io_uring: fortify tctx/io_wq cleanup

We don't want anyone poking into tctx->io_wq awhile it's being destroyed
by io_wq_put_and_exit(), and even though it shouldn't even happen, if
buggy would be preferable to get a NULL-deref instead of subtle delayed
failure or UAF.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/827b021de17926fd807610b3e53a5a5fa8530856.1621513214.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 89ec10471b30b669acce973f19a4dbba82efed69..5f82954004f613ee95a6cf08acc62af8dfcde2a6 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9035,15 +9035,15 @@ static void io_uring_del_task_file(unsigned long index)
 
 static void io_uring_clean_tctx(struct io_uring_task *tctx)
 {
+       struct io_wq *wq = tctx->io_wq;
        struct io_tctx_node *node;
        unsigned long index;
 
+       tctx->io_wq = NULL;
        xa_for_each(&tctx->xa, index, node)
                io_uring_del_task_file(index);
-       if (tctx->io_wq) {
-               io_wq_put_and_exit(tctx->io_wq);
-               tctx->io_wq = NULL;
-       }
+       if (wq)
+               io_wq_put_and_exit(wq);
 }
 
 static s64 tctx_inflight(struct io_uring_task *tctx, bool tracked)