[PATCH 5.13 031/104] io_uring: fix io_prep_async_link locking

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

commit 44eff40a32e8f5228ae041006352e32638ad2368 upstream.

io_prep_async_link() may be called after arming a linked timeout,
automatically making it unsafe to traverse the linked list. Guard
with completion_lock if there was a linked timeout.

Cc: stable@xxxxxxxxxxxxxxx # 5.9+
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Link: https://lore.kernel.org/r/93f7c617e2b4f012a2a175b3dab6bc2f27cebc48.1627304436.git.asml.silence@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/io_uring.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1258,8 +1258,17 @@ static void io_prep_async_link(struct io
 {
 	struct io_kiocb *cur;
 
-	io_for_each_link(cur, req)
-		io_prep_async_work(cur);
+	if (req->flags & REQ_F_LINK_TIMEOUT) {
+		struct io_ring_ctx *ctx = req->ctx;
+
+		spin_lock_irq(&ctx->completion_lock);
+		io_for_each_link(cur, req)
+			io_prep_async_work(cur);
+		spin_unlock_irq(&ctx->completion_lock);
+	} else {
+		io_for_each_link(cur, req)
+			io_prep_async_work(cur);
+	}
 }
 
 static void io_queue_async_work(struct io_kiocb *req)