mqueue: fix kernel BUG caused by double free() on mq_open()

In case of aborting because we reach the maximum amount of memory which
can be allocated to message queues per user (RLIMIT_MSGQUEUE), we would
try to free the message area twice when bailing out: first by the error
handling code itself, and then later when cleaning up the inode through
delete_inode().
Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/mqueue.c

@@ -158,7 +158,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		 	    u->mq_bytes + mq_bytes >
 			    task_rlimit(p, RLIMIT_MSGQUEUE)) {
 				spin_unlock(&mq_lock);
-				kfree(info->messages);
+				/* mqueue_delete_inode() releases info->messages */
 				goto out_inode;
 			}
 			u->mq_bytes += mq_bytes;