From: Oliver Hartkopp socketcan@hartkopp.net

As discussed with Dae R. Jeong and Hillf Danton here [1] the sendmsg() function in isotp.c might get into a race condition when restoring the former tx.state from the old_state.

Remove the old_state concept and implement proper locking for the ISOTP_IDLE transitions in isotp_sendmsg(), inspired by a simplification idea from Hillf Danton.

Introduce a new tx.state ISOTP_SHUTDOWN and use the same locking mechanism from isotp_release() which resolves a potential race between isotp_sendsmg() and isotp_release().

[1] https://lore.kernel.org/linux-can/ZB%2F93xJxq%2FBUqAgG@dragonet

v1: https://lore.kernel.org/all/20230331102114.15164-1-socketcan@hartkopp.net v2: https://lore.kernel.org/all/20230331123600.3550-1-socketcan@hartkopp.net take care of signal interrupts for wait_event_interruptible() in isotp_release() v3: https://lore.kernel.org/all/20230331130654.9886-1-socketcan@hartkopp.net take care of signal interrupts for wait_event_interruptible() in isotp_sendmsg() in the wait_tx_done case v4: https://lore.kernel.org/all/20230331131935.21465-1-socketcan@hartkopp.net take care of signal interrupts for wait_event_interruptible() in isotp_sendmsg() in ALL cases

Cc: Dae R. Jeong threeearcat@gmail.com Cc: Hillf Danton hdanton@sina.com Signed-off-by: Oliver Hartkopp socketcan@hartkopp.net Fixes: 4f027cba8216 ("can: isotp: split tx timer into transmission and timeout") Link: https://lore.kernel.org/all/20230331131935.21465-1-socketcan@hartkopp.net Cc: stable@vger.kernel.org [mkl: rephrase commit message] Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- net/can/isotp.c | 55 ++++++++++++++++++++++++++++--------------------- 1 file changed, 31 insertions(+), 24 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c index 281b7766c54e..5761d4ab839d 100644 --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -119,7 +119,8 @@ enum { ISOTP_WAIT_FIRST_FC, ISOTP_WAIT_FC, ISOTP_WAIT_DATA, - ISOTP_SENDING + ISOTP_SENDING, + ISOTP_SHUTDOWN, };

struct tpcon { @@ -880,8 +881,8 @@ static enum hrtimer_restart isotp_tx_timer_handler(struct hrtimer *hrtimer) txtimer); struct sock *sk = &so->sk;

- /* don't handle timeouts in IDLE state */ - if (so->tx.state == ISOTP_IDLE) + /* don't handle timeouts in IDLE or SHUTDOWN state */ + if (so->tx.state == ISOTP_IDLE || so->tx.state == ISOTP_SHUTDOWN) return HRTIMER_NORESTART;

/* we did not get any flow control or echo frame in time */ @@ -918,7 +919,6 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size) { struct sock *sk = sock->sk; struct isotp_sock *so = isotp_sk(sk); - u32 old_state = so->tx.state; struct sk_buff *skb; struct net_device *dev; struct canfd_frame *cf; @@ -928,23 +928,24 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size) int off; int err;

- if (!so->bound) + if (!so->bound || so->tx.state == ISOTP_SHUTDOWN) return -EADDRNOTAVAIL;

+wait_free_buffer: /* we do not support multiple buffers - for now */ - if (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE || - wq_has_sleeper(&so->wait)) { - if (msg->msg_flags & MSG_DONTWAIT) { - err = -EAGAIN; - goto err_out; - } + if (wq_has_sleeper(&so->wait) && (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_out; + /* wait for complete transmission of current pdu */ + err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); + if (err) + goto err_event_drop;

- so->tx.state = ISOTP_SENDING; + if (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE) { + if (so->tx.state == ISOTP_SHUTDOWN) + return -EADDRNOTAVAIL; + + goto wait_free_buffer; }

if (!size || size > MAX_MSG_LENGTH) { @@ -1074,7 +1075,9 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)

if (wait_tx_done) { /* wait for complete transmission of current pdu */ - wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); + err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); + if (err) + goto err_event_drop;

if (sk->sk_err) return -sk->sk_err; @@ -1082,13 +1085,15 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)

return size;

+err_event_drop: + /* got signal: force tx state machine to be idle */ + so->tx.state = ISOTP_IDLE; + hrtimer_cancel(&so->txfrtimer); + hrtimer_cancel(&so->txtimer); err_out_drop: /* drop this PDU and unlock a potential wait queue */ - old_state = ISOTP_IDLE; -err_out: - so->tx.state = old_state; - if (so->tx.state == ISOTP_IDLE) - wake_up_interruptible(&so->wait); + so->tx.state = ISOTP_IDLE; + wake_up_interruptible(&so->wait);

return err; } @@ -1150,10 +1155,12 @@ static int isotp_release(struct socket *sock) net = sock_net(sk);

/* wait for complete transmission of current pdu */ - wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE); + while (wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE) == 0 && + cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SHUTDOWN) != ISOTP_IDLE) + ;

/* force state machines to be idle also when a signal occurred */ - so->tx.state = ISOTP_IDLE; + so->tx.state = ISOTP_SHUTDOWN; so->rx.state = ISOTP_IDLE;

spin_lock(&isotp_notifier_lock);