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selinux: fall back to ref-walk if audit is required

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commit bda0be7ad9 ("security: make inode_follow_link RCU-walk aware")
passed down the rcu flag to the SELinux AVC, but failed to adjust the
test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY.
Previously, we only returned -ECHILD if generating an audit record with
LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission.
Move the handling of MAY_NOT_BLOCK to avc_audit() and its inlined
equivalent in selinux_inode_permission() immediately after we determine
that audit is required, and always fall back to ref-walk in this case.

Fixes: bda0be7ad9 ("security: make inode_follow_link RCU-walk aware")
Reported-by: Will Deacon <will@kernel.org>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Stephen Smalley
2019-11-22 12:22:45 -05:00
committed by Paul Moore
parent 1a37079c23
commit 0188d5c025
3 changed files with 17 additions and 26 deletions
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24
security/selinux/avc.c
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@@ -424,7 +424,7 @@ static inline int avc_xperms_audit(struct selinux_state *state,
if (likely(!audited))
return 0;
return slow_avc_audit(state, ssid, tsid, tclass, requested,
audited, denied, result, ad, 0);
audited, denied, result, ad);
}
static void avc_node_free(struct rcu_head *rhead)
@@ -758,8 +758,7 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
noinline int slow_avc_audit(struct selinux_state *state,
u32 ssid, u32 tsid, u16 tclass,
u32 requested, u32 audited, u32 denied, int result,
struct common_audit_data *a,
unsigned int flags)
struct common_audit_data *a)
{
struct common_audit_data stack_data;
struct selinux_audit_data sad;
@@ -772,17 +771,6 @@ noinline int slow_avc_audit(struct selinux_state *state,
a->type = LSM_AUDIT_DATA_NONE;
}
/*
* When in a RCU walk do the audit on the RCU retry. This is because
* the collection of the dname in an inode audit message is not RCU
* safe. Note this may drop some audits when the situation changes
* during retry. However this is logically just as if the operation
* happened a little later.
*/
if ((a->type == LSM_AUDIT_DATA_INODE) &&
(flags & MAY_NOT_BLOCK))
return -ECHILD;
sad.tclass = tclass;
sad.requested = requested;
sad.ssid = ssid;
@@ -855,16 +843,14 @@ static int avc_update_node(struct selinux_avc *avc,
/*
* If we are in a non-blocking code path, e.g. VFS RCU walk,
* then we must not add permissions to a cache entry
* because we cannot safely audit the denial. Otherwise,
* because we will not audit the denial. Otherwise,
* during the subsequent blocking retry (e.g. VFS ref walk), we
* will find the permissions already granted in the cache entry
* and won't audit anything at all, leading to silent denials in
* permissive mode that only appear when in enforcing mode.
*
* See the corresponding handling in slow_avc_audit(), and the
* logic in selinux_inode_follow_link and selinux_inode_permission
* for the VFS MAY_NOT_BLOCK flag, which is transliterated into
* AVC_NONBLOCKING for avc_has_perm_noaudit().
* See the corresponding handling of MAY_NOT_BLOCK in avc_audit()
* and selinux_inode_permission().
*/
if (flags & AVC_NONBLOCKING)
return 0;