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Fri, 01 May 2026 15:52:53 -0700 (PDT) From: Kai Aizen To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, axboe@kernel.dk, io-uring@vger.kernel.org Subject: [PATCH 6.6.y] io_uring/poll: fix multishot recv missing EOF on wakeup race Date: Sat, 2 May 2026 01:51:55 +0300 Message-ID: <20260501225250.90152-2-kai.aizen.dev@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260501225250.90152-1-kai.aizen.dev@gmail.com> References: <20260501225250.90152-1-kai.aizen.dev@gmail.com> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jens Axboe [ Upstream commit a68ed2df72131447d131531a08fe4dfcf4fa4653 ] When a socket send and shutdown() happen back-to-back, both fire wake-ups before the receiver's task_work has a chance to run. The first wake gets poll ownership (poll_refs=1), and the second bumps it to 2. When io_poll_check_events() runs, it calls io_poll_issue() which does a recv that reads the data and returns IOU_RETRY. The loop then drains all accumulated refs (atomic_sub_return(2) -> 0) and exits, even though only the first event was consumed. Since the shutdown is a persistent state change, no further wakeups will happen, and the multishot recv can hang forever. Check specifically for HUP in the poll loop, and ensure that another loop is done to check for status if more than a single poll activation is pending. This ensures we don't lose the shutdown event. Backport notes for linux-6.6.y: - In 6.6.y the do-while masks v in the while-condition itself (`atomic_sub_return(v & IO_POLL_REF_MASK, ...) & IO_POLL_REF_MASK`), so v can carry IO_POLL_RETRY_FLAG / IO_POLL_CANCEL_FLAG bits when we reach the multishot branch. The HUP check therefore compares `(v & IO_POLL_REF_MASK) != 1` rather than the upstream `v != 1`, to avoid reacting to flag bits. - io_poll_issue takes `ts` (struct io_tw_state *) here. CVE: CVE-2026-23473 Cc: stable@vger.kernel.org # 6.6.y Fixes: dbc2564cfe0f ("io_uring: let fast poll support multishot") Reported-by: Francis Brosseau Link: https://github.com/axboe/liburing/issues/1549 Signed-off-by: Jens Axboe [backport for linux-6.6.y, verified 2026-05-01] --- io_uring/poll.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/io_uring/poll.c b/io_uring/poll.c --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -321,7 +321,13 @@ static int io_poll_check_events(struct io_kiocb *req, struct io_tw_state *ts) return IOU_POLL_REMOVE_POLL_USE_RES; } } else { - int ret = io_poll_issue(req, ts); + int ret; + + /* multiple refs and HUP, ensure we loop once more */ + if ((req->cqe.res & (POLLHUP | POLLRDHUP)) && + (v & IO_POLL_REF_MASK) != 1) + v--; + ret = io_poll_issue(req, ts); if (ret == IOU_STOP_MULTISHOT) return IOU_POLL_REMOVE_POLL_USE_RES; else if (ret == IOU_REQUEUE) -- 2.43.0