SELinux: more careful use of avd in avc_has_perm_noaudit

we are often needlessly jumping through hoops when it comes to avd
entries in avc_has_perm_noaudit and we have extra initialization and memcpy
which are just wasting performance.  Try to clean the function up a bit.

This patch resulted in a 13% drop in time spent in avc_has_perm_noaudit in my
oprofile sampling of a tbench benchmark.
Signed-off-by: Eric Paris <eparis@redhat.com>
Reviewed-by: Paul Moore <paul.moore@hp.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/avc.c

@@ -350,12 +350,12 @@ static struct avc_node *avc_alloc_node(void)
 	return node;
 }
 
-static void avc_node_populate(struct avc_node *node, u32 ssid, u32 tsid, u16 tclass, struct avc_entry *ae)
+static void avc_node_populate(struct avc_node *node, u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
 {
 	node->ae.ssid = ssid;
 	node->ae.tsid = tsid;
 	node->ae.tclass = tclass;
-	memcpy(&node->ae.avd, &ae->avd, sizeof(node->ae.avd));
+	memcpy(&node->ae.avd, avd, sizeof(node->ae.avd));
 }
 
 static inline struct avc_node *avc_search_node(u32 ssid, u32 tsid, u16 tclass)
@@ -435,31 +435,31 @@ static int avc_latest_notif_update(int seqno, int is_insert)
  * @ssid: source security identifier
  * @tsid: target security identifier
  * @tclass: target security class
- * @ae: AVC entry
+ * @avd: resulting av decision
  *
  * Insert an AVC entry for the SID pair
  * (@ssid, @tsid) and class @tclass.
  * The access vectors and the sequence number are
  * normally provided by the security server in
  * response to a security_compute_av() call.  If the
- * sequence number @ae->avd.seqno is not less than the latest
+ * sequence number @avd->seqno is not less than the latest
  * revocation notification, then the function copies
  * the access vectors into a cache entry, returns
  * avc_node inserted. Otherwise, this function returns NULL.
  */
-static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct avc_entry *ae)
+static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
 {
 	struct avc_node *pos, *node = NULL;
 	int hvalue;
 	unsigned long flag;
 
-	if (avc_latest_notif_update(ae->avd.seqno, 1))
+	if (avc_latest_notif_update(avd->seqno, 1))
 		goto out;
 
 	node = avc_alloc_node();
 	if (node) {
 		hvalue = avc_hash(ssid, tsid, tclass);
-		avc_node_populate(node, ssid, tsid, tclass, ae);
+		avc_node_populate(node, ssid, tsid, tclass, avd);
 
 		spin_lock_irqsave(&avc_cache.slots_lock[hvalue], flag);
 		list_for_each_entry(pos, &avc_cache.slots[hvalue], list) {
@@ -772,7 +772,7 @@ static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
 	 * Copy and replace original node.
 	 */
 
-	avc_node_populate(node, ssid, tsid, tclass, &orig->ae);
+	avc_node_populate(node, ssid, tsid, tclass, &orig->ae.avd);
 
 	switch (event) {
 	case AVC_CALLBACK_GRANT:
@@ -864,10 +864,10 @@ int avc_ss_reset(u32 seqno)
 int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 			 u16 tclass, u32 requested,
 			 unsigned flags,
-			 struct av_decision *avd)
+			 struct av_decision *in_avd)
 {
 	struct avc_node *node;
-	struct avc_entry entry, *p_ae;
+	struct av_decision avd_entry, *avd;
 	int rc = 0;
 	u32 denied;
 
@@ -878,26 +878,31 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 	node = avc_lookup(ssid, tsid, tclass, requested);
 	if (!node) {
 		rcu_read_unlock();
-		rc = security_compute_av(ssid, tsid, tclass, requested, &entry.avd);
+
+		if (in_avd)
+			avd = in_avd;
+		else
+			avd = &avd_entry;
+
+		rc = security_compute_av(ssid, tsid, tclass, requested, avd);
 		if (rc)
 			goto out;
 		rcu_read_lock();
-		node = avc_insert(ssid, tsid, tclass, &entry);
+		node = avc_insert(ssid, tsid, tclass, avd);
+	} else {
+		if (in_avd)
+			memcpy(in_avd, &node->ae.avd, sizeof(*in_avd));
+		avd = &node->ae.avd;
 	}
 
-	p_ae = node ? &node->ae : &entry;
-
-	if (avd)
-		memcpy(avd, &p_ae->avd, sizeof(*avd));
-
-	denied = requested & ~(p_ae->avd.allowed);
+	denied = requested & ~(avd->allowed);
 
 	if (denied) {
 		if (flags & AVC_STRICT)
 			rc = -EACCES;
 		else if (!selinux_enforcing || security_permissive_sid(ssid))
 			avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,
-					tsid, tclass, p_ae->avd.seqno);
+					tsid, tclass, avd->seqno);
 		else
 			rc = -EACCES;
 	}