selinux: fix avdcache auditing

The per-task avdcache was incorrectly saving and reusing the
audited vector computed by avc_audit_required() rather than
recomputing based on the currently requested permissions and
distinguishing the denied versus allowed cases. As a result,
some permission checks were not being audited, e.g.
directory write checks after a previously cached directory
search check.

Cc: stable@vger.kernel.org
Fixes: dde3a5d ("selinux: move avdcache to per-task security struct")
Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
[PM: line wrap tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: stephensmalley

security/selinux/hooks.c

@@ -3209,15 +3209,13 @@ static inline int task_avdcache_search(struct task_security_struct *tsec,
  * @tsec: the task's security state
  * @isec: the inode associated with the cache entry
  * @avd: the AVD to cache
- * @audited: the permission audit bitmask to cache
  *
- * Update the AVD cache in @tsec with the @avdc and @audited info associated
+ * Update the AVD cache in @tsec with the @avd info associated
  * with @isec.
  */
 static inline void task_avdcache_update(struct task_security_struct *tsec,
 					struct inode_security_struct *isec,
-					struct av_decision *avd,
-					u32 audited)
+					struct av_decision *avd)
 {
 	int spot;
 
@@ -3229,9 +3227,7 @@ static inline void task_avdcache_update(struct task_security_struct *tsec,
 	spot = (tsec->avdcache.dir_spot + 1) & (TSEC_AVDC_DIR_SIZE - 1);
 	tsec->avdcache.dir_spot = spot;
 	tsec->avdcache.dir[spot].isid = isec->sid;
-	tsec->avdcache.dir[spot].audited = audited;
-	tsec->avdcache.dir[spot].allowed = avd->allowed;
-	tsec->avdcache.dir[spot].permissive = avd->flags & AVD_FLAGS_PERMISSIVE;
+	tsec->avdcache.dir[spot].avd = *avd;
 	tsec->avdcache.permissive_neveraudit =
 		(avd->flags == (AVD_FLAGS_PERMISSIVE|AVD_FLAGS_NEVERAUDIT));
 }
@@ -3252,6 +3248,7 @@ static int selinux_inode_permission(struct inode *inode, int requested)
 	struct task_security_struct *tsec;
 	struct inode_security_struct *isec;
 	struct avdc_entry *avdc;
+	struct av_decision avd, *avdp = &avd;
 	int rc, rc2;
 	u32 audited, denied;
 
@@ -3273,23 +3270,21 @@ static int selinux_inode_permission(struct inode *inode, int requested)
 	rc = task_avdcache_search(tsec, isec, &avdc);
 	if (likely(!rc)) {
 		/* Cache hit. */
-		audited = perms & avdc->audited;
-		denied = perms & ~avdc->allowed;
-		if (unlikely(denied && enforcing_enabled() &&
-			     !avdc->permissive))
+		avdp = &avdc->avd;
+		denied = perms & ~avdp->allowed;
+		if (unlikely(denied) && enforcing_enabled() &&
+			!(avdp->flags & AVD_FLAGS_PERMISSIVE))
 			rc = -EACCES;
 	} else {
-		struct av_decision avd;
-
 		/* Cache miss. */
 		rc = avc_has_perm_noaudit(sid, isec->sid, isec->sclass,
-					  perms, 0, &avd);
-		audited = avc_audit_required(perms, &avd, rc,
-			(requested & MAY_ACCESS) ? FILE__AUDIT_ACCESS : 0,
-			&denied);
-		task_avdcache_update(tsec, isec, &avd, audited);
+					  perms, 0, avdp);
+		task_avdcache_update(tsec, isec, avdp);
 	}
 
+	audited = avc_audit_required(perms, avdp, rc,
+				     (requested & MAY_ACCESS) ?
+				     FILE__AUDIT_ACCESS : 0, &denied);
 	if (likely(!audited))
 		return rc;
 

security/selinux/include/objsec.h

@@ -32,9 +32,7 @@
 
 struct avdc_entry {
 	u32 isid; /* inode SID */
-	u32 allowed; /* allowed permission bitmask */
-	u32 audited; /* audited permission bitmask */
-	bool permissive; /* AVC permissive flag */
+	struct av_decision avd; /* av decision */
 };
 
 struct cred_security_struct {