[PATCH] io_uring: Fix LINK_TIMEOUT checks

[Pavel Begunkov <asml.silence@gmail.com>]

If IORING_OP_LINK_TIMEOUT request is a head of a link or an individual
request, pass it further through the submission path, where it will
eventually fail in __io_submit_sqe(). So respecting links and drains.

The case, which is really need to be checked, is if a
IORING_OP_LINK_TIMEOUT request is 3rd or later in a link, that is
invalid from the user API perspective (judging by the code). Moreover,
put/free and friends will try to io_link_cancel_timeout() such request,
even though it wasn't initialised.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 55f8b1d378df..fd2ba35f53e3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2952,6 +2952,12 @@ static void io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state,
 	if (*link) {
 		struct io_kiocb *prev = *link;
 
+		if (unlikely(READ_ONCE(s->sqe->opcode) == IORING_OP_LINK_TIMEOUT
+			&& !list_empty(&prev->link_list))) {
+			ret = -EINVAL;
+			goto err_req;
+		}
+
 		sqe_copy = kmemdup(s->sqe, sizeof(*sqe_copy), GFP_KERNEL);
 		if (!sqe_copy) {
 			ret = -EAGAIN;
@@ -2966,10 +2972,6 @@ static void io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state,
 
 		INIT_LIST_HEAD(&req->link_list);
 		*link = req;
-	} else if (READ_ONCE(s->sqe->opcode) == IORING_OP_LINK_TIMEOUT) {
-		/* Only valid as a linked SQE */
-		ret = -EINVAL;
-		goto err_req;
 	} else {
 		io_queue_sqe(req);
 	}
-- 
2.24.0