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* [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure
@ 2021-04-27 11:37 Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 1/6] reiserfs: Add missing calls to reiserfs_security_free() Roberto Sassu
                   ` (6 more replies)
  0 siblings, 7 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

This patch set depends on:

https://lore.kernel.org/linux-integrity/20210409114313.4073-1-roberto.sassu@huawei.com/
https://lore.kernel.org/linux-integrity/20210407105252.30721-1-roberto.sassu@huawei.com/

One of the challenges that must be tackled to move IMA and EVM to the LSM
infrastructure is to ensure that EVM is capable to correctly handle
multiple stacked LSMs providing an xattr at file creation. At the moment,
there are few issues that would prevent a correct integration. This patch
set aims at solving them.

From the LSM infrastructure side, the LSM stacking feature added the
possibility of registering multiple implementations of the security hooks,
that are called sequentially whenever someone calls the corresponding
security hook. However, security_inode_init_security() and
security_old_inode_init_security() are currently limited to support one
xattr provided by LSM and one by EVM.

In addition, using the call_int_hook() macro causes some issues. According
to the documentation in include/linux/lsm_hooks.h, it is a legitimate case
that an LSM returns -EOPNOTSUPP when it does not want to provide an xattr.
However, the loop defined in the macro would stop calling subsequent LSMs
if that happens. In the case of security_old_inode_init_security(), using
the macro would also cause a memory leak due to replacing the *value
pointer, if multiple LSMs provide an xattr.

From EVM side, the first operation to be done is to change the definition
of evm_inode_init_security() to be compatible with the security hook
definition. Unfortunately, the current definition does not provide enough
information for EVM, as it must have visibility of all xattrs provided by
LSMs to correctly calculate the HMAC. This patch set changes the security
hook definition by replacing the name, value and len triple with the xattr
array allocated by security_inode_init_security().

Secondly, EVM must know how many elements are in the xattr array. EVM can
rely on the fact that the xattr array must be terminated with an element
with name field set to NULL, but can also benefit from the enhancements
that have been included in this version of the patch set.

Casey suggested to use the reservation mechanism currently implemented for
other security blobs, for xattrs. In this way,
security_inode_init_security() can know after LSM initialization how many
slots for xattrs should be allocated, and LSMs know the offset in the
array from where they can start writing xattrs.

One of the problem was that LSMs can decide at run-time, although they
reserved a slot, to not use it (for example because they were not
initialized). Given that the initxattrs() method implemented by filesystems
expect that the array is continuous, they would miss the slots after the
one not being initialized. security_inode_init_security() should have been
modified to compact the array.

Instead, the preferred solution was to introduce the base slot as a
parameter, in addition to the xattr array, containing the up to date
information about the slots used by previous LSMs. The correctness of the
update of the slot is ensured by both the LSMs, if they use the new helper
lsm_find_xattr_slot(), and by security_inode_init_security() which checks
the slot each time after an LSM executes the inode_init_security hook.

This patch set has been tested by introducing several instances of a
TestLSM (some providing an xattr, some not, one with a wrong implementation
to see how the LSM infrastructure handles it). The patch is not included
in this set but it is available here:

https://github.com/robertosassu/linux/commit/c7e01af6cb2c6780f0b143070269fff7e30053f9

The test, added to ima-evm-utils, is available here:

https://github.com/robertosassu/ima-evm-utils/blob/evm-multiple-lsms-v3-devel-v7/tests/evm_multiple_lsms.test

The test takes a UML kernel built by Travis and launches it several times,
each time with a different combination of LSMs. After boot, it first checks
that there is an xattr for each LSM providing it, and then calculates the
HMAC in user space and compares it with the HMAC calculated by EVM in
kernel space.

A test report can be obtained here:

https://travis-ci.com/github/robertosassu/ima-evm-utils/jobs/501101861

SELinux Test Suite result (diff 5.11.14-200.fc33.x86_64 5.12.0-rc8+):
-Files=70, Tests=1099, 82 wallclock secs ( 0.35 usr  0.09 sys +  7.39 cusr 10.14 csys = 17.97 CPU)
+Files=70, Tests=1108, 85 wallclock secs ( 0.34 usr  0.10 sys +  7.25 cusr 11.39 csys = 19.08 CPU)
 Result: FAIL
-Failed 2/70 test programs. 5/1099 subtests failed.
+Failed 2/70 test programs. 5/1108 subtests failed.

Smack Test Suite result:
smack_set_ambient 1 TPASS: Test "smack_set_ambient" success.
smack_set_current 1 TPASS: Test "smack_set_current" success.
smack_set_doi 1 TPASS: Test "smack_set_doi" success.
smack_set_netlabel 1 TPASS: Test "smack_set_netlabel" success.
smack_set_socket_labels    1  TPASS  :  Test smack_set_socket_labels success.
smack_set_cipso 1 TPASS: Test "smack_set_cipso" success.
smack_set_direct 1 TPASS: Test "smack_set_direct" success.
smack_set_load 1 TPASS: Test "smack_set_load" success.
smack_set_onlycap 1 TFAIL: The smack label reported for "/smack/onlycap"

Lastly, running the test on reiserfs to check
security_old_inode_init_security(), some issues have been discovered: a
free of xattr->name which is not correct after commit 9548906b2bb7 ('xattr:
Constify ->name member of "struct xattr"'), missing calls to
reiserfs_security_free() and a misalignment with
security_inode_init_security() (the old version expects the full xattr name
with the security. prefix, the new version just the suffix). The last issue
has not been fixed yet.

Changelog

v2:
- rewrite selinux_old_inode_init_security() to use
  security_inode_init_security()
- add lbs_xattr field to lsm_blob_sizes structure, to give the ability to
  LSMs to reserve slots in the xattr array (suggested by Casey)
- add new parameter base_slot to inode_init_security hook definition

v1:
- add calls to reiserfs_security_free() and initialize sec->value to NULL
  (suggested by Tetsuo and Mimi)
- change definition of inode_init_security hook, replace the name, value
  and len triple with the xattr array (suggested by Casey)
- introduce lsm_find_xattr_slot() helper for LSMs to find an unused slot in
  the passed xattr array

Roberto Sassu (6):
  reiserfs: Add missing calls to reiserfs_security_free()
  security: Rewrite security_old_inode_init_security()
  security: Pass xattrs allocated by LSMs to the inode_init_security
    hook
  security: Support multiple LSMs implementing the inode_init_security
    hook
  evm: Align evm_inode_init_security() definition with LSM
    infrastructure
  evm: Support multiple LSMs providing an xattr

 fs/reiserfs/namei.c                 |   4 +
 fs/reiserfs/xattr_security.c        |   1 +
 include/linux/evm.h                 |  19 +++--
 include/linux/lsm_hook_defs.h       |   4 +-
 include/linux/lsm_hooks.h           |  22 +++++-
 security/integrity/evm/evm.h        |   2 +
 security/integrity/evm/evm_crypto.c |   9 ++-
 security/integrity/evm/evm_main.c   |  30 +++++--
 security/security.c                 | 116 +++++++++++++++++++++++-----
 security/selinux/hooks.c            |  18 +++--
 security/smack/smack_lsm.c          |  27 ++++---
 11 files changed, 194 insertions(+), 58 deletions(-)

-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 1/6] reiserfs: Add missing calls to reiserfs_security_free()
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 2/6] security: Rewrite security_old_inode_init_security() Roberto Sassu
                   ` (5 subsequent siblings)
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu, stable, Jeff Mahoney,
	Tetsuo Handa

Commit 57fe60df6241 ("reiserfs: add atomic addition of selinux attributes
during inode creation") defined reiserfs_security_free() to free the name
and value of a security xattr allocated by the active LSM through
security_old_inode_init_security(). However, this function is not called
in the reiserfs code.

Thus, this patch adds a call to reiserfs_security_free() whenever
reiserfs_security_init() is called, and initializes value to NULL, to avoid
to call kfree() on an uninitialized pointer.

Fixes: 57fe60df6241 ("reiserfs: add atomic addition of selinux attributes during inode creation")
Cc: stable@vger.kernel.org
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: Mimi Zohar <zohar@linux.ibm.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 fs/reiserfs/namei.c          | 4 ++++
 fs/reiserfs/xattr_security.c | 1 +
 2 files changed, 5 insertions(+)

diff --git a/fs/reiserfs/namei.c b/fs/reiserfs/namei.c
index e6eb05e2b2f1..6b5c51a77fae 100644
--- a/fs/reiserfs/namei.c
+++ b/fs/reiserfs/namei.c
@@ -695,6 +695,7 @@ static int reiserfs_create(struct user_namespace *mnt_userns, struct inode *dir,
 
 out_failed:
 	reiserfs_write_unlock(dir->i_sb);
+	reiserfs_security_free(&security);
 	return retval;
 }
 
@@ -778,6 +779,7 @@ static int reiserfs_mknod(struct user_namespace *mnt_userns, struct inode *dir,
 
 out_failed:
 	reiserfs_write_unlock(dir->i_sb);
+	reiserfs_security_free(&security);
 	return retval;
 }
 
@@ -877,6 +879,7 @@ static int reiserfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 	retval = journal_end(&th);
 out_failed:
 	reiserfs_write_unlock(dir->i_sb);
+	reiserfs_security_free(&security);
 	return retval;
 }
 
@@ -1193,6 +1196,7 @@ static int reiserfs_symlink(struct user_namespace *mnt_userns,
 	retval = journal_end(&th);
 out_failed:
 	reiserfs_write_unlock(parent_dir->i_sb);
+	reiserfs_security_free(&security);
 	return retval;
 }
 
diff --git a/fs/reiserfs/xattr_security.c b/fs/reiserfs/xattr_security.c
index bb2a0062e0e5..b1ad93b60475 100644
--- a/fs/reiserfs/xattr_security.c
+++ b/fs/reiserfs/xattr_security.c
@@ -50,6 +50,7 @@ int reiserfs_security_init(struct inode *dir, struct inode *inode,
 	int error;
 
 	sec->name = NULL;
+	sec->value = NULL;
 
 	/* Don't add selinux attributes on xattrs - they'll never get used */
 	if (IS_PRIVATE(dir))
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 2/6] security: Rewrite security_old_inode_init_security()
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 1/6] reiserfs: Add missing calls to reiserfs_security_free() Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 3/6] security: Pass xattrs allocated by LSMs to the inode_init_security hook Roberto Sassu
                   ` (4 subsequent siblings)
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

With upcoming changes, LSMs will be able to write their xattrs in the
reserved slots. Boundary checking will be performed to ensure that LSMs
don't write outside the passed xattr array. However, the xattr array is
created only in security_inode_init_security() and not in
security_old_inode_init_security().

Instead of duplicating the code for array allocation, this patch calls
security_inode_init_security() from security_old_inode_init_security() and
introduces a new callback, called security_initxattrs(), to copy the first
element of the xattr array allocated by former function into the
destination pointer provided by the latter function.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/security.c | 41 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/security/security.c b/security/security.c
index 7f14e59c4f8e..692a148ce764 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1024,6 +1024,20 @@ int security_dentry_create_files_as(struct dentry *dentry, int mode,
 }
 EXPORT_SYMBOL(security_dentry_create_files_as);
 
+static int security_initxattrs(struct inode *inode, const struct xattr *xattrs,
+			       void *fs_info)
+{
+	struct xattr *dest = (struct xattr *)fs_info;
+
+	if (!dest)
+		return 0;
+
+	dest->name = xattrs->name;
+	dest->value = xattrs->value;
+	dest->value_len = xattrs->value_len;
+	return 0;
+}
+
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 const initxattrs initxattrs, void *fs_data)
@@ -1053,8 +1067,14 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
-	for (xattr = new_xattrs; xattr->value != NULL; xattr++)
+	for (xattr = new_xattrs; xattr->value != NULL; xattr++) {
+		if (xattr == new_xattrs && initxattrs == &security_initxattrs &&
+		    !ret && fs_data != NULL)
+			continue;
 		kfree(xattr->value);
+	}
+	if (initxattrs == &security_initxattrs)
+		return ret;
 	return (ret == -EOPNOTSUPP) ? 0 : ret;
 }
 EXPORT_SYMBOL(security_inode_init_security);
@@ -1071,10 +1091,25 @@ int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len)
 {
+	struct xattr xattr = { .name = NULL, .value = NULL, .value_len = 0 };
+	struct xattr *lsm_xattr = (name && value && len) ? &xattr : NULL;
+	int ret;
+
 	if (unlikely(IS_PRIVATE(inode)))
 		return -EOPNOTSUPP;
-	return call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir,
-			     qstr, name, value, len);
+
+	ret = security_inode_init_security(inode, dir, qstr,
+					   security_initxattrs, lsm_xattr);
+	if (ret)
+		return ret;
+
+	if (lsm_xattr) {
+		*name = lsm_xattr->name;
+		*value = lsm_xattr->value;
+		*len = lsm_xattr->value_len;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(security_old_inode_init_security);
 
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 3/6] security: Pass xattrs allocated by LSMs to the inode_init_security hook
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 1/6] reiserfs: Add missing calls to reiserfs_security_free() Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 2/6] security: Rewrite security_old_inode_init_security() Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 4/6] security: Support multiple LSMs implementing " Roberto Sassu
                   ` (3 subsequent siblings)
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

In preparation for moving EVM to the LSM infrastructure, this patch
replaces the name, value, len triple with the xattr array pointer provided
by security_inode_init_security(), and the base slot in the xattr array
where LSMs can write xattrs.

This patch also introduces the new helper lsm_find_xattr_slot(), to help
LSMs find available slots in the xattr array (with a subsequent patch it
will be possible to reserve more than one slot). The helper takes three
arguments: the xattr array, the pointer of the base slot, whose value is
incremented each time the helper is called, and the end slot so that the
helper does not return a slot outside the array.

Finally, this patch modifies also SELinux and Smack to use the new helper.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/lsm_hook_defs.h |  4 ++--
 include/linux/lsm_hooks.h     | 21 ++++++++++++++++++---
 security/security.c           | 15 ++++++---------
 security/selinux/hooks.c      | 15 ++++++++-------
 security/smack/smack_lsm.c    | 24 +++++++++++++-----------
 5 files changed, 47 insertions(+), 32 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 477a597db013..20f91e93f511 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -111,8 +111,8 @@ LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask,
 LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
 LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
 LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
-	 struct inode *dir, const struct qstr *qstr, const char **name,
-	 void **value, size_t *len)
+	 struct inode *dir, const struct qstr *qstr, struct xattr *xattrs,
+	 int *base_slot, void *fs_data)
 LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
 	 const struct qstr *name, const struct inode *context_inode)
 LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c5498f5174ce..197d6662b262 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -27,6 +27,7 @@
 
 #include <linux/security.h>
 #include <linux/init.h>
+#include <linux/xattr.h>
 #include <linux/rculist.h>
 
 /**
@@ -227,9 +228,13 @@
  *	@inode contains the inode structure of the newly created inode.
  *	@dir contains the inode structure of the parent directory.
  *	@qstr contains the last path component of the new object
- *	@name will be set to the allocated name suffix (e.g. selinux).
- *	@value will be set to the allocated attribute value.
- *	@len will be set to the length of the value.
+ *	@xattrs contains the full array of xattrs allocated by LSMs where
+ *	->name will be set to the allocated name suffix (e.g. selinux).
+ *	->value will be set to the allocated attribute value.
+ *	->len will be set to the length of the value.
+ *	@base_slot contains the position in @xattrs from where xattrs
+ *	can be written.
+ *	@fs_data contains filesystem-specific data.
  *	Returns 0 if @name and @value have been successfully set,
  *	-EOPNOTSUPP if no security attribute is needed, or
  *	-ENOMEM on memory allocation failure.
@@ -1660,5 +1665,15 @@ static inline void security_delete_hooks(struct security_hook_list *hooks,
 #endif /* CONFIG_SECURITY_WRITABLE_HOOKS */
 
 extern int lsm_inode_alloc(struct inode *inode);
+static inline struct xattr *lsm_find_xattr_slot(struct xattr *xattrs,
+						int *base_slot, int end_slot)
+{
+	if (!xattrs)
+		return xattrs;
+
+	if (*base_slot >= end_slot)
+		return NULL;
 
+	return xattrs + (*base_slot)++;
+}
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/security/security.c b/security/security.c
index 692a148ce764..527a18fd6742 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1043,26 +1043,23 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const initxattrs initxattrs, void *fs_data)
 {
 	struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1];
-	struct xattr *lsm_xattr, *evm_xattr, *xattr;
-	int ret;
+	struct xattr *xattr;
+	int ret, base_slot = 0;
 
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
 	if (!initxattrs)
 		return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
-				     dir, qstr, NULL, NULL, NULL);
+				     dir, qstr, NULL, &base_slot, fs_data);
 	memset(new_xattrs, 0, sizeof(new_xattrs));
-	lsm_xattr = new_xattrs;
 	ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
-						&lsm_xattr->name,
-						&lsm_xattr->value,
-						&lsm_xattr->value_len);
+			    new_xattrs, &base_slot, fs_data);
 	if (ret)
 		goto out;
 
-	evm_xattr = lsm_xattr + 1;
-	ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr);
+	ret = evm_inode_init_security(inode, new_xattrs,
+				      new_xattrs + base_slot);
 	if (ret)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ddd097790d47..6319417129af 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2916,11 +2916,13 @@ static int selinux_dentry_create_files_as(struct dentry *dentry, int mode,
 
 static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 				       const struct qstr *qstr,
-				       const char **name,
-				       void **value, size_t *len)
+				       struct xattr *xattrs, int *base_slot,
+				       void *fs_data)
 {
 	const struct task_security_struct *tsec = selinux_cred(current_cred());
 	struct superblock_security_struct *sbsec;
+	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
+						  *base_slot + 1);
 	u32 newsid, clen;
 	int rc;
 	char *context;
@@ -2947,16 +2949,15 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	    !(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
-	if (name)
-		*name = XATTR_SELINUX_SUFFIX;
+	if (xattr) {
+		xattr->name = XATTR_SELINUX_SUFFIX;
 
-	if (value && len) {
 		rc = security_sid_to_context_force(&selinux_state, newsid,
 						   &context, &clen);
 		if (rc)
 			return rc;
-		*value = context;
-		*len = clen;
+		xattr->value = context;
+		xattr->value_len = clen;
 	}
 
 	return 0;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 12a45e61c1a5..53e32cde09fb 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -962,26 +962,28 @@ static int smack_inode_alloc_security(struct inode *inode)
  * @inode: the newly created inode
  * @dir: containing directory object
  * @qstr: unused
- * @name: where to put the attribute name
- * @value: where to put the attribute value
- * @len: where to put the length of the attribute
+ * @xattrs: where to put the attribute
+ * @base_slot: where to start to write in @xattrs
+ * @fs_data: unused
  *
  * Returns 0 if it all works out, -ENOMEM if there's no memory
  */
 static int smack_inode_init_security(struct inode *inode, struct inode *dir,
-				     const struct qstr *qstr, const char **name,
-				     void **value, size_t *len)
+				     const struct qstr *qstr,
+				     struct xattr *xattrs, int *base_slot,
+				     void *fs_data)
 {
 	struct inode_smack *issp = smack_inode(inode);
 	struct smack_known *skp = smk_of_current();
 	struct smack_known *isp = smk_of_inode(inode);
 	struct smack_known *dsp = smk_of_inode(dir);
+	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
+						  *base_slot + 1);
 	int may;
 
-	if (name)
-		*name = XATTR_SMACK_SUFFIX;
+	if (xattr) {
+		xattr->name = XATTR_SMACK_SUFFIX;
 
-	if (value && len) {
 		rcu_read_lock();
 		may = smk_access_entry(skp->smk_known, dsp->smk_known,
 				       &skp->smk_rules);
@@ -999,11 +1001,11 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 			issp->smk_flags |= SMK_INODE_CHANGED;
 		}
 
-		*value = kstrdup(isp->smk_known, GFP_NOFS);
-		if (*value == NULL)
+		xattr->value = kstrdup(isp->smk_known, GFP_NOFS);
+		if (xattr->value == NULL)
 			return -ENOMEM;
 
-		*len = strlen(isp->smk_known);
+		xattr->value_len = strlen(isp->smk_known);
 	}
 
 	return 0;
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 4/6] security: Support multiple LSMs implementing the inode_init_security hook
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
                   ` (2 preceding siblings ...)
  2021-04-27 11:37 ` [PATCH v3 3/6] security: Pass xattrs allocated by LSMs to the inode_init_security hook Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure Roberto Sassu
                   ` (2 subsequent siblings)
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

The current implementation of security_inode_init_security() is capable of
handling only one LSM providing an xattr to be set at inode creation. That
xattr is then passed to EVM to calculate the HMAC.

To support multiple LSMs, each providing one or multiple xattrs, this patch
makes the following modifications to security_inode_init_security():
- dynamically allocates new_xattrs, based on the number of slots requested
  by LSMs (through the new field lbs_xattr introduced in the lsm_blob_sizes
  structure);
- replaces the call_int_hook() macro with its definition, to correctly
  handle the case of an LSM returning -EOPNOTSUPP (the loop should not be
  stopped);
- verifies whether or not inode_init_security hook implementations operated
  correctly:
  - LSMs returning zero must fill at least a slot;
  - LSMs must not fill a slot outside the xattr array;
  - LSMs must set an xattr name for each filled slot.

The modifications necessary for EVM to calculate the HMAC on all xattrs
will be done in a separate patch.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/lsm_hooks.h  |  1 +
 security/security.c        | 64 ++++++++++++++++++++++++++++++++------
 security/selinux/hooks.c   |  5 ++-
 security/smack/smack_lsm.c |  5 ++-
 4 files changed, 64 insertions(+), 11 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 197d6662b262..cb6329ce8b0c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1581,6 +1581,7 @@ struct lsm_blob_sizes {
 	int	lbs_ipc;
 	int	lbs_msg_msg;
 	int	lbs_task;
+	int	lbs_xattr;
 };
 
 /*
diff --git a/security/security.c b/security/security.c
index 527a18fd6742..91675003a5cf 100644
--- a/security/security.c
+++ b/security/security.c
@@ -30,8 +30,6 @@
 #include <linux/msg.h>
 #include <net/flow.h>
 
-#define MAX_LSM_EVM_XATTR	2
-
 /* How many LSMs were built into the kernel? */
 #define LSM_COUNT (__end_lsm_info - __start_lsm_info)
 
@@ -204,6 +202,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
 	lsm_set_blob_size(&needed->lbs_ipc, &blob_sizes.lbs_ipc);
 	lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
 	lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task);
+	lsm_set_blob_size(&needed->lbs_xattr, &blob_sizes.lbs_xattr);
 }
 
 /* Prepare LSM for initialization. */
@@ -339,6 +338,7 @@ static void __init ordered_lsm_init(void)
 	init_debug("ipc blob size      = %d\n", blob_sizes.lbs_ipc);
 	init_debug("msg_msg blob size  = %d\n", blob_sizes.lbs_msg_msg);
 	init_debug("task blob size     = %d\n", blob_sizes.lbs_task);
+	init_debug("xattr slots        = %d\n", blob_sizes.lbs_xattr);
 
 	/*
 	 * Create any kmem_caches needed for blobs
@@ -1042,9 +1042,9 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 const initxattrs initxattrs, void *fs_data)
 {
-	struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1];
-	struct xattr *xattr;
-	int ret, base_slot = 0;
+	struct xattr *new_xattrs, *xattr;
+	struct security_hook_list *P;
+	int ret, base_slot = 0, old_base_slot;
 
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
@@ -1052,11 +1052,56 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	if (!initxattrs)
 		return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
 				     dir, qstr, NULL, &base_slot, fs_data);
-	memset(new_xattrs, 0, sizeof(new_xattrs));
-	ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
-			    new_xattrs, &base_slot, fs_data);
-	if (ret)
+
+	/* Allocate +1 for EVM and +1 as terminator. */
+	new_xattrs = kcalloc(blob_sizes.lbs_xattr + 2, sizeof(*new_xattrs),
+			     GFP_NOFS);
+	if (!new_xattrs)
+		return -ENOMEM;
+
+	hlist_for_each_entry(P, &security_hook_heads.inode_init_security,
+			     list) {
+		old_base_slot = base_slot;
+		ret = P->hook.inode_init_security(inode, dir, qstr, new_xattrs,
+						  &base_slot, fs_data);
+		if (ret) {
+			if (ret != -EOPNOTSUPP)
+				goto out;
+
+			continue;
+		}
+
+		if (base_slot == old_base_slot) {
+			WARN_ONCE(
+			    "LSM %s: returned zero but didn't fill any slot\n",
+			    P->lsm);
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (base_slot > blob_sizes.lbs_xattr) {
+			WARN_ONCE(
+			    "LSM %s: wrote xattr outside array (%d/%d)\n",
+			    P->lsm, base_slot, blob_sizes.lbs_xattr);
+			ret = -EINVAL;
+			goto out;
+		}
+
+		while (old_base_slot < base_slot) {
+			if (new_xattrs[old_base_slot++].name != NULL)
+				continue;
+
+			WARN_ONCE("LSM %s: ret = 0 but xattr name = NULL\n",
+				  P->lsm);
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+
+	if (!base_slot) {
+		ret = -EOPNOTSUPP;
 		goto out;
+	}
 
 	ret = evm_inode_init_security(inode, new_xattrs,
 				      new_xattrs + base_slot);
@@ -1070,6 +1115,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 			continue;
 		kfree(xattr->value);
 	}
+	kfree(new_xattrs);
 	if (initxattrs == &security_initxattrs)
 		return ret;
 	return (ret == -EOPNOTSUPP) ? 0 : ret;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6319417129af..3ea56c706a58 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -104,6 +104,8 @@
 #include "audit.h"
 #include "avc_ss.h"
 
+#define SELINUX_INODE_INIT_XATTRS 1
+
 struct selinux_state selinux_state;
 
 /* SECMARK reference count */
@@ -2922,7 +2924,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	const struct task_security_struct *tsec = selinux_cred(current_cred());
 	struct superblock_security_struct *sbsec;
 	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
-						  *base_slot + 1);
+		selinux_blob_sizes.lbs_xattr + SELINUX_INODE_INIT_XATTRS);
 	u32 newsid, clen;
 	int rc;
 	char *context;
@@ -6976,6 +6978,7 @@ struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
 	.lbs_inode = sizeof(struct inode_security_struct),
 	.lbs_ipc = sizeof(struct ipc_security_struct),
 	.lbs_msg_msg = sizeof(struct msg_security_struct),
+	.lbs_xattr = SELINUX_INODE_INIT_XATTRS,
 };
 
 #ifdef CONFIG_PERF_EVENTS
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 53e32cde09fb..cecba1228602 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -51,6 +51,8 @@
 #define SMK_RECEIVING	1
 #define SMK_SENDING	2
 
+#define SMACK_INODE_INIT_XATTRS 1
+
 static DEFINE_MUTEX(smack_ipv6_lock);
 static LIST_HEAD(smk_ipv6_port_list);
 struct kmem_cache *smack_rule_cache;
@@ -978,7 +980,7 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 	struct smack_known *isp = smk_of_inode(inode);
 	struct smack_known *dsp = smk_of_inode(dir);
 	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
-						  *base_slot + 1);
+			smack_blob_sizes.lbs_xattr + SMACK_INODE_INIT_XATTRS);
 	int may;
 
 	if (xattr) {
@@ -4702,6 +4704,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
 	.lbs_inode = sizeof(struct inode_smack),
 	.lbs_ipc = sizeof(struct smack_known *),
 	.lbs_msg_msg = sizeof(struct smack_known *),
+	.lbs_xattr = SMACK_INODE_INIT_XATTRS,
 };
 
 static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
                   ` (3 preceding siblings ...)
  2021-04-27 11:37 ` [PATCH v3 4/6] security: Support multiple LSMs implementing " Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-04-27 11:37 ` [PATCH v3 6/6] evm: Support multiple LSMs providing an xattr Roberto Sassu
  2021-06-08 13:02 ` [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

This patch changes the evm_inode_init_security() definition to align with
the LSM infrastructure, in preparation for moving IMA and EVM to that
infrastructure.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/evm.h               | 19 ++++++++++++-------
 security/integrity/evm/evm_main.c | 19 +++++++++++++------
 security/security.c               |  6 +++---
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 8cad46bcec9d..8b1c36c19e97 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -34,9 +34,10 @@ extern int evm_inode_removexattr(struct user_namespace *mnt_userns,
 				 struct dentry *dentry, const char *xattr_name);
 extern void evm_inode_post_removexattr(struct dentry *dentry,
 				       const char *xattr_name);
-extern int evm_inode_init_security(struct inode *inode,
-				   const struct xattr *xattr_array,
-				   struct xattr *evm);
+extern int evm_inode_init_security(struct inode *inode, struct inode *dir,
+				   const struct qstr *qstr,
+				   struct xattr *xattrs, int *base_slot,
+				   void *fs_data);
 extern bool evm_status_revalidate(const char *xattr_name);
 #ifdef CONFIG_FS_POSIX_ACL
 extern int posix_xattr_acl(const char *xattrname);
@@ -102,11 +103,15 @@ static inline void evm_inode_post_removexattr(struct dentry *dentry,
 	return;
 }
 
-static inline int evm_inode_init_security(struct inode *inode,
-					  const struct xattr *xattr_array,
-					  struct xattr *evm)
+static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
+					  const struct qstr *qstr,
+					  struct xattr *xattrs, int *base_slot,
+					  void *fs_data)
 {
-	return 0;
+	if (!xattrs || !xattrs->name)
+		return 0;
+
+	return -EOPNOTSUPP;
 }
 
 static inline bool evm_status_revalidate(const char *xattr_name)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 84a9b7a69b1f..d647bfd0adcd 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -17,6 +17,7 @@
 #include <linux/xattr.h>
 #include <linux/integrity.h>
 #include <linux/evm.h>
+#include <linux/lsm_hooks.h>
 #include <linux/magic.h>
 #include <linux/posix_acl_xattr.h>
 
@@ -706,23 +707,29 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 /*
  * evm_inode_init_security - initializes security.evm HMAC value
  */
-int evm_inode_init_security(struct inode *inode,
-				 const struct xattr *lsm_xattr,
-				 struct xattr *evm_xattr)
+int evm_inode_init_security(struct inode *inode, struct inode *dir,
+			    const struct qstr *qstr,
+			    struct xattr *xattrs, int *base_slot,
+			    void *fs_data)
 {
 	struct evm_xattr *xattr_data;
+	struct xattr *evm_xattr = lsm_find_xattr_slot(xattrs, base_slot,
+						      *base_slot + 1);
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) ||
-	    !evm_protected_xattr(lsm_xattr->name))
+	if (!xattrs || !xattrs->name)
 		return 0;
 
+	if (!(evm_initialized & EVM_INIT_HMAC) ||
+	    !evm_protected_xattr(xattrs->name))
+		return -EOPNOTSUPP;
+
 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 	if (!xattr_data)
 		return -ENOMEM;
 
 	xattr_data->data.type = EVM_XATTR_HMAC;
-	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
+	rc = evm_init_hmac(inode, xattrs, xattr_data->digest);
 	if (rc < 0)
 		goto out;
 
diff --git a/security/security.c b/security/security.c
index 91675003a5cf..f090362550fa 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1103,9 +1103,9 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 		goto out;
 	}
 
-	ret = evm_inode_init_security(inode, new_xattrs,
-				      new_xattrs + base_slot);
-	if (ret)
+	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs, &base_slot,
+				      fs_data);
+	if (ret && ret != -EOPNOTSUPP)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH v3 6/6] evm: Support multiple LSMs providing an xattr
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
                   ` (4 preceding siblings ...)
  2021-04-27 11:37 ` [PATCH v3 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure Roberto Sassu
@ 2021-04-27 11:37 ` Roberto Sassu
  2021-06-08 13:02 ` [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-04-27 11:37 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel, Roberto Sassu

Currently, evm_inode_init_security() processes a single LSM xattr from
the array passed by security_inode_init_security(), and calculates the
HMAC on it and other inode metadata.

Given that initxattrs(), called by security_inode_init_security(), expects
that this array is terminated when the xattr name is set to NULL, this
patch reuses the same assumption for to scan all xattrs and to calculate
the HMAC on all of them.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/evm/evm.h        |  2 ++
 security/integrity/evm/evm_crypto.c |  9 ++++++++-
 security/integrity/evm/evm_main.c   | 15 +++++++++++----
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index ae590f71ce7d..24eac42b9f32 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -49,6 +49,8 @@ struct evm_digest {
 	char digest[IMA_MAX_DIGEST_SIZE];
 } __packed;
 
+int evm_protected_xattr(const char *req_xattr_name);
+
 int evm_init_key(void);
 int __init evm_init_crypto(void);
 int evm_update_evmxattr(struct dentry *dentry,
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index b66264b53d5d..35c5eec0517d 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -358,6 +358,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 		  char *hmac_val)
 {
 	struct shash_desc *desc;
+	const struct xattr *xattr;
 
 	desc = init_desc(EVM_XATTR_HMAC, evm_hash_algo);
 	if (IS_ERR(desc)) {
@@ -365,7 +366,13 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 		return PTR_ERR(desc);
 	}
 
-	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
+	for (xattr = lsm_xattr; xattr->name != NULL; xattr++) {
+		if (!evm_protected_xattr(xattr->name))
+			continue;
+
+		crypto_shash_update(desc, xattr->value, xattr->value_len);
+	}
+
 	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 	kfree(desc);
 	return 0;
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index d647bfd0adcd..cd2f46770646 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -261,7 +261,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 	return evm_status;
 }
 
-static int evm_protected_xattr(const char *req_xattr_name)
+int evm_protected_xattr(const char *req_xattr_name)
 {
 	int namelen;
 	int found = 0;
@@ -713,15 +713,22 @@ int evm_inode_init_security(struct inode *inode, struct inode *dir,
 			    void *fs_data)
 {
 	struct evm_xattr *xattr_data;
+	struct xattr *xattr;
 	struct xattr *evm_xattr = lsm_find_xattr_slot(xattrs, base_slot,
 						      *base_slot + 1);
-	int rc;
+	int rc, evm_protected_xattrs = 0;
 
 	if (!xattrs || !xattrs->name)
 		return 0;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) ||
-	    !evm_protected_xattr(xattrs->name))
+	if (!(evm_initialized & EVM_INIT_HMAC))
+		return -EOPNOTSUPP;
+
+	for (xattr = xattrs; xattr->name != NULL && xattr < evm_xattr; xattr++)
+		if (evm_protected_xattr(xattr->name))
+			evm_protected_xattrs++;
+
+	if (!evm_protected_xattrs)
 		return -EOPNOTSUPP;
 
 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
-- 
2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

* RE: [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure
  2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
                   ` (5 preceding siblings ...)
  2021-04-27 11:37 ` [PATCH v3 6/6] evm: Support multiple LSMs providing an xattr Roberto Sassu
@ 2021-06-08 13:02 ` Roberto Sassu
  6 siblings, 0 replies; 8+ messages in thread
From: Roberto Sassu @ 2021-06-08 13:02 UTC (permalink / raw)
  To: zohar, jmorris, paul, casey
  Cc: linux-integrity, linux-security-module, reiserfs-devel, selinux,
	linux-fsdevel, linux-kernel

> From: Roberto Sassu
> Sent: Tuesday, April 27, 2021 1:37 PM
> This patch set depends on:
> 
> https://lore.kernel.org/linux-integrity/20210409114313.4073-1-
> roberto.sassu@huawei.com/
> https://lore.kernel.org/linux-integrity/20210407105252.30721-1-
> roberto.sassu@huawei.com/
> 
> One of the challenges that must be tackled to move IMA and EVM to the
> LSM
> infrastructure is to ensure that EVM is capable to correctly handle
> multiple stacked LSMs providing an xattr at file creation. At the moment,
> there are few issues that would prevent a correct integration. This patch
> set aims at solving them.

Hi

anything I should do more for this patch set?

The first two patches are bug fixes and should be ready for merge.

For the rest, this patch set would be still useful even if IMA/EVM are
not moved to the LSM infrastructure. Its main purpose is to make it
possible to use multiple LSMs providing an implementation for the
inode_init_security hook.

Although this wouldn't be needed by LSMs already in the kernel,
as there can be only one major LSM, it would be useful for people
developing new LSMs.

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> From the LSM infrastructure side, the LSM stacking feature added the
> possibility of registering multiple implementations of the security hooks,
> that are called sequentially whenever someone calls the corresponding
> security hook. However, security_inode_init_security() and
> security_old_inode_init_security() are currently limited to support one
> xattr provided by LSM and one by EVM.
> 
> In addition, using the call_int_hook() macro causes some issues. According
> to the documentation in include/linux/lsm_hooks.h, it is a legitimate case
> that an LSM returns -EOPNOTSUPP when it does not want to provide an
> xattr.
> However, the loop defined in the macro would stop calling subsequent LSMs
> if that happens. In the case of security_old_inode_init_security(), using
> the macro would also cause a memory leak due to replacing the *value
> pointer, if multiple LSMs provide an xattr.
> 
> From EVM side, the first operation to be done is to change the definition
> of evm_inode_init_security() to be compatible with the security hook
> definition. Unfortunately, the current definition does not provide enough
> information for EVM, as it must have visibility of all xattrs provided by
> LSMs to correctly calculate the HMAC. This patch set changes the security
> hook definition by replacing the name, value and len triple with the xattr
> array allocated by security_inode_init_security().
> 
> Secondly, EVM must know how many elements are in the xattr array. EVM
> can
> rely on the fact that the xattr array must be terminated with an element
> with name field set to NULL, but can also benefit from the enhancements
> that have been included in this version of the patch set.
> 
> Casey suggested to use the reservation mechanism currently implemented
> for
> other security blobs, for xattrs. In this way,
> security_inode_init_security() can know after LSM initialization how many
> slots for xattrs should be allocated, and LSMs know the offset in the
> array from where they can start writing xattrs.
> 
> One of the problem was that LSMs can decide at run-time, although they
> reserved a slot, to not use it (for example because they were not
> initialized). Given that the initxattrs() method implemented by filesystems
> expect that the array is continuous, they would miss the slots after the
> one not being initialized. security_inode_init_security() should have been
> modified to compact the array.
> 
> Instead, the preferred solution was to introduce the base slot as a
> parameter, in addition to the xattr array, containing the up to date
> information about the slots used by previous LSMs. The correctness of the
> update of the slot is ensured by both the LSMs, if they use the new helper
> lsm_find_xattr_slot(), and by security_inode_init_security() which checks
> the slot each time after an LSM executes the inode_init_security hook.
> 
> This patch set has been tested by introducing several instances of a
> TestLSM (some providing an xattr, some not, one with a wrong
> implementation
> to see how the LSM infrastructure handles it). The patch is not included
> in this set but it is available here:
> 
> https://github.com/robertosassu/linux/commit/c7e01af6cb2c6780f0b143070
> 269fff7e30053f9
> 
> The test, added to ima-evm-utils, is available here:
> 
> https://github.com/robertosassu/ima-evm-utils/blob/evm-multiple-lsms-v3-
> devel-v7/tests/evm_multiple_lsms.test
> 
> The test takes a UML kernel built by Travis and launches it several times,
> each time with a different combination of LSMs. After boot, it first checks
> that there is an xattr for each LSM providing it, and then calculates the
> HMAC in user space and compares it with the HMAC calculated by EVM in
> kernel space.
> 
> A test report can be obtained here:
> 
> https://travis-ci.com/github/robertosassu/ima-evm-utils/jobs/501101861
> 
> SELinux Test Suite result (diff 5.11.14-200.fc33.x86_64 5.12.0-rc8+):
> -Files=70, Tests=1099, 82 wallclock secs ( 0.35 usr  0.09 sys +  7.39 cusr 10.14
> csys = 17.97 CPU)
> +Files=70, Tests=1108, 85 wallclock secs ( 0.34 usr  0.10 sys +  7.25 cusr 11.39
> csys = 19.08 CPU)
>  Result: FAIL
> -Failed 2/70 test programs. 5/1099 subtests failed.
> +Failed 2/70 test programs. 5/1108 subtests failed.
> 
> Smack Test Suite result:
> smack_set_ambient 1 TPASS: Test "smack_set_ambient" success.
> smack_set_current 1 TPASS: Test "smack_set_current" success.
> smack_set_doi 1 TPASS: Test "smack_set_doi" success.
> smack_set_netlabel 1 TPASS: Test "smack_set_netlabel" success.
> smack_set_socket_labels    1  TPASS  :  Test smack_set_socket_labels
> success.
> smack_set_cipso 1 TPASS: Test "smack_set_cipso" success.
> smack_set_direct 1 TPASS: Test "smack_set_direct" success.
> smack_set_load 1 TPASS: Test "smack_set_load" success.
> smack_set_onlycap 1 TFAIL: The smack label reported for "/smack/onlycap"
> 
> Lastly, running the test on reiserfs to check
> security_old_inode_init_security(), some issues have been discovered: a
> free of xattr->name which is not correct after commit 9548906b2bb7 ('xattr:
> Constify ->name member of "struct xattr"'), missing calls to
> reiserfs_security_free() and a misalignment with
> security_inode_init_security() (the old version expects the full xattr name
> with the security. prefix, the new version just the suffix). The last issue
> has not been fixed yet.
> 
> Changelog
> 
> v2:
> - rewrite selinux_old_inode_init_security() to use
>   security_inode_init_security()
> - add lbs_xattr field to lsm_blob_sizes structure, to give the ability to
>   LSMs to reserve slots in the xattr array (suggested by Casey)
> - add new parameter base_slot to inode_init_security hook definition
> 
> v1:
> - add calls to reiserfs_security_free() and initialize sec->value to NULL
>   (suggested by Tetsuo and Mimi)
> - change definition of inode_init_security hook, replace the name, value
>   and len triple with the xattr array (suggested by Casey)
> - introduce lsm_find_xattr_slot() helper for LSMs to find an unused slot in
>   the passed xattr array
> 
> Roberto Sassu (6):
>   reiserfs: Add missing calls to reiserfs_security_free()
>   security: Rewrite security_old_inode_init_security()
>   security: Pass xattrs allocated by LSMs to the inode_init_security
>     hook
>   security: Support multiple LSMs implementing the inode_init_security
>     hook
>   evm: Align evm_inode_init_security() definition with LSM
>     infrastructure
>   evm: Support multiple LSMs providing an xattr
> 
>  fs/reiserfs/namei.c                 |   4 +
>  fs/reiserfs/xattr_security.c        |   1 +
>  include/linux/evm.h                 |  19 +++--
>  include/linux/lsm_hook_defs.h       |   4 +-
>  include/linux/lsm_hooks.h           |  22 +++++-
>  security/integrity/evm/evm.h        |   2 +
>  security/integrity/evm/evm_crypto.c |   9 ++-
>  security/integrity/evm/evm_main.c   |  30 +++++--
>  security/security.c                 | 116 +++++++++++++++++++++++-----
>  security/selinux/hooks.c            |  18 +++--
>  security/smack/smack_lsm.c          |  27 ++++---
>  11 files changed, 194 insertions(+), 58 deletions(-)
> 
> --
> 2.25.1


^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, other threads:[~2021-06-08 13:02 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-27 11:37 [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 1/6] reiserfs: Add missing calls to reiserfs_security_free() Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 2/6] security: Rewrite security_old_inode_init_security() Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 3/6] security: Pass xattrs allocated by LSMs to the inode_init_security hook Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 4/6] security: Support multiple LSMs implementing " Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure Roberto Sassu
2021-04-27 11:37 ` [PATCH v3 6/6] evm: Support multiple LSMs providing an xattr Roberto Sassu
2021-06-08 13:02 ` [PATCH v3 0/6] evm: Prepare for moving to the LSM infrastructure Roberto Sassu

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