io_uring/net: fix accept multishot handling

commit f6a89bf upstream.

REQ_F_APOLL_MULTISHOT doesn't guarantee it's executed from the multishot
context, so a multishot accept may get executed inline, fail
io_req_post_cqe(), and ask the core code to kill the request with
-ECANCELED by returning IOU_STOP_MULTISHOT even when a socket has been
accepted and installed.

Cc: stable@vger.kernel.org
Fixes: 390ed29 ("io_uring: add IORING_ACCEPT_MULTISHOT for accept")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/51c6deb01feaa78b08565ca8f24843c017f5bc80.1740331076.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: isilence

io_uring/net.c

@@ -1616,6 +1616,8 @@ int io_accept(struct io_kiocb *req, unsigned int issue_flags)
 	}
 
 	io_req_set_res(req, ret, cflags);
+	if (!(issue_flags & IO_URING_F_MULTISHOT))
+		return IOU_OK;
 	return IOU_STOP_MULTISHOT;
 }