mm: reorder can_do_mlock to fix audit denial

A userspace call to mmap(MAP_LOCKED) may result in the successful locking
of memory while also producing a confusing audit log denial.  can_do_mlock
checks capable and rlimit.  If either of these return positive
can_do_mlock returns true.  The capable check leads to an LSM hook used by
apparmour and selinux which produce the audit denial.  Reordering so
rlimit is checked first eliminates the denial on success, only recording a
denial when the lock is unsuccessful as a result of the denial.

Signed-off-by: Jeff Vander Stoep <[email protected]>
Acked-by: Nick Kralevich <[email protected]>
Cc: Jeff Vander Stoep <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Paul Cassella <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/mlock.c

@@ -26,10 +26,10 @@
 
 int can_do_mlock(void)
 {
-	if (capable(CAP_IPC_LOCK))
-		return 1;
 	if (rlimit(RLIMIT_MEMLOCK) != 0)
 		return 1;
+	if (capable(CAP_IPC_LOCK))
+		return 1;
 	return 0;
 }
 EXPORT_SYMBOL(can_do_mlock);