From: Lukas Magel <lukas.magel@xxxxxxxxxx> With patch [1], isotp_poll was updated to also queue the poller in the so->wait queue, which is used for send state changes. Since the queue now also contains polling tasks that are not interested in sending, the queue fill state can no longer be used as an indication of send readiness. As a consequence, nonblocking writes can lead to a race and lock-up of the socket if there is a second task polling the socket in parallel. With this patch, isotp_sendmsg does not consult wq_has_sleepers but instead tries to atomically set so->tx.state and waits on so->wait if it is unable to do so. This behavior is in alignment with isotp_poll, which also checks so->tx.state to determine send readiness. V2: - Revert direct exit to goto err_event_drop [1] https://lore.kernel.org/all/20230331125511.372783-1-michal.sojka@xxxxxxx Reported-by: Maxime Jayat <maxime.jayat@xxxxxxxxxxxxxxxxx> Closes: https://lore.kernel.org/linux-can/11328958-453f-447f-9af8-3b5824dfb041@xxxxxxxx/ Signed-off-by: Lukas Magel <lukas.magel@xxxxxxxxxx> Reviewed-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx> Fixes: 79e19fa79cb5 ("can: isotp: isotp_ops: fix poll() to not report false EPOLLOUT events") Link: https://github.com/pylessard/python-udsoncan/issues/178#issuecomment-1743786590 Link: https://lore.kernel.org/all/20230827092205.7908-1-lukas.magel@xxxxxxxxxx Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> --- net/can/isotp.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-) diff --git a/net/can/isotp.c b/net/can/isotp.c index f02b5d3e4733..d1c6f206f429 100644 --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -948,21 +948,18 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size) if (!so->bound || so->tx.state == ISOTP_SHUTDOWN) return -EADDRNOTAVAIL; -wait_free_buffer: - /* we do not support multiple buffers - for now */ - if (wq_has_sleeper(&so->wait) && (msg->msg_flags & MSG_DONTWAIT)) - return -EAGAIN; + while (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE) { + /* we do not support multiple buffers - for now */ + if (msg->msg_flags & MSG_DONTWAIT) + return -EAGAIN; - /* wait for complete transmission of current pdu */ - err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); - if (err) - goto err_event_drop; - - if (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE) { if (so->tx.state == ISOTP_SHUTDOWN) return -EADDRNOTAVAIL; - goto wait_free_buffer; + /* wait for complete transmission of current pdu */ + err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); + if (err) + goto err_event_drop; } /* PDU size > default => try max_pdu_size */ base-commit: d0f95894fda7d4f895b29c1097f92d7fee278cb2 -- 2.42.0
