selinux: don't pass in NULL avd to avc_has_perm_noaudit

Right now security_get_user_sids() will pass in a NULL avd pointer to
avc_has_perm_noaudit(), which then forces that function to have a dummy
entry for that case and just generally test it.

Don't do it.  The normal callers all pass a real avd pointer, and this
helper function is incredibly hot.  So don't make avc_has_perm_noaudit()
do conditional stuff that isn't needed for the common case.

This also avoids some duplicated stack space.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/selinux/avc.c

@@ -752,10 +752,9 @@ int avc_ss_reset(u32 seqno)
 int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 			 u16 tclass, u32 requested,
 			 unsigned flags,
-			 struct av_decision *in_avd)
+			 struct av_decision *avd)
 {
 	struct avc_node *node;
-	struct av_decision avd_entry, *avd;
 	int rc = 0;
 	u32 denied;
 
@@ -766,18 +765,11 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 	node = avc_lookup(ssid, tsid, tclass);
 	if (unlikely(!node)) {
 		rcu_read_unlock();
-
-		if (in_avd)
-			avd = in_avd;
-		else
-			avd = &avd_entry;
-
 		security_compute_av(ssid, tsid, tclass, avd);
 		rcu_read_lock();
 		node = avc_insert(ssid, tsid, tclass, avd);
 	} else {
-		if (in_avd)
-			memcpy(in_avd, &node->ae.avd, sizeof(*in_avd));
+		memcpy(avd, &node->ae.avd, sizeof(*avd));
 		avd = &node->ae.avd;
 	}
 

security/selinux/ss/services.c

@@ -2217,10 +2217,11 @@ int security_get_user_sids(u32 fromsid,
 		goto out;
 	}
 	for (i = 0, j = 0; i < mynel; i++) {
+		struct av_decision dummy_avd;
 		rc = avc_has_perm_noaudit(fromsid, mysids[i],
 					  SECCLASS_PROCESS, /* kernel value */
 					  PROCESS__TRANSITION, AVC_STRICT,
-					  NULL);
+					  &dummy_avd);
 		if (!rc)
 			mysids2[j++] = mysids[i];
 		cond_resched();