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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
View File

@ -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;

11
security/selinux/hooks.c
View File

@ -3011,8 +3011,7 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
static noinline int audit_inode_permission(struct inode *inode,
u32 perms, u32 audited, u32 denied,
int result,
unsigned flags)
int result)
{
struct common_audit_data ad;
struct inode_security_struct *isec = selinux_inode(inode);
@ -3023,7 +3022,7 @@ static noinline int audit_inode_permission(struct inode *inode,
rc = slow_avc_audit(&selinux_state,
current_sid(), isec->sid, isec->sclass, perms,
audited, denied, result, &ad, flags);
audited, denied, result, &ad);
if (rc)
return rc;
return 0;
@ -3070,7 +3069,11 @@ static int selinux_inode_permission(struct inode *inode, int mask)
if (likely(!audited))
return rc;
rc2 = audit_inode_permission(inode, perms, audited, denied, rc, flags);
/* fall back to ref-walk if we have to generate audit */
if (flags & MAY_NOT_BLOCK)
return -ECHILD;
rc2 = audit_inode_permission(inode, perms, audited, denied, rc);
if (rc2)
return rc2;
return rc;

8
security/selinux/include/avc.h
View File

@ -100,8 +100,7 @@ static inline u32 avc_audit_required(u32 requested,
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 flags);
struct common_audit_data *a);
/**
* avc_audit - Audit the granting or denial of permissions.
@ -135,9 +134,12 @@ static inline int avc_audit(struct selinux_state *state,
audited = avc_audit_required(requested, avd, result, 0, &denied);
if (likely(!audited))
return 0;
/* fall back to ref-walk if we have to generate audit */
if (flags & MAY_NOT_BLOCK)
return -ECHILD;
return slow_avc_audit(state, ssid, tsid, tclass,
requested, audited, denied, result,
a, flags);
a);
}
#define AVC_STRICT 1 /* Ignore permissive mode. */