[PATCH stable-5.15 5/5] io_uring/rw: fix unexpected link breakage

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[ upstream commit bf68b5b34311ee57ed40749a1257a30b46127556 ]

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@xxxxxxxxxxxxxxx
Reported-and-Tested-by: Beld Zhang <beldzhang@xxxxxxxxx>
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Link: https://lore.kernel.org/r/3a1088440c7be98e5800267af922a67da0ef9f13.1664235732.git.asml.silence@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/io_uring.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f667197c8bb9..837dd96228b2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3606,6 +3606,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 			return -EAGAIN;
 		}
 
+		req->result = iov_iter_count(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
-- 
2.38.0




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