From: Michal Sojka <michal.sojka@xxxxxxx> commit 79e19fa79cb5d5f1b3bf3e3ae24989ccb93c7b7b upstream. When using select()/poll()/epoll() with a non-blocking ISOTP socket to wait for when non-blocking write is possible, a false EPOLLOUT event is sometimes returned. This can happen at least after sending a message which must be split to multiple CAN frames. The reason is that isotp_sendmsg() returns -EAGAIN when tx.state is not equal to ISOTP_IDLE and this behavior is not reflected in datagram_poll(), which is used in isotp_ops. This is fixed by introducing ISOTP-specific poll function, which suppresses the EPOLLOUT events in that case. v2: https://lore.kernel.org/all/20230302092812.320643-1-michal.sojka@xxxxxxx v1: https://lore.kernel.org/all/20230224010659.48420-1-michal.sojka@xxxxxxx https://lore.kernel.org/all/b53a04a2-ba1f-3858-84c1-d3eb3301ae15@xxxxxxxxxxxx Signed-off-by: Michal Sojka <michal.sojka@xxxxxxx> Reported-by: Jakub Jira <jirajak2@xxxxxxxxxxx> Tested-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx> Acked-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx> Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol") Link: https://lore.kernel.org/all/20230331125511.372783-1-michal.sojka@xxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/can/isotp.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -1615,6 +1615,21 @@ static int isotp_init(struct sock *sk) return 0; } +static __poll_t isotp_poll(struct file *file, struct socket *sock, poll_table *wait) +{ + struct sock *sk = sock->sk; + struct isotp_sock *so = isotp_sk(sk); + + __poll_t mask = datagram_poll(file, sock, wait); + poll_wait(file, &so->wait, wait); + + /* Check for false positives due to TX state */ + if ((mask & EPOLLWRNORM) && (so->tx.state != ISOTP_IDLE)) + mask &= ~(EPOLLOUT | EPOLLWRNORM); + + return mask; +} + static int isotp_sock_no_ioctlcmd(struct socket *sock, unsigned int cmd, unsigned long arg) { @@ -1630,7 +1645,7 @@ static const struct proto_ops isotp_ops .socketpair = sock_no_socketpair, .accept = sock_no_accept, .getname = isotp_getname, - .poll = datagram_poll, + .poll = isotp_poll, .ioctl = isotp_sock_no_ioctlcmd, .gettstamp = sock_gettstamp, .listen = sock_no_listen,
