[PATCH 5.19 011/717] io_uring/rw: fix unexpected link breakage

Greg Kroah-Hartman
2022-10-22T07:34:15Z

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

commit bf68b5b34311ee57ed40749a1257a30b46127556 upstream.

req->cqe.res is set in io_read() to the amount of bytes left to be done,
which is used to figure out whether to fail a read or not. However,
io_read() may do another without returning, and we stash the previous
value into ->bytes_done but forget to update cqe.res. Then we ask a read
to do strictly less than cqe.res but expect the return to be exactly
cqe.res.

Fix the bug by updating cqe.res for retries.

Cc: stable@vger.kernel.org
Reported-and-Tested-by: Beld Zhang <beldzhang@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3a1088440c7be98e5800267af922a67da0ef9f13.1664235732.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/io_uring.c | 1 +
1 file changed, 1 insertion(+)

--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -4215,6 +4215,7 @@ static int io_read(struct io_kiocb *req,
return -EAGAIN;
}

+ req->cqe.res = iov_iter_count(&s->iter);
/*
* Now retry read with the IOCB_WAITQ parts set in the iocb. If
* we get -EIOCBQUEUED, then we'll get a notification when the