[PATCH 6.1 110/127] io_uring: annotate offset timeout races

Greg Kroah-Hartman
2023-08-09T10:56:17Z

From: Pavel Begunkov <asml.silence@gmail.com>

commit 5498bf28d8f2bd63a46ad40f4427518615fb793f upstream.

It's racy to read ->cached_cq_tail without taking proper measures
(usually grabbing ->completion_lock) as timeout requests with CQE
offsets do, however they have never had a good semantics for from
when they start counting. Annotate racy reads with data_race().

Reported-by: syzbot+cb265db2f3f3468ef436@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4de3685e185832a92a572df2be2c735d2e21a83d.1684506056.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/timeout.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -545,7 +545,7 @@ int io_timeout(struct io_kiocb *req, uns
goto add;
}

- tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
+ tail = data_race(ctx->cached_cq_tail) - atomic_read(&ctx->cq_timeouts);
timeout->target_seq = tail + off;

/* Update the last seq here in case io_flush_timeouts() hasn't.