linux-kernel - [PATCH 6.0 013/862] io_uring/rw: fix unexpected link breakage

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Message-Id: <20221019083250.585656755@linuxfoundation.org>
Date:   Wed, 19 Oct 2022 10:21:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Beld Zhang <beldzhang@...il.com>
Subject: [PATCH 6.0 013/862] io_uring/rw: fix unexpected link breakage

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

--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -823,6 +823,7 @@ int io_read(struct io_kiocb *req, unsign
 			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