From: Eric Biggers <ebiggers@kernel.org>
To: linux-fscrypt@vger.kernel.org
Cc: Satya Tangirala <satyat@google.com>,
linux-api@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net, keyrings@vger.kernel.org,
linux-mtd@lists.infradead.org, linux-crypto@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
Paul Crowley <paulcrowley@google.com>
Subject: [f2fs-dev] [PATCH v7 12/16] fscrypt: require that key be added when setting a v2 encryption policy
Date: Fri, 26 Jul 2019 15:41:37 -0700 [thread overview]
Message-ID: <20190726224141.14044-13-ebiggers@kernel.org> (raw)
In-Reply-To: <20190726224141.14044-1-ebiggers@kernel.org>
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 2445b0fc4f01c..8d61f410aa677 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -408,6 +408,9 @@ 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);
/* keysetup.c */
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 307533d4d7c51..258409d0c7409 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -562,6 +562,53 @@ 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 shrink_dcache_inode(struct inode *inode)
{
struct dentry *dentry;
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 0141d338c1fdb..60de9048ed4d1 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -233,6 +233,7 @@ static int set_encryption_policy(struct inode *inode,
{
union fscrypt_context ctx;
int ctxsize;
+ int err;
if (!fscrypt_supported_policy(policy, inode))
return -EINVAL;
@@ -251,6 +252,11 @@ 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);
--
2.22.0
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next prev parent reply other threads:[~2019-07-26 22:46 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 22:41 [f2fs-dev] [PATCH v7 00/16] fscrypt: key management improvements Eric Biggers
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 01/16] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
2019-07-28 15:08 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 02/16] fscrypt: use FSCRYPT_ prefix for uapi constants Eric Biggers
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 03/16] fscrypt: use FSCRYPT_* definitions, not FS_* Eric Biggers
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 04/16] fscrypt: add ->ci_inode to fscrypt_info Eric Biggers
2019-07-28 15:09 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 05/16] fscrypt: refactor v1 policy key setup into keysetup_legacy.c Eric Biggers
2019-07-28 15:40 ` Theodore Y. Ts'o
2019-07-29 19:37 ` Eric Biggers
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 06/16] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl Eric Biggers
2019-07-28 18:50 ` Theodore Y. Ts'o
2019-07-29 19:46 ` Eric Biggers
2019-07-29 20:14 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 07/16] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
2019-07-28 19:24 ` Theodore Y. Ts'o
2019-07-29 19:58 ` Eric Biggers
2019-07-31 18:38 ` Eric Biggers
2019-07-31 23:38 ` Theodore Y. Ts'o
2019-08-01 1:11 ` Eric Biggers
2019-08-01 5:31 ` Theodore Y. Ts'o
2019-08-01 18:35 ` Eric Biggers
2019-08-01 18:46 ` Eric Biggers
2019-08-01 22:04 ` Eric Biggers
2019-08-02 4:38 ` Eric Biggers
2019-08-12 14:16 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 08/16] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl Eric Biggers
2019-07-28 19:30 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 09/16] fscrypt: add an HKDF-SHA512 implementation Eric Biggers
2019-07-28 19:39 ` Theodore Y. Ts'o
2019-07-29 20:29 ` Eric Biggers
2019-07-29 21:42 ` James Bottomley
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 10/16] fscrypt: v2 encryption policy support Eric Biggers
2019-07-28 21:17 ` Theodore Y. Ts'o
2019-07-29 20:46 ` Eric Biggers
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 11/16] fscrypt: allow unprivileged users to add/remove keys for v2 policies Eric Biggers
2019-07-28 21:22 ` Theodore Y. Ts'o
2019-07-26 22:41 ` Eric Biggers [this message]
2019-07-28 21:24 ` [f2fs-dev] [PATCH v7 12/16] fscrypt: require that key be added when setting a v2 encryption policy Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 13/16] ext4: wire up new fscrypt ioctls Eric Biggers
2019-07-28 21:24 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 14/16] f2fs: " Eric Biggers
2019-07-30 0:36 ` Jaegeuk Kim
2019-08-02 8:10 ` Chao Yu
2019-08-02 17:31 ` Eric Biggers
2019-08-04 9:42 ` Chao Yu
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 15/16] ubifs: " Eric Biggers
2019-07-30 0:39 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [f2fs-dev] [PATCH v7 16/16] fscrypt: document the new ioctls and policy version Eric Biggers
2019-07-29 2:00 ` Theodore Y. Ts'o
2019-07-29 21:36 ` Eric Biggers
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