[PATCH 5.10 backport] io_uring: only assign io_uring_enter() SQPOLL error in actual error case

[PATCH 5.10 backport] io_uring: only assign io_uring_enter() SQPOLL error in actual error case

[Pavel Begunkov]

From: Jens Axboe <axboe@kernel.dk>

[ upstream commit 21f965221e7c42609521342403e8fb91b8b3e76e ]

If an SQPOLL based ring is newly created and an application issues an
io_uring_enter(2) system call on it, then we can return a spurious
-EOWNERDEAD error. This happens because there's nothing to submit, and
if the caller doesn't specify any other action, the initial error
assignment of -EOWNERDEAD never gets overwritten. This causes us to
return it directly, even if it isn't valid.

Move the error assignment into the actual failure case instead.

Cc: stable@vger.kernel.org
Fixes: d9d05217cb69 ("io_uring: stop SQPOLL submit on creator's death")
Reported-by: Sherlock Holo sherlockya@gmail.com
Link: https://github.com/axboe/liburing/issues/413
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index ed641dca7957..8492b4e7c4d7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9078,9 +9078,10 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		io_cqring_overflow_flush(ctx, false, NULL, NULL);
 
-		ret = -EOWNERDEAD;
-		if (unlikely(ctx->sqo_dead))
+		if (unlikely(ctx->sqo_dead)) {
+			ret = -EOWNERDEAD;
 			goto out;
+		}
 		if (flags & IORING_ENTER_SQ_WAKEUP)
 			wake_up(&ctx->sq_data->wait);
 		if (flags & IORING_ENTER_SQ_WAIT) {
-- 
2.32.0

Re: [PATCH 5.10 backport] io_uring: only assign io_uring_enter() SQPOLL error in actual error case

[Sasha Levin]

On Tue, Aug 24, 2021 at 01:15:31PM +0100, Pavel Begunkov wrote:
>From: Jens Axboe <axboe@kernel.dk>
>
>[ upstream commit 21f965221e7c42609521342403e8fb91b8b3e76e ]
>
>If an SQPOLL based ring is newly created and an application issues an
>io_uring_enter(2) system call on it, then we can return a spurious
>-EOWNERDEAD error. This happens because there's nothing to submit, and
>if the caller doesn't specify any other action, the initial error
>assignment of -EOWNERDEAD never gets overwritten. This causes us to
>return it directly, even if it isn't valid.
>
>Move the error assignment into the actual failure case instead.
>
>Cc: stable@vger.kernel.org
>Fixes: d9d05217cb69 ("io_uring: stop SQPOLL submit on creator's death")
>Reported-by: Sherlock Holo sherlockya@gmail.com
>Link: https://github.com/axboe/liburing/issues/413
>Signed-off-by: Jens Axboe <axboe@kernel.dk>
>Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>

Queued up, thanks!

-- 
Thanks,
Sasha