret);
+
+	format_mk_description(description, mk_spec);
+	key = key_alloc(&key_type_fscrypt, description,
+			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
+			KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
+			KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(key)) {
+		err = PTR_ERR(key);
+		goto out_free_mk;
+	}
+	err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
+	key_put(key);
+	if (err)
+		goto out_free_mk;
+
+	return 0;
+
+out_free_mk:
+	free_master_key(mk);
+	return err;
+}
+
+static int add_master_key(struct super_block *sb,
+			  struct fscrypt_master_key_secret *secret,
+			  const struct fscrypt_key_specifier *mk_spec)
+{
+	static DEFINE_MUTEX(fscrypt_add_key_mutex);
+	struct key *key;
+	int err;
+
+	mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
+	key = fscrypt_find_master_key(sb, mk_spec);
+	if (IS_ERR(key)) {
+		err = PTR_ERR(key);
+		if (err != -ENOKEY)
+			goto out_unlock;
+		/* Didn't find the key in ->s_master_keys.  Add it. */
+		err = allocate_filesystem_keyring(sb);
+		if (err)
+			goto out_unlock;
+		err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
+	} else {
+		key_put(key);
+		err = 0;
+	}
+out_unlock:
+	mutex_unlock(&fscrypt_add_key_mutex);
+	return err;
+}
+
+/*
+ * Add a master encryption key to the filesystem, causing all files which were
+ * encrypted with it to appear "unlocked" (decrypted) when accessed.
+ */
+int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
+{
+	struct super_block *sb = file_inode(filp)->i_sb;
+	struct fscrypt_add_key_arg __user *uarg = _uarg;
+	struct fscrypt_add_key_arg arg;
+	struct fscrypt_master_key_secret secret;
+	int err;
+
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+
+	if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
+	    arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
+		return -EINVAL;
+
+	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
+		return -EINVAL;
+
+	if (!valid_key_spec(&arg.key_spec))
+		return -EINVAL;
+
+	memset(&secret, 0, sizeof(secret));
+	secret.size = arg.raw_size;
+	err = -EFAULT;
+	if (copy_from_user(secret.raw, uarg->raw, secret.size))
+		goto out_wipe_secret;
+
+	err = -EACCES;
+	if (!capable(CAP_SYS_ADMIN))
+		goto out_wipe_secret;
+
+	err = add_master_key(sb, &secret, &arg.key_spec);
+out_wipe_secret:
+	wipe_master_key_secret(&secret);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
+
+int __init fscrypt_init_keyring(void)
+{
+	return register_key_type(&key_type_fscrypt);
+}
+
+void fscrypt_exit_keyring(void)
+{
+	unregister_key_type(&key_type_fscrypt);
+}
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 898a82d5ff3c..b63fb4e8aebd 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -213,7 +213,39 @@ int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
  */
 static int setup_file_encryption_key(struct fscrypt_info *ci)
 {
-	return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
+	struct key *key;
+	struct fscrypt_master_key *mk = NULL;
+	struct fscrypt_key_specifier mk_spec;
+	int err;
+
+	mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
+	memcpy(mk_spec.u.descriptor, ci->ci_master_key_descriptor,
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+
+	key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
+	if (IS_ERR(key)) {
+		if (key != ERR_PTR(-ENOKEY))
+			return PTR_ERR(key);
+
+		return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
+	}
+
+	mk = key->payload.data[0];
+
+	if (mk->mk_secret.size < ci->ci_mode->keysize) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
+			     key->description, mk->mk_secret.size,
+			     ci->ci_mode->keysize);
+		err = -ENOKEY;
+		goto out_release_key;
+	}
+
+	err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
+
+out_release_key:
+	key_put(key);
+	return err;
 }
 
 static void put_crypt_info(struct fscrypt_info *ci)
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 5afb9fc13ef4..ddb54b8eab81 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -112,6 +112,9 @@ extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
 extern int fscrypt_inherit_context(struct inode *, struct inode *,
 					void *, bool);
+/* keyring.c */
+extern int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
+
 /* keysetup.c */
 extern int fscrypt_get_encryption_info(struct inode *);
 extern void fscrypt_put_encryption_info(struct inode *);
@@ -312,6 +315,12 @@ static inline int fscrypt_inherit_context(struct inode *parent,
 	return -EOPNOTSUPP;
 }
 
+/* keyring.c */
+static inline int fscrypt_ioctl_add_key(struct file *filp, void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
 /* keysetup.c */
 static inline int fscrypt_get_encryption_info(struct inode *inode)
 {
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 3bbc5dfbde21..7bed24632bda 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -34,22 +34,42 @@ struct fscrypt_policy {
 	__u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 };
 
-#define FS_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct fscrypt_policy)
-#define FS_IOC_GET_ENCRYPTION_PWSALT	_IOW('f', 20, __u8[16])
-#define FS_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct fscrypt_policy)
-
-/* Parameters for passing an encryption key into the kernel keyring */
+/*
+ * Process-subscribed "logon" key description prefix and payload format.
+ * Deprecated; prefer FS_IOC_ADD_ENCRYPTION_KEY instead.
+ */
 #define FSCRYPT_KEY_DESC_PREFIX		"fscrypt:"
-#define FSCRYPT_KEY_DESC_PREFIX_SIZE		8
-
-/* Structure that userspace passes to the kernel keyring */
-#define FSCRYPT_MAX_KEY_SIZE			64
-
+#define FSCRYPT_KEY_DESC_PREFIX_SIZE	8
+#define FSCRYPT_MAX_KEY_SIZE		64
 struct fscrypt_key {
 	__u32 mode;
 	__u8 raw[FSCRYPT_MAX_KEY_SIZE];
 	__u32 size;
 };
+
+struct fscrypt_key_specifier {
+#define FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR	1
+	__u32 type;
+	__u32 __reserved;
+	union {
+		__u8 __reserved[32]; /* reserve some extra space */
+		__u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+	} u;
+};
+
+/* Struct passed to FS_IOC_ADD_ENCRYPTION_KEY */
+struct fscrypt_add_key_arg {
+	struct fscrypt_key_specifier key_spec;
+	__u32 raw_size;
+	__u32 __reserved[9];
+	__u8 raw[];
+};
+
+#define FS_IOC_SET_ENCRYPTION_POLICY	  _IOR('f', 19, struct fscrypt_policy)
+#define FS_IOC_GET_ENCRYPTION_PWSALT	  _IOW('f', 20, __u8[16])
+#define FS_IOC_GET_ENCRYPTION_POLICY	  _IOW('f', 21, struct fscrypt_policy)
+#define FS_IOC_ADD_ENCRYPTION_KEY	 _IOWR('f', 23, struct fscrypt_add_key_arg)
+
 /**********************************************************************/
 
 /* old names; don't add anything new here! */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 08/20] fs/inode.c: export inode_lru_list_del()
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (6 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 07/20] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 09/20] fs/inode.c: rename and export dispose_list() Eric Biggers
                   ` (11 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

When a filesystem encryption key is removed, we need all files which had
been "unlocked" (had ->i_crypt_info set up) with it to appear "locked"
again.  This is most easily done by evicting the inodes.  This can
currently be done using 'echo 2 > /proc/sys/vm/drop_caches'; however,
that is overkill and not usable by non-root users.

In preparation for allowing fs/crypto/ to evict just the needed inodes,
make inode_lru_list_del() non-static.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/inode.c         | 4 +---
 include/linux/fs.h | 1 +
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 0cd47fe0dbe5..037df483c9af 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -426,10 +426,8 @@ void inode_add_lru(struct inode *inode)
 		inode_lru_list_add(inode);
 }
 
-
-static void inode_lru_list_del(struct inode *inode)
+void inode_lru_list_del(struct inode *inode)
 {
-
 	if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru))
 		this_cpu_dec(nr_unused);
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 70d929ac89f9..326cbb044596 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2986,6 +2986,7 @@ extern void unlock_new_inode(struct inode *);
 extern void discard_new_inode(struct inode *);
 extern unsigned int get_next_ino(void);
 extern void evict_inodes(struct super_block *sb);
+extern void inode_lru_list_del(struct inode *inode);
 
 extern void __iget(struct inode * inode);
 extern void iget_failed(struct inode *);
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 09/20] fs/inode.c: rename and export dispose_list()
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (7 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 08/20] fs/inode.c: export inode_lru_list_del() Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 10/20] fs/dcache.c: add shrink_dcache_inode() Eric Biggers
                   ` (10 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

When a filesystem encryption key is removed, we need all files which had
been "unlocked" (had ->i_crypt_info set up) with it to appear "locked"
again.  This is most easily done by evicting the inodes.  This can
currently be done using 'echo 2 > /proc/sys/vm/drop_caches'; however,
that is overkill and not usable by non-root users.  In preparation for
allowing fs/crypto/ to evict just the needed inodes, make dispose_list()
non-static.  For clarity also rename it to evict_inode_list().

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/inode.c         | 18 +++++++++---------
 include/linux/fs.h |  1 +
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 037df483c9af..10147197c1de 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -574,13 +574,13 @@ static void evict(struct inode *inode)
 }
 
 /*
- * dispose_list - dispose of the contents of a local list
- * @head: the head of the list to free
+ * evict_inode_list - evict each inode in a local list of inodes
+ * @head: the head of the list
  *
- * Dispose-list gets a local list with local inodes in it, so it doesn't
+ * This gets a local list with local inodes in it, so it doesn't
  * need to worry about list corruption and SMP locks.
  */
-static void dispose_list(struct list_head *head)
+void evict_inode_list(struct list_head *head)
 {
 	while (!list_empty(head)) {
 		struct inode *inode;
@@ -632,13 +632,13 @@ void evict_inodes(struct super_block *sb)
 		if (need_resched()) {
 			spin_unlock(&sb->s_inode_list_lock);
 			cond_resched();
-			dispose_list(&dispose);
+			evict_inode_list(&dispose);
 			goto again;
 		}
 	}
 	spin_unlock(&sb->s_inode_list_lock);
 
-	dispose_list(&dispose);
+	evict_inode_list(&dispose);
 }
 EXPORT_SYMBOL_GPL(evict_inodes);
 
@@ -683,7 +683,7 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
 	}
 	spin_unlock(&sb->s_inode_list_lock);
 
-	dispose_list(&dispose);
+	evict_inode_list(&dispose);
 
 	return busy;
 }
@@ -770,7 +770,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
  * Walk the superblock inode LRU for freeable inodes and attempt to free them.
  * This is called from the superblock shrinker function with a number of inodes
  * to trim from the LRU. Inodes to be freed are moved to a temporary list and
- * then are freed outside inode_lock by dispose_list().
+ * then are freed outside inode_lock by evict_inode_list().
  */
 long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 {
@@ -779,7 +779,7 @@ long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 
 	freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,
 				     inode_lru_isolate, &freeable);
-	dispose_list(&freeable);
+	evict_inode_list(&freeable);
 	return freed;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 326cbb044596..ce18ece60da4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2987,6 +2987,7 @@ extern void discard_new_inode(struct inode *);
 extern unsigned int get_next_ino(void);
 extern void evict_inodes(struct super_block *sb);
 extern void inode_lru_list_del(struct inode *inode);
+extern void evict_inode_list(struct list_head *head);
 
 extern void __iget(struct inode * inode);
 extern void iget_failed(struct inode *);
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 10/20] fs/dcache.c: add shrink_dcache_inode()
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (8 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 09/20] fs/inode.c: rename and export dispose_list() Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
                   ` (9 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

When a filesystem encryption key is removed, we need all files which had
been "unlocked" (had ->i_crypt_info set up) with it to appear "locked"
again.  This is most easily done by evicting the inodes.  This can
currently be done using 'echo 2 > /proc/sys/vm/drop_caches'; however,
that is overkill and not usable by non-root users.

To evict just the needed inodes we also need the ability to evict those
inodes' dentries, since an inode is pinned by its dentries.  Therefore,
add a function shrink_dcache_inode() which iterates through an inode's
dentries and evicts any unused ones as well as any unused descendants
(since there may be negative dentries pinning the inode's dentries).

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/dcache.c            | 32 ++++++++++++++++++++++++++++++++
 include/linux/dcache.h |  1 +
 2 files changed, 33 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 2593153471cf..6a7db8797b2d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1484,6 +1484,38 @@ void shrink_dcache_parent(struct dentry *parent)
 }
 EXPORT_SYMBOL(shrink_dcache_parent);
 
+/**
+ * shrink_dcache_inode - prune dcache for inode
+ * @inode: inode to prune
+ *
+ * Evict all unused aliases of the specified inode from the dcache.  This is
+ * intended to be used when trying to evict a specific inode, since inodes are
+ * pinned by their dentries.  We also have to descend to ->d_subdirs for each
+ * alias, since aliases may be pinned by negative child dentries.
+ */
+void shrink_dcache_inode(struct inode *inode)
+{
+	for (;;) {
+		struct select_data data;
+		struct dentry *dentry;
+
+		INIT_LIST_HEAD(&data.dispose);
+		data.start = NULL;
+		data.found = 0;
+
+		spin_lock(&inode->i_lock);
+		hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias)
+			d_walk(dentry, &data, select_collect);
+		spin_unlock(&inode->i_lock);
+
+		if (!data.found)
+			break;
+
+		shrink_dentry_list(&data.dispose);
+		cond_resched();
+	}
+}
+
 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
 {
 	/* it has busy descendents; complain about those instead */
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index ef4b70f64f33..c02dab98bc97 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -245,6 +245,7 @@ extern struct dentry * d_obtain_alias(struct inode *);
 extern struct dentry * d_obtain_root(struct inode *);
 extern void shrink_dcache_sb(struct super_block *);
 extern void shrink_dcache_parent(struct dentry *);
+extern void shrink_dcache_inode(struct inode *);
 extern void shrink_dcache_for_umount(struct super_block *);
 extern void d_invalidate(struct dentry *);
 
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (9 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 10/20] fs/dcache.c: add shrink_dcache_inode() Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 22:12   ` Dave Chinner
  2019-02-11 17:27 ` [RFC PATCH v2 12/20] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl Eric Biggers
                   ` (8 subsequent siblings)
  19 siblings, 1 reply; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add a new fscrypt ioctl, FS_IOC_REMOVE_ENCRYPTION_KEY.  This ioctl
removes an encryption key that was added by FS_IOC_ADD_ENCRYPTION_KEY.
It wipes the secret key itself, then "locks" the encrypted files and
directories that had been unlocked using that key -- implemented by
evicting the relevant dentries and inodes from the VFS caches.

The problem this solves is that many fscrypt users want the ability to
remove encryption keys, causing the corresponding encrypted directories
to appear "locked" (presented in ciphertext form) again.  Moreover,
users want removing an encryption key to *really* remove it, in the
sense that the removed keys cannot be recovered even if kernel memory is
compromised, e.g. by the exploit of a kernel security vulnerability or
by a physical attack.  This is desirable after a user logs out of the
system, for example.  In many cases users even already assume this to be
the case and are surprised to hear when it's not.

It is not sufficient to simply unlink the master key from the keyring
(or to revoke or invalidate it), since the actual encryption transform
objects are still pinned in memory by their inodes.  Therefore, to
really remove a key we must also evict the relevant inodes.

Currently one workaround is to run 'sync && echo 2 >
/proc/sys/vm/drop_caches'.  But, that evicts all unused inodes in the
system rather than just the inodes associated with the key being
removed, causing severe performance problems.  Moreover, it requires
root privileges, so regular users can't "lock" their encrypted files.

Another workaround, used in Chromium OS kernels, is to add a new
VFS-level ioctl FS_IOC_DROP_CACHE which is a more restricted version of
drop_caches that operates on a single super_block.  It does:

        shrink_dcache_sb(sb);
        invalidate_inodes(sb, false);

But it's still a hack.  Yet, the major users of filesystem encryption
want this feature badly enough that they are actually using these hacks.

To properly solve the problem, start maintaining a list of the inodes
which have been "unlocked" using each master key.  Originally this
wasn't possible because the kernel didn't keep track of in-use master
keys at all.  But, with the ->s_master_keys keyring it is now possible.

Then, add an ioctl FS_IOC_REMOVE_ENCRYPTION_KEY.  It finds the specified
master key in ->s_master_keys, then wipes the secret key itself, which
prevents any additional inodes from being unlocked with the key.  Then,
it syncs the filesystem and evicts the inodes in the key's list.  The
normal inode eviction code will free and wipe the per-file keys (in
->i_crypt_info).  Note that freeing ->i_crypt_info without evicting the
inodes was also considered, but would have been racy.

Some inodes may still be in use when a master key is removed, and we
can't simply revoke random file descriptors, mmap's, etc.  Thus, the
ioctl simply skips in-use inodes, and returns -EBUSY to indicate that
some inodes weren't evicted.  The master key *secret* is still removed,
but the fscrypt_master_key struct remains to keep track of the remaining
inodes.  Userspace can then retry the ioctl to evict the remaining
inodes.  Alternatively, if userspace adds the key again, the refreshed
secret will be associated with the existing list of inodes so they
remain correctly tracked for future key removals.

The ioctl doesn't wipe pagecache pages.  Thus, we tolerate that after a
kernel compromise some portions of plaintext file contents may still be
recoverable from memory.  This can be solved be enabling page poisoning
system-wide, which security conscious users may choose to do.  But it's
very difficult to solve otherwise, e.g. note that plaintext file
contents may have been read in other places than pagecache pages.

Like FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY is
initially restricted to privileged users only.  This is sufficient for
some use cases, but not all.  A later patch will relax this restriction,
but it will require introducing key hashes, among other changes.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h  |  46 ++++++-
 fs/crypto/keyring.c          | 240 ++++++++++++++++++++++++++++++++++-
 fs/crypto/keysetup.c         |  67 +++++++++-
 include/linux/fscrypt.h      |   7 +
 include/uapi/linux/fscrypt.h |   7 +
 5 files changed, 362 insertions(+), 5 deletions(-)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index b4c431208555..b09fc2939a89 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -78,6 +78,19 @@ struct fscrypt_info {
 	/* Back-pointer to the inode */
 	struct inode *ci_inode;
 
+	/*
+	 * The master key with which this inode was unlocked (decrypted).  This
+	 * will be NULL if the master key was found in a process-subscribed
+	 * keyring rather than in the filesystem-level keyring.
+	 */
+	struct key *ci_master_key;
+
+	/*
+	 * Link in list of inodes that were unlocked with the master key.
+	 * Only used when ->ci_master_key is set.
+	 */
+	struct list_head ci_master_key_link;
+
 	/*
 	 * If non-NULL, then encryption is done using the master key directly
 	 * and ci_ctfm will equal ci_direct_key->dk_ctfm.
@@ -186,14 +199,45 @@ struct fscrypt_master_key_secret {
  */
 struct fscrypt_master_key {
 
-	/* The secret key material */
+	/*
+	 * The secret key material.  After FS_IOC_REMOVE_ENCRYPTION_KEY is
+	 * executed, this is wiped and no new inodes can be unlocked with this
+	 * key; however, there may still be inodes in ->mk_decrypted_inodes
+	 * which could not be evicted.  As long as some inodes still remain,
+	 * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
+	 * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
+	 *
+	 * Locking: protected by key->sem.
+	 */
 	struct fscrypt_master_key_secret	mk_secret;
 
 	/* Arbitrary key descriptor which was assigned by userspace */
 	struct fscrypt_key_specifier		mk_spec;
 
+	/*
+	 * Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
+	 * Once this goes to 0, the master key is removed from ->s_master_keys.
+	 * The 'struct fscrypt_master_key' will continue to live as long as the
+	 * 'struct key' whose payload it is, but we won't let this reference
+	 * count rise again.
+	 */
+	refcount_t		mk_refcount;
+
+	/*
+	 * List of inodes that were unlocked using this key.  This allows the
+	 * inodes to be evicted efficiently if the key is removed.
+	 */
+	struct list_head	mk_decrypted_inodes;
+	spinlock_t		mk_decrypted_inodes_lock;
+
 } __randomize_layout;
 
+static inline bool
+is_master_key_secret_present(const struct fscrypt_master_key_secret *secret)
+{
+	return secret->size != 0;
+}
+
 extern struct key *
 fscrypt_find_master_key(struct super_block *sb,
 			const struct fscrypt_key_specifier *mk_spec);
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 252e863d681d..82d272c20969 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -10,6 +10,7 @@
  * filesystem-level keyring, including the ioctls:
  *
  * - FS_IOC_ADD_ENCRYPTION_KEY: add a key
+ * - FS_IOC_REMOVE_ENCRYPTION_KEY: remove a key
  */
 
 #include <linux/key-type.h>
@@ -66,6 +67,13 @@ static void fscrypt_key_destroy(struct key *key)
 static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
 {
 	seq_puts(m, key->description);
+
+	if (key_is_positive(key)) {
+		const struct fscrypt_master_key *mk = key->payload.data[0];
+
+		if (!is_master_key_secret_present(&mk->mk_secret))
+			seq_puts(m, ": secret removed");
+	}
 }
 
 /*
@@ -186,6 +194,10 @@ static int add_new_master_key(struct fscrypt_master_key_secret *secret,
 
 	move_master_key_secret(&mk->mk_secret, secret);
 
+	refcount_set(&mk->mk_refcount, 1); /* secret is present */
+	INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
+	spin_lock_init(&mk->mk_decrypted_inodes_lock);
+
 	format_mk_description(description, mk_spec);
 	key = key_alloc(&key_type_fscrypt, description,
 			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
@@ -207,6 +219,22 @@ static int add_new_master_key(struct fscrypt_master_key_secret *secret,
 	return err;
 }
 
+#define KEY_DEAD	1
+
+static int add_existing_master_key(struct fscrypt_master_key *mk,
+				   struct fscrypt_master_key_secret *secret,
+				   const struct fscrypt_key_specifier *mk_spec)
+{
+	if (is_master_key_secret_present(&mk->mk_secret))
+		return 0;
+
+	if (!refcount_inc_not_zero(&mk->mk_refcount))
+		return KEY_DEAD;
+
+	move_master_key_secret(&mk->mk_secret, secret);
+	return 0;
+}
+
 static int add_master_key(struct super_block *sb,
 			  struct fscrypt_master_key_secret *secret,
 			  const struct fscrypt_key_specifier *mk_spec)
@@ -216,6 +244,7 @@ static int add_master_key(struct super_block *sb,
 	int err;
 
 	mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
+retry:
 	key = fscrypt_find_master_key(sb, mk_spec);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
@@ -227,8 +256,21 @@ static int add_master_key(struct super_block *sb,
 			goto out_unlock;
 		err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
 	} else {
+		/*
+		 * Found the key in ->s_master_keys.  Re-add the secret if
+		 * needed.
+		 */
+		down_write(&key->sem);
+		err = add_existing_master_key(key->payload.data[0], secret,
+					      mk_spec);
+		up_write(&key->sem);
+		if (err == KEY_DEAD) {
+			/* Key being removed or needs to be removed */
+			key_invalidate(key);
+			key_put(key);
+			goto retry;
+		}
 		key_put(key);
-		err = 0;
 	}
 out_unlock:
 	mutex_unlock(&fscrypt_add_key_mutex);
@@ -277,6 +319,202 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
 
+static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
+{
+	struct fscrypt_info *ci;
+	struct inode *inode;
+	struct inode *toput_inode = NULL;
+
+	spin_lock(&mk->mk_decrypted_inodes_lock);
+
+	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
+		inode = ci->ci_inode;
+		spin_lock(&inode->i_lock);
+		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&mk->mk_decrypted_inodes_lock);
+
+		shrink_dcache_inode(inode);
+		iput(toput_inode);
+		toput_inode = inode;
+
+		spin_lock(&mk->mk_decrypted_inodes_lock);
+	}
+
+	spin_unlock(&mk->mk_decrypted_inodes_lock);
+	iput(toput_inode);
+}
+
+static int evict_decrypted_inodes(struct fscrypt_master_key *mk,
+				  struct super_block *sb)
+{
+	struct fscrypt_info *ci;
+	struct inode *inode;
+	LIST_HEAD(dispose);
+	unsigned long num_busy = 0;
+	unsigned long busy_ino;
+
+	spin_lock(&mk->mk_decrypted_inodes_lock);
+
+	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
+		inode = ci->ci_inode;
+		spin_lock(&inode->i_lock);
+
+		if (inode->i_state & (I_FREEING | I_WILL_FREE))
+			goto next;
+
+		if (atomic_read(&inode->i_count) ||
+		    (inode->i_state & ~I_REFERENCED)) {
+			num_busy++;
+			busy_ino = inode->i_ino;
+			goto next;
+		}
+
+		inode->i_state |= I_FREEING;
+		inode_lru_list_del(inode);
+		list_add(&inode->i_lru, &dispose);
+next:
+		spin_unlock(&inode->i_lock);
+	}
+
+	spin_unlock(&mk->mk_decrypted_inodes_lock);
+
+	evict_inode_list(&dispose);
+
+	if (unlikely(num_busy)) {
+		fscrypt_warn(sb, "%lu inodes still busy after removing key with description %*phN (%sino: %lu)",
+			     num_busy, master_key_spec_len(&mk->mk_spec),
+			     (u8 *)&mk->mk_spec.u,
+			     (num_busy > 1 ? "example " : ""), busy_ino);
+		return -EBUSY;
+	}
+
+	return 0;
+}
+
+static int try_to_lock_encrypted_files(struct super_block *sb,
+				       struct fscrypt_master_key *mk)
+{
+	int err1;
+	int err2;
+
+	/*
+	 * An inode can't be evicted while it still has dirty pages, or while
+	 * the inode itself is still dirty.  Thus, we first have to clean all
+	 * the inodes in ->mk_decrypted_inodes.
+	 *
+	 * Just do it the easy way: call sync_filesystem().  It's overkill, but
+	 * it works, and it's more important to minimize the amount of caches we
+	 * drop than the amount of data we sync.  Also, unprivileged users can
+	 * already call sync_filesystem() via sys_syncfs() or sys_sync().
+	 */
+	down_read(&sb->s_umount);
+	err1 = sync_filesystem(sb);
+	up_read(&sb->s_umount);
+
+	/*
+	 * Inodes are pinned by their dentries, so we have to evict the dentries
+	 * first.  We could potentially just call shrink_dcache_sb() here, but
+	 * that would be overkill, and an unprivileged user shouldn't be able to
+	 * evict all dentries for the entire filesystem.  Instead, go through
+	 * the inodes' alias lists and try to evict each dentry.
+	 */
+	evict_dentries_for_decrypted_inodes(mk);
+
+	/*
+	 * Finally, iterate through ->mk_decrypted_inodes and evict as many
+	 * inodes as we can.  Similarly, we could potentially just call
+	 * invalidate_inodes() here, but that would be overkill, and an
+	 * unprivileged user shouldn't be able to evict all inodes for the
+	 * entire filesystem.
+	 *
+	 * Note that ideally, we wouldn't really evict the inodes, but rather
+	 * just free their ->i_crypt_info and pagecache.  But eviction is *much*
+	 * easier to correctly implement.
+	 */
+	err2 = evict_decrypted_inodes(mk, sb);
+
+	return err1 ?: err2;
+}
+
+/*
+ * Try to remove an fscrypt master encryption key.  If other users have also
+ * added the key, we'll remove the current user's usage of the key, then return
+ * -EUSERS.  Otherwise we'll continue on and try to actually remove the key.
+ *
+ * First we wipe the actual master key secret from memory, so that no more
+ * inodes can be unlocked with it.  Then, we try to evict all cached inodes that
+ * had been unlocked using the key.  Since this can fail for in-use inodes, this
+ * is expected to be used in cooperation with userspace ensuring that none of
+ * the files are still open.
+ *
+ * If, nevertheless, some inodes could not be evicted, we return -EBUSY
+ * (although we still evicted as many inodes as possible) and keep the 'struct
+ * key' and the 'struct fscrypt_master_key' around to keep track of the list of
+ * remaining inodes.  Userspace can then retry the ioctl later to retry evicting
+ * the remaining inodes, or alternatively can add the secret key again.
+ *
+ * Note that even though we wipe the encryption *keys* from memory, decrypted
+ * data can likely still be found in memory, e.g. in pagecache pages that have
+ * been freed.  Wiping such data is currently out of scope, short of users who
+ * may choose to enable page and slab poisoning systemwide.
+ */
+int fscrypt_ioctl_remove_key(struct file *filp, const void __user *uarg)
+{
+	struct super_block *sb = file_inode(filp)->i_sb;
+	struct fscrypt_remove_key_arg arg;
+	struct key *key;
+	struct fscrypt_master_key *mk;
+	int err;
+	bool dead;
+
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+
+	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
+		return -EINVAL;
+
+	if (!valid_key_spec(&arg.key_spec))
+		return -EINVAL;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
+	/* Find the key being removed. */
+	key = fscrypt_find_master_key(sb, &arg.key_spec);
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+	mk = key->payload.data[0];
+
+	down_write(&key->sem);
+
+	/* Wipe the secret. */
+	dead = false;
+	if (is_master_key_secret_present(&mk->mk_secret)) {
+		wipe_master_key_secret(&mk->mk_secret);
+		dead = refcount_dec_and_test(&mk->mk_refcount);
+	}
+	up_write(&key->sem);
+	if (dead) {
+		/*
+		 * We wiped the secret and no inodes reference the key anymore,
+		 * so it's free to remove.
+		 */
+		key_invalidate(key);
+		err = 0;
+	} else {
+		/* Some inodes still reference this key; try to evict them. */
+		err = try_to_lock_encrypted_files(sb, mk);
+	}
+	key_put(key);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
+
 int __init fscrypt_init_keyring(void)
 {
 	return register_key_type(&key_type_fscrypt);
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index b63fb4e8aebd..8ffcfee73702 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -210,8 +210,16 @@ int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
 
 /*
  * Find the master key, then set up the inode's actual encryption key.
+ *
+ * If the master key is found in the filesystem-level keyring, then the
+ * corresponding 'struct key' is returned in *master_key_ret with
+ * ->sem read-locked.  This is needed to ensure that only one task links the
+ * fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race to create
+ * an fscrypt_info for the same inode), and to synchronize the key being removed
+ * with a new inode starting to use it.
  */
-static int setup_file_encryption_key(struct fscrypt_info *ci)
+static int setup_file_encryption_key(struct fscrypt_info *ci,
+				     struct key **master_key_ret)
 {
 	struct key *key;
 	struct fscrypt_master_key *mk = NULL;
@@ -231,6 +239,13 @@ static int setup_file_encryption_key(struct fscrypt_info *ci)
 	}
 
 	mk = key->payload.data[0];
+	down_read(&key->sem);
+
+	/* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
+	if (!is_master_key_secret_present(&mk->mk_secret)) {
+		err = -ENOKEY;
+		goto out_release_key;
+	}
 
 	if (mk->mk_secret.size < ci->ci_mode->keysize) {
 		fscrypt_warn(NULL,
@@ -242,14 +257,22 @@ static int setup_file_encryption_key(struct fscrypt_info *ci)
 	}
 
 	err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
+	if (err)
+		goto out_release_key;
+
+	*master_key_ret = key;
+	return 0;
 
 out_release_key:
+	up_read(&key->sem);
 	key_put(key);
 	return err;
 }
 
 static void put_crypt_info(struct fscrypt_info *ci)
 {
+	struct key *key;
+
 	if (!ci)
 		return;
 
@@ -259,6 +282,26 @@ static void put_crypt_info(struct fscrypt_info *ci)
 		crypto_free_skcipher(ci->ci_ctfm);
 		crypto_free_cipher(ci->ci_essiv_tfm);
 	}
+
+	key = ci->ci_master_key;
+	if (key) {
+		struct fscrypt_master_key *mk = key->payload.data[0];
+
+		/*
+		 * Remove this inode from the list of inodes that were unlocked
+		 * with the master key.
+		 *
+		 * In addition, if we're removing the last inode from a key that
+		 * already had its secret removed, invalidate the key so that it
+		 * gets removed from ->s_master_keys.
+		 */
+		spin_lock(&mk->mk_decrypted_inodes_lock);
+		list_del(&ci->ci_master_key_link);
+		spin_unlock(&mk->mk_decrypted_inodes_lock);
+		if (refcount_dec_and_test(&mk->mk_refcount))
+			key_invalidate(key);
+		key_put(key);
+	}
 	kmem_cache_free(fscrypt_info_cachep, ci);
 }
 
@@ -267,6 +310,7 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	struct fscrypt_info *crypt_info;
 	struct fscrypt_context ctx;
 	struct fscrypt_mode *mode;
+	struct key *master_key = NULL;
 	int res;
 
 	if (inode->i_crypt_info)
@@ -319,13 +363,30 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
 	crypt_info->ci_mode = mode;
 
-	res = setup_file_encryption_key(crypt_info);
+	res = setup_file_encryption_key(crypt_info, &master_key);
 	if (res)
 		goto out;
 
-	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
+	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
+		if (master_key) {
+			struct fscrypt_master_key *mk =
+				master_key->payload.data[0];
+
+			refcount_inc(&mk->mk_refcount);
+			crypt_info->ci_master_key = key_get(master_key);
+			spin_lock(&mk->mk_decrypted_inodes_lock);
+			list_add(&crypt_info->ci_master_key_link,
+				 &mk->mk_decrypted_inodes);
+			spin_unlock(&mk->mk_decrypted_inodes_lock);
+		}
 		crypt_info = NULL;
+	}
+	res = 0;
 out:
+	if (master_key) {
+		up_read(&master_key->sem);
+		key_put(master_key);
+	}
 	if (res == -ENOKEY)
 		res = 0;
 	put_crypt_info(crypt_info);
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index ddb54b8eab81..a8fabae9a5fe 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -114,6 +114,7 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *,
 					void *, bool);
 /* keyring.c */
 extern int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
+extern int fscrypt_ioctl_remove_key(struct file *filp, const void __user *arg);
 
 /* keysetup.c */
 extern int fscrypt_get_encryption_info(struct inode *);
@@ -321,6 +322,12 @@ static inline int fscrypt_ioctl_add_key(struct file *filp, void __user *arg)
 	return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_ioctl_remove_key(struct file *filp,
+					   const void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
 /* keysetup.c */
 static inline int fscrypt_get_encryption_info(struct inode *inode)
 {
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 7bed24632bda..3302a407131e 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -65,10 +65,17 @@ struct fscrypt_add_key_arg {
 	__u8 raw[];
 };
 
+/* Struct passed to FS_IOC_REMOVE_ENCRYPTION_KEY */
+struct fscrypt_remove_key_arg {
+	struct fscrypt_key_specifier key_spec;
+	__u32 __reserved[6];
+};
+
 #define FS_IOC_SET_ENCRYPTION_POLICY	  _IOR('f', 19, struct fscrypt_policy)
 #define FS_IOC_GET_ENCRYPTION_PWSALT	  _IOW('f', 20, __u8[16])
 #define FS_IOC_GET_ENCRYPTION_POLICY	  _IOW('f', 21, struct fscrypt_policy)
 #define FS_IOC_ADD_ENCRYPTION_KEY	 _IOWR('f', 23, struct fscrypt_add_key_arg)
+#define FS_IOC_REMOVE_ENCRYPTION_KEY	  _IOW('f', 24, struct fscrypt_remove_key_arg)
 
 /**********************************************************************/
 
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 12/20] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (10 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 13/20] fscrypt: add an HKDF-SHA512 implementation Eric Biggers
                   ` (7 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add a new fscrypt ioctl, FS_IOC_GET_ENCRYPTION_KEY_STATUS.  Given a key
specified by 'struct fscrypt_key_specifier' (the same way a key is
specified for the other fscrypt key management ioctls), it returns
status information in a 'struct fscrypt_get_key_status_arg'.

The main motivation for this is that applications need to be able to
check whether an encrypted directory is "unlocked" or not, so that they
can add the key if it is not, and avoid adding the key (which may
involve prompting the user for a passphrase) if it already is.

It's possible to use some workarounds such as checking whether opening a
regular file fails with ENOKEY, or checking whether the filenames "look
like gibberish" or not.  However, no workaround is usable in all cases.

Like the other key management ioctls, the keyrings syscalls may seem at
first to be a good fit for this.  Unfortunately, they are not.  Even if
we exposed the keyring ID of the ->s_master_keys keyring and gave
everyone Search permission on it (note: currently the keyrings
permission system would also allow everyone to "invalidate" the keyring
too), the fscrypt keys have an additional state that doesn't map cleanly
to the keyrings API: the secret can be removed, but we can be still
tracking the files that were using the key, and the removal can be
re-attempted or the secret added again.

After later patches, some applications will also need a way to determine
whether a key was added by the current user vs. by some other user.
Reserved fields are included in fscrypt_get_key_status_arg for this and
other future extensions.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/keyring.c          | 60 ++++++++++++++++++++++++++++++++++++
 include/linux/fscrypt.h      |  7 +++++
 include/uapi/linux/fscrypt.h | 15 +++++++++
 3 files changed, 82 insertions(+)

diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 82d272c20969..73be8bda49bd 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -11,6 +11,7 @@
  *
  * - FS_IOC_ADD_ENCRYPTION_KEY: add a key
  * - FS_IOC_REMOVE_ENCRYPTION_KEY: remove a key
+ * - FS_IOC_GET_ENCRYPTION_KEY_STATUS: get key status
  */
 
 #include <linux/key-type.h>
@@ -515,6 +516,65 @@ int fscrypt_ioctl_remove_key(struct file *filp, const void __user *uarg)
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
 
+/*
+ * Retrieve the status of an fscrypt master encryption key.
+ *
+ * We set ->status to indicate whether the key is absent, present, or
+ * incompletely removed.  "Incompletely removed" means that the master key
+ * secret has been removed, but some files which had been unlocked with it are
+ * still in use.  This field allows applications to easily determine the state
+ * of an encrypted directory without using a hack such as trying to open a
+ * regular file in it (which can confuse the "incompletely removed" state with
+ * absent or present).
+ */
+int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
+{
+	struct super_block *sb = file_inode(filp)->i_sb;
+	struct fscrypt_get_key_status_arg arg;
+	struct key *key;
+	struct fscrypt_master_key *mk;
+	int err;
+
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+
+	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
+		return -EINVAL;
+
+	if (!valid_key_spec(&arg.key_spec))
+		return -EINVAL;
+
+	memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
+
+	key = fscrypt_find_master_key(sb, &arg.key_spec);
+	if (IS_ERR(key)) {
+		if (key != ERR_PTR(-ENOKEY))
+			return PTR_ERR(key);
+		arg.status = FSCRYPT_KEY_STATUS_ABSENT;
+		err = 0;
+		goto out;
+	}
+	mk = key->payload.data[0];
+	down_read(&key->sem);
+
+	if (!is_master_key_secret_present(&mk->mk_secret)) {
+		arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
+		err = 0;
+		goto out_release_key;
+	}
+
+	arg.status = FSCRYPT_KEY_STATUS_PRESENT;
+	err = 0;
+out_release_key:
+	up_read(&key->sem);
+	key_put(key);
+out:
+	if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
+		err = -EFAULT;
+	return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
+
 int __init fscrypt_init_keyring(void)
 {
 	return register_key_type(&key_type_fscrypt);
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index a8fabae9a5fe..dace3fd1bf19 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -115,6 +115,7 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *,
 /* keyring.c */
 extern int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
 extern int fscrypt_ioctl_remove_key(struct file *filp, const void __user *arg);
+extern int fscrypt_ioctl_get_key_status(struct file *filp, void __user *arg);
 
 /* keysetup.c */
 extern int fscrypt_get_encryption_info(struct inode *);
@@ -339,6 +340,12 @@ static inline void fscrypt_put_encryption_info(struct inode *inode)
 	return;
 }
 
+static inline int fscrypt_ioctl_get_key_status(struct file *filp,
+					       void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
  /* fname.c */
 static inline int fscrypt_setup_filename(struct inode *dir,
 					 const struct qstr *iname,
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 3302a407131e..042e70a4ff7e 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -71,11 +71,26 @@ struct fscrypt_remove_key_arg {
 	__u32 __reserved[6];
 };
 
+/* Struct passed to FS_IOC_GET_ENCRYPTION_KEY_STATUS */
+struct fscrypt_get_key_status_arg {
+	/* input */
+	struct fscrypt_key_specifier key_spec;
+	__u32 __reserved[6];
+
+	/* output */
+#define FSCRYPT_KEY_STATUS_ABSENT		1
+#define FSCRYPT_KEY_STATUS_PRESENT		2
+#define FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED	3
+	__u32 status;
+	__u32 __out_reserved[15];
+};
+
 #define FS_IOC_SET_ENCRYPTION_POLICY	  _IOR('f', 19, struct fscrypt_policy)
 #define FS_IOC_GET_ENCRYPTION_PWSALT	  _IOW('f', 20, __u8[16])
 #define FS_IOC_GET_ENCRYPTION_POLICY	  _IOW('f', 21, struct fscrypt_policy)
 #define FS_IOC_ADD_ENCRYPTION_KEY	 _IOWR('f', 23, struct fscrypt_add_key_arg)
 #define FS_IOC_REMOVE_ENCRYPTION_KEY	  _IOW('f', 24, struct fscrypt_remove_key_arg)
+#define FS_IOC_GET_ENCRYPTION_KEY_STATUS _IOWR('f', 25, struct fscrypt_get_key_status_arg)
 
 /**********************************************************************/
 
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 13/20] fscrypt: add an HKDF-SHA512 implementation
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (11 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 12/20] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 14/20] fscrypt: v2 encryption policy support Eric Biggers
                   ` (6 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add an implementation of HKDF (RFC 5869) to fscrypt, for the purpose of
deriving additional key material from the fscrypt master keys for v2
encryption policies.  HKDF is a key derivation function built on top of
HMAC.  We choose SHA-512 for the underlying unkeyed hash, and use an
"hmac(sha512)" transform allocated from the crypto API.

We'll be using this to replace the AES-ECB based KDF currently used to
derive the per-file encryption keys.  While the AES-ECB based KDF is
believed to meet the original security requirements, it is nonstandard
and has problems that don't exist in modern KDFs such as HKDF:

1. It's reversible.  Given a derived key and nonce, an attacker can
   easily compute the master key.  This is okay if the master key and
   derived keys are equally hard to compromise, but now we'd like to be
   more robust against threats such as a derived key being compromised
   through a timing attack, or a derived key for an in-use file being
   compromised after the master key has already been removed.

2. It doesn't evenly distribute the entropy from the master key; each 16
   input bytes only affects the corresponding 16 output bytes.

3. It isn't easily extensible to deriving other values or keys that are
   or will be needed, such as per-mode keys (which is what DIRECT_KEY
   policies really should use, rather than the master key directly as
   they do now) or a public hash for securely identifying the key (to
   ensure that an encrypted file cannot be set up with the wrong key).

HKDF solves all the above problems.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/Kconfig           |   2 +
 fs/crypto/Makefile          |   1 +
 fs/crypto/fscrypt_private.h |  15 +++
 fs/crypto/hkdf.c            | 188 ++++++++++++++++++++++++++++++++++++
 4 files changed, 206 insertions(+)
 create mode 100644 fs/crypto/hkdf.c

diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
index f0de238000c0..c160598a9fe2 100644
--- a/fs/crypto/Kconfig
+++ b/fs/crypto/Kconfig
@@ -7,6 +7,8 @@ config FS_ENCRYPTION
 	select CRYPTO_XTS
 	select CRYPTO_CTS
 	select CRYPTO_SHA256
+	select CRYPTO_SHA512
+	select CRYPTO_HMAC
 	select KEYS
 	help
 	  Enable encryption of files and directories.  This
diff --git a/fs/crypto/Makefile b/fs/crypto/Makefile
index accdd622c908..4977b4347928 100644
--- a/fs/crypto/Makefile
+++ b/fs/crypto/Makefile
@@ -2,6 +2,7 @@ obj-$(CONFIG_FS_ENCRYPTION)	+= fscrypto.o
 
 fscrypto-y := crypto.o \
 	      fname.o \
+	      hkdf.o \
 	      hooks.o \
 	      keyring.o \
 	      keysetup.o \
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index b09fc2939a89..f8b8358e9527 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -175,6 +175,21 @@ extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
 					 u32 orig_len, u32 max_len,
 					 u32 *encrypted_len_ret);
 
+/* hkdf.c */
+
+struct fscrypt_hkdf {
+	struct crypto_shash *hmac_tfm;
+};
+
+extern int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
+			     unsigned int master_key_size);
+
+extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
+			       const u8 *info, unsigned int infolen,
+			       u8 *okm, unsigned int okmlen);
+
+extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
+
 /* keyring.c */
 
 /*
diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c
new file mode 100644
index 000000000000..9c6346e3f227
--- /dev/null
+++ b/fs/crypto/hkdf.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implementation of HKDF ("HMAC-based Extract-and-Expand Key Derivation
+ * Function"), aka RFC 5869.  See also the original paper (Krawczyk 2010):
+ * "Cryptographic Extraction and Key Derivation: The HKDF Scheme".
+ *
+ * This is used to derive keys from the fscrypt master keys.
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include <crypto/hash.h>
+#include <crypto/sha.h>
+
+#include "fscrypt_private.h"
+
+/*
+ * HKDF supports any unkeyed cryptographic hash algorithm, but fscrypt uses
+ * SHA-512 because it is reasonably secure and efficient; and since it produces
+ * a 64-byte digest, deriving an AES-256-XTS key preserves all 64 bytes of
+ * entropy from the master key and requires only one iteration of HKDF-Expand.
+ */
+#define HKDF_HMAC_ALG		"hmac(sha512)"
+#define HKDF_HASHLEN		SHA512_DIGEST_SIZE
+
+/*
+ * HKDF consists of two steps:
+ *
+ * 1. HKDF-Extract: extract a pseudorandom key of length HKDF_HASHLEN bytes from
+ *    the input keying material and optional salt.
+ * 2. HKDF-Expand: expand the pseudorandom key into output keying material of
+ *    any length, parameterized by an application-specific info string.
+ *
+ * HKDF-Extract can be skipped if the input is already a pseudorandom key of
+ * length HKDF_HASHLEN bytes.  However, cipher modes other than AES-256-XTS take
+ * shorter keys, and we don't want to force users of those modes to generate
+ * unnecessarily long keys.  Thus fscrypt still does HKDF-Extract.
+ *
+ * HKDF-Extract also supports a salt.  Choosing a random salt per input key
+ * would permit the input key to come from *any* source with sufficient entropy,
+ * even if it's not distributed uniformly.  However, fscrypt doesn't take
+ * advantage of this because userspace should already provide good pseudorandom
+ * keys, which makes this unnecessary; also, having to persist a random salt per
+ * key from kernel mode would pose significant implementation complexity.  Thus
+ * fscrypt uses a fixed salt.  But to be slightly more robust against userspace
+ * (unwisely) reusing the fscrypt keys for another purpose, and to force
+ * brute-force attacks to target the fscrypt KDF specifically, fscrypt uses
+ * "fscrypt_hkdf_salt" rather than the default of all 0's defined by RFC 5869.
+ */
+
+#define HKDF_SALT		"fscrypt_hkdf_salt"
+#define HKDF_SALT_LEN		CONST_STRLEN(HKDF_SALT)
+
+/* HKDF-Extract (RFC 5869 section 2.2), see explanation above */
+static int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
+			unsigned int ikmlen, u8 prk[HKDF_HASHLEN])
+{
+	SHASH_DESC_ON_STACK(desc, hmac_tfm);
+	int err;
+
+	desc->tfm = hmac_tfm;
+	desc->flags = 0;
+
+	err = crypto_shash_setkey(hmac_tfm, HKDF_SALT, HKDF_SALT_LEN);
+	if (err)
+		goto out;
+
+	err = crypto_shash_digest(desc, ikm, ikmlen, prk);
+out:
+	shash_desc_zero(desc);
+	return err;
+}
+
+/*
+ * Compute HKDF-Extract using the given master key as the input keying material,
+ * and prepare an HMAC transform object keyed by the resulting pseudorandom key.
+ *
+ * Afterwards, the keyed HMAC transform object can be used for HKDF-Expand many
+ * times without having to recompute HKDF-Extract each time.
+ */
+int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
+		      unsigned int master_key_size)
+{
+	struct crypto_shash *hmac_tfm;
+	u8 prk[HKDF_HASHLEN];
+	int err;
+
+	hmac_tfm = crypto_alloc_shash(HKDF_HMAC_ALG, 0, 0);
+	if (IS_ERR(hmac_tfm)) {
+		fscrypt_warn(NULL, "error allocating " HKDF_HMAC_ALG ": %ld",
+			     PTR_ERR(hmac_tfm));
+		return PTR_ERR(hmac_tfm);
+	}
+
+	BUG_ON(crypto_shash_digestsize(hmac_tfm) != sizeof(prk));
+
+	err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk);
+	if (err)
+		goto err_free_tfm;
+
+	err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk));
+	if (err)
+		goto err_free_tfm;
+
+	hkdf->hmac_tfm = hmac_tfm;
+	goto out;
+
+err_free_tfm:
+	crypto_free_shash(hmac_tfm);
+out:
+	memzero_explicit(prk, sizeof(prk));
+	return err;
+}
+
+/*
+ * HKDF-Expand (RFC 5869 section 2.3).  This expands the pseudorandom key, which
+ * was already keyed into 'hkdf->hmac_tfm' by fscrypt_init_hkdf(), into 'okmlen'
+ * bytes of output keying material parameterized by the application-specific
+ * 'info' of length 'infolen' bytes, prefixed with the 'context' byte.  This is
+ * thread-safe and may be called by multiple threads in parallel.
+ *
+ * ('context' isn't part of the HKDF specification; it's just a prefix fscrypt
+ * adds to its application-specific info strings to guarantee that it doesn't
+ * accidentally repeat an info string when using HKDF for different purposes.)
+ */
+int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
+			const u8 *info, unsigned int infolen,
+			u8 *okm, unsigned int okmlen)
+{
+	SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm);
+	int err;
+	const u8 *prev = NULL;
+	unsigned int i;
+	u8 counter = 1;
+	u8 tmp[HKDF_HASHLEN];
+
+	desc->tfm = hkdf->hmac_tfm;
+	desc->flags = 0;
+
+	if (WARN_ON(okmlen > 255 * HKDF_HASHLEN))
+		return -EINVAL;
+
+	for (i = 0; i < okmlen; i += HKDF_HASHLEN) {
+
+		err = crypto_shash_init(desc);
+		if (err)
+			goto out;
+
+		if (prev) {
+			err = crypto_shash_update(desc, prev, HKDF_HASHLEN);
+			if (err)
+				goto out;
+		}
+
+		err = crypto_shash_update(desc, &context, 1);
+		if (err)
+			goto out;
+
+		err = crypto_shash_update(desc, info, infolen);
+		if (err)
+			goto out;
+
+		if (okmlen - i < HKDF_HASHLEN) {
+			err = crypto_shash_finup(desc, &counter, 1, tmp);
+			if (err)
+				goto out;
+			memcpy(&okm[i], tmp, okmlen - i);
+			memzero_explicit(tmp, sizeof(tmp));
+		} else {
+			err = crypto_shash_finup(desc, &counter, 1, &okm[i]);
+			if (err)
+				goto out;
+		}
+		counter++;
+		prev = &okm[i];
+	}
+	err = 0;
+out:
+	if (unlikely(err))
+		memzero_explicit(okm, okmlen); /* so caller doesn't need to */
+	shash_desc_zero(desc);
+	return err;
+}
+
+void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf)
+{
+	crypto_free_shash(hkdf->hmac_tfm);
+}
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 14/20] fscrypt: v2 encryption policy support
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (12 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 13/20] fscrypt: add an HKDF-SHA512 implementation Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 15/20] fscrypt: allow unprivileged users to add/remove keys for v2 policies Eric Biggers
                   ` (5 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Add a new fscrypt policy version, "v2".  It has the following changes
from the original policy version, which we call "v1" (*):

- The encryption key is identified by a 16-byte master_key_identifier,
  which is derived from the key itself using HKDF-SHA512.  This prevents
  users from associating the wrong key with an encrypted file or
  directory.  This was easily possible with v1 policies, which
  identified the key by an arbitrary 8-byte master_key_descriptor.

- Per-file keys are derived using HKDF-SHA512 rather than the
  AES-128-ECB based KDF.  This has various advantages, e.g. it's
  nonreversible and it evenly distributes entropy from the master key.

- The semantics of the DIRECT_KEY flag are implemented by deriving a
  per-mode key, again with HKDF-SHA512, rather than using the master key
  directly.  Thus the master key is only ever used as HKDF input, and
  it's much more difficult for userspace to screw things up.

- The key must be provided in the filesystem-level keyring, not in a
  process-subscribed keyring.

The following UAPI additions are made:

- The existing ioctl FS_IOC_SET_ENCRYPTION_POLICY can now be passed a
  fscrypt_policy_v2 to set a v2 encryption policy.  It's disambiguated
  from fscrypt_policy/fscrypt_policy_v1 by the version code prefix.

- A new ioctl FS_IOC_GET_ENCRYPTION_POLICY_EX is added.  It allows
  getting the v1 or v2 encryption policy of an encrypted file or
  directory.  The existing FS_IOC_GET_ENCRYPTION_POLICY ioctl could not
  be used because it did not have a way for userspace to indicate which
  policy structure is expected.  The new ioctl includes a size field, so
  it is extensible to future fscrypt policy versions.

- The ioctls FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY,
  and FS_IOC_GET_ENCRYPTION_KEY_STATUS now support managing keys for v2
  encryption policies.  Such keys are kept logically separate from keys
  for v1 encryption policies, and are identified by 'identifier' rather
  than by 'descriptor'.  The 'identifier' need not be provided when
  adding a key, since the kernel will calculate it anyway.

This patch temporarily keeps adding/removing v2 policy keys behind the
same permission check done for adding/removing v1 policy keys:
capable(CAP_SYS_ADMIN).  However, the next patch will carefully take
advantage of the cryptographically secure master_key_identifier to allow
non-root users to add/remove v2 policy keys, thus providing a full
replacement for v1 policies.

(*) Actually, in the API fscrypt_policy::version is 0 while on-disk
    fscrypt_context::format is 1.  But I believe it makes the most sense
    to advance both to '2' to have them be in sync, and to consider the
    numbering to start at 1 except for the API quirk.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/crypto.c           |   3 +-
 fs/crypto/fname.c            |   3 +-
 fs/crypto/fscrypt_private.h  | 180 ++++++++++++++---
 fs/crypto/keyring.c          |  37 +++-
 fs/crypto/keysetup.c         | 174 ++++++++++++----
 fs/crypto/keysetup_legacy.c  |  18 +-
 fs/crypto/policy.c           | 382 +++++++++++++++++++++++++----------
 include/linux/fscrypt.h      |   9 +-
 include/uapi/linux/fscrypt.h |  42 +++-
 9 files changed, 665 insertions(+), 183 deletions(-)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 8726c4e94077..7abc6695fa4d 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -26,7 +26,6 @@
 #include <linux/ratelimit.h>
 #include <linux/dcache.h>
 #include <linux/namei.h>
-#include <crypto/aes.h>
 #include <crypto/skcipher.h>
 #include "fscrypt_private.h"
 
@@ -139,7 +138,7 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 	memset(iv, 0, ci->ci_mode->ivsize);
 	iv->lblk_num = cpu_to_le64(lblk_num);
 
-	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
+	if (fscrypt_is_direct_key_policy(&ci->ci_policy))
 		memcpy(iv->nonce, ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 
 	if (ci->ci_essiv_tfm != NULL)
diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 37c26ad36d0e..57e0caba9d12 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -186,7 +186,8 @@ static int digest_decode(const char *src, int len, char *dst)
 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 				  u32 max_len, u32 *encrypted_len_ret)
 {
-	int padding = 4 << (inode->i_crypt_info->ci_flags &
+	const struct fscrypt_info *ci = inode->i_crypt_info;
+	int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
 			    FSCRYPT_POLICY_FLAGS_PAD_MASK);
 	u32 encrypted_len;
 
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index f8b8358e9527..1a40f7359655 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -20,27 +20,125 @@
 
 #define FSCRYPT_MIN_KEY_SIZE		16
 
-/**
- * Encryption context for inode
- *
- * Protector format:
- *  1 byte: Protector format (1 = this version)
- *  1 byte: File contents encryption mode
- *  1 byte: File names encryption mode
- *  1 byte: Flags
- *  8 bytes: Master Key descriptor
- *  16 bytes: Encryption Key derivation nonce
- */
-struct fscrypt_context {
-	u8 format;
+#define FSCRYPT_CONTEXT_V1	1
+#define FSCRYPT_CONTEXT_V2	2
+
+struct fscrypt_context_v1 {
+	u8 version; /* FSCRYPT_CONTEXT_V1 */
 	u8 contents_encryption_mode;
 	u8 filenames_encryption_mode;
 	u8 flags;
 	u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 	u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
-} __packed;
+};
+
+struct fscrypt_context_v2 {
+	u8 version; /* FSCRYPT_CONTEXT_V2 */
+	u8 contents_encryption_mode;
+	u8 filenames_encryption_mode;
+	u8 flags;
+	u8 __reserved[4];
+	u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
+	u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
+};
+
+/**
+ * fscrypt_context - the encryption context of an inode
+ *
+ * This is the on-disk equivalent of an fscrypt_policy, stored alongside each
+ * encrypted file usually in a hidden extended attribute.  It contains the
+ * fields from the fscrypt_policy, in order to identify the encryption algorithm
+ * and key with which the file is encrypted.  It also contains a nonce that was
+ * randomly generated by fscrypt itself; this is used as KDF input or as a tweak
+ * to cause different files to be encrypted differently.
+ */
+union fscrypt_context {
+	struct fscrypt_context_v1 v1;
+	struct fscrypt_context_v2 v2;
+};
+
+/*
+ * Return the size expected for the given fscrypt_context based on its version
+ * number, or 0 if the context version is unrecognized.
+ */
+static inline int fscrypt_context_size(const union fscrypt_context *ctx)
+{
+	switch (ctx->v1.version) {
+	case FSCRYPT_CONTEXT_V1:
+		BUILD_BUG_ON(sizeof(ctx->v1) != 28);
+		return sizeof(ctx->v1);
+	case FSCRYPT_CONTEXT_V2:
+		BUILD_BUG_ON(sizeof(ctx->v2) != 40);
+		return sizeof(ctx->v2);
+	}
+	return 0;
+}
+
+#undef fscrypt_policy
+union fscrypt_policy {
+	struct fscrypt_policy_v1 v1;
+	struct fscrypt_policy_v2 v2;
+};
+
+/*
+ * Return the size expected for the given fscrypt_policy based on its version
+ * number, or 0 if the policy version is unrecognized.
+ */
+static inline int fscrypt_policy_size(const union fscrypt_policy *policy)
+{
+	switch (policy->v1.version) {
+	case FSCRYPT_POLICY_V1:
+		return sizeof(policy->v1);
+	case FSCRYPT_POLICY_V2:
+		return sizeof(policy->v2);
+	}
+	return 0;
+}
 
-#define FS_ENCRYPTION_CONTEXT_FORMAT_V1		1
+/* Return the contents encryption mode of a valid encryption policy */
+static inline u8
+fscrypt_policy_contents_mode(const union fscrypt_policy *policy)
+{
+	switch (policy->v1.version) {
+	case FSCRYPT_POLICY_V1:
+		return policy->v1.contents_encryption_mode;
+	case FSCRYPT_POLICY_V2:
+		return policy->v2.contents_encryption_mode;
+	}
+	BUG();
+}
+
+/* Return the filenames encryption mode of a valid encryption policy */
+static inline u8
+fscrypt_policy_fnames_mode(const union fscrypt_policy *policy)
+{
+	switch (policy->v1.version) {
+	case FSCRYPT_POLICY_V1:
+		return policy->v1.filenames_encryption_mode;
+	case FSCRYPT_POLICY_V2:
+		return policy->v2.filenames_encryption_mode;
+	}
+	BUG();
+}
+
+/* Return the flags (FSCRYPT_POLICY_FLAG*) of a valid encryption policy */
+static inline u8
+fscrypt_policy_flags(const union fscrypt_policy *policy)
+{
+	switch (policy->v1.version) {
+	case FSCRYPT_POLICY_V1:
+		return policy->v1.flags;
+	case FSCRYPT_POLICY_V2:
+		return policy->v2.flags;
+	}
+	BUG();
+}
+
+static inline bool
+fscrypt_is_direct_key_policy(const union fscrypt_policy *policy)
+{
+	return fscrypt_policy_flags(policy) & FSCRYPT_POLICY_FLAG_DIRECT_KEY;
+}
 
 /**
  * For encrypted symlinks, the ciphertext length is stored at the beginning
@@ -70,8 +168,8 @@ struct fscrypt_info {
 	struct crypto_cipher *ci_essiv_tfm;
 
 	/*
-	 * Encryption mode used for this inode.  It corresponds to either
-	 * ci_data_mode or ci_filename_mode, depending on the inode type.
+	 * Encryption mode used for this inode.  It corresponds to either the
+	 * contents or filenames encryption mode, depending on the inode type.
 	 */
 	struct fscrypt_mode *ci_mode;
 
@@ -97,11 +195,10 @@ struct fscrypt_info {
 	 */
 	struct fscrypt_direct_key *ci_direct_key;
 
-	/* fields from the fscrypt_context */
-	u8 ci_data_mode;
-	u8 ci_filename_mode;
-	u8 ci_flags;
-	u8 ci_master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+	/* The encryption policy used by this inode */
+	union fscrypt_policy ci_policy;
+
+	/* This inode's nonce, copied from the fscrypt_context */
 	u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 };
 
@@ -184,6 +281,17 @@ struct fscrypt_hkdf {
 extern int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
 			     unsigned int master_key_size);
 
+/*
+ * The list of contexts in which fscrypt uses HKDF.  These values are used as
+ * the first byte of the HKDF application-specific info string to guarantee that
+ * info strings are never repeated between contexts.  This ensures that all HKDF
+ * outputs are unique and cryptographically isolated, i.e. knowledge of one
+ * output doesn't reveal another.
+ */
+#define HKDF_CONTEXT_KEY_IDENTIFIER	1
+#define HKDF_CONTEXT_PER_FILE_KEY	2
+#define HKDF_CONTEXT_PER_MODE_KEY	3
+
 extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
 			       const u8 *info, unsigned int infolen,
 			       u8 *okm, unsigned int okmlen);
@@ -197,10 +305,16 @@ extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
  */
 struct fscrypt_master_key_secret {
 
-	/* Size of the raw key in bytes */
+	/*
+	 * For v2 policy keys: HKDF context keyed by this master key.
+	 * For v1 policy keys: not set (hkdf.hmac_tfm == NULL).
+	 */
+	struct fscrypt_hkdf	hkdf;
+
+	/* Size of the raw key in bytes.  Set even if ->raw isn't set. */
 	u32			size;
 
-	/* The raw key */
+	/* For v1 policy keys: the raw key.  Wiped for v2 policy keys. */
 	u8			raw[FSCRYPT_MAX_KEY_SIZE];
 
 } __randomize_layout;
@@ -226,7 +340,12 @@ struct fscrypt_master_key {
 	 */
 	struct fscrypt_master_key_secret	mk_secret;
 
-	/* Arbitrary key descriptor which was assigned by userspace */
+	/*
+	 * For v1 policy keys: an arbitrary key descriptor which was assigned by
+	 * userspace (->descriptor).
+	 *
+	 * For v2 policy keys: a cryptographic hash of this key (->identifier).
+	 */
 	struct fscrypt_key_specifier		mk_spec;
 
 	/*
@@ -245,6 +364,9 @@ struct fscrypt_master_key {
 	struct list_head	mk_decrypted_inodes;
 	spinlock_t		mk_decrypted_inodes_lock;
 
+	/* Per-mode tfms for DIRECT_KEY policies, allocated on-demand */
+	struct crypto_skcipher	*mk_mode_keys[__FSCRYPT_MODE_MAX + 1];
+
 } __randomize_layout;
 
 static inline bool
@@ -295,5 +417,13 @@ extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
 
 extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
 					struct fscrypt_info *ci);
+/* policy.c */
+
+extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
+				   const union fscrypt_policy *policy2);
+extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u);
+extern int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
+				       const union fscrypt_context *ctx_u,
+				       int ctx_size);
 
 #endif /* _FSCRYPT_PRIVATE_H */
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 73be8bda49bd..6bf1e0672a09 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -14,6 +14,7 @@
  * - FS_IOC_GET_ENCRYPTION_KEY_STATUS: get key status
  */
 
+#include <crypto/skcipher.h>
 #include <linux/key-type.h>
 #include <linux/seq_file.h>
 
@@ -21,6 +22,7 @@
 
 static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
 {
+	fscrypt_destroy_hkdf(&secret->hkdf);
 	memzero_explicit(secret, sizeof(*secret));
 }
 
@@ -33,7 +35,13 @@ static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
 
 static void free_master_key(struct fscrypt_master_key *mk)
 {
+	size_t i;
+
 	wipe_master_key_secret(&mk->mk_secret);
+
+	for (i = 0; i < ARRAY_SIZE(mk->mk_mode_keys); i++)
+		crypto_free_skcipher(mk->mk_mode_keys[i]);
+
 	kzfree(mk);
 }
 
@@ -42,6 +50,8 @@ static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
 	switch (spec->type) {
 	case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
 		return FSCRYPT_KEY_DESCRIPTOR_SIZE;
+	case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
+		return FSCRYPT_KEY_IDENTIFIER_SIZE;
 	}
 	return 0;
 }
@@ -115,7 +125,7 @@ static struct key *search_fscrypt_keyring(struct key *keyring,
 #define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE	\
 	(CONST_STRLEN("fscrypt-") + FIELD_SIZEOF(struct super_block, s_id))
 
-#define FSCRYPT_MK_DESCRIPTION_SIZE	(2 * FSCRYPT_KEY_DESCRIPTOR_SIZE + 1)
+#define FSCRYPT_MK_DESCRIPTION_SIZE	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
 
 static void format_fs_keyring_description(
 			char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
@@ -313,6 +323,31 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 	if (!capable(CAP_SYS_ADMIN))
 		goto out_wipe_secret;
 
+	if (arg.key_spec.type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
+		err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
+		if (err)
+			goto out_wipe_secret;
+
+		/*
+		 * Now that the HKDF context is initialized, the raw key is no
+		 * longer needed.
+		 */
+		memzero_explicit(secret.raw, sizeof(secret.raw));
+
+		/* Calculate the key identifier and return it to userspace. */
+		err = fscrypt_hkdf_expand(&secret.hkdf,
+					  HKDF_CONTEXT_KEY_IDENTIFIER,
+					  NULL, 0, arg.key_spec.u.identifier,
+					  FSCRYPT_KEY_IDENTIFIER_SIZE);
+		if (err)
+			goto out_wipe_secret;
+		err = -EFAULT;
+		if (copy_to_user(uarg->key_spec.u.identifier,
+				 arg.key_spec.u.identifier,
+				 FSCRYPT_KEY_IDENTIFIER_SIZE))
+			goto out_wipe_secret;
+	}
+
 	err = add_master_key(sb, &secret, &arg.key_spec);
 out_wipe_secret:
 	wipe_master_key_secret(&secret);
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 8ffcfee73702..a15a4bbafa3c 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -52,21 +52,14 @@ static struct fscrypt_mode available_modes[] = {
 };
 
 static struct fscrypt_mode *
-select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
+select_encryption_mode(const union fscrypt_policy *policy,
+		       const struct inode *inode)
 {
-	if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
-		fscrypt_warn(inode->i_sb,
-			     "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
-			     inode->i_ino, ci->ci_data_mode,
-			     ci->ci_filename_mode);
-		return ERR_PTR(-EINVAL);
-	}
-
 	if (S_ISREG(inode->i_mode))
-		return &available_modes[ci->ci_data_mode];
+		return &available_modes[fscrypt_policy_contents_mode(policy)];
 
 	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
-		return &available_modes[ci->ci_filename_mode];
+		return &available_modes[fscrypt_policy_fnames_mode(policy)];
 
 	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
 		  inode->i_ino, (inode->i_mode & S_IFMT));
@@ -208,6 +201,83 @@ int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
 	return 0;
 }
 
+static int setup_per_mode_key(struct fscrypt_info *ci,
+			      struct fscrypt_master_key *mk)
+{
+	u8 mode_num = ci->ci_mode - available_modes;
+	struct crypto_skcipher **tfm_p;
+	struct crypto_skcipher *tfm;
+	u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
+	int err;
+
+	if (WARN_ON(mode_num >= ARRAY_SIZE(mk->mk_mode_keys)))
+		return -EINVAL;
+	tfm_p = &mk->mk_mode_keys[mode_num];
+retry:
+	/* pairs with cmpxchg_release() below */
+	tfm = smp_load_acquire(tfm_p);
+	if (likely(tfm != NULL))
+		goto done;
+
+	BUILD_BUG_ON(sizeof(mode_num) != 1);
+	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
+				  HKDF_CONTEXT_PER_MODE_KEY,
+				  &mode_num, sizeof(mode_num),
+				  mode_key, ci->ci_mode->keysize);
+	if (err)
+		return err;
+	tfm = fscrypt_allocate_skcipher(ci->ci_mode, mode_key, ci->ci_inode);
+	memzero_explicit(mode_key, ci->ci_mode->keysize);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	/* pairs with smp_load_acquire() above */
+	if (cmpxchg_release(tfm_p, NULL, tfm) != NULL) {
+		crypto_free_skcipher(tfm);
+		goto retry;
+	}
+done:
+	ci->ci_ctfm = tfm;
+	return 0;
+}
+
+static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
+				     struct fscrypt_master_key *mk)
+{
+	u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
+	int err;
+
+	if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
+		/*
+		 * DIRECT_KEY: instead of deriving per-file keys, the per-file
+		 * nonce will be included in all the IVs.  But unlike v1
+		 * policies, for v2 policies in this case we don't encrypt with
+		 * the master key directly but rather derive a per-mode key.
+		 * This ensures that the master key is consistently used only
+		 * for HKDF, avoiding key reuse issues.
+		 */
+		if (!fscrypt_mode_supports_direct_key(ci->ci_mode)) {
+			fscrypt_warn(ci->ci_inode->i_sb,
+				     "direct key flag not allowed with %s",
+				     ci->ci_mode->friendly_name);
+			return -EINVAL;
+		}
+		return setup_per_mode_key(ci, mk);
+	}
+
+	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
+				  HKDF_CONTEXT_PER_FILE_KEY,
+				  ci->ci_nonce,
+				  FS_KEY_DERIVATION_NONCE_SIZE,
+				  derived_key, ci->ci_mode->keysize);
+	if (err)
+		return err;
+
+	err = fscrypt_set_derived_key(ci, derived_key);
+	memzero_explicit(derived_key, ci->ci_mode->keysize);
+	return err;
+}
+
 /*
  * Find the master key, then set up the inode's actual encryption key.
  *
@@ -226,15 +296,30 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 	struct fscrypt_key_specifier mk_spec;
 	int err;
 
-	mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
-	memcpy(mk_spec.u.descriptor, ci->ci_master_key_descriptor,
-	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	if (ci->ci_policy.v1.version == FSCRYPT_POLICY_V1) {
+		mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
+		memcpy(mk_spec.u.descriptor,
+		       ci->ci_policy.v1.master_key_descriptor,
+		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	} else {
+		mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
+		memcpy(mk_spec.u.identifier,
+		       ci->ci_policy.v2.master_key_identifier,
+		       FSCRYPT_KEY_IDENTIFIER_SIZE);
+	}
 
 	key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
 	if (IS_ERR(key)) {
-		if (key != ERR_PTR(-ENOKEY))
+		if (key != ERR_PTR(-ENOKEY) ||
+		    ci->ci_policy.v1.version != FSCRYPT_POLICY_V1)
 			return PTR_ERR(key);
 
+		/*
+		 * As a legacy fallback for v1 policies, search for the key in
+		 * the current task's subscribed keyrings too.  Don't move this
+		 * to before the search of ->s_master_keys, since users
+		 * shouldn't be able to override filesystem-level keys.
+		 */
 		return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
 	}
 
@@ -247,6 +332,12 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 		goto out_release_key;
 	}
 
+	/*
+	 * Require that the master key be at least as long as the derived key.
+	 * Otherwise, the derived key cannot possibly contain as much entropy as
+	 * that required by the encryption mode it will be used for.  For v1
+	 * policies it's also required for the KDF to work at all.
+	 */
 	if (mk->mk_secret.size < ci->ci_mode->keysize) {
 		fscrypt_warn(NULL,
 			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
@@ -256,7 +347,10 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 		goto out_release_key;
 	}
 
-	err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
+	if (ci->ci_policy.v1.version == FSCRYPT_POLICY_V1)
+		err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
+	else
+		err = fscrypt_setup_v2_file_key(ci, mk);
 	if (err)
 		goto out_release_key;
 
@@ -278,7 +372,8 @@ static void put_crypt_info(struct fscrypt_info *ci)
 
 	if (ci->ci_direct_key) {
 		fscrypt_put_direct_key(ci->ci_direct_key);
-	} else {
+	} else if ((ci->ci_ctfm != NULL || ci->ci_essiv_tfm != NULL) &&
+		   !fscrypt_is_direct_key_policy(&ci->ci_policy)) {
 		crypto_free_skcipher(ci->ci_ctfm);
 		crypto_free_cipher(ci->ci_essiv_tfm);
 	}
@@ -308,7 +403,7 @@ static void put_crypt_info(struct fscrypt_info *ci)
 int fscrypt_get_encryption_info(struct inode *inode)
 {
 	struct fscrypt_info *crypt_info;
-	struct fscrypt_context ctx;
+	union fscrypt_context ctx;
 	struct fscrypt_mode *mode;
 	struct key *master_key = NULL;
 	int res;
@@ -327,35 +422,40 @@ int fscrypt_get_encryption_info(struct inode *inode)
 			return res;
 		/* Fake up a context for an unencrypted directory */
 		memset(&ctx, 0, sizeof(ctx));
-		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
-		ctx.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
-		ctx.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
-		memset(ctx.master_key_descriptor, 0x42,
+		ctx.v1.version = FSCRYPT_CONTEXT_V1;
+		ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
+		ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
+		memset(ctx.v1.master_key_descriptor, 0x42,
 		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	} else if (res != sizeof(ctx)) {
-		return -EINVAL;
+		res = sizeof(ctx.v1);
 	}
 
-	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
-		return -EINVAL;
-
-	if (ctx.flags & ~FSCRYPT_POLICY_FLAGS_VALID)
-		return -EINVAL;
-
 	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
 	if (!crypt_info)
 		return -ENOMEM;
 
 	crypt_info->ci_inode = inode;
 
-	crypt_info->ci_flags = ctx.flags;
-	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
-	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
-	memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
-	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
+	res = fscrypt_policy_from_context(&crypt_info->ci_policy, &ctx, res);
+	if (res)
+		goto out;
+
+	if (ctx.v1.version == FSCRYPT_CONTEXT_V1)
+		memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
+		       FS_KEY_DERIVATION_NONCE_SIZE);
+	else
+		memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
+		       FS_KEY_DERIVATION_NONCE_SIZE);
+
+	if (!fscrypt_supported_policy(&crypt_info->ci_policy)) {
+		fscrypt_warn(inode->i_sb,
+			     "inode %lu uses unsupported encryption policy",
+			     inode->i_ino);
+		res = -EINVAL;
+		goto out;
+	}
 
-	mode = select_encryption_mode(crypt_info, inode);
+	mode = select_encryption_mode(&crypt_info->ci_policy, inode);
 	if (IS_ERR(mode)) {
 		res = PTR_ERR(mode);
 		goto out;
diff --git a/fs/crypto/keysetup_legacy.c b/fs/crypto/keysetup_legacy.c
index a48588458f07..a35a7a9c204c 100644
--- a/fs/crypto/keysetup_legacy.c
+++ b/fs/crypto/keysetup_legacy.c
@@ -189,12 +189,13 @@ find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
 	 */
 
 	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
+	memcpy(&hash_key, ci->ci_policy.v1.master_key_descriptor,
+	       sizeof(hash_key));
 
 	spin_lock(&fscrypt_direct_keys_lock);
 	hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) {
-		if (memcmp(ci->ci_master_key_descriptor, dk->dk_descriptor,
-			   FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
+		if (memcmp(ci->ci_policy.v1.master_key_descriptor,
+			   dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
 			continue;
 		if (ci->ci_mode != dk->dk_mode)
 			continue;
@@ -237,7 +238,7 @@ fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key)
 		dk->dk_ctfm = NULL;
 		goto err_free_dk;
 	}
-	memcpy(dk->dk_descriptor, ci->ci_master_key_descriptor,
+	memcpy(dk->dk_descriptor, ci->ci_policy.v1.master_key_descriptor,
 	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);
 
@@ -262,7 +263,8 @@ static int setup_v1_file_key_direct(struct fscrypt_info *ci,
 		return -EINVAL;
 	}
 
-	if (ci->ci_data_mode != ci->ci_filename_mode) {
+	if (ci->ci_policy.v1.contents_encryption_mode !=
+	    ci->ci_policy.v1.filenames_encryption_mode) {
 		fscrypt_warn(ci->ci_inode->i_sb,
 			     "direct key flag not allowed with different contents and filenames modes");
 		return -EINVAL;
@@ -309,7 +311,7 @@ static int setup_v1_file_key_derived(struct fscrypt_info *ci,
 
 int fscrypt_setup_v1_file_key(struct fscrypt_info *ci, const u8 *raw_master_key)
 {
-	if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
+	if (ci->ci_policy.v1.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
 		return setup_v1_file_key_direct(ci, raw_master_key);
 	else
 		return setup_v1_file_key_derived(ci, raw_master_key);
@@ -322,11 +324,11 @@ int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci)
 	int err;
 
 	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
-					ci->ci_master_key_descriptor,
+					ci->ci_policy.v1.master_key_descriptor,
 					ci->ci_mode->keysize, &payload);
 	if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
 		key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
-						ci->ci_master_key_descriptor,
+						ci->ci_policy.v1.master_key_descriptor,
 						ci->ci_mode->keysize, &payload);
 	}
 
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 1e0563cea1a5..07fec2f7fc72 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -5,8 +5,9 @@
  * Copyright (C) 2015, Google, Inc.
  * Copyright (C) 2015, Motorola Mobility.
  *
- * Written by Michael Halcrow, 2015.
+ * Originally written by Michael Halcrow, 2015.
  * Modified by Jaegeuk Kim, 2015.
+ * Modified by Eric Biggers, 2019 for v2 policy support.
  */
 
 #include <linux/random.h>
@@ -14,84 +15,263 @@
 #include <linux/mount.h>
 #include "fscrypt_private.h"
 
-/*
- * check whether an encryption policy is consistent with an encryption context
+/**
+ * fscrypt_policies_equal - check whether two encryption policies are the same
+ *
+ * Return: %true if equal, else %false
+ */
+bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
+			    const union fscrypt_policy *policy2)
+{
+	if (policy1->v1.version != policy2->v1.version)
+		return false;
+
+	return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
+}
+
+/**
+ * fscrypt_supported_policy - check whether an encryption policy is supported
+ *
+ * Given an encryption policy, check whether all its encryption modes and other
+ * settings are supported by this kernel.  (But we don't currently don't check
+ * for crypto API support here, so attempting to use an algorithm not configured
+ * into the crypto API will still fail later.)
+ *
+ * Return: %true if supported, else %false
  */
-static bool is_encryption_context_consistent_with_policy(
-				const struct fscrypt_context *ctx,
-				const struct fscrypt_policy *policy)
+bool fscrypt_supported_policy(const union fscrypt_policy *policy_u)
 {
-	return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
-		      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
-		(ctx->flags == policy->flags) &&
-		(ctx->contents_encryption_mode ==
-		 policy->contents_encryption_mode) &&
-		(ctx->filenames_encryption_mode ==
-		 policy->filenames_encryption_mode);
+	switch (policy_u->v1.version) {
+	case FSCRYPT_POLICY_V1: {
+		const struct fscrypt_policy_v1 *policy = &policy_u->v1;
+
+		if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
+					     policy->filenames_encryption_mode))
+			return false;
+
+		if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID)
+			return false;
+
+		return true;
+	}
+	case FSCRYPT_POLICY_V2: {
+		const struct fscrypt_policy_v2 *policy = &policy_u->v2;
+
+		if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
+					     policy->filenames_encryption_mode))
+			return false;
+
+		if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID)
+			return false;
+
+		if (memchr_inv(policy->__reserved, 0,
+			       sizeof(policy->__reserved)))
+			return false;
+
+		return true;
+	}
+	}
+	return false;
 }
 
-static int create_encryption_context_from_policy(struct inode *inode,
-				const struct fscrypt_policy *policy)
+/**
+ * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
+ *
+ * Create an fscrypt_context for an inode that is being assigned the given
+ * encryption policy.  A new nonce is randomly generated.
+ *
+ * Return: the size of the new context in bytes.
+ */
+static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
+					   const union fscrypt_policy *policy_u)
 {
-	struct fscrypt_context ctx;
+	memset(ctx_u, 0, sizeof(*ctx_u));
+
+	switch (policy_u->v1.version) {
+	case FSCRYPT_POLICY_V1: {
+		const struct fscrypt_policy_v1 *policy = &policy_u->v1;
+		struct fscrypt_context_v1 *ctx = &ctx_u->v1;
+
+		ctx->version = FSCRYPT_CONTEXT_V1;
+		ctx->contents_encryption_mode =
+			policy->contents_encryption_mode;
+		ctx->filenames_encryption_mode =
+			policy->filenames_encryption_mode;
+		ctx->flags = policy->flags;
+		memcpy(ctx->master_key_descriptor,
+		       policy->master_key_descriptor,
+		       sizeof(ctx->master_key_descriptor));
+		get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
+		return sizeof(*ctx);
+	}
+	case FSCRYPT_POLICY_V2: {
+		const struct fscrypt_policy_v2 *policy = &policy_u->v2;
+		struct fscrypt_context_v2 *ctx = &ctx_u->v2;
+
+		ctx->version = FSCRYPT_CONTEXT_V2;
+		ctx->contents_encryption_mode =
+			policy->contents_encryption_mode;
+		ctx->filenames_encryption_mode =
+			policy->filenames_encryption_mode;
+		ctx->flags = policy->flags;
+		memcpy(ctx->master_key_identifier,
+		       policy->master_key_identifier,
+		       sizeof(ctx->master_key_identifier));
+		get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
+		return sizeof(*ctx);
+	}
+	}
+	BUG();
+}
 
-	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
-	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
-					FSCRYPT_KEY_DESCRIPTOR_SIZE);
+/**
+ * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
+ *
+ * Given an fscrypt_context, build the corresponding fscrypt_policy.
+ *
+ * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
+ * version number or size.
+ *
+ * This does *not* validate the settings within the policy itself, e.g. the
+ * modes, flags, and reserved bits.  Use fscrypt_supported_policy() for that.
+ */
+int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
+				const union fscrypt_context *ctx_u,
+				int ctx_size)
+{
+	memset(policy_u, 0, sizeof(*policy_u));
 
-	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
-				     policy->filenames_encryption_mode))
+	if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
 		return -EINVAL;
 
-	if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID)
+	switch (ctx_u->v1.version) {
+	case FSCRYPT_CONTEXT_V1: {
+		const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
+		struct fscrypt_policy_v1 *policy = &policy_u->v1;
+
+		policy->version = FSCRYPT_POLICY_V1;
+		policy->contents_encryption_mode =
+			ctx->contents_encryption_mode;
+		policy->filenames_encryption_mode =
+			ctx->filenames_encryption_mode;
+		policy->flags = ctx->flags;
+		memcpy(policy->master_key_descriptor,
+		       ctx->master_key_descriptor,
+		       sizeof(policy->master_key_descriptor));
+		return 0;
+	}
+	case FSCRYPT_CONTEXT_V2: {
+		const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
+		struct fscrypt_policy_v2 *policy = &policy_u->v2;
+
+		policy->version = FSCRYPT_POLICY_V2;
+		policy->contents_encryption_mode =
+			ctx->contents_encryption_mode;
+		policy->filenames_encryption_mode =
+			ctx->filenames_encryption_mode;
+		policy->flags = ctx->flags;
+		memcpy(policy->__reserved, ctx->__reserved,
+		       sizeof(policy->__reserved));
+		memcpy(policy->master_key_identifier,
+		       ctx->master_key_identifier,
+		       sizeof(policy->master_key_identifier));
+		return 0;
+	}
+	}
+	/* unreachable */
+	return -EINVAL;
+}
+
+/* Retrieve an inode's encryption policy */
+static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
+{
+	union fscrypt_context ctx;
+	int ret;
+
+	if (inode->i_crypt_info) {
+		/* key available, use the cached policy */
+		*policy = inode->i_crypt_info->ci_policy;
+		return 0;
+	}
+
+	if (!IS_ENCRYPTED(inode))
+		return -ENODATA;
+
+	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
+	if (ret < 0)
+		return (ret == -ERANGE) ? -EINVAL : ret;
+
+	return fscrypt_policy_from_context(policy, &ctx, ret);
+}
+
+static int set_encryption_policy(struct inode *inode,
+				 const union fscrypt_policy *policy)
+{
+	union fscrypt_context ctx;
+	int ctxsize;
+
+	if (!fscrypt_supported_policy(policy))
 		return -EINVAL;
 
-	ctx.contents_encryption_mode = policy->contents_encryption_mode;
-	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
-	ctx.flags = policy->flags;
-	BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
-	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
+	if (policy->v1.version == FSCRYPT_POLICY_V1) {
+		/*
+		 * The original encryption policy version provided no way of
+		 * verifying that the correct master key was supplied, which was
+		 * insecure in scenarios where multiple users have access to the
+		 * same encrypted files (even just read-only access).  The new
+		 * encryption policy version fixes this and also implies use of
+		 * an improved key derivation function and allows non-root users
+		 * to securely remove keys.  So as long as compatibility with
+		 * old kernels isn't required, it is recommended to use the new
+		 * policy version for all new encrypted directories.
+		 */
+		pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
+			     current->comm, current->pid);
+	}
+
+	ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
 
-	return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
+	return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
 }
 
 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
 {
-	struct fscrypt_policy policy;
+	union fscrypt_policy policy;
+	union fscrypt_policy existing_policy;
 	struct inode *inode = file_inode(filp);
+	int size;
 	int ret;
-	struct fscrypt_context ctx;
 
-	if (copy_from_user(&policy, arg, sizeof(policy)))
+	if (copy_from_user(&policy, arg, sizeof(u8)))
+		return -EFAULT;
+
+	size = fscrypt_policy_size(&policy);
+	if (size <= 0)
+		return -EINVAL;
+
+	if (copy_from_user((u8 *)&policy + 1, arg + 1, size - 1))
 		return -EFAULT;
 
 	if (!inode_owner_or_capable(inode))
 		return -EACCES;
 
-	if (policy.version != 0)
-		return -EINVAL;
-
 	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;
 
 	inode_lock(inode);
 
-	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
+	ret = fscrypt_get_policy(inode, &existing_policy);
 	if (ret == -ENODATA) {
 		if (!S_ISDIR(inode->i_mode))
 			ret = -ENOTDIR;
 		else if (!inode->i_sb->s_cop->empty_dir(inode))
 			ret = -ENOTEMPTY;
 		else
-			ret = create_encryption_context_from_policy(inode,
-								    &policy);
-	} else if (ret == sizeof(ctx) &&
-		   is_encryption_context_consistent_with_policy(&ctx,
-								&policy)) {
-		/* The file already uses the same encryption policy. */
-		ret = 0;
-	} else if (ret >= 0 || ret == -ERANGE) {
+			ret = set_encryption_policy(inode, &policy);
+	} else if (ret == -EINVAL ||
+		   (ret == 0 && !fscrypt_policies_equal(&policy,
+							&existing_policy))) {
 		/* The file already uses a different encryption policy. */
 		ret = -EEXIST;
 	}
@@ -103,37 +283,55 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
 }
 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 
+/* Original ioctl version; can only get the original policy version */
 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 {
-	struct inode *inode = file_inode(filp);
-	struct fscrypt_context ctx;
-	struct fscrypt_policy policy;
-	int res;
+	union fscrypt_policy policy;
+	int err;
 
-	if (!IS_ENCRYPTED(inode))
-		return -ENODATA;
+	err = fscrypt_get_policy(file_inode(filp), &policy);
+	if (err)
+		return err;
 
-	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
-	if (res < 0 && res != -ERANGE)
-		return res;
-	if (res != sizeof(ctx))
-		return -EINVAL;
-	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
+	if (policy.v1.version != FSCRYPT_POLICY_V1)
 		return -EINVAL;
 
-	policy.version = 0;
-	policy.contents_encryption_mode = ctx.contents_encryption_mode;
-	policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
-	policy.flags = ctx.flags;
-	memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
-				FSCRYPT_KEY_DESCRIPTOR_SIZE);
-
-	if (copy_to_user(arg, &policy, sizeof(policy)))
+	if (copy_to_user(arg, &policy, sizeof(policy.v1)))
 		return -EFAULT;
 	return 0;
 }
 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 
+/* Extended ioctl version; can get policies of any version */
+int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *_uarg)
+{
+	struct fscrypt_get_policy_ex_arg __user *uarg = _uarg;
+	struct fscrypt_get_policy_ex_arg arg;
+	union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
+	u64 avail_size;
+	int err;
+
+	BUILD_BUG_ON(sizeof(arg.policy) != sizeof(union fscrypt_policy));
+	BUILD_BUG_ON(sizeof(arg.policy_size) !=
+		     offsetof(struct fscrypt_get_policy_ex_arg, policy));
+
+	err = fscrypt_get_policy(file_inode(filp), policy);
+	if (err)
+		return err;
+	arg.policy_size = fscrypt_policy_size(policy);
+
+	if (get_user(avail_size, &uarg->policy_size))
+		return -EFAULT;
+
+	if (avail_size < arg.policy_size)
+		return -EOVERFLOW;
+
+	if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + arg.policy_size))
+		return -EFAULT;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
+
 /**
  * fscrypt_has_permitted_context() - is a file's encryption policy permitted
  *				     within its directory?
@@ -155,10 +353,8 @@ EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
  */
 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 {
-	const struct fscrypt_operations *cops = parent->i_sb->s_cop;
-	const struct fscrypt_info *parent_ci, *child_ci;
-	struct fscrypt_context parent_ctx, child_ctx;
-	int res;
+	union fscrypt_policy parent_policy, child_policy;
+	int err;
 
 	/* No restrictions on file types which are never encrypted */
 	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
@@ -188,41 +384,22 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 	 * In any case, if an unexpected error occurs, fall back to "forbidden".
 	 */
 
-	res = fscrypt_get_encryption_info(parent);
-	if (res)
+	err = fscrypt_get_encryption_info(parent);
+	if (err)
 		return 0;
-	res = fscrypt_get_encryption_info(child);
-	if (res)
+	err = fscrypt_get_encryption_info(child);
+	if (err)
 		return 0;
-	parent_ci = parent->i_crypt_info;
-	child_ci = child->i_crypt_info;
-
-	if (parent_ci && child_ci) {
-		return memcmp(parent_ci->ci_master_key_descriptor,
-			      child_ci->ci_master_key_descriptor,
-			      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
-			(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
-			(parent_ci->ci_filename_mode ==
-			 child_ci->ci_filename_mode) &&
-			(parent_ci->ci_flags == child_ci->ci_flags);
-	}
 
-	res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
-	if (res != sizeof(parent_ctx))
+	err = fscrypt_get_policy(parent, &parent_policy);
+	if (err)
 		return 0;
 
-	res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
-	if (res != sizeof(child_ctx))
+	err = fscrypt_get_policy(child, &child_policy);
+	if (err)
 		return 0;
 
-	return memcmp(parent_ctx.master_key_descriptor,
-		      child_ctx.master_key_descriptor,
-		      FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
-		(parent_ctx.contents_encryption_mode ==
-		 child_ctx.contents_encryption_mode) &&
-		(parent_ctx.filenames_encryption_mode ==
-		 child_ctx.filenames_encryption_mode) &&
-		(parent_ctx.flags == child_ctx.flags);
+	return fscrypt_policies_equal(&parent_policy, &child_policy);
 }
 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 
@@ -238,7 +415,8 @@ EXPORT_SYMBOL(fscrypt_has_permitted_context);
 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 						void *fs_data, bool preload)
 {
-	struct fscrypt_context ctx;
+	union fscrypt_context ctx;
+	int ctxsize;
 	struct fscrypt_info *ci;
 	int res;
 
@@ -250,16 +428,10 @@ int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 	if (ci == NULL)
 		return -ENOKEY;
 
-	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
-	ctx.contents_encryption_mode = ci->ci_data_mode;
-	ctx.filenames_encryption_mode = ci->ci_filename_mode;
-	ctx.flags = ci->ci_flags;
-	memcpy(ctx.master_key_descriptor, ci->ci_master_key_descriptor,
-	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
+	ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);
+
 	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
-	res = parent->i_sb->s_cop->set_context(child, &ctx,
-						sizeof(ctx), fs_data);
+	res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data);
 	if (res)
 		return res;
 	return preload ? fscrypt_get_encryption_info(child): 0;
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index dace3fd1bf19..ec84b48fcc11 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -42,7 +42,7 @@ struct fscrypt_name {
 #define fname_len(p)		((p)->disk_name.len)
 
 /* Maximum value for the third parameter of fscrypt_operations.set_context(). */
-#define FSCRYPT_SET_CONTEXT_MAX_SIZE	28
+#define FSCRYPT_SET_CONTEXT_MAX_SIZE	40
 
 #ifdef CONFIG_FS_ENCRYPTION
 /*
@@ -109,6 +109,7 @@ extern void fscrypt_restore_control_page(struct page *);
 /* policy.c */
 extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
 extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
+extern int fscrypt_ioctl_get_policy_ex(struct file *, void __user *);
 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
 extern int fscrypt_inherit_context(struct inode *, struct inode *,
 					void *, bool);
@@ -304,6 +305,12 @@ static inline int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 	return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_ioctl_get_policy_ex(struct file *filp,
+					      void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int fscrypt_has_permitted_context(struct inode *parent,
 						struct inode *child)
 {
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 042e70a4ff7e..26879e669dfa 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -8,7 +8,6 @@
  * File system encryption support
  */
 /* Policy provided via an ioctl on the topmost directory */
-#define FSCRYPT_KEY_DESCRIPTOR_SIZE	8
 
 /* Encryption policy flags */
 #define FSCRYPT_POLICY_FLAGS_PAD_4		0x00
@@ -16,7 +15,7 @@
 #define FSCRYPT_POLICY_FLAGS_PAD_16		0x02
 #define FSCRYPT_POLICY_FLAGS_PAD_32		0x03
 #define FSCRYPT_POLICY_FLAGS_PAD_MASK		0x03
-#define FSCRYPT_POLICY_FLAG_DIRECT_KEY		0x04	/* use master key directly */
+#define FSCRYPT_POLICY_FLAG_DIRECT_KEY		0x04
 #define FSCRYPT_POLICY_FLAGS_VALID		0x07
 
 /* Encryption algorithms */
@@ -25,14 +24,24 @@
 #define FSCRYPT_MODE_AES_128_CBC		5
 #define FSCRYPT_MODE_AES_128_CTS		6
 #define FSCRYPT_MODE_ADIANTUM			9
+#define __FSCRYPT_MODE_MAX			9
 
-struct fscrypt_policy {
+/*
+ * Legacy policy version; ad-hoc KDF and no key verification.
+ * For new encrypted directories, use fscrypt_policy_v2 instead.
+ *
+ * Careful: the .version field for this is actually 0, not 1.
+ */
+#define FSCRYPT_POLICY_V1		0
+#define FSCRYPT_KEY_DESCRIPTOR_SIZE	8
+struct fscrypt_policy_v1 {
 	__u8 version;
 	__u8 contents_encryption_mode;
 	__u8 filenames_encryption_mode;
 	__u8 flags;
 	__u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 };
+#define fscrypt_policy	fscrypt_policy_v1
 
 /*
  * Process-subscribed "logon" key description prefix and payload format.
@@ -47,13 +56,39 @@ struct fscrypt_key {
 	__u32 size;
 };
 
+/*
+ * New policy version with HKDF and key verification (recommended).
+ */
+#define FSCRYPT_POLICY_V2		2
+#define FSCRYPT_KEY_IDENTIFIER_SIZE	16
+struct fscrypt_policy_v2 {
+	__u8 version;
+	__u8 contents_encryption_mode;
+	__u8 filenames_encryption_mode;
+	__u8 flags;
+	__u8 __reserved[4];
+	__u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
+};
+
+/* Struct passed to FS_IOC_GET_ENCRYPTION_POLICY_EX */
+struct fscrypt_get_policy_ex_arg {
+	__u64 policy_size; /* input/output */
+	union {
+		__u8 version;
+		struct fscrypt_policy_v1 v1;
+		struct fscrypt_policy_v2 v2;
+	} policy; /* output */
+};
+
 struct fscrypt_key_specifier {
 #define FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR	1
+#define FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER	2
 	__u32 type;
 	__u32 __reserved;
 	union {
 		__u8 __reserved[32]; /* reserve some extra space */
 		__u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+		__u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
 	} u;
 };
 
@@ -88,6 +123,7 @@ struct fscrypt_get_key_status_arg {
 #define FS_IOC_SET_ENCRYPTION_POLICY	  _IOR('f', 19, struct fscrypt_policy)
 #define FS_IOC_GET_ENCRYPTION_PWSALT	  _IOW('f', 20, __u8[16])
 #define FS_IOC_GET_ENCRYPTION_POLICY	  _IOW('f', 21, struct fscrypt_policy)
+#define FS_IOC_GET_ENCRYPTION_POLICY_EX	 _IOWR('f', 22, __u8[9]) /* size + version */
 #define FS_IOC_ADD_ENCRYPTION_KEY	 _IOWR('f', 23, struct fscrypt_add_key_arg)
 #define FS_IOC_REMOVE_ENCRYPTION_KEY	  _IOW('f', 24, struct fscrypt_remove_key_arg)
 #define FS_IOC_GET_ENCRYPTION_KEY_STATUS _IOWR('f', 25, struct fscrypt_get_key_status_arg)
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 15/20] fscrypt: allow unprivileged users to add/remove keys for v2 policies
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (13 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 14/20] fscrypt: v2 encryption policy support Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 16/20] fscrypt: require that key be added when setting a v2 encryption policy Eric Biggers
                   ` (4 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Allow the FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY
ioctls to be used by non-root users to add and remove encryption keys
from the filesystem-level crypto keyrings, subject to limitations.

Motivation: while privileged fscrypt key management is sufficient for
some users (e.g. Android and Chromium OS, where a privileged process
manages all keys), the old API by design also allows non-root users to
set up and use encrypted directories, and we don't want to regress on
that.  Especially, we don't want to force users to continue using the
old API, running into the visibility mismatch between files and keyrings
and being unable to "lock" encrypted directories.

Intuitively, the ioctls have to be privileged since they manipulate
filesystem-level state.  However, it's actually safe to make them
unprivileged if we very carefully enforce some specific limitations.

First, each key must be identified by a cryptographic hash so that a
user can't add the wrong key for another user's files.  For v2
encryption policies, we use the key_identifier for this.  v1 policies
don't have this, so managing keys for them remains privileged.

Second, each key a user adds is charged to their quota for the keyrings
service.  Thus, a user can't exhaust memory by adding a huge number of
keys.  By default each non-root user is allowed up to 200 keys; this can
be changed using the existing sysctl 'kernel.keys.maxkeys'.

Third, if multiple users add the same key, we keep track of those users
of the key (of which there remains a single copy), and won't really
remove the key, i.e. "lock" the encrypted files, until all those users
have removed it.  This prevents denial of service attacks that would be
possible under simpler schemes, such allowing the first user who added a
key to remove it -- since that could be a malicious user who has
compromised the key.  Of course, encryption keys should be kept secret,
but the idea is that using encryption should never be *less* secure than
not using encryption, even if your key was compromised.

We tolerate that a user will be unable to really remove a key, i.e.
unable to "lock" their encrypted files, if another user has added the
same key.  But in a sense, this is actually a good thing because it will
avoid providing a false notion of security where a key appears to have
been removed when actually it's still in memory, available to any
attacker who compromises the operating system kernel.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h  |  25 ++-
 fs/crypto/keyring.c          | 310 +++++++++++++++++++++++++++++++++--
 fs/crypto/keysetup.c         |  16 +-
 include/uapi/linux/fscrypt.h |   9 +-
 4 files changed, 336 insertions(+), 24 deletions(-)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 1a40f7359655..b16cf3bd6cf1 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -336,9 +336,16 @@ struct fscrypt_master_key {
 	 * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
 	 * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
 	 *
-	 * Locking: protected by key->sem.
+	 * Locking: protected by key->sem (outer) and mk_secret_sem (inner).
+	 * The reason for two locks is that key->sem also protects modifying
+	 * mk_users, which ranks it above the semaphore for the keyring key
+	 * type, which is in turn above page faults (via keyring_read).  But
+	 * sometimes filesystems call fscrypt_get_encryption_info() from within
+	 * a transaction, which ranks it below page faults.  So we need a
+	 * separate lock which protects mk_secret but not also mk_users.
 	 */
 	struct fscrypt_master_key_secret	mk_secret;
+	struct rw_semaphore			mk_secret_sem;
 
 	/*
 	 * For v1 policy keys: an arbitrary key descriptor which was assigned by
@@ -348,6 +355,22 @@ struct fscrypt_master_key {
 	 */
 	struct fscrypt_key_specifier		mk_spec;
 
+	/*
+	 * Keyring which contains a key of type 'key_type_fscrypt_user' for each
+	 * user who has added this key.  Normally each key will be added by just
+	 * one user, but it's possible that multiple users share a key, and in
+	 * that case we need to keep track of those users so that one user can't
+	 * remove the key before the others want it removed too.
+	 *
+	 * This is NULL for v1 policy keys; those can only be added by root.
+	 *
+	 * Locking: in addition to this keyrings own semaphore, this is
+	 * protected by the master key's key->sem, so we can do atomic
+	 * search+insert.  It can also be searched without taking any locks, but
+	 * in that case the returned key may have already been removed.
+	 */
+	struct key		*mk_users;
+
 	/*
 	 * Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
 	 * Once this goes to 0, the master key is removed from ->s_master_keys.
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 6bf1e0672a09..15ca0f1d04e7 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -42,6 +42,7 @@ static void free_master_key(struct fscrypt_master_key *mk)
 	for (i = 0; i < ARRAY_SIZE(mk->mk_mode_keys); i++)
 		crypto_free_skcipher(mk->mk_mode_keys[i]);
 
+	key_put(mk->mk_users);
 	kzfree(mk);
 }
 
@@ -101,7 +102,39 @@ static struct key_type key_type_fscrypt = {
 	.describe		= fscrypt_key_describe,
 };
 
-/* Search ->s_master_keys */
+static int fscrypt_user_key_instantiate(struct key *key,
+					struct key_preparsed_payload *prep)
+{
+	/*
+	 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
+	 * each key, regardless of the exact key size.  The amount of memory
+	 * actually used is greater than the size of the raw key anyway.
+	 */
+	return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
+}
+
+static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
+{
+	seq_puts(m, key->description);
+}
+
+/*
+ * Type of key in ->mk_users.  Each key of this type represents a particular
+ * user who has added a particular master key.
+ *
+ * Note that the name of this key type really should be something like
+ * ".fscrypt-user" instead of simply ".fscrypt".  But the shorter name is chosen
+ * mainly for simplicity of presentation in /proc/keys when read by a non-root
+ * user.  And it is expected to be rare that a key is actually added by multiple
+ * users, since users should keep their encryption keys confidential.
+ */
+static struct key_type key_type_fscrypt_user = {
+	.name			= ".fscrypt",
+	.instantiate		= fscrypt_user_key_instantiate,
+	.describe		= fscrypt_user_key_describe,
+};
+
+/* Search ->s_master_keys or ->mk_users */
 static struct key *search_fscrypt_keyring(struct key *keyring,
 					  struct key_type *type,
 					  const char *description)
@@ -127,6 +160,13 @@ static struct key *search_fscrypt_keyring(struct key *keyring,
 
 #define FSCRYPT_MK_DESCRIPTION_SIZE	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
 
+#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE	\
+	(CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
+	 CONST_STRLEN("-users") + 1)
+
+#define FSCRYPT_MK_USER_DESCRIPTION_SIZE	\
+	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
+
 static void format_fs_keyring_description(
 			char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
 			const struct super_block *sb)
@@ -142,6 +182,23 @@ static void format_mk_description(
 		master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
 }
 
+static void format_mk_users_keyring_description(
+			char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
+			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
+{
+	sprintf(description, "fscrypt-%*phN-users",
+		FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
+}
+
+static void format_mk_user_description(
+			char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
+			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
+{
+
+	sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
+		mk_identifier, __kuid_val(current_fsuid()));
+}
+
 /* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
 static int allocate_filesystem_keyring(struct super_block *sb)
 {
@@ -183,6 +240,81 @@ struct key *fscrypt_find_master_key(struct super_block *sb,
 	return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
 }
 
+static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
+{
+	char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
+	struct key *keyring;
+
+	format_mk_users_keyring_description(description,
+					    mk->mk_spec.u.identifier);
+	keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+				current_cred(), KEY_POS_SEARCH |
+				  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
+				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
+	if (IS_ERR(keyring))
+		return PTR_ERR(keyring);
+
+	mk->mk_users = keyring;
+	return 0;
+}
+
+/*
+ * Find the current user's key in the master key's ->mk_users.
+ * Returns ERR_PTR(-ENOKEY) if not found.
+ */
+static struct key *find_master_key_user(struct fscrypt_master_key *mk)
+{
+	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
+
+	format_mk_user_description(description, mk->mk_spec.u.identifier);
+	return search_fscrypt_keyring(mk->mk_users, &key_type_fscrypt_user,
+				      description);
+}
+
+/*
+ * Give the current user a key in ->mk_users.  This charges the user's quota and
+ * marks the master key as added by the current user, so that it cannot be
+ * removed by another user with the key.  Either the master key's key->sem must
+ * be held for write, or the master key must be still undergoing initialization.
+ */
+static int add_master_key_user(struct fscrypt_master_key *mk)
+{
+	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
+	struct key *mk_user;
+	int err;
+
+	format_mk_user_description(description, mk->mk_spec.u.identifier);
+	mk_user = key_alloc(&key_type_fscrypt_user, description,
+			    current_fsuid(), current_gid(), current_cred(),
+			    KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
+	if (IS_ERR(mk_user))
+		return PTR_ERR(mk_user);
+
+	err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
+	key_put(mk_user);
+	return err;
+}
+
+/*
+ * Remove the current user's key from ->mk_users, if present.
+ * The master key's key->sem must be held for write.
+ */
+static int remove_master_key_user(struct fscrypt_master_key *mk)
+{
+	struct key *mk_user;
+	int err;
+
+	mk_user = find_master_key_user(mk);
+	if (IS_ERR(mk_user)) {
+		if (mk_user != ERR_PTR(-ENOKEY))
+			return PTR_ERR(mk_user);
+		return 0;
+	}
+	err = key_unlink(mk->mk_users, mk_user);
+	key_put(mk_user);
+	return err;
+}
+
 /*
  * Allocate a new fscrypt_master_key which contains the given secret, set it as
  * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
@@ -204,11 +336,26 @@ static int add_new_master_key(struct fscrypt_master_key_secret *secret,
 	mk->mk_spec = *mk_spec;
 
 	move_master_key_secret(&mk->mk_secret, secret);
+	init_rwsem(&mk->mk_secret_sem);
 
 	refcount_set(&mk->mk_refcount, 1); /* secret is present */
 	INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
 	spin_lock_init(&mk->mk_decrypted_inodes_lock);
 
+	if (mk_spec->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
+		err = allocate_master_key_users_keyring(mk);
+		if (err)
+			goto out_free_mk;
+		err = add_master_key_user(mk);
+		if (err)
+			goto out_free_mk;
+	}
+
+	/*
+	 * Note that we don't charge this key to anyone's quota, since when
+	 * ->mk_users is in use those keys are charged instead, and otherwise
+	 * (when ->mk_users isn't in use) only root can add these keys.
+	 */
 	format_mk_description(description, mk_spec);
 	key = key_alloc(&key_type_fscrypt, description,
 			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
@@ -236,13 +383,45 @@ static int add_existing_master_key(struct fscrypt_master_key *mk,
 				   struct fscrypt_master_key_secret *secret,
 				   const struct fscrypt_key_specifier *mk_spec)
 {
-	if (is_master_key_secret_present(&mk->mk_secret))
-		return 0;
+	struct key *mk_user;
+	bool rekey;
+	int err;
+
+	/*
+	 * If the current user is already in ->mk_users, then there's nothing to
+	 * do.  (Not applicable for v1 policy keys, which have NULL ->mk_users.)
+	 */
+	if (mk->mk_users) {
+		mk_user = find_master_key_user(mk);
+		if (mk_user != ERR_PTR(-ENOKEY)) {
+			if (IS_ERR(mk_user))
+				return PTR_ERR(mk_user);
+			key_put(mk_user);
+			return 0;
+		}
+	}
 
-	if (!refcount_inc_not_zero(&mk->mk_refcount))
+	/* If we'll be re-adding ->mk_secret, try to take the reference. */
+	rekey = !is_master_key_secret_present(&mk->mk_secret);
+	if (rekey && !refcount_inc_not_zero(&mk->mk_refcount))
 		return KEY_DEAD;
 
-	move_master_key_secret(&mk->mk_secret, secret);
+	/* Add the current user to ->mk_users, if applicable. */
+	if (mk->mk_users) {
+		err = add_master_key_user(mk);
+		if (err) {
+			if (rekey && refcount_dec_and_test(&mk->mk_refcount))
+				return KEY_DEAD;
+			return err;
+		}
+	}
+
+	/* Re-add the secret if needed. */
+	if (rekey) {
+		down_write(&mk->mk_secret_sem);
+		move_master_key_secret(&mk->mk_secret, secret);
+		up_write(&mk->mk_secret_sem);
+	}
 	return 0;
 }
 
@@ -269,7 +448,7 @@ static int add_master_key(struct super_block *sb,
 	} else {
 		/*
 		 * Found the key in ->s_master_keys.  Re-add the secret if
-		 * needed.
+		 * needed, and add the user to ->mk_users if needed.
 		 */
 		down_write(&key->sem);
 		err = add_existing_master_key(key->payload.data[0], secret,
@@ -291,6 +470,23 @@ static int add_master_key(struct super_block *sb,
 /*
  * Add a master encryption key to the filesystem, causing all files which were
  * encrypted with it to appear "unlocked" (decrypted) when accessed.
+ *
+ * When adding a key for use by v1 encryption policies, this ioctl is
+ * privileged, and userspace must provide the 'key_descriptor'.
+ *
+ * When adding a key for use by v2+ encryption policies, this ioctl is
+ * unprivileged.  This is needed, in general, to allow non-root users to use
+ * encryption without encountering the visibility problems of process-subscribed
+ * keyrings and the inability to properly remove keys.  This works by having
+ * each key identified by its cryptographically secure hash --- the
+ * 'key_identifier'.  The cryptographic hash ensures that a malicious user
+ * cannot add the wrong key for a given identifier.  Furthermore, each added key
+ * is charged to the appropriate user's quota for the keyrings service, which
+ * prevents a malicious user from adding too many keys.  Finally, we forbid a
+ * user from removing a key while other users have added it too, which prevents
+ * a user who knows another user's key from causing a denial-of-service by
+ * removing it at an inopportune time.  (We tolerate that a user who knows a key
+ * can prevent other users from removing it.)
  */
 int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 {
@@ -319,11 +515,16 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 	if (copy_from_user(secret.raw, uarg->raw, secret.size))
 		goto out_wipe_secret;
 
-	err = -EACCES;
-	if (!capable(CAP_SYS_ADMIN))
-		goto out_wipe_secret;
-
-	if (arg.key_spec.type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
+	if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
+		/*
+		 * Only root can add keys that are identified by an arbitrary
+		 * descriptor rather than by a cryptographic hash --- since
+		 * otherwise a malicious user could add the wrong key.
+		 */
+		err = -EACCES;
+		if (!capable(CAP_SYS_ADMIN))
+			goto out_wipe_secret;
+	} else {
 		err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
 		if (err)
 			goto out_wipe_secret;
@@ -511,13 +712,29 @@ int fscrypt_ioctl_remove_key(struct file *filp, const void __user *uarg)
 	if (copy_from_user(&arg, uarg, sizeof(arg)))
 		return -EFAULT;
 
+	if (arg.flags & ~FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS)
+		return -EINVAL;
+
 	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
 		return -EINVAL;
 
 	if (!valid_key_spec(&arg.key_spec))
 		return -EINVAL;
 
-	if (!capable(CAP_SYS_ADMIN))
+	/*
+	 * Only root can request that the key be removed no matter how many
+	 * users have added it.
+	 */
+	if ((arg.flags & FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS) &&
+	    !capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
+	/*
+	 * Only root can add and remove keys that are identified by an arbitrary
+	 * descriptor rather than by a cryptographic hash.
+	 */
+	if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
+	    !capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
 	/* Find the key being removed. */
@@ -528,11 +745,35 @@ int fscrypt_ioctl_remove_key(struct file *filp, const void __user *uarg)
 
 	down_write(&key->sem);
 
-	/* Wipe the secret. */
+	/* If relevant, remove current user's (or all users) usage of the key */
+	if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
+		if (arg.flags & FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS)
+			err = keyring_clear(mk->mk_users);
+		else
+			err = remove_master_key_user(mk);
+		if (err) {
+			up_write(&key->sem);
+			goto out_put_key;
+		}
+		if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
+			/*
+			 * Other users have still added the key too.  We removed
+			 * the current user's usage of the key if there was one,
+			 * but we still can't remove the key itself.
+			 */
+			err = -EUSERS;
+			up_write(&key->sem);
+			goto out_put_key;
+		}
+	}
+
+	/* No usages remaining.  Go ahead and wipe the secret. */
 	dead = false;
 	if (is_master_key_secret_present(&mk->mk_secret)) {
+		down_write(&mk->mk_secret_sem);
 		wipe_master_key_secret(&mk->mk_secret);
 		dead = refcount_dec_and_test(&mk->mk_refcount);
+		up_write(&mk->mk_secret_sem);
 	}
 	up_write(&key->sem);
 	if (dead) {
@@ -546,6 +787,7 @@ int fscrypt_ioctl_remove_key(struct file *filp, const void __user *uarg)
 		/* Some inodes still reference this key; try to evict them. */
 		err = try_to_lock_encrypted_files(sb, mk);
 	}
+out_put_key:
 	key_put(key);
 	return err;
 }
@@ -561,6 +803,15 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
  * of an encrypted directory without using a hack such as trying to open a
  * regular file in it (which can confuse the "incompletely removed" state with
  * absent or present).
+ *
+ * In addition, for v2 policy keys we allow applications to determine, via
+ * ->status_flags and ->user_count, whether the key has been added by the
+ * current user, by other users, or by both.  Most applications should not need
+ * this, since ordinarily only one user should know a given key.  However, if a
+ * secret key is shared by multiple users, applications may wish to add an
+ * already-present key to prevent other users from removing it.  This ioctl can
+ * be used to check whether that really is the case before the work is done to
+ * add the key --- which might e.g. require prompting the user for a passphrase.
  */
 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 {
@@ -579,6 +830,8 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 	if (!valid_key_spec(&arg.key_spec))
 		return -EINVAL;
 
+	arg.status_flags = 0;
+	arg.user_count = 0;
 	memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
 
 	key = fscrypt_find_master_key(sb, &arg.key_spec);
@@ -599,6 +852,20 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 	}
 
 	arg.status = FSCRYPT_KEY_STATUS_PRESENT;
+	if (mk->mk_users) {
+		struct key *mk_user;
+
+		arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
+		mk_user = find_master_key_user(mk);
+		if (!IS_ERR(mk_user)) {
+			arg.status_flags |=
+				FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
+			key_put(mk_user);
+		} else if (mk_user != ERR_PTR(-ENOKEY)) {
+			err = PTR_ERR(mk_user);
+			goto out_release_key;
+		}
+	}
 	err = 0;
 out_release_key:
 	up_read(&key->sem);
@@ -612,10 +879,25 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
 
 int __init fscrypt_init_keyring(void)
 {
-	return register_key_type(&key_type_fscrypt);
+	int err;
+
+	err = register_key_type(&key_type_fscrypt);
+	if (err)
+		return err;
+
+	err = register_key_type(&key_type_fscrypt_user);
+	if (err)
+		goto err_unregister_fscrypt;
+
+	return 0;
+
+err_unregister_fscrypt:
+	unregister_key_type(&key_type_fscrypt);
+	return err;
 }
 
 void fscrypt_exit_keyring(void)
 {
 	unregister_key_type(&key_type_fscrypt);
+	unregister_key_type(&key_type_fscrypt_user);
 }
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index a15a4bbafa3c..a783b6195618 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -283,10 +283,10 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
  *
  * If the master key is found in the filesystem-level keyring, then the
  * corresponding 'struct key' is returned in *master_key_ret with
- * ->sem read-locked.  This is needed to ensure that only one task links the
- * fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race to create
- * an fscrypt_info for the same inode), and to synchronize the key being removed
- * with a new inode starting to use it.
+ * ->mk_secret_sem read-locked.  This is needed to ensure that only one task
+ * links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race
+ * to create an fscrypt_info for the same inode), and to synchronize the key
+ * being removed with a new inode starting to use it.
  */
 static int setup_file_encryption_key(struct fscrypt_info *ci,
 				     struct key **master_key_ret)
@@ -324,7 +324,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 	}
 
 	mk = key->payload.data[0];
-	down_read(&key->sem);
+	down_read(&mk->mk_secret_sem);
 
 	/* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
 	if (!is_master_key_secret_present(&mk->mk_secret)) {
@@ -358,7 +358,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 	return 0;
 
 out_release_key:
-	up_read(&key->sem);
+	up_read(&mk->mk_secret_sem);
 	key_put(key);
 	return err;
 }
@@ -484,7 +484,9 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	res = 0;
 out:
 	if (master_key) {
-		up_read(&master_key->sem);
+		struct fscrypt_master_key *mk = master_key->payload.data[0];
+
+		up_read(&mk->mk_secret_sem);
 		key_put(master_key);
 	}
 	if (res == -ENOKEY)
diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h
index 26879e669dfa..fd1c3e2b0b7c 100644
--- a/include/uapi/linux/fscrypt.h
+++ b/include/uapi/linux/fscrypt.h
@@ -103,7 +103,9 @@ struct fscrypt_add_key_arg {
 /* Struct passed to FS_IOC_REMOVE_ENCRYPTION_KEY */
 struct fscrypt_remove_key_arg {
 	struct fscrypt_key_specifier key_spec;
-	__u32 __reserved[6];
+#define FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS	0x00000001
+	__u32 flags;
+	__u32 __reserved[5];
 };
 
 /* Struct passed to FS_IOC_GET_ENCRYPTION_KEY_STATUS */
@@ -117,7 +119,10 @@ struct fscrypt_get_key_status_arg {
 #define FSCRYPT_KEY_STATUS_PRESENT		2
 #define FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED	3
 	__u32 status;
-	__u32 __out_reserved[15];
+#define FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF   0x00000001
+	__u32 status_flags;
+	__u32 user_count;
+	__u32 __out_reserved[13];
 };
 
 #define FS_IOC_SET_ENCRYPTION_POLICY	  _IOR('f', 19, struct fscrypt_policy)
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 16/20] fscrypt: require that key be added when setting a v2 encryption policy
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (14 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 15/20] fscrypt: allow unprivileged users to add/remove keys for v2 policies Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 17/20] ext4: wire up new fscrypt ioctls Eric Biggers
                   ` (3 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

By looking up the master keys in a filesystem-level keyring rather than
in the calling processes' key hierarchy, it becomes possible for a user
to set an encryption policy which refers to some key they don't actually
know, then encrypt their files using that key.  Cryptographically this
isn't much of a problem, but the semantics of this would be a bit weird.
Thus, enforce that a v2 encryption policy can only be set if the user
has previously added the key, or has capable(CAP_FOWNER).

We tolerate that this problem will continue to exist for v1 encryption
policies, however; there is no way around that.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h |  3 +++
 fs/crypto/keyring.c         | 47 +++++++++++++++++++++++++++++++++++++
 fs/crypto/policy.c          |  6 +++++
 3 files changed, 56 insertions(+)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index b16cf3bd6cf1..2b58520ab0e2 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -402,6 +402,9 @@ extern struct key *
 fscrypt_find_master_key(struct super_block *sb,
 			const struct fscrypt_key_specifier *mk_spec);
 
+extern int fscrypt_verify_key_added(struct super_block *sb,
+				    const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
+
 extern int __init fscrypt_init_keyring(void);
 extern void fscrypt_exit_keyring(void);
 
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 15ca0f1d04e7..42462452e34e 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -556,6 +556,53 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
 
+/*
+ * Verify that the current user has added a master key with the given identifier
+ * (returns -ENOKEY if not).  This is needed to prevent a user from encrypting
+ * their files using some other user's key which they don't actually know.
+ * Cryptographically this isn't much of a problem, but the semantics of this
+ * would be a bit weird, so it's best to just forbid it.
+ *
+ * The system administrator (CAP_FOWNER) can override this, which should be
+ * enough for any use cases where encryption policies are being set using keys
+ * that were chosen ahead of time but aren't available at the moment.
+ *
+ * Note that the key may have already removed by the time this returns, but
+ * that's okay; we just care whether the key was there at some point.
+ *
+ * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
+ */
+int fscrypt_verify_key_added(struct super_block *sb,
+			     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
+{
+	struct fscrypt_key_specifier mk_spec;
+	struct key *key, *mk_user;
+	struct fscrypt_master_key *mk;
+	int err;
+
+	mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
+	memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
+
+	key = fscrypt_find_master_key(sb, &mk_spec);
+	if (IS_ERR(key)) {
+		err = PTR_ERR(key);
+		goto out;
+	}
+	mk = key->payload.data[0];
+	mk_user = find_master_key_user(mk);
+	if (IS_ERR(mk_user)) {
+		err = PTR_ERR(mk_user);
+	} else {
+		key_put(mk_user);
+		err = 0;
+	}
+	key_put(key);
+out:
+	if (err == -ENOKEY && capable(CAP_FOWNER))
+		err = 0;
+	return err;
+}
+
 static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
 {
 	struct fscrypt_info *ci;
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 07fec2f7fc72..456c25796844 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -209,6 +209,7 @@ static int set_encryption_policy(struct inode *inode,
 {
 	union fscrypt_context ctx;
 	int ctxsize;
+	int err;
 
 	if (!fscrypt_supported_policy(policy))
 		return -EINVAL;
@@ -227,6 +228,11 @@ static int set_encryption_policy(struct inode *inode,
 		 */
 		pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
 			     current->comm, current->pid);
+	} else {
+		err = fscrypt_verify_key_added(inode->i_sb,
+					       policy->v2.master_key_identifier);
+		if (err)
+			return err;
 	}
 
 	ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 17/20] ext4: wire up new fscrypt ioctls
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (15 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 16/20] fscrypt: require that key be added when setting a v2 encryption policy Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 18/20] f2fs: " Eric Biggers
                   ` (2 subsequent siblings)
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.

For more details see Documentation/filesystems/fscrypt.rst, as well as
the fscrypt patches that added the implementation of these ioctls.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/ext4/ioctl.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index d26bcac291bb..c939dbd2f2ac 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1020,6 +1020,26 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	case EXT4_IOC_GET_ENCRYPTION_POLICY:
 		return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
 
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_get_policy_ex(filp, (void __user *)arg);
+
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_add_key(filp, (void __user *)arg);
+
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_remove_key(filp, (const void __user *)arg);
+
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_get_key_status(filp, (void __user *)arg);
+
 	case EXT4_IOC_FSGETXATTR:
 	{
 		struct fsxattr fa;
@@ -1138,6 +1158,10 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case EXT4_IOC_SET_ENCRYPTION_POLICY:
 	case EXT4_IOC_GET_ENCRYPTION_PWSALT:
 	case EXT4_IOC_GET_ENCRYPTION_POLICY:
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
 	case EXT4_IOC_SHUTDOWN:
 	case FS_IOC_GETFSMAP:
 		break;
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 18/20] f2fs: wire up new fscrypt ioctls
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (16 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 17/20] ext4: wire up new fscrypt ioctls Eric Biggers
@ 2019-02-11 17:27 ` " Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 19/20] ubifs: " Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 20/20] fscrypt: document the new ioctls and policy version Eric Biggers
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.

For more details see Documentation/filesystems/fscrypt.rst, as well as
the fscrypt patches that added the implementation of these ioctls.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/f2fs/file.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ba5954f41e14..3e6da48e0530 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2093,6 +2093,40 @@ static int f2fs_ioc_get_encryption_pwsalt(struct file *filp, unsigned long arg)
 	return err;
 }
 
+static int f2fs_ioc_get_encryption_policy_ex(struct file *filp,
+					     unsigned long arg)
+{
+	if (!f2fs_sb_has_encrypt(F2FS_I_SB(file_inode(filp))))
+		return -EOPNOTSUPP;
+
+	return fscrypt_ioctl_get_policy_ex(filp, (void __user *)arg);
+}
+
+static int f2fs_ioc_add_encryption_key(struct file *filp, unsigned long arg)
+{
+	if (!f2fs_sb_has_encrypt(F2FS_I_SB(file_inode(filp))))
+		return -EOPNOTSUPP;
+
+	return fscrypt_ioctl_add_key(filp, (void __user *)arg);
+}
+
+static int f2fs_ioc_remove_encryption_key(struct file *filp, unsigned long arg)
+{
+	if (!f2fs_sb_has_encrypt(F2FS_I_SB(file_inode(filp))))
+		return -EOPNOTSUPP;
+
+	return fscrypt_ioctl_remove_key(filp, (const void __user *)arg);
+}
+
+static int f2fs_ioc_get_encryption_key_status(struct file *filp,
+					      unsigned long arg)
+{
+	if (!f2fs_sb_has_encrypt(F2FS_I_SB(file_inode(filp))))
+		return -EOPNOTSUPP;
+
+	return fscrypt_ioctl_get_key_status(filp, (void __user *)arg);
+}
+
 static int f2fs_ioc_gc(struct file *filp, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -2998,6 +3032,14 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_get_encryption_policy(filp, arg);
 	case F2FS_IOC_GET_ENCRYPTION_PWSALT:
 		return f2fs_ioc_get_encryption_pwsalt(filp, arg);
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+		return f2fs_ioc_get_encryption_policy_ex(filp, arg);
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+		return f2fs_ioc_add_encryption_key(filp, arg);
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+		return f2fs_ioc_remove_encryption_key(filp, arg);
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+		return f2fs_ioc_get_encryption_key_status(filp, arg);
 	case F2FS_IOC_GARBAGE_COLLECT:
 		return f2fs_ioc_gc(filp, arg);
 	case F2FS_IOC_GARBAGE_COLLECT_RANGE:
@@ -3117,6 +3159,10 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case F2FS_IOC_SET_ENCRYPTION_POLICY:
 	case F2FS_IOC_GET_ENCRYPTION_PWSALT:
 	case F2FS_IOC_GET_ENCRYPTION_POLICY:
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
 	case F2FS_IOC_GARBAGE_COLLECT:
 	case F2FS_IOC_GARBAGE_COLLECT_RANGE:
 	case F2FS_IOC_WRITE_CHECKPOINT:
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 19/20] ubifs: wire up new fscrypt ioctls
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (17 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 18/20] f2fs: " Eric Biggers
@ 2019-02-11 17:27 ` " Eric Biggers
  2019-02-11 17:27 ` [RFC PATCH v2 20/20] fscrypt: document the new ioctls and policy version Eric Biggers
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.

For more details see Documentation/filesystems/fscrypt.rst, as well as
the fscrypt patches that added the implementation of these ioctls.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/ubifs/ioctl.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/fs/ubifs/ioctl.c b/fs/ubifs/ioctl.c
index 0f9c362a3402..5f4c4620f9c4 100644
--- a/fs/ubifs/ioctl.c
+++ b/fs/ubifs/ioctl.c
@@ -197,13 +197,21 @@ long ubifs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return -EOPNOTSUPP;
 #endif
 	}
-	case FS_IOC_GET_ENCRYPTION_POLICY: {
-#ifdef CONFIG_FS_ENCRYPTION
+
+	case FS_IOC_GET_ENCRYPTION_POLICY:
 		return fscrypt_ioctl_get_policy(file, (void __user *)arg);
-#else
-		return -EOPNOTSUPP;
-#endif
-	}
+
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+		return fscrypt_ioctl_get_policy_ex(file, (void __user *)arg);
+
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+		return fscrypt_ioctl_add_key(file, (void __user *)arg);
+
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+		return fscrypt_ioctl_remove_key(file, (const void __user *)arg);
+
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+		return fscrypt_ioctl_get_key_status(file, (void __user *)arg);
 
 	default:
 		return -ENOTTY;
@@ -222,6 +230,10 @@ long ubifs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		break;
 	case FS_IOC_SET_ENCRYPTION_POLICY:
 	case FS_IOC_GET_ENCRYPTION_POLICY:
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
+	case FS_IOC_ADD_ENCRYPTION_KEY:
+	case FS_IOC_REMOVE_ENCRYPTION_KEY:
+	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
 		break;
 	default:
 		return -ENOIOCTLCMD;
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [RFC PATCH v2 20/20] fscrypt: document the new ioctls and policy version
  2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
                   ` (18 preceding siblings ...)
  2019-02-11 17:27 ` [RFC PATCH v2 19/20] ubifs: " Eric Biggers
@ 2019-02-11 17:27 ` Eric Biggers
  19 siblings, 0 replies; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 17:27 UTC (permalink / raw)
  To: linux-fscrypt
  Cc: linux-ext4, linux-f2fs-devel, linux-mtd, linux-fsdevel,
	linux-crypto, linux-api, keyrings, Satya Tangirala, Paul Crowley

From: Eric Biggers <ebiggers@google.com>

Update the fscrypt documentation file to catch up to all the latest
changes, including the new ioctls to manage master encryption keys in
the filesystem-level keyring and the support for v2 encryption policies.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/filesystems/fscrypt.rst | 646 +++++++++++++++++++++-----
 1 file changed, 530 insertions(+), 116 deletions(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 4f9df6ba669e..c5d6c34ddf79 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -72,6 +72,9 @@ Online attacks
 fscrypt (and storage encryption in general) can only provide limited
 protection, if any at all, against online attacks.  In detail:
 
+Side-channel attacks
+~~~~~~~~~~~~~~~~~~~~
+
 fscrypt is only resistant to side-channel attacks, such as timing or
 electromagnetic attacks, to the extent that the underlying Linux
 Cryptographic API algorithms are.  If a vulnerable algorithm is used,
@@ -80,29 +83,84 @@ attacker to mount a side channel attack against the online system.
 Side channel attacks may also be mounted against applications
 consuming decrypted data.
 
-After an encryption key has been provided, fscrypt is not designed to
-hide the plaintext file contents or filenames from other users on the
-same system, regardless of the visibility of the keyring key.
-Instead, existing access control mechanisms such as file mode bits,
-POSIX ACLs, LSMs, or mount namespaces should be used for this purpose.
-Also note that as long as the encryption keys are *anywhere* in
-memory, an online attacker can necessarily compromise them by mounting
-a physical attack or by exploiting any kernel security vulnerability
-which provides an arbitrary memory read primitive.
-
-While it is ostensibly possible to "evict" keys from the system,
-recently accessed encrypted files will remain accessible at least
-until the filesystem is unmounted or the VFS caches are dropped, e.g.
-using ``echo 2 > /proc/sys/vm/drop_caches``.  Even after that, if the
-RAM is compromised before being powered off, it will likely still be
-possible to recover portions of the plaintext file contents, if not
-some of the encryption keys as well.  (Since Linux v4.12, all
-in-kernel keys related to fscrypt are sanitized before being freed.
-However, userspace would need to do its part as well.)
-
-Currently, fscrypt does not prevent a user from maliciously providing
-an incorrect key for another user's existing encrypted files.  A
-protection against this is planned.
+Unauthorized file access
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+After an encryption key has been added, fscrypt does not hide the
+plaintext file contents or filenames from other users on the same
+system.  Instead, existing access control mechanisms such as file mode
+bits, POSIX ACLs, LSMs, or namespaces should be used for this purpose.
+
+(For the reasoning behind this, understand that while the key is
+added, the confidentiality of the data, from the perspective of the
+system itself, is *not* protected by the mathematical properties of
+encryption but rather only by the correctness of the kernel.
+Therefore, any encryption-specific access control checks would merely
+be enforced by kernel *code* and therefore would be largely redundant
+with the wide variety of access control mechanisms already available.)
+
+Kernel memory compromise
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+An attacker who compromises the system enough to read from arbitrary
+memory, e.g. by mounting a physical attack or by exploiting a kernel
+security vulnerability, can compromise all encryption keys that are
+currently in use.
+
+However, fscrypt allows encryption keys to be removed from the kernel,
+which may protect them from later compromise.
+
+In more detail, the FS_IOC_REMOVE_ENCRYPTION_KEY ioctl will wipe a
+master encryption key from kernel memory.  Moreover, it will try to
+evict all cached inodes which had been "unlocked" using the key,
+thereby wiping their per-file keys and making them once again appear
+"locked", i.e. in ciphertext or encrypted form.
+
+However, FS_IOC_REMOVE_ENCRYPTION_KEY has some limitations:
+
+- Per-file keys for in-use files will *not* be removed or wiped.
+  Therefore, for maximum effect, userspace should close the relevant
+  encrypted files and directories before removing a master key, as
+  well as kill any processes whose working directory is in an affected
+  encrypted directory.
+
+- The kernel cannot magically wipe copies of the master key(s) that
+  userspace might have as well.  Therefore, userspace must wipe all
+  copies of the master key(s) it makes as well.  Naturally, the same
+  also applies to all higher levels in the key hierarchy.  Userspace
+  should also follow other security precautions such as mlock()ing
+  memory containing keys to prevent it from being swapped out.
+
+- In general, decrypted contents and filenames in the kernel VFS
+  caches are freed but not wiped.  Therefore, portions thereof may be
+  recoverable from freed memory, even after the corresponding key(s)
+  were wiped.  To partially solve this, you can set
+  CONFIG_PAGE_POISONING=y in your kernel config and add page_poison=1
+  to your kernel command line.  However, this has a performance cost.
+
+- Secret keys might still exist in CPU registers, in crypto
+  accelerator hardware (if used by the crypto API to implement any of
+  the algorithms), or in other places not explicitly considered here.
+
+Limitations of v1 policies
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+v1 encryption policies have some weaknesses with respect to online
+attacks:
+
+- There is no verification that the provided master key is correct.
+  Consequently, malicious users can associate the wrong key with
+  encrypted files, even files to which they have only read-only
+  access.
+
+- A compromise of a per-file key also compromises the master key from
+  which it was derived.
+
+- Non-root users cannot securely remove encryption keys.
+
+All the above problems are fixed with v2 encryption policies.  For
+this reason among others, it is recommended to use v2 encryption
+policies on all new encrypted directories.
 
 Key hierarchy
 =============
@@ -123,11 +181,46 @@ appropriate master key.  There can be any number of master keys, each
 of which protects any number of directory trees on any number of
 filesystems.
 
-Userspace should generate master keys either using a cryptographically
-secure random number generator, or by using a KDF (Key Derivation
-Function).  Note that whenever a KDF is used to "stretch" a
-lower-entropy secret such as a passphrase, it is critical that a KDF
-designed for this purpose be used, such as scrypt, PBKDF2, or Argon2.
+Master keys should be pseudorandom, i.e. indistinguishable from random
+bytestrings of the same length.  This implies that users **must not**
+directly use a password as a master key, zero-pad a shorter key, or
+repeat a shorter key.  Instead, users should generate master keys
+either using a cryptographically secure random number generator, or by
+using a KDF (Key Derivation Function).  Note that whenever a KDF is
+used to "stretch" a lower-entropy secret such as a passphrase, it is
+critical that a KDF designed for this purpose be used, such as scrypt,
+PBKDF2, or Argon2.
+
+Key derivation function
+-----------------------
+
+With one exception, fscrypt never uses the master key(s) for
+encryption directly.  Instead, they are only used as input to a KDF
+(Key Derivation Function) to derive the actual keys.
+
+The KDF used for a particular master key differs depending on whether
+the key is used for v1 encryption policies or for v2 encryption
+policies.  Users **must not** use the same key for both v1 and v2
+encryption policies.
+
+For v1 encryption policies, the KDF only supports deriving per-file
+encryption keys.  It works by encrypting the master key with
+AES-128-ECB, using the file's 16-byte nonce as the AES key.  The
+resulting ciphertext is used as the derived key.  If the ciphertext is
+longer than needed, then it is truncated to the needed length.
+
+For v2 encryption policies, the KDF is HKDF-SHA512.  The master key is
+passed as the "input keying material", a fixed value is passed as the
+"salt", and a distinct "application-specific information string" is
+used for each distinct key to be derived.  For example, when a
+per-file encryption key is derived, the application-specific
+information string is the file's nonce prefixed with a context byte.
+Different context bytes are used for other types of derived keys.
+
+HKDF-SHA512 is preferred to the original AES-128-ECB based KDF because
+HKDF is more flexible, is nonreversible, and evenly distributes
+entropy from the master key.  HKDF is also standardized and widely
+used by other software, whereas the AES-128-ECB based KDF is ad-hoc.
 
 Per-file keys
 -------------
@@ -138,29 +231,9 @@ files doesn't map to the same ciphertext, or vice versa.  In most
 cases, fscrypt does this by deriving per-file keys.  When a new
 encrypted inode (regular file, directory, or symlink) is created,
 fscrypt randomly generates a 16-byte nonce and stores it in the
-inode's encryption xattr.  Then, it uses a KDF (Key Derivation
-Function) to derive the file's key from the master key and nonce.
-
-The Adiantum encryption mode (see `Encryption modes and usage`_) is
-special, since it accepts longer IVs and is suitable for both contents
-and filenames encryption.  For it, a "direct key" option is offered
-where the file's nonce is included in the IVs and the master key is
-used for encryption directly.  This improves performance; however,
-users must not use the same master key for any other encryption mode.
-
-Below, the KDF and design considerations are described in more detail.
-
-The current KDF works by encrypting the master key with AES-128-ECB,
-using the file's nonce as the AES key.  The output is used as the
-derived key.  If the output is longer than needed, then it is
-truncated to the needed length.
-
-Note: this KDF meets the primary security requirement, which is to
-produce unique derived keys that preserve the entropy of the master
-key, assuming that the master key is already a good pseudorandom key.
-However, it is nonstandard and has some problems such as being
-reversible, so it is generally considered to be a mistake!  It may be
-replaced with HKDF or another more standard KDF in the future.
+inode's encryption xattr.  Then, it uses a KDF (as described in `Key
+derivation function`_) to derive the file's key from the master key
+and nonce.
 
 Key derivation was chosen over key wrapping because wrapped keys would
 require larger xattrs which would be less likely to fit in-line in the
@@ -176,6 +249,37 @@ rejected as it would have prevented ext4 filesystems from being
 resized, and by itself still wouldn't have been sufficient to prevent
 the same key from being directly reused for both XTS and CTS-CBC.
 
+DIRECT_KEY and per-mode keys
+----------------------------
+
+The Adiantum encryption mode (see `Encryption modes and usage`_) is
+suitable for both contents and filenames encryption, and it accepts
+long IVs --- long enough to hold both an 8-byte logical block number
+and a 16-byte per-file nonce.  Also, the overhead of each Adiantum key
+is greater than that of an AES-256-XTS key.
+
+Therefore, to improve performance and save memory, for Adiantum a
+"direct key" configuration is supported.  When the user has enabled
+this by setting FSCRYPT_POLICY_FLAG_DIRECT_KEY in the fscrypt policy,
+per-file keys are not used.  Instead, whenever any data (contents or
+filenames) is encrypted, the file's 16-byte nonce is included in the
+IV.  Moreover:
+
+- For v1 encryption policies, the encryption is done directly with the
+  master key.  Because of this, users **must not** use the same master
+  key for any other purpose, even for other v1 policies.
+
+- For v2 encryption policies, the encryption is done with a per-mode
+  key derived using the KDF.  Users may use the same master key for
+  other v2 encryption policies.
+
+Key identifiers
+---------------
+
+For master keys used for v2 encryption policies, a unique 16-byte "key
+identifier" is also derived using the KDF.  This value is stored in
+the clear, since it is needed to reliably identify the key itself.
+
 Encryption modes and usage
 ==========================
 
@@ -271,21 +375,38 @@ Setting an encryption policy
 The FS_IOC_SET_ENCRYPTION_POLICY ioctl sets an encryption policy on an
 empty directory or verifies that a directory or regular file already
 has the specified encryption policy.  It takes in a pointer to a
-:c:type:`struct fscrypt_policy`, defined as follows::
+:c:type:`struct fscrypt_policy_v1` or a :c:type:`struct
+fscrypt_policy_v2`, defined as follows::
 
-    #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
-
-    struct fscrypt_policy {
+    #define FSCRYPT_POLICY_V1               0
+    #define FSCRYPT_KEY_DESCRIPTOR_SIZE     8
+    struct fscrypt_policy_v1 {
             __u8 version;
             __u8 contents_encryption_mode;
             __u8 filenames_encryption_mode;
             __u8 flags;
             __u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
     };
+    #define fscrypt_policy  fscrypt_policy_v1
+
+    #define FSCRYPT_POLICY_V2               2
+    #define FSCRYPT_KEY_IDENTIFIER_SIZE     16
+    struct fscrypt_policy_v2 {
+            __u8 version;
+            __u8 contents_encryption_mode;
+            __u8 filenames_encryption_mode;
+            __u8 flags;
+            __u8 __reserved[4];
+            __u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
+    };
 
 This structure must be initialized as follows:
 
-- ``version`` must be 0.
+- ``version`` must be FSCRYPT_POLICY_V1 (0) if the struct is
+  :c:type:`fscrypt_policy_v1` or FSCRYPT_POLICY_V2 (2) if the struct
+  is :c:type:`fscrypt_policy_v2`.  (Note: we refer to the original
+  policy version as "v1", though its version code is really 0.)  For
+  new encrypted directories, use v2 policies.
 
 - ``contents_encryption_mode`` and ``filenames_encryption_mode`` must
   be set to constants from ``<linux/fs.h>`` which identify the
@@ -295,21 +416,30 @@ This structure must be initialized as follows:
 
 - ``flags`` must contain a value from ``<linux/fs.h>`` which
   identifies the amount of NUL-padding to use when encrypting
-  filenames.  If unsure, use FSCRYPT_POLICY_FLAGS_PAD_32 (0x3).  In
-  addition, if the chosen encryption modes are both
+  filenames.  If unsure, use FSCRYPT_POLICY_FLAGS_PAD_32 (0x3).
+  Additionally, if the encryption modes are both
   FSCRYPT_MODE_ADIANTUM, this can contain
-  FSCRYPT_POLICY_FLAG_DIRECT_KEY to specify that the master key should
-  be used directly, without key derivation.
+  FSCRYPT_POLICY_FLAG_DIRECT_KEY; see `DIRECT_KEY and per-mode keys`_.
 
-- ``master_key_descriptor`` specifies how to find the master key in
-  the keyring; see `Adding keys`_.  It is up to userspace to choose a
-  unique ``master_key_descriptor`` for each master key.  The e4crypt
-  and fscrypt tools use the first 8 bytes of
+- For v2 encryption policies, ``__reserved`` must be zeroed.
+
+- For v1 encryption policies, ``master_key_descriptor`` specifies how
+  to find the master key in a keyring; see `Adding keys`_.  It is up
+  to userspace to choose a unique ``master_key_descriptor`` for each
+  master key.  The e4crypt and fscrypt tools use the first 8 bytes of
   ``SHA-512(SHA-512(master_key))``, but this particular scheme is not
   required.  Also, the master key need not be in the keyring yet when
   FS_IOC_SET_ENCRYPTION_POLICY is executed.  However, it must be added
   before any files can be created in the encrypted directory.
 
+  For v2 encryption policies, ``master_key_descriptor`` has been
+  replaced with ``master_key_identifier``, which is longer and cannot
+  be arbitrarily chosen.  Instead, the key must first be added using
+  FS_IOC_ADD_ENCRYPTION_KEY, as described in `Adding keys`_.  Then,
+  the ``key_spec.u.identifier`` the kernel returned in the
+  :c:type:`struct fscrypt_add_key_arg` must be used as the
+  ``master_key_identifier`` in the :c:type:`struct fscrypt_policy_v2`.
+
 If the file is not yet encrypted, then FS_IOC_SET_ENCRYPTION_POLICY
 verifies that the file is an empty directory.  If so, the specified
 encryption policy is assigned to the directory, turning it into an
@@ -325,6 +455,15 @@ policy exactly matches the actual one.  If they match, then the ioctl
 returns 0.  Otherwise, it fails with EEXIST.  This works on both
 regular files and directories, including nonempty directories.
 
+When a v2 encryption policy is assigned to a directory, it is also
+required that either the specified key has been added by the current
+user or that the caller has CAP_FOWNER in the initial user namespace.
+(This is needed to prevent a user from encrypting their data with
+another user's key.)  The key must remain added while
+FS_IOC_SET_ENCRYPTION_POLICY is executing.  However, if the new
+encrypted directory does not need to be accessed immediately, then the
+key can be removed right away afterwards.
+
 Note that the ext4 filesystem does not allow the root directory to be
 encrypted, even if it is empty.  Users who want to encrypt an entire
 filesystem with one key should consider using dm-crypt instead.
@@ -337,7 +476,11 @@ FS_IOC_SET_ENCRYPTION_POLICY can fail with the following errors:
 - ``EEXIST``: the file is already encrypted with an encryption policy
   different from the one specified
 - ``EINVAL``: an invalid encryption policy was specified (invalid
-  version, mode(s), or flags)
+  version, mode(s), or flags; or reserved bits were set)
+- ``ENOKEY``: a v2 encryption policy was specified, but the key with
+  the specified ``master_key_identifier`` has not been added, nor does
+  the process have the CAP_FOWNER capability in the initial user
+  namespace
 - ``ENOTDIR``: the file is unencrypted and is a regular file, not a
   directory
 - ``ENOTEMPTY``: the file is unencrypted and is a nonempty directory
@@ -356,25 +499,78 @@ FS_IOC_SET_ENCRYPTION_POLICY can fail with the following errors:
 Getting an encryption policy
 ----------------------------
 
-The FS_IOC_GET_ENCRYPTION_POLICY ioctl retrieves the :c:type:`struct
-fscrypt_policy`, if any, for a directory or regular file.  See above
-for the struct definition.  No additional permissions are required
-beyond the ability to open the file.
+Two ioctls are available to get a file's encryption policy:
+
+- FS_IOC_GET_ENCRYPTION_POLICY_EX
+- FS_IOC_GET_ENCRYPTION_POLICY
+
+The extended (_EX) version of the ioctl is more general and is
+recommended to use when possible.  However, on older kernels only the
+original ioctl is available.  Applications should try the extended
+version, and if it fails with ENOTTY fall back to the original
+version.
+
+Preferred method
+~~~~~~~~~~~~~~~~
+
+The FS_IOC_GET_ENCRYPTION_POLICY_EX ioctl retrieves the encryption
+policy, if any, for a directory or regular file.  No additional
+permissions are required beyond the ability to open the file.  It
+takes in a pointer to a :c:type:`struct fscrypt_get_policy_ex_arg`,
+defined as follows::
+
+    struct fscrypt_get_policy_ex_arg {
+            __u64 policy_size; /* input/output */
+            union {
+                    __u8 version;
+                    struct fscrypt_policy_v1 v1;
+                    struct fscrypt_policy_v2 v2;
+            } policy; /* output */
+    };
+
+The caller must initialize ``policy_size`` to the size available for
+the policy struct, i.e. ``sizeof(arg.policy)``.
+
+On success, the policy struct is returned in ``policy``, and its
+actual size is returned in ``policy_size``.  ``policy.version`` should
+be checked to determine the version of policy returned.  Note that the
+version code for the "v1" policy is actually 0 (FSCRYPT_POLICY_V1).
 
-FS_IOC_GET_ENCRYPTION_POLICY can fail with the following errors:
+FS_IOC_GET_ENCRYPTION_POLICY_EX can fail with the following errors:
 
 - ``EINVAL``: the file is encrypted, but it uses an unrecognized
-  encryption context format
+  encryption policy version
 - ``ENODATA``: the file is not encrypted
-- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``ENOTTY``: this type of filesystem does not implement encryption,
+  or this kernel is too old to support FS_IOC_GET_ENCRYPTION_POLICY_EX
+  (try FS_IOC_GET_ENCRYPTION_POLICY instead)
 - ``EOPNOTSUPP``: the kernel was not configured with encryption
   support for this filesystem
+- ``EOVERFLOW``: the file is encrypted and uses a recognized
+  encryption policy version, but the policy struct does not fit into
+  the provided buffer
 
 Note: if you only need to know whether a file is encrypted or not, on
 most filesystems it is also possible to use the FS_IOC_GETFLAGS ioctl
 and check for FS_ENCRYPT_FL, or to use the statx() system call and
 check for STATX_ATTR_ENCRYPTED in stx_attributes.
 
+Legacy method
+~~~~~~~~~~~~~
+
+The FS_IOC_GET_ENCRYPTION_POLICY ioctl can also retrieve the
+encryption policy, if any, for a directory or regular file.  However,
+unlike the extended version (FS_IOC_GET_ENCRYPTION_POLICY_EX),
+FS_IOC_GET_ENCRYPTION_POLICY only supports the original policy
+version.  It takes in a pointer directly to a :c:type:`struct
+fscrypt_policy_v1` rather than a :c:type:`struct
+fscrypt_get_policy_ex_arg`.
+
+The error codes for FS_IOC_GET_ENCRYPTION_POLICY are the same as those
+for FS_IOC_GET_ENCRYPTION_POLICY_EX, except that
+FS_IOC_GET_ENCRYPTION_POLICY also returns ``EINVAL`` if the file is
+encrypted using a newer encryption policy version.
+
 Getting the per-filesystem salt
 -------------------------------
 
@@ -390,8 +586,98 @@ generate and manage any needed salt(s) in userspace.
 Adding keys
 -----------
 
-To provide a master key, userspace must add it to an appropriate
-keyring using the add_key() system call (see:
+Preferred method
+~~~~~~~~~~~~~~~~
+
+The FS_IOC_ADD_ENCRYPTION_KEY ioctl adds a master encryption key to
+the filesystem, making all files on the filesystem which were
+encrypted using that key appear "unlocked", i.e. in plaintext form.
+It can be executed on any file or directory on the target filesystem,
+but using the filesystem's root directory is recommended.  It takes in
+a pointer to a :c:type:`struct fscrypt_add_key_arg`, defined as
+follows::
+
+    struct fscrypt_add_key_arg {
+            struct fscrypt_key_specifier key_spec;
+            __u32 raw_size;
+            __u32 __reserved[9];
+            __u8 raw[];
+    };
+
+    struct fscrypt_key_specifier {
+    #define FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR        1
+    #define FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER        2
+            __u32 type;
+            __u32 __reserved;
+            union {
+                    __u8 __reserved[32]; /* reserve some extra space */
+                    __u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+                    __u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
+            } u;
+    };
+
+:c:type:`struct fscrypt_add_key_arg` must be zeroed, then initialized
+as follows:
+
+- If the key is being added for use by v1 encryption policies, then
+  ``key_spec.type`` must contain FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR, and
+  ``key_spec.u.descriptor`` must contain the descriptor of the key
+  being added, corresponding to the value in the
+  ``master_key_descriptor`` field of :c:type:`struct
+  fscrypt_policy_v1`.  To add this type of key, the calling process
+  must have the CAP_SYS_ADMIN capability in the initial user
+  namespace.
+
+  Alternatively, if the key is being added for use by v2 encryption
+  policies, then ``key_spec.type`` must contain
+  FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER, and ``key_spec.u.identifier`` is
+  an *output* field which the kernel fills in with a cryptographic
+  hash of the key.  To add this type of key, the calling process does
+  not need any privileges.  However, the number of keys that can be
+  added is limited by the user's quota for the keyrings service (see
+  ``Documentation/security/keys/core.rst``).
+
+- ``raw_size`` must be the size of the ``raw`` key provided, in bytes.
+
+- ``raw`` is a variable-length field which must contain the actual
+  key, ``raw_size`` bytes long.
+
+FS_IOC_ADD_ENCRYPTION_KEY can fail with the following errors:
+
+- ``EACCES``: FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR was specified, but the
+  caller does not have the CAP_SYS_ADMIN capability in the initial
+  user namespace
+- ``EDQUOT``: the key quota for this user would be exceeded by adding
+  the key
+- ``EINVAL``: invalid key size or key specifier type, or reserved bits
+  were set
+- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``EOPNOTSUPP``: the kernel was not configured with encryption
+  support for this filesystem, or the filesystem superblock has not
+  had encryption enabled on it
+
+Legacy method
+~~~~~~~~~~~~~
+
+For v1 encryption policies, a master encryption key can also be
+provided by adding it to a process-subscribed keyring, e.g. to a
+session keyring, or to a user keyring if the user keyring is linked
+into the session keyring.
+
+This method is deprecated (and not supported for v2 encryption
+policies) for several reasons.  First, it cannot be used in
+combination with FS_IOC_REMOVE_ENCRYPTION_KEY (see `Removing keys`_),
+so for removing a key a workaround such as keyctl_unlink() in
+combination with ``sync; echo 2 > /proc/sys/vm/drop_caches`` would
+have to be used.  Second, it doesn't match the fact that the
+locked/unlocked status of encrypted files (i.e. whether they appear to
+be in plaintext form or in ciphertext form) is global.  This mismatch
+has caused much confusion as well as real problems when processes
+running under different UIDs, such as a ``sudo`` command, need to
+access encrypted files.
+
+Nevertheless, to add a key to one of the process-subscribed keyrings,
+the add_key() system call can be used (see:
 ``Documentation/security/keys/core.rst``).  The key type must be
 "logon"; keys of this type are kept in kernel memory and cannot be
 read back by userspace.  The key description must be "fscrypt:"
@@ -399,12 +685,12 @@ followed by the 16-character lower case hex representation of the
 ``master_key_descriptor`` that was set in the encryption policy.  The
 key payload must conform to the following structure::
 
-    #define FSCRYPT_MAX_KEY_SIZE 64
+    #define FSCRYPT_MAX_KEY_SIZE            64
 
     struct fscrypt_key {
-            u32 mode;
-            u8 raw[FSCRYPT_MAX_KEY_SIZE];
-            u32 size;
+            __u32 mode;
+            __u8 raw[FSCRYPT_MAX_KEY_SIZE];
+            __u32 size;
     };
 
 ``mode`` is ignored; just set it to 0.  The actual key is provided in
@@ -416,26 +702,143 @@ with a filesystem-specific prefix such as "ext4:".  However, the
 filesystem-specific prefixes are deprecated and should not be used in
 new programs.
 
-There are several different types of keyrings in which encryption keys
-may be placed, such as a session keyring, a user session keyring, or a
-user keyring.  Each key must be placed in a keyring that is "attached"
-to all processes that might need to access files encrypted with it, in
-the sense that request_key() will find the key.  Generally, if only
-processes belonging to a specific user need to access a given
-encrypted directory and no session keyring has been installed, then
-that directory's key should be placed in that user's user session
-keyring or user keyring.  Otherwise, a session keyring should be
-installed if needed, and the key should be linked into that session
-keyring, or in a keyring linked into that session keyring.
-
-Note: introducing the complex visibility semantics of keyrings here
-was arguably a mistake --- especially given that by design, after any
-process successfully opens an encrypted file (thereby setting up the
-per-file key), possessing the keyring key is not actually required for
-any process to read/write the file until its in-memory inode is
-evicted.  In the future there probably should be a way to provide keys
-directly to the filesystem instead, which would make the intended
-semantics clearer.
+Removing keys
+-------------
+
+The FS_IOC_REMOVE_ENCRYPTION_KEY ioctl can be used to remove a master
+encryption key from the kernel, wiping the corresponding secrets from
+memory and causing any files which were "unlocked" with the key to
+appear "locked" again.  It can be executed on any file or directory on
+the target filesystem, but using the filesystem's root directory is
+recommended.  It takes in a pointer to a :c:type:`struct
+fscrypt_remove_key_arg`, defined as follows::
+
+    struct fscrypt_remove_key_arg {
+            struct fscrypt_key_specifier key_spec;
+    #define FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS       0x00000001
+            __u32 flags;
+            __u32 __reserved[5];
+    };
+
+This structure must be zeroed, then initialized as follows:
+
+- The key to remove is specified by ``key_spec``:
+
+    - To remove a key used by v1 encryption policies, set
+      ``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR and fill
+      in ``key_spec.u.descriptor``.  To remove this type of key, the
+      calling process must have the CAP_SYS_ADMIN capability in the
+      initial user namespace.
+
+    - To remove a key used by v2 encryption policies, set
+      ``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER and fill
+      in ``key_spec.u.identifier``.  To remove this type of key, no
+      privileges are needed.  However, users can only remove keys that
+      they added themselves, subject to privileged override with
+      FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS.
+
+- ``flags`` can contain the following flags:
+
+    - ``FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS`` specifies that the key
+      should be removed even if it has also been added by other users.
+      Specifying this flag requires the CAP_SYS_ADMIN capability in
+      the initial user namespace.
+
+FS_IOC_REMOVE_ENCRYPTION_KEY can fail with the following errors:
+
+- ``EACCES``: The FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR key specifier type
+  and/or the FSCRYPT_REMOVE_KEY_FLAG_ALL_USERS flag was specified, but
+  the caller does not have the CAP_SYS_ADMIN capability in the initial
+  user namespace
+- ``EBUSY``: the master key secret was wiped from memory, but some
+  files which were unlocked with it are still in use.  Such files
+  could not be locked, nor could their per-file keys be wiped from
+  memory.  The ioctl may be retried later to re-attempt locking the
+  remaining files.
+- ``EINVAL``: invalid flags or key specifier type, or reserved bits
+  were set
+- ``ENOKEY``: the key is not present or has already been removed
+- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``EOPNOTSUPP``: the kernel was not configured with encryption
+  support for this filesystem, or the filesystem superblock has not
+  had encryption enabled on it
+- ``EUSERS``: the key cannot be removed because other users have added
+  it too
+
+Before using this ioctl, read the `Kernel memory compromise`_ section
+for a discussion of the security goals and limitations of this ioctl.
+
+Getting key status
+------------------
+
+The FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl retrieves the status of a
+master encryption key.  It can be executed on any file or directory on
+the target filesystem, but using the filesystem's root directory is
+recommended.  It takes in a pointer to a :c:type:`struct
+fscrypt_get_key_status_arg`, defined as follows::
+
+    struct fscrypt_get_key_status_arg {
+            /* input */
+            struct fscrypt_key_specifier key_spec;
+            __u32 __reserved[6];
+
+            /* output */
+    #define FSCRYPT_KEY_STATUS_ABSENT               1
+    #define FSCRYPT_KEY_STATUS_PRESENT              2
+    #define FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED 3
+            __u32 status;
+    #define FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF   0x00000001
+            __u32 status_flags;
+            __u32 user_count;
+            __u32 __out_reserved[13];
+    };
+
+The caller must zero all input fields, then fill in ``key_spec``:
+
+    - To get the status of a key for v1 encryption policies, set
+      ``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR and fill
+      in ``key_spec.u.descriptor``.
+
+    - To get the status of a key for v2 encryption policies, set
+      ``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER and fill
+      in ``key_spec.u.identifier``.
+
+On success, 0 is returned and the kernel fills in the output fields:
+
+- ``status`` indicates whether the key is absent, present, or
+  incompletely removed.  Incompletely removed means that the master
+  secret has been removed, but some files are still in use; i.e.,
+  FS_IOC_REMOVE_ENCRYPTION_KEY returned EBUSY.
+
+- ``status_flags`` can contain the following flags:
+
+    - ``FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF`` indicates that the key
+      has added by the current user.  This is only set for keys
+      identified by ``identifier`` rather than by ``descriptor``.
+
+- ``user_count`` specifies the number of users who have added the key.
+  This is only set for keys identified by ``identifier`` rather than
+  by ``descriptor``.
+
+FS_IOC_GET_ENCRYPTION_KEY_STATUS can fail with the following errors:
+
+- ``EINVAL``: invalid key specifier type, or reserved bits were set
+- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``EOPNOTSUPP``: the kernel was not configured with encryption
+  support for this filesystem, or the filesystem superblock has not
+  had encryption enabled on it
+
+Among other use cases, FS_IOC_GET_ENCRYPTION_KEY_STATUS might be
+useful for determining whether the key for a given encrypted directory
+needs to be added before prompting the user for the passphrase needed
+to derive the key.
+
+FS_IOC_GET_ENCRYPTION_KEY_STATUS can only get the status of keys in
+the filesystem-level keyring, i.e. the keyring managed by
+FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.  It cannot
+get the status of a key that has only been added for use by v1
+encryption policies using the legacy mechanism involving
+process-subscribed keyrings.
 
 Access semantics
 ================
@@ -498,7 +901,7 @@ Without the key
 
 Some filesystem operations may be performed on encrypted regular
 files, directories, and symlinks even before their encryption key has
-been provided:
+been added, or after their encryption key has been removed:
 
 - File metadata may be read, e.g. using stat().
 
@@ -563,20 +966,20 @@ Encryption context
 ------------------
 
 An encryption policy is represented on-disk by a :c:type:`struct
-fscrypt_context`.  It is up to individual filesystems to decide where
-to store it, but normally it would be stored in a hidden extended
-attribute.  It should *not* be exposed by the xattr-related system
-calls such as getxattr() and setxattr() because of the special
-semantics of the encryption xattr.  (In particular, there would be
-much confusion if an encryption policy were to be added to or removed
-from anything other than an empty directory.)  The struct is defined
-as follows::
+fscrypt_context_v1` or a :c:type:`struct fscrypt_context_v2`.  It is
+up to individual filesystems to decide where to store it, but normally
+it would be stored in a hidden extended attribute.  It should *not* be
+exposed by the xattr-related system calls such as getxattr() and
+setxattr() because of the special semantics of the encryption xattr.
+(In particular, there would be much confusion if an encryption policy
+were to be added to or removed from anything other than an empty
+directory.)  These structs are defined as follows::
 
-    #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
     #define FS_KEY_DERIVATION_NONCE_SIZE 16
 
-    struct fscrypt_context {
-            u8 format;
+    #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
+    struct fscrypt_context_v1 {
+            u8 version;
             u8 contents_encryption_mode;
             u8 filenames_encryption_mode;
             u8 flags;
@@ -584,12 +987,23 @@ as follows::
             u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
     };
 
-Note that :c:type:`struct fscrypt_context` contains the same
-information as :c:type:`struct fscrypt_policy` (see `Setting an
-encryption policy`_), except that :c:type:`struct fscrypt_context`
-also contains a nonce.  The nonce is randomly generated by the kernel
-and is used to derive the inode's encryption key as described in
-`Per-file keys`_.
+    #define FSCRYPT_KEY_IDENTIFIER_SIZE  16
+    struct fscrypt_context_v2 {
+            u8 version;
+            u8 contents_encryption_mode;
+            u8 filenames_encryption_mode;
+            u8 flags;
+            u8 __reserved[4];
+            u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
+            u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
+    };
+
+The context structs contain the same information as the corresponding
+policy structs (see `Setting an encryption policy`_), except that the
+context structs also contain a nonce.  The nonce is randomly generated
+by the kernel and is used as KDF input or as a tweak to cause
+different files to be encrypted differently; see `Per-file keys`_ and
+`DIRECT_KEY and per-mode keys`_.
 
 Data path changes
 -----------------
-- 
2.20.1


^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl
  2019-02-11 17:27 ` [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
@ 2019-02-11 22:12   ` Dave Chinner
  2019-02-11 23:31     ` Eric Biggers
  0 siblings, 1 reply; 24+ messages in thread
From: Dave Chinner @ 2019-02-11 22:12 UTC (permalink / raw)
  To: Eric Biggers
  Cc: linux-fscrypt, linux-ext4, linux-f2fs-devel, linux-mtd,
	linux-fsdevel, linux-crypto, linux-api, keyrings,
	Satya Tangirala, Paul Crowley

On Mon, Feb 11, 2019 at 09:27:29AM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> Add a new fscrypt ioctl, FS_IOC_REMOVE_ENCRYPTION_KEY.  This ioctl
> removes an encryption key that was added by FS_IOC_ADD_ENCRYPTION_KEY.
> It wipes the secret key itself, then "locks" the encrypted files and
> directories that had been unlocked using that key -- implemented by
> evicting the relevant dentries and inodes from the VFS caches.
> 
> The problem this solves is that many fscrypt users want the ability to
> remove encryption keys, causing the corresponding encrypted directories
> to appear "locked" (presented in ciphertext form) again.  Moreover,
> users want removing an encryption key to *really* remove it, in the
> sense that the removed keys cannot be recovered even if kernel memory is
> compromised, e.g. by the exploit of a kernel security vulnerability or
> by a physical attack.  This is desirable after a user logs out of the
> system, for example.  In many cases users even already assume this to be
> the case and are surprised to hear when it's not.
> 
> It is not sufficient to simply unlink the master key from the keyring
> (or to revoke or invalidate it), since the actual encryption transform
> objects are still pinned in memory by their inodes.  Therefore, to
> really remove a key we must also evict the relevant inodes.
> 
> Currently one workaround is to run 'sync && echo 2 >
> /proc/sys/vm/drop_caches'.  But, that evicts all unused inodes in the
> system rather than just the inodes associated with the key being
> removed, causing severe performance problems.  Moreover, it requires
> root privileges, so regular users can't "lock" their encrypted files.
> 
> Another workaround, used in Chromium OS kernels, is to add a new
> VFS-level ioctl FS_IOC_DROP_CACHE which is a more restricted version of
> drop_caches that operates on a single super_block.  It does:
> 
>         shrink_dcache_sb(sb);
>         invalidate_inodes(sb, false);
> 
> But it's still a hack.  Yet, the major users of filesystem encryption
> want this feature badly enough that they are actually using these hacks.
> 
> To properly solve the problem, start maintaining a list of the inodes
> which have been "unlocked" using each master key.  Originally this
> wasn't possible because the kernel didn't keep track of in-use master
> keys at all.  But, with the ->s_master_keys keyring it is now possible.
> 
> Then, add an ioctl FS_IOC_REMOVE_ENCRYPTION_KEY.  It finds the specified
> master key in ->s_master_keys, then wipes the secret key itself, which
> prevents any additional inodes from being unlocked with the key.  Then,
> it syncs the filesystem and evicts the inodes in the key's list.  The
> normal inode eviction code will free and wipe the per-file keys (in
> ->i_crypt_info).  Note that freeing ->i_crypt_info without evicting the
> inodes was also considered, but would have been racy.

The solution is still so gross. Exporting all the inode cache
internal functions so you can invalidate an external list of inodes
is, IMO, not an appropriate solution for anything.

Indeed, this is exactly what ->drop_inode() is for.

Take this function:

> +static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
> +{
> +	struct fscrypt_info *ci;
> +	struct inode *inode;
> +	struct inode *toput_inode = NULL;
> +
> +	spin_lock(&mk->mk_decrypted_inodes_lock);
> +
> +	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
> +		inode = ci->ci_inode;
> +		spin_lock(&inode->i_lock);
> +		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +		__iget(inode);
> +		spin_unlock(&inode->i_lock);
> +		spin_unlock(&mk->mk_decrypted_inodes_lock);
> +
> +		shrink_dcache_inode(inode);
> +		iput(toput_inode);
> +		toput_inode = inode;
> +
> +		spin_lock(&mk->mk_decrypted_inodes_lock);
> +	}
> +
> +	spin_unlock(&mk->mk_decrypted_inodes_lock);
> +	iput(toput_inode);
> +}

It takes a new reference to each decrypted inode, and then drops it
again after all the dentry cache references have been killed and
we've got a reference to the next inode in the list.  Killing the
dentry references to the inode means it should only have in-use
references and the reference this function holds on it.

If the inode is not in use then there will be only one, and so it
will fall into iput_final() and the ->drop_inode() function
determines if the inode should be evicted from the cache and
destroyed immediately.  IOWs, implement fscrypt_drop_inode() to do
the right thing when the key has been destroyed, and you can get rid
of all this crazy inode cache walk-and-invalidate hackery.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl
  2019-02-11 22:12   ` Dave Chinner
@ 2019-02-11 23:31     ` Eric Biggers
  2019-02-12  0:03       ` Dave Chinner
  0 siblings, 1 reply; 24+ messages in thread
From: Eric Biggers @ 2019-02-11 23:31 UTC (permalink / raw)
  To: Dave Chinner
  Cc: linux-fscrypt, linux-ext4, linux-f2fs-devel, linux-mtd,
	linux-fsdevel, linux-crypto, linux-api, keyrings,
	Satya Tangirala, Paul Crowley

Hi Dave,

On Tue, Feb 12, 2019 at 09:12:49AM +1100, Dave Chinner wrote:
> On Mon, Feb 11, 2019 at 09:27:29AM -0800, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > Add a new fscrypt ioctl, FS_IOC_REMOVE_ENCRYPTION_KEY.  This ioctl
> > removes an encryption key that was added by FS_IOC_ADD_ENCRYPTION_KEY.
> > It wipes the secret key itself, then "locks" the encrypted files and
> > directories that had been unlocked using that key -- implemented by
> > evicting the relevant dentries and inodes from the VFS caches.
> > 
> > The problem this solves is that many fscrypt users want the ability to
> > remove encryption keys, causing the corresponding encrypted directories
> > to appear "locked" (presented in ciphertext form) again.  Moreover,
> > users want removing an encryption key to *really* remove it, in the
> > sense that the removed keys cannot be recovered even if kernel memory is
> > compromised, e.g. by the exploit of a kernel security vulnerability or
> > by a physical attack.  This is desirable after a user logs out of the
> > system, for example.  In many cases users even already assume this to be
> > the case and are surprised to hear when it's not.
> > 
> > It is not sufficient to simply unlink the master key from the keyring
> > (or to revoke or invalidate it), since the actual encryption transform
> > objects are still pinned in memory by their inodes.  Therefore, to
> > really remove a key we must also evict the relevant inodes.
> > 
> > Currently one workaround is to run 'sync && echo 2 >
> > /proc/sys/vm/drop_caches'.  But, that evicts all unused inodes in the
> > system rather than just the inodes associated with the key being
> > removed, causing severe performance problems.  Moreover, it requires
> > root privileges, so regular users can't "lock" their encrypted files.
> > 
> > Another workaround, used in Chromium OS kernels, is to add a new
> > VFS-level ioctl FS_IOC_DROP_CACHE which is a more restricted version of
> > drop_caches that operates on a single super_block.  It does:
> > 
> >         shrink_dcache_sb(sb);
> >         invalidate_inodes(sb, false);
> > 
> > But it's still a hack.  Yet, the major users of filesystem encryption
> > want this feature badly enough that they are actually using these hacks.
> > 
> > To properly solve the problem, start maintaining a list of the inodes
> > which have been "unlocked" using each master key.  Originally this
> > wasn't possible because the kernel didn't keep track of in-use master
> > keys at all.  But, with the ->s_master_keys keyring it is now possible.
> > 
> > Then, add an ioctl FS_IOC_REMOVE_ENCRYPTION_KEY.  It finds the specified
> > master key in ->s_master_keys, then wipes the secret key itself, which
> > prevents any additional inodes from being unlocked with the key.  Then,
> > it syncs the filesystem and evicts the inodes in the key's list.  The
> > normal inode eviction code will free and wipe the per-file keys (in
> > ->i_crypt_info).  Note that freeing ->i_crypt_info without evicting the
> > inodes was also considered, but would have been racy.
> 
> The solution is still so gross. Exporting all the inode cache
> internal functions so you can invalidate an external list of inodes
> is, IMO, not an appropriate solution for anything.
> 
> Indeed, this is exactly what ->drop_inode() is for.
> 
> Take this function:
> 
> > +static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
> > +{
> > +	struct fscrypt_info *ci;
> > +	struct inode *inode;
> > +	struct inode *toput_inode = NULL;
> > +
> > +	spin_lock(&mk->mk_decrypted_inodes_lock);
> > +
> > +	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
> > +		inode = ci->ci_inode;
> > +		spin_lock(&inode->i_lock);
> > +		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
> > +			spin_unlock(&inode->i_lock);
> > +			continue;
> > +		}
> > +		__iget(inode);
> > +		spin_unlock(&inode->i_lock);
> > +		spin_unlock(&mk->mk_decrypted_inodes_lock);
> > +
> > +		shrink_dcache_inode(inode);
> > +		iput(toput_inode);
> > +		toput_inode = inode;
> > +
> > +		spin_lock(&mk->mk_decrypted_inodes_lock);
> > +	}
> > +
> > +	spin_unlock(&mk->mk_decrypted_inodes_lock);
> > +	iput(toput_inode);
> > +}
> 
> It takes a new reference to each decrypted inode, and then drops it
> again after all the dentry cache references have been killed and
> we've got a reference to the next inode in the list.  Killing the
> dentry references to the inode means it should only have in-use
> references and the reference this function holds on it.
> 
> If the inode is not in use then there will be only one, and so it
> will fall into iput_final() and the ->drop_inode() function
> determines if the inode should be evicted from the cache and
> destroyed immediately.  IOWs, implement fscrypt_drop_inode() to do
> the right thing when the key has been destroyed, and you can get rid
> of all this crazy inode cache walk-and-invalidate hackery.
> 

Thanks for the feedback!  If I understand correctly, your suggestion is:

- Keep evict_dentries_for_decrypted_inodes() as-is, i.e. fscrypt would still
  evict the dentries for all inodes in ->mk_decrypted_inodes.
  (I don't see how it could work otherwise.)

- However, evict_decrypted_inodes() would be removed and fscrypt would not
  directly evict the list of inodes.  Instead, the filesystem's ->drop_inode()
  would be made to return 1 if the inode's master key has been removed.  Thus
  each inode, if no longer in use, would end up getting evicted during the
  iput() in evict_dentries_for_decrypted_inodes().

I hadn't thought of this, and I think it would work; I'll try implementing it.
It would also have the advantage that if a key is removed while an inode is
still in-use, that inode will be evicted as soon as it's no longer in use rather
than waiting around until another FS_IOC_REMOVE_ENCRYPTION_KEY.

The ioctl will need a different way to determine whether any inodes couldn't be
evicted, but simply checking whether ->mk_decrypted_inodes ended up empty or not
should work.

FWIW, originally I also considered leaving the inodes in the inode cache and
instead only freeing ->i_crypt_info and truncating the pagecache.  But I don't
see a way to do it even with this new idea; for one, ->drop_inode() is called
under ->i_lock.  So it seems that eviction is still the way to go.

- Eric

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl
  2019-02-11 23:31     ` Eric Biggers
@ 2019-02-12  0:03       ` Dave Chinner
  0 siblings, 0 replies; 24+ messages in thread
From: Dave Chinner @ 2019-02-12  0:03 UTC (permalink / raw)
  To: Eric Biggers
  Cc: linux-fscrypt, linux-ext4, linux-f2fs-devel, linux-mtd,
	linux-fsdevel, linux-crypto, linux-api, keyrings,
	Satya Tangirala, Paul Crowley

On Mon, Feb 11, 2019 at 03:31:29PM -0800, Eric Biggers wrote:
> Hi Dave,
> 
> On Tue, Feb 12, 2019 at 09:12:49AM +1100, Dave Chinner wrote:
> > On Mon, Feb 11, 2019 at 09:27:29AM -0800, Eric Biggers wrote:
> > 
> > Indeed, this is exactly what ->drop_inode() is for.
> > 
> > Take this function:
> > 
> > > +static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
> > > +{
> > > +	struct fscrypt_info *ci;
> > > +	struct inode *inode;
> > > +	struct inode *toput_inode = NULL;
> > > +
> > > +	spin_lock(&mk->mk_decrypted_inodes_lock);
> > > +
> > > +	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
> > > +		inode = ci->ci_inode;
> > > +		spin_lock(&inode->i_lock);
> > > +		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
> > > +			spin_unlock(&inode->i_lock);
> > > +			continue;
> > > +		}
> > > +		__iget(inode);
> > > +		spin_unlock(&inode->i_lock);
> > > +		spin_unlock(&mk->mk_decrypted_inodes_lock);
> > > +
> > > +		shrink_dcache_inode(inode);
> > > +		iput(toput_inode);
> > > +		toput_inode = inode;
> > > +
> > > +		spin_lock(&mk->mk_decrypted_inodes_lock);
> > > +	}
> > > +
> > > +	spin_unlock(&mk->mk_decrypted_inodes_lock);
> > > +	iput(toput_inode);
> > > +}
> > 
> > It takes a new reference to each decrypted inode, and then drops it
> > again after all the dentry cache references have been killed and
> > we've got a reference to the next inode in the list.  Killing the
> > dentry references to the inode means it should only have in-use
> > references and the reference this function holds on it.
> > 
> > If the inode is not in use then there will be only one, and so it
> > will fall into iput_final() and the ->drop_inode() function
> > determines if the inode should be evicted from the cache and
> > destroyed immediately.  IOWs, implement fscrypt_drop_inode() to do
> > the right thing when the key has been destroyed, and you can get rid
> > of all this crazy inode cache walk-and-invalidate hackery.
> > 
> 
> Thanks for the feedback!  If I understand correctly, your suggestion is:
> 
> - Keep evict_dentries_for_decrypted_inodes() as-is, i.e. fscrypt would still
>   evict the dentries for all inodes in ->mk_decrypted_inodes.
>   (I don't see how it could work otherwise.)
> 
> - However, evict_decrypted_inodes() would be removed and fscrypt would not
>   directly evict the list of inodes.  Instead, the filesystem's ->drop_inode()
>   would be made to return 1 if the inode's master key has been removed.  Thus
>   each inode, if no longer in use, would end up getting evicted during the
>   iput() in evict_dentries_for_decrypted_inodes().

*nod*

> I hadn't thought of this, and I think it would work; I'll try implementing it.
> It would also have the advantage that if a key is removed while an inode is
> still in-use, that inode will be evicted as soon as it's no longer in use rather
> than waiting around until another FS_IOC_REMOVE_ENCRYPTION_KEY.

*nod*

> The ioctl will need a different way to determine whether any inodes couldn't be
> evicted, but simply checking whether ->mk_decrypted_inodes ended up empty or not
> should work.

*nod*

> FWIW, originally I also considered leaving the inodes in the inode cache and
> instead only freeing ->i_crypt_info and truncating the pagecache.  But I don't
> see a way to do it even with this new idea; for one, ->drop_inode() is called
> under ->i_lock.  So it seems that eviction is still the way to go.

Yeah, eviction is by far the easiest way to deal with this. If it's
being frequently referenced/written, the backing buffer should be in
memory anyway and the next access simply has to re-instantiate the
inode cache from the buffer and won't need to do IO.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

^ permalink raw reply	[flat|nested] 24+ messages in thread

end of thread, back to index

Thread overview: 24+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-11 17:27 [RFC PATCH v2 00/20] fscrypt: key management improvements Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 01/20] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 02/20] fscrypt: use FSCRYPT_ prefix for uapi constants Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 03/20] fscrypt: use FSCRYPT_* definitions, not FS_* Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 04/20] fs: add ->s_master_keys to struct super_block Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 05/20] fscrypt: add ->ci_inode to fscrypt_info Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 06/20] fscrypt: refactor v1 policy key setup into keysetup_legacy.c Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 07/20] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 08/20] fs/inode.c: export inode_lru_list_del() Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 09/20] fs/inode.c: rename and export dispose_list() Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 10/20] fs/dcache.c: add shrink_dcache_inode() Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 11/20] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
2019-02-11 22:12   ` Dave Chinner
2019-02-11 23:31     ` Eric Biggers
2019-02-12  0:03       ` Dave Chinner
2019-02-11 17:27 ` [RFC PATCH v2 12/20] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 13/20] fscrypt: add an HKDF-SHA512 implementation Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 14/20] fscrypt: v2 encryption policy support Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 15/20] fscrypt: allow unprivileged users to add/remove keys for v2 policies Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 16/20] fscrypt: require that key be added when setting a v2 encryption policy Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 17/20] ext4: wire up new fscrypt ioctls Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 18/20] f2fs: " Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 19/20] ubifs: " Eric Biggers
2019-02-11 17:27 ` [RFC PATCH v2 20/20] fscrypt: document the new ioctls and policy version Eric Biggers

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