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/ss/services.c

@@ -2217,10 +2217,11 @@ out_unlock:
 		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();