io_uring/zcrx: fix user_struct uaf

io_free_rbuf_ring() usees a struct user_struct, which
io_zcrx_ifq_free() puts it down before destroying the ring.

Cc: [email protected]
Fixes: 5c68645 ("io_uring/zcrx: add user_struct and mm_struct to io_zcrx_ifq")
Signed-off-by: Pavel Begunkov <[email protected]>
Link: https://patch.msgid.link/e560ae00960d27a810522a7efc0e201c82dff351.1776760917.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <[email protected]>

Author: isilence

io_uring/zcrx.c

@@ -579,13 +579,13 @@ static void io_zcrx_ifq_free(struct io_zcrx_ifq *ifq)
 
 	if (ifq->area)
 		io_zcrx_free_area(ifq, ifq->area);
-	free_uid(ifq->user);
 	if (ifq->mm_account)
 		mmdrop(ifq->mm_account);
 	if (ifq->dev)
 		put_device(ifq->dev);
 
 	io_free_rbuf_ring(ifq);
+	free_uid(ifq->user);
 	mutex_destroy(&ifq->pp_lock);
 	kfree(ifq);
 }