thr3ads.net - Ocfs2 devel - [Ocfs2-devel] [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes [Mar 2023]

If this information is useful, please help other people find it:
Share via:

Roberto Sassu

2023-Mar-14 08:17 UTC

[Ocfs2-devel] [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes

From: Roberto Sassu <roberto.sassu at huawei.com>

One of the major goals of LSM stacking is to run multiple LSMs side by side
without interfering with each other. The ultimate decision will depend on
individual LSM decision.

Several changes need to be made to the LSM infrastructure to be able to
support that. This patch set tackles one of them: gives to each LSM the
ability to specify one or multiple xattrs to be set at inode creation
time and, at the same time, gives to EVM the ability to access all those
xattrs and calculate the HMAC on them.

The first problem that this patch set addresses is to make the
inode_init_security hook definition suitable to use with EVM which, unlike
other LSMs, needs to have visibility of all xattrs and not only the one
that the LSM infrastructure passes to the LSM to be set.

The solution is to replace in the inode_init_security definition the
name/value/len parameters with the beginning of the array containing all
xattrs set by LSMs. Due to security_old_inode_init_security() API
limitation of setting only one xattr, it has been dropped and the remaining
users, ocfs2 and reiserfs, switch to security_inode_init_security().
However, due to the complexity of the changes required to fully exploit the
ability of security_inode_init_security() to set multiple xattrs, those
users can still set only one xattr (the first set in the xattr array) where
previously they called security_old_inode_init_security().

Furthermore, while EVM is invoked unlike before, its xattr will not be set
as it would not be the first set in the xattr array, or if it is the first,
there would not be protected xattrs to calculate the HMAC on.

The second problem this patch set addresses is the limitation of the
call_int_hook() of stopping the loop when the return value from a hook
implementation is not zero. Unfortunately, for the inode_init_security hook
it is a legitimate case to return -EOPNOTSUPP, but this would not
necessarily mean that there is an error to report to the LSM infrastructure
but just that an LSM does not will to set an xattr. Other LSMs should be
still consulted as well.

The solution for this specific case is to replace the call_int_hook() with
the loop itself, so that -EOPNOTSUPP can be ignored.

Next, this patch set removes the limitation of creating only two xattrs,
one by an active LSM and another by EVM. This patch set extends the
reservation mechanism of the LSM infrastructure, to allow each LSM to
request one or multiple xattrs. While this could potentially lead to
reaching the filesystem limits of number/size of the xattrs, it seems not
an issue that need to be solved by the LSM infrastructure but by the
filesystems themselves. Currently, if the limit is reached, the only
workaround would be to use fewer LSMs.

The reservation mechanism concept makes it very easy for LSMs to position
themselves correctly in the xattr array, as the LSM infrastructure at
initialization time changes the number of xattrs requested by each LSM with
an offset. LSMs can just take that offset as the starting index in the
xattr array and fill the next slots depending on how many xattrs they
requested.

However, while this concept is intuitive, it needs extra care. While for
security blobs (the main reason of the reservation mechanism) it is not
relevant for an LSM if other LSMs filled their portion, it matters for
xattrs, as both EVM and initxattrs() callbacks scan the entire array until
a terminator (xattr with NULL name). If an LSM did not provide an xattr,
which could happen if it is loaded but not initialized, consumers of the
xattr array would stop prematurely.

This patch set avoids this problem by compacting the xattr array each time
after an LSM executed its implementation of the inode_init_security hook.
It needs to be done after each LSM, and not after all, since there might be
LSMs scanning that xattr array too. Compacting the array after all LSMs
would be too late.

Finally, this patch set modifies the evm_inode_init_security() definition
to be compatible with the inode_init_security hook definition and adds
support for scanning the whole xattr array and for calculating the HMAC
on all xattrs provided by LSMs.

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, one providing multiple xattrs
and another providing an xattr but in a disabled state). The patch is not
included in this set but it is available here:

https://github.com/robertosassu/linux/commit/311b83a98757915cc3ccb363f545578e7c38df54

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

https://github.com/robertosassu/ima-evm-utils/blob/evm-multiple-lsms-v8-devel-v2/tests/evm_multiple_lsms.test

The test takes a UML kernel built by Github Actions and launches it several
times, each time with a different combination of LSMs and filesystems (ext4,
reiserfs, ocfs2). After boot, it first checks that there is an xattr for each
LSM providing it (for reiserfs and ocfs2 just the first LSM), and then (for
ext4) 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://github.com/robertosassu/ima-evm-utils/actions/runs/4403223954/jobs/7722101662

The patch set has been tested with both the SElinux and Smack test suites.
Below, there is the summary of the test results:

SELinux Test Suite result (without patches):
All tests successful.
Files=76, Tests=1343, 255 wallclock secs ( 0.51 usr  0.19 sys +  6.30 cusr 58.15
csys = 65.15 CPU)
Result: PASS

SELinux Test Suite result (with patches):
All tests successful.
Files=76, Tests=1343, 258 wallclock secs ( 0.49 usr  0.21 sys +  6.46 cusr 59.27
csys = 66.43 CPU)
Result: PASS

Smack Test Suite result (without patches):
95 Passed, 0 Failed, 100% Success rate

Smack Test Suite result (with patches):
95 Passed, 0 Failed, 100% Success rate

Changelog

v7:
- Add a patch dependency comment in patch 1 (suggested by Mimi)
- Restore check of -EOPNOTSUPP status in ocfs2_mknod() and ocfs2_symlink()
  (reported by Mimi)
- Add explanation in evm_inode_init_security() why walking through the
  xattrs array is safe (suggested by Mimi)
- Document the lbs_xattr field of struct lsm_blob_sizes (suggested by
  Casey)
- Move documentation changes of the inode_init_security hook to security.c,
  after LSM documentation reorganization by Paul
- Use attributes in plural form in the description of the xattrs parameter
  of smack_inode_init_security()
- Check xattr name instead of xattr value in evm_inode_init_security(),
  for consistency with evm_init_hmac(); equivalent, since
  security_check_compact_filled_xattrs() rejects xattrs with xattr name
  NULL and value not NULL, and viceversa

v6:
- Add a comment in Smack to introduce its xattrs (suggested by Casey)
- Document the overloaded meaning of -EOPNOTSUPP in
  security_inode_init_security() (suggested by Mimi)

v5:
- Modify the cover letter to explain that the goal of this patch set is
  supporting multiple per LSM xattrs in EVM, and not moving IMA and EVM to
  the LSM infrastructure (suggested by Mimi)
- Remove references in the patches description about moving IMA and EVM
  to the LSM infrastructure (suggested by Mimi)
- Explain that the additional EVM invocation due to the switch to
  security_inode_init_security() will not cause the EVM xattr to be added
  (suggested by Mimi)

v4:
- Remove patch to call reiserfs_security_free(), already queued
- Switch ocfs2 and reiserfs to security_inode_init_security() (suggested by
  Mimi)
- Remove security_old_inode_init_security() (suggested by Paul)
- Rename security_check_compact_xattrs() to
  security_check_compact_filled_xattrs() and add function description
  (suggested by Mimi)
- Rename checked_xattrs parameter of security_check_compact_filled_xattrs()
  to num_filled_xattrs (suggested by Mimi)
- Rename cur_xattrs variable in security_inode_init_security() to
  num_filled_xattrs (suggested by Mimi)

v3:
- Don't free the xattr name in reiserfs_security_free()
- Don't include fs_data parameter in inode_init_security hook
- Don't change evm_inode_init_security(), as it will be removed if EVM is
  stacked
- Fix inode_init_security hook documentation
- Drop lsm_find_xattr_slot(), use simple xattr reservation mechanism and
  introduce security_check_compact_xattrs() to compact the xattr array
- Don't allocate xattr array if LSMs didn't reserve any xattr
- Return zero if initxattrs() is not provided to
  security_inode_init_security(), -EOPNOTSUPP if value is not provided to
  security_old_inode_init_security()
- Request LSMs to fill xattrs if only value (not the triple) is provided to
  security_old_inode_init_security(), to avoid unnecessary memory
  allocation

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: Switch to security_inode_init_security()
  ocfs2: Switch to security_inode_init_security()
  security: Remove security_old_inode_init_security()
  security: Allow all LSMs to provide xattrs for inode_init_security
    hook
  evm: Align evm_inode_init_security() definition with LSM
    infrastructure
  evm: Support multiple LSMs providing an xattr

 fs/ocfs2/namei.c                    |   2 +
 fs/ocfs2/xattr.c                    |  30 ++++++-
 fs/reiserfs/xattr_security.c        |  23 +++--
 include/linux/evm.h                 |  12 +--
 include/linux/lsm_hook_defs.h       |   3 +-
 include/linux/lsm_hooks.h           |   1 +
 include/linux/security.h            |  12 ---
 security/integrity/evm/evm.h        |   2 +
 security/integrity/evm/evm_crypto.c |   9 +-
 security/integrity/evm/evm_main.c   |  33 +++++--
 security/security.c                 | 131 +++++++++++++++++++++-------
 security/selinux/hooks.c            |  19 ++--
 security/smack/smack_lsm.c          |  33 ++++---
 13 files changed, 224 insertions(+), 86 deletions(-)

-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 1/6] reiserfs: Switch to security_inode_init_security()

From: Roberto Sassu <roberto.sassu at huawei.com>

In preparation for removing security_old_inode_init_security(), switch to
security_inode_init_security(). Commit 572302af1258 ("reiserfs: Add missing
calls to reiserfs_security_free()") fixed possible memory leaks and another
issue related to adding an xattr at inode creation time.

Define the initxattrs callback reiserfs_initxattrs(), to populate the
name/value/len triple in the reiserfs_security_handle() with the first
xattr provided by LSMs. Make a copy of the xattr value, as
security_inode_init_security() frees it.

After the call to security_inode_init_security(), remove the check for
returning -EOPNOTSUPP, as security_inode_init_security() changes it to
zero.

Multiple xattrs are currently not supported, as the
reiserfs_security_handle structure is exported to user space. As a
consequence, even if EVM is invoked, it will not provide an xattr (if it
is not the first to set it, its xattr will be discarded; if it is the
first, it does not have xattrs to calculate the HMAC on).

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 fs/reiserfs/xattr_security.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/reiserfs/xattr_security.c b/fs/reiserfs/xattr_security.c
index 41c0ea84fbf..6bffdf9a4fd 100644
--- a/fs/reiserfs/xattr_security.c
+++ b/fs/reiserfs/xattr_security.c
@@ -39,6 +39,22 @@ static bool security_list(struct dentry *dentry)
 	return !IS_PRIVATE(d_inode(dentry));
 }
 
+static int
+reiserfs_initxattrs(struct inode *inode, const struct xattr *xattr_array,
+		    void *fs_info)
+{
+	struct reiserfs_security_handle *sec = fs_info;
+
+	sec->value = kmemdup(xattr_array->value, xattr_array->value_len,
+			     GFP_KERNEL);
+	if (!sec->value)
+		return -ENOMEM;
+
+	sec->name = xattr_array->name;
+	sec->length = xattr_array->value_len;
+	return 0;
+}
+
 /* Initializes the security context for a new inode and returns the number
  * of blocks needed for the transaction. If successful, reiserfs_security
  * must be released using reiserfs_security_free when the caller is done. */
@@ -56,12 +72,9 @@ int reiserfs_security_init(struct inode *dir, struct inode
*inode,
 	if (IS_PRIVATE(dir))
 		return 0;
 
-	error = security_old_inode_init_security(inode, dir, qstr, &sec->name,
-						 &sec->value, &sec->length);
+	error = security_inode_init_security(inode, dir, qstr,
+					     &reiserfs_initxattrs, sec);
 	if (error) {
-		if (error == -EOPNOTSUPP)
-			error = 0;
-
 		sec->name = NULL;
 		sec->value = NULL;
 		sec->length = 0;
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 2/6] ocfs2: Switch to security_inode_init_security()

From: Roberto Sassu <roberto.sassu at huawei.com>

In preparation for removing security_old_inode_init_security(), switch to
security_inode_init_security().

Extend the existing ocfs2_initxattrs() to take the
ocfs2_security_xattr_info structure from fs_info, and populate the
name/value/len triple with the first xattr provided by LSMs.

As fs_info was not used before, ocfs2_initxattrs() can now handle the case
of replicating the behavior of security_old_inode_init_security(), i.e.
just obtaining the xattr, in addition to setting all xattrs provided by
LSMs.

Supporting multiple xattrs is not currently supported where
security_old_inode_init_security() was called (mknod, symlink), as it
requires non-trivial changes that can be done at a later time. Like for
reiserfs, even if EVM is invoked, it will not provide an xattr (if it is
not the first to set it, its xattr will be discarded; if it is the first,
it does not have xattrs to calculate the HMAC on).

Finally, since security_inode_init_security(), unlike
security_old_inode_init_security(), returns zero instead of -EOPNOTSUPP if
no xattrs were provided by LSMs or if inodes are private, additionally
check in ocfs2_init_security_get() if the xattr name is set.

If not, act as if security_old_inode_init_security() returned -EOPNOTSUPP,
and set si->enable to zero to notify to the functions following
ocfs2_init_security_get() that no xattrs are available.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Acked-by: Joseph Qi <joseph.qi at linux.alibaba.com>
---
 fs/ocfs2/namei.c |  2 ++
 fs/ocfs2/xattr.c | 30 ++++++++++++++++++++++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
index 9175dbc4720..17c52225b87 100644
--- a/fs/ocfs2/namei.c
+++ b/fs/ocfs2/namei.c
@@ -242,6 +242,7 @@ static int ocfs2_mknod(struct mnt_idmap *idmap,
 	int want_meta = 0;
 	int xattr_credits = 0;
 	struct ocfs2_security_xattr_info si = {
+		.name = NULL,
 		.enable = 1,
 	};
 	int did_quota_inode = 0;
@@ -1805,6 +1806,7 @@ static int ocfs2_symlink(struct mnt_idmap *idmap,
 	int want_clusters = 0;
 	int xattr_credits = 0;
 	struct ocfs2_security_xattr_info si = {
+		.name = NULL,
 		.enable = 1,
 	};
 	int did_quota = 0, did_quota_inode = 0;
diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 389308efe85..469ec45baee 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -7259,9 +7259,21 @@ static int ocfs2_xattr_security_set(const struct
xattr_handler *handler,
 static int ocfs2_initxattrs(struct inode *inode, const struct xattr
*xattr_array,
 		     void *fs_info)
 {
+	struct ocfs2_security_xattr_info *si = fs_info;
 	const struct xattr *xattr;
 	int err = 0;
 
+	if (si) {
+		si->value = kmemdup(xattr_array->value, xattr_array->value_len,
+				    GFP_KERNEL);
+		if (!si->value)
+			return -ENOMEM;
+
+		si->name = xattr_array->name;
+		si->value_len = xattr_array->value_len;
+		return 0;
+	}
+
 	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
 		err = ocfs2_xattr_set(inode, OCFS2_XATTR_INDEX_SECURITY,
 				      xattr->name, xattr->value,
@@ -7277,13 +7289,23 @@ int ocfs2_init_security_get(struct inode *inode,
 			    const struct qstr *qstr,
 			    struct ocfs2_security_xattr_info *si)
 {
+	int ret;
+
 	/* check whether ocfs2 support feature xattr */
 	if (!ocfs2_supports_xattr(OCFS2_SB(dir->i_sb)))
 		return -EOPNOTSUPP;
-	if (si)
-		return security_old_inode_init_security(inode, dir, qstr,
-							&si->name, &si->value,
-							&si->value_len);
+	if (si) {
+		ret = security_inode_init_security(inode, dir, qstr,
+						   &ocfs2_initxattrs, si);
+		/*
+		 * security_inode_init_security() does not return -EOPNOTSUPP,
+		 * we have to check the xattr ourselves.
+		 */
+		if (!ret && !si->name)
+			si->enable = 0;
+
+		return ret;
+	}
 
 	return security_inode_init_security(inode, dir, qstr,
 					    &ocfs2_initxattrs, NULL);
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 3/6] security: Remove security_old_inode_init_security()

From: Roberto Sassu <roberto.sassu at huawei.com>

As the remaining two users reiserfs and ocfs2 switched to
security_inode_init_security(), security_old_inode_init_security() can be
now removed.

Out-of-tree kernel modules should switch to security_inode_init_security()
too.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 include/linux/security.h | 12 ------------
 security/security.c      | 11 -----------
 2 files changed, 23 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 5984d0d550b..cd23221ce9e 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -336,9 +336,6 @@ int security_inode_init_security(struct inode *inode, struct
inode *dir,
 int security_inode_init_security_anon(struct inode *inode,
 				      const struct qstr *name,
 				      const struct inode *context_inode);
-int security_old_inode_init_security(struct inode *inode, struct inode *dir,
-				     const struct qstr *qstr, const char **name,
-				     void **value, size_t *len);
 int security_inode_create(struct inode *dir, struct dentry *dentry, umode_t
mode);
 int security_inode_link(struct dentry *old_dentry, struct inode *dir,
 			 struct dentry *new_dentry);
@@ -778,15 +775,6 @@ static inline int security_inode_init_security_anon(struct
inode *inode,
 	return 0;
 }
 
-static inline int security_old_inode_init_security(struct inode *inode,
-						   struct inode *dir,
-						   const struct qstr *qstr,
-						   const char **name,
-						   void **value, size_t *len)
-{
-	return -EOPNOTSUPP;
-}
-
 static inline int security_inode_create(struct inode *dir,
 					 struct dentry *dentry,
 					 umode_t mode)
diff --git a/security/security.c b/security/security.c
index b808e1b8655..f4170efcddd 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1655,17 +1655,6 @@ int security_inode_init_security_anon(struct inode
*inode,
 			     context_inode);
 }
 
-int security_old_inode_init_security(struct inode *inode, struct inode *dir,
-				     const struct qstr *qstr, const char **name,
-				     void **value, size_t *len)
-{
-	if (unlikely(IS_PRIVATE(inode)))
-		return -EOPNOTSUPP;
-	return call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir,
-			     qstr, name, value, len);
-}
-EXPORT_SYMBOL(security_old_inode_init_security);
-
 #ifdef CONFIG_SECURITY_PATH
 /**
  * security_path_mknod() - Check if creating a special file is allowed
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook

From: Roberto Sassu <roberto.sassu at huawei.com>

Currently, security_inode_init_security() supports only one LSM providing
an xattr and EVM calculating the HMAC on that xattr, plus other inode
metadata.

Allow all LSMs to provide one or multiple xattrs, by extending the security
blob reservation mechanism. Introduce the new lbs_xattr field of the
lsm_blob_sizes structure, so that each LSM can specify how many xattrs it
needs, and the LSM infrastructure knows how many xattr slots it should
allocate.

Dynamically allocate the xattrs array to be populated by LSMs with the
inode_init_security hook, and pass it to the latter instead of the
name/value/len triple. Update the documentation accordingly, and fix the
description of the xattr name, as it is not allocated anymore.

Since the LSM infrastructure, at initialization time, updates the number of
the requested xattrs provided by each LSM with a corresponding offset in
the security blob (in this case the xattr array), it makes straightforward
for an LSM to access the right position in the xattr array.

There is still the issue that an LSM might not fill the xattr, even if it
requests it (legitimate case, for example it might have been loaded but not
initialized with a policy). Since users of the xattr array (e.g. the
initxattrs() callbacks) detect the end of the xattr array by checking if
the xattr name is NULL, not filling an xattr would cause those users to
stop scanning xattrs prematurely.

Solve that issue by introducing security_check_compact_filled_xattrs(),
which does a basic check of the xattr array (if the xattr name is filled,
the xattr value should be too, and viceversa), and compacts the xattr array
by removing the holes.

An alternative solution would be to let users of the xattr array know the
number of elements of that array, so that they don't have to check the
termination. However, this seems more invasive, compared to a simple move
of few array elements.

security_check_compact_filled_xattrs() also determines how many xattrs in
the xattr array have been filled. If there is none, skip
evm_inode_init_security() and initxattrs(). Skipping the former also avoids
EVM to crash the kernel, as it is expecting a filled xattr.

Finally, adapt both SELinux and Smack to use the new definition of the
inode_init_security hook, and to correctly fill the designated slots in the
xattr array. For Smack, reserve space for the other defined xattrs although
they are not set yet in smack_inode_init_security().

Reported-by: Nicolas Bouchinet <nicolas.bouchinet at clip-os.org> (EVM
crash)
Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS at archlinux/
Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 include/linux/lsm_hook_defs.h |   3 +-
 include/linux/lsm_hooks.h     |   1 +
 security/security.c           | 119 +++++++++++++++++++++++++++++-----
 security/selinux/hooks.c      |  19 ++++--
 security/smack/smack_lsm.c    |  33 ++++++----
 5 files changed, 137 insertions(+), 38 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 6bb55e61e8e..b814955ae70 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -112,8 +112,7 @@ 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)
 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 c2be66c669a..75a2f85b49d 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -63,6 +63,7 @@ struct lsm_blob_sizes {
 	int	lbs_ipc;
 	int	lbs_msg_msg;
 	int	lbs_task;
+	int	lbs_xattr; /* number of xattr slots in new_xattrs array */
 };
 
 /*
diff --git a/security/security.c b/security/security.c
index f4170efcddd..f1f5f62f7fa 100644
--- a/security/security.c
+++ b/security/security.c
@@ -31,8 +31,6 @@
 #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)
 
@@ -212,6 +210,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes
*needed)
 	lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
 	lsm_set_blob_size(&needed->lbs_superblock,
&blob_sizes.lbs_superblock);
 	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. */
@@ -378,6 +377,7 @@ static void __init ordered_lsm_init(void)
 	init_debug("msg_msg blob size    = %d\n", blob_sizes.lbs_msg_msg);
 	init_debug("superblock blob size = %d\n",
blob_sizes.lbs_superblock);
 	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
@@ -1579,6 +1579,52 @@ int security_dentry_create_files_as(struct dentry
*dentry, int mode,
 }
 EXPORT_SYMBOL(security_dentry_create_files_as);
 
+/**
+ * security_check_compact_filled_xattrs - check xattrs and make array
contiguous
+ * @xattrs: xattr array filled by LSMs
+ * @num_xattrs: length of xattr array
+ * @num_filled_xattrs: number of already processed xattrs
+ *
+ * Ensure that each xattr slot is correctly filled and close the gaps in the
+ * xattr array if an LSM didn't provide an xattr for which it asked space
+ * (legitimate case, it might have been loaded but not initialized). An LSM
+ * might request space in the xattr array for one or multiple xattrs. The LSM
+ * infrastructure ensures that all requests by LSMs are satisfied.
+ *
+ * Track the number of filled xattrs in @num_filled_xattrs, so that it is easy
+ * to determine whether the currently processed xattr is fine in its position
+ * (if all previous xattrs were filled) or it should be moved after the last
+ * filled xattr.
+ *
+ * Return: zero if all xattrs are valid, -EINVAL otherwise.
+ */
+static int security_check_compact_filled_xattrs(struct xattr *xattrs,
+						int num_xattrs,
+						int *num_filled_xattrs)
+{
+	int i;
+
+	for (i = *num_filled_xattrs; i < num_xattrs; i++) {
+		if ((!xattrs[i].name && xattrs[i].value) ||
+		    (xattrs[i].name && !xattrs[i].value))
+			return -EINVAL;
+
+		if (!xattrs[i].name)
+			continue;
+
+		if (i == *num_filled_xattrs) {
+			(*num_filled_xattrs)++;
+			continue;
+		}
+
+		memcpy(xattrs + (*num_filled_xattrs)++, xattrs + i,
+		       sizeof(*xattrs));
+		memset(xattrs + i, 0, sizeof(*xattrs));
+	}
+
+	return 0;
+}
+
 /**
  * security_inode_init_security() - Initialize an inode's LSM context
  * @inode: the inode
@@ -1591,9 +1637,13 @@ EXPORT_SYMBOL(security_dentry_create_files_as);
  * created inode and set up the incore security field for the new inode.  This
  * hook is called by the fs code as part of the inode creation transaction and
  * provides for atomic labeling of the inode, unlike the post_create/mkdir/...
- * hooks called by the VFS.  The hook function is expected to allocate the name
- * and value via kmalloc, with the caller being responsible for calling kfree
- * after using them.  If the security module does not use security attributes
+ * hooks called by the VFS.  The hook function is expected to populate the
+ * @xattrs array, depending on how many xattrs have been specified by the
+ * security module in the lbs_xattr field of the lsm_blob_sizes structure.  For
+ * each array element, the hook function is expected to set ->name to the
+ * attribute name suffix (e.g. selinux), to allocate ->value (will be freed
by
+ * the caller) and set it to the attribute value, to set ->value_len to the
+ * length of the value.  If the security module does not use security
attributes
  * or does not wish to put a security attribute on this particular inode, then
  * it should return -EOPNOTSUPP to skip this processing.
  *
@@ -1604,33 +1654,66 @@ 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 *lsm_xattr, *evm_xattr, *xattr;
-	int ret;
+	struct security_hook_list *P;
+	struct xattr *new_xattrs;
+	struct xattr *xattr;
+	int ret = -EOPNOTSUPP, num_filled_xattrs = 0;
 
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
+	if (!blob_sizes.lbs_xattr)
+		return 0;
+
 	if (!initxattrs)
 		return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
-				     dir, qstr, NULL, NULL, NULL);
-	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);
-	if (ret)
+				    dir, qstr, NULL);
+	/* 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) {
+		ret = P->hook.inode_init_security(inode, dir, qstr, new_xattrs);
+		if (ret && ret != -EOPNOTSUPP)
+			goto out;
+		/*
+		 * As documented in lsm_hooks.h, -EOPNOTSUPP in this context
+		 * means that the LSM is not willing to provide an xattr, not
+		 * that it wants to signal an error. Thus, continue to invoke
+		 * the remaining LSMs.
+		 */
+		if (ret == -EOPNOTSUPP)
+			continue;
+		/*
+		 * As the number of xattrs reserved by LSMs is not directly
+		 * available, directly use the total number blob_sizes.lbs_xattr
+		 * to keep the code simple, while being not the most efficient
+		 * way.
+		 */
+		ret = security_check_compact_filled_xattrs(new_xattrs,
+							   blob_sizes.lbs_xattr,
+							   &num_filled_xattrs);
+		if (ret < 0) {
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+
+	if (!num_filled_xattrs)
 		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 + num_filled_xattrs);
 	if (ret)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
 	for (xattr = new_xattrs; xattr->value != NULL; xattr++)
 		kfree(xattr->value);
+	kfree(new_xattrs);
 	return (ret == -EOPNOTSUPP) ? 0 : ret;
 }
 EXPORT_SYMBOL(security_inode_init_security);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9a5bdfc2131..3e4308dd336 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 */
@@ -2868,11 +2870,11 @@ 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)
 {
 	const struct task_security_struct *tsec = selinux_cred(current_cred());
 	struct superblock_security_struct *sbsec;
+	struct xattr *xattr = NULL;
 	u32 newsid, clen;
 	int rc;
 	char *context;
@@ -2899,16 +2901,18 @@ 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 (xattrs)
+		xattr = xattrs + selinux_blob_sizes.lbs_xattr;
+
+	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;
@@ -6918,6 +6922,7 @@ struct lsm_blob_sizes selinux_blob_sizes
__lsm_ro_after_init = {
 	.lbs_ipc = sizeof(struct ipc_security_struct),
 	.lbs_msg_msg = sizeof(struct msg_security_struct),
 	.lbs_superblock = sizeof(struct superblock_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 cfcbb748da2..c8cf8df268b 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -52,6 +52,15 @@
 #define SMK_RECEIVING	1
 #define SMK_SENDING	2
 
+/*
+ * Smack uses multiple xattrs.
+ * SMACK64 - for access control, SMACK64EXEC - label for the program,
+ * SMACK64MMAP - controls library loading,
+ * SMACK64TRANSMUTE - label initialization,
+ * Not saved on files - SMACK64IPIN and SMACK64IPOUT
+ */
+#define SMACK_INODE_INIT_XATTRS 4
+
 #ifdef SMACK_IPV6_PORT_LABELING
 static DEFINE_MUTEX(smack_ipv6_lock);
 static LIST_HEAD(smk_ipv6_port_list);
@@ -939,26 +948,27 @@ 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 attributes
  *
  * 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)
 {
 	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 = NULL;
 	int may;
 
-	if (name)
-		*name = XATTR_SMACK_SUFFIX;
+	if (xattrs)
+		xattr = xattrs + smack_blob_sizes.lbs_xattr;
+
+	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);
@@ -976,11 +986,11 @@ 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;
@@ -4854,6 +4864,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init
= {
 	.lbs_ipc = sizeof(struct smack_known *),
 	.lbs_msg_msg = sizeof(struct smack_known *),
 	.lbs_superblock = sizeof(struct superblock_smack),
+	.lbs_xattr = SMACK_INODE_INIT_XATTRS,
 };
 
 static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure

From: Roberto Sassu <roberto.sassu at huawei.com>

Change the evm_inode_init_security() definition to align with the LSM
infrastructure. Keep the existing behavior of including in the HMAC
calculation only the first xattr provided by LSMs.

Changing the evm_inode_init_security() definition requires passing only the
xattr array allocated by security_inode_init_security(), instead of the
first LSM xattr and the place where the EVM xattr should be filled. In lieu
of passing the EVM xattr, EVM must position itself after the last filled
xattr (by checking the xattr name), since only the beginning of the xattr
array is given.

Finally, make evm_inode_init_security() return value compatible with the
inode_init_security hook conventions, i.e. return -EOPNOTSUPP if it is not
setting an xattr.

EVM is a bit tricky, because xattrs is both an input and an output. If it
was just output, EVM should have returned zero if xattrs is NULL. But,
since xattrs is also input, EVM is unable to do its calculations, so return
-EOPNOTSUPP and handle this error in security_inode_init_security().

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 include/linux/evm.h               | 12 ++++++------
 security/integrity/evm/evm_main.c | 25 ++++++++++++++++++-------
 security/security.c               |  5 ++---
 3 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 7dc1ee74169..cc64cea354e 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -56,9 +56,9 @@ static inline void evm_inode_post_set_acl(struct dentry
*dentry,
 {
 	return evm_inode_post_setxattr(dentry, acl_name, NULL, 0);
 }
-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);
 extern bool evm_revalidate_status(const char *xattr_name);
 extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
 extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
@@ -157,9 +157,9 @@ static inline void evm_inode_post_set_acl(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)
 {
 	return 0;
 }
diff --git a/security/integrity/evm/evm_main.c
b/security/integrity/evm/evm_main.c
index cf24c525558..7d20ce83915 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -864,23 +864,34 @@ 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)
 {
 	struct evm_xattr *xattr_data;
+	struct xattr *xattr, *evm_xattr;
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) ||
-	    !evm_protected_xattr(lsm_xattr->name))
-		return 0;
+	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs ||
+	    !evm_protected_xattr(xattrs->name))
+		return -EOPNOTSUPP;
+
+	/*
+	 * security_inode_init_security() makes sure that the xattrs array is
+	 * contiguous, there is enough space for security.evm, and that there is
+	 * a terminator at the end of the array.
+	 */
+	for (xattr = xattrs; xattr->name != NULL; xattr++)
+		;
+
+	evm_xattr = xattr;
 
 	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 f1f5f62f7fa..d0e20b26b6c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1705,9 +1705,8 @@ int security_inode_init_security(struct inode *inode,
struct inode *dir,
 	if (!num_filled_xattrs)
 		goto out;
 
-	ret = evm_inode_init_security(inode, new_xattrs,
-				      new_xattrs + num_filled_xattrs);
-	if (ret)
+	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs);
+	if (ret && ret != -EOPNOTSUPP)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:17 UTC

head link

[Ocfs2-devel] [PATCH v8 6/6] evm: Support multiple LSMs providing an xattr

From: Roberto Sassu <roberto.sassu at huawei.com>

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() callbacks, called by
security_inode_init_security(), expect that this array is terminated when
the xattr name is set to NULL, reuse the same assumption to scan all xattrs
and to calculate the HMAC on all of them.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 security/integrity/evm/evm.h        |  2 ++
 security/integrity/evm/evm_crypto.c |  9 ++++++++-
 security/integrity/evm/evm_main.c   | 16 +++++++++++-----
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index f8b8c5004fc..f799d72a59f 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -46,6 +46,8 @@ 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 evm_update_evmxattr(struct dentry *dentry,
 			const char *req_xattr_name,
diff --git a/security/integrity/evm/evm_crypto.c
b/security/integrity/evm/evm_crypto.c
index 033804f5a5f..5d8b5ecf594 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -389,6 +389,7 @@ 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, HASH_ALGO_SHA1);
 	if (IS_ERR(desc)) {
@@ -396,7 +397,13 @@ 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 7d20ce83915..013eb220cc5 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -305,7 +305,7 @@ static int evm_protected_xattr_common(const char
*req_xattr_name,
 	return found;
 }
 
-static int evm_protected_xattr(const char *req_xattr_name)
+int evm_protected_xattr(const char *req_xattr_name)
 {
 	return evm_protected_xattr_common(req_xattr_name, false);
 }
@@ -870,10 +870,10 @@ int evm_inode_init_security(struct inode *inode, struct
inode *dir,
 {
 	struct evm_xattr *xattr_data;
 	struct xattr *xattr, *evm_xattr;
+	bool evm_protected_xattrs = false;
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs ||
-	    !evm_protected_xattr(xattrs->name))
+	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs)
 		return -EOPNOTSUPP;
 
 	/*
@@ -881,8 +881,14 @@ int evm_inode_init_security(struct inode *inode, struct
inode *dir,
 	 * contiguous, there is enough space for security.evm, and that there is
 	 * a terminator at the end of the array.
 	 */
-	for (xattr = xattrs; xattr->name != NULL; xattr++)
-		;
+	for (xattr = xattrs; xattr->name != NULL; xattr++) {
+		if (evm_protected_xattr(xattr->name))
+			evm_protected_xattrs = true;
+	}
+
+	/* EVM xattr not needed. */
+	if (!evm_protected_xattrs)
+		return -EOPNOTSUPP;
 
 	evm_xattr = xattr;
 
-- 
2.25.1

Roberto Sassu

2023-Mar-14 08:21 UTC

head link

[Ocfs2-devel] [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes

On Tue, 2023-03-14 at 09:17 +0100, Roberto Sassu wrote:> From: Roberto Sassu <roberto.sassu at huawei.com>
> 
> One of the major goals of LSM stacking is to run multiple LSMs side by side
> without interfering with each other. The ultimate decision will depend on
> individual LSM decision.
> 
> Several changes need to be made to the LSM infrastructure to be able to
> support that. This patch set tackles one of them: gives to each LSM the
> ability to specify one or multiple xattrs to be set at inode creation
> time and, at the same time, gives to EVM the ability to access all those
> xattrs and calculate the HMAC on them.
> 
> The first problem that this patch set addresses is to make the
> inode_init_security hook definition suitable to use with EVM which, unlike
> other LSMs, needs to have visibility of all xattrs and not only the one
> that the LSM infrastructure passes to the LSM to be set.
> 
> The solution is to replace in the inode_init_security definition the
> name/value/len parameters with the beginning of the array containing all
> xattrs set by LSMs. Due to security_old_inode_init_security() API
> limitation of setting only one xattr, it has been dropped and the remaining
> users, ocfs2 and reiserfs, switch to security_inode_init_security().
> However, due to the complexity of the changes required to fully exploit the
> ability of security_inode_init_security() to set multiple xattrs, those
> users can still set only one xattr (the first set in the xattr array) where
> previously they called security_old_inode_init_security().
> 
> Furthermore, while EVM is invoked unlike before, its xattr will not be set
> as it would not be the first set in the xattr array, or if it is the first,
> there would not be protected xattrs to calculate the HMAC on.
> 
> The second problem this patch set addresses is the limitation of the
> call_int_hook() of stopping the loop when the return value from a hook
> implementation is not zero. Unfortunately, for the inode_init_security hook
> it is a legitimate case to return -EOPNOTSUPP, but this would not
> necessarily mean that there is an error to report to the LSM infrastructure
> but just that an LSM does not will to set an xattr. Other LSMs should be
> still consulted as well.
> 
> The solution for this specific case is to replace the call_int_hook() with
> the loop itself, so that -EOPNOTSUPP can be ignored.
> 
> Next, this patch set removes the limitation of creating only two xattrs,
> one by an active LSM and another by EVM. This patch set extends the
> reservation mechanism of the LSM infrastructure, to allow each LSM to
> request one or multiple xattrs. While this could potentially lead to
> reaching the filesystem limits of number/size of the xattrs, it seems not
> an issue that need to be solved by the LSM infrastructure but by the
> filesystems themselves. Currently, if the limit is reached, the only
> workaround would be to use fewer LSMs.
> 
> The reservation mechanism concept makes it very easy for LSMs to position
> themselves correctly in the xattr array, as the LSM infrastructure at
> initialization time changes the number of xattrs requested by each LSM with
> an offset. LSMs can just take that offset as the starting index in the
> xattr array and fill the next slots depending on how many xattrs they
> requested.
> 
> However, while this concept is intuitive, it needs extra care. While for
> security blobs (the main reason of the reservation mechanism) it is not
> relevant for an LSM if other LSMs filled their portion, it matters for
> xattrs, as both EVM and initxattrs() callbacks scan the entire array until
> a terminator (xattr with NULL name). If an LSM did not provide an xattr,
> which could happen if it is loaded but not initialized, consumers of the
> xattr array would stop prematurely.
> 
> This patch set avoids this problem by compacting the xattr array each time
> after an LSM executed its implementation of the inode_init_security hook.
> It needs to be done after each LSM, and not after all, since there might be
> LSMs scanning that xattr array too. Compacting the array after all LSMs
> would be too late.
> 
> Finally, this patch set modifies the evm_inode_init_security() definition
> to be compatible with the inode_init_security hook definition and adds
> support for scanning the whole xattr array and for calculating the HMAC
> on all xattrs provided by LSMs.
> 
> 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, one providing multiple xattrs
> and another providing an xattr but in a disabled state). The patch is not
> included in this set but it is available here:
> 
>
https://github.com/robertosassu/linux/commit/311b83a98757915cc3ccb363f545578e7c38df54
> 
> The test, added to ima-evm-utils, is available here:
> 
>
https://github.com/robertosassu/ima-evm-utils/blob/evm-multiple-lsms-v8-devel-v2/tests/evm_multiple_lsms.test
> 
> The test takes a UML kernel built by Github Actions and launches it several
> times, each time with a different combination of LSMs and filesystems
(ext4,
> reiserfs, ocfs2). After boot, it first checks that there is an xattr for
each
> LSM providing it (for reiserfs and ocfs2 just the first LSM), and then (for
> ext4) 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://github.com/robertosassu/ima-evm-utils/actions/runs/4403223954/jobs/7722101662
> 
> The patch set has been tested with both the SElinux and Smack test suites.
> Below, there is the summary of the test results:
> 
> SELinux Test Suite result (without patches):
> All tests successful.
> Files=76, Tests=1343, 255 wallclock secs ( 0.51 usr  0.19 sys +  6.30 cusr
58.15 csys = 65.15 CPU)
> Result: PASS
> 
> SELinux Test Suite result (with patches):
> All tests successful.
> Files=76, Tests=1343, 258 wallclock secs ( 0.49 usr  0.21 sys +  6.46 cusr
59.27 csys = 66.43 CPU)
> Result: PASS
Side note:

https://github.com/SELinuxProject/selinux-testsuite/blob/master/tests/mmap/test#L51

This test fails if CONFIG_LSM_MMAP_MIN_ADDR=0

Roberto
> Smack Test Suite result (without patches):
> 95 Passed, 0 Failed, 100% Success rate
> 
> Smack Test Suite result (with patches):
> 95 Passed, 0 Failed, 100% Success rate
> 
> Changelog
> 
> v7:
> - Add a patch dependency comment in patch 1 (suggested by Mimi)
> - Restore check of -EOPNOTSUPP status in ocfs2_mknod() and ocfs2_symlink()
>   (reported by Mimi)
> - Add explanation in evm_inode_init_security() why walking through the
>   xattrs array is safe (suggested by Mimi)
> - Document the lbs_xattr field of struct lsm_blob_sizes (suggested by
>   Casey)
> - Move documentation changes of the inode_init_security hook to security.c,
>   after LSM documentation reorganization by Paul
> - Use attributes in plural form in the description of the xattrs parameter
>   of smack_inode_init_security()
> - Check xattr name instead of xattr value in evm_inode_init_security(),
>   for consistency with evm_init_hmac(); equivalent, since
>   security_check_compact_filled_xattrs() rejects xattrs with xattr name
>   NULL and value not NULL, and viceversa
> 
> v6:
> - Add a comment in Smack to introduce its xattrs (suggested by Casey)
> - Document the overloaded meaning of -EOPNOTSUPP in
>   security_inode_init_security() (suggested by Mimi)
> 
> v5:
> - Modify the cover letter to explain that the goal of this patch set is
>   supporting multiple per LSM xattrs in EVM, and not moving IMA and EVM to
>   the LSM infrastructure (suggested by Mimi)
> - Remove references in the patches description about moving IMA and EVM
>   to the LSM infrastructure (suggested by Mimi)
> - Explain that the additional EVM invocation due to the switch to
>   security_inode_init_security() will not cause the EVM xattr to be added
>   (suggested by Mimi)
> 
> v4:
> - Remove patch to call reiserfs_security_free(), already queued
> - Switch ocfs2 and reiserfs to security_inode_init_security() (suggested by
>   Mimi)
> - Remove security_old_inode_init_security() (suggested by Paul)
> - Rename security_check_compact_xattrs() to
>   security_check_compact_filled_xattrs() and add function description
>   (suggested by Mimi)
> - Rename checked_xattrs parameter of security_check_compact_filled_xattrs()
>   to num_filled_xattrs (suggested by Mimi)
> - Rename cur_xattrs variable in security_inode_init_security() to
>   num_filled_xattrs (suggested by Mimi)
> 
> v3:
> - Don't free the xattr name in reiserfs_security_free()
> - Don't include fs_data parameter in inode_init_security hook
> - Don't change evm_inode_init_security(), as it will be removed if EVM
is
>   stacked
> - Fix inode_init_security hook documentation
> - Drop lsm_find_xattr_slot(), use simple xattr reservation mechanism and
>   introduce security_check_compact_xattrs() to compact the xattr array
> - Don't allocate xattr array if LSMs didn't reserve any xattr
> - Return zero if initxattrs() is not provided to
>   security_inode_init_security(), -EOPNOTSUPP if value is not provided to
>   security_old_inode_init_security()
> - Request LSMs to fill xattrs if only value (not the triple) is provided to
>   security_old_inode_init_security(), to avoid unnecessary memory
>   allocation
> 
> 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: Switch to security_inode_init_security()
>   ocfs2: Switch to security_inode_init_security()
>   security: Remove security_old_inode_init_security()
>   security: Allow all LSMs to provide xattrs for inode_init_security
>     hook
>   evm: Align evm_inode_init_security() definition with LSM
>     infrastructure
>   evm: Support multiple LSMs providing an xattr
> 
>  fs/ocfs2/namei.c                    |   2 +
>  fs/ocfs2/xattr.c                    |  30 ++++++-
>  fs/reiserfs/xattr_security.c        |  23 +++--
>  include/linux/evm.h                 |  12 +--
>  include/linux/lsm_hook_defs.h       |   3 +-
>  include/linux/lsm_hooks.h           |   1 +
>  include/linux/security.h            |  12 ---
>  security/integrity/evm/evm.h        |   2 +
>  security/integrity/evm/evm_crypto.c |   9 +-
>  security/integrity/evm/evm_main.c   |  33 +++++--
>  security/security.c                 | 131 +++++++++++++++++++++-------
>  security/selinux/hooks.c            |  19 ++--
>  security/smack/smack_lsm.c          |  33 ++++---
>  13 files changed, 224 insertions(+), 86 deletions(-)
>

Possibly Parallel Threads

Search for more apparently analagous threads

Ocfs2 devel - Mar 2023 - [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes

[Ocfs2-devel] [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes

[Ocfs2-devel] [PATCH v8 1/6] reiserfs: Switch to security_inode_init_security()

[Ocfs2-devel] [PATCH v8 2/6] ocfs2: Switch to security_inode_init_security()

[Ocfs2-devel] [PATCH v8 3/6] security: Remove security_old_inode_init_security()

[Ocfs2-devel] [PATCH v8 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook

[Ocfs2-devel] [PATCH v8 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure

[Ocfs2-devel] [PATCH v8 6/6] evm: Support multiple LSMs providing an xattr

[Ocfs2-devel] [PATCH v8 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes

Possibly Parallel Threads