can: isotp: stop timeout monitoring when no first frame was sent

The first attempt to fix a the 'impossible' WARN_ON_ONCE(1) in
isotp_tx_timer_handler() focussed on the identical CAN IDs created by
the syzbot reproducer and lead to upstream fix/commit 3ea566422c
("can: isotp: sanitize CAN ID checks in isotp_bind()"). But this did
not catch the root cause of the wrong tx.state in the tx_timer handler.

In the isotp 'first frame' case a timeout monitoring needs to be started
before the 'first frame' is send. But when this sending failed the timeout
monitoring for this specific frame has to be disabled too.

Otherwise the tx_timer is fired with the 'warn me' tx.state of ISOTP_IDLE.

Fixes: e057dd3fc2 ("can: add ISO 15765-2:2016 transport protocol")
Link: https://lore.kernel.org/all/20220405175112.2682-1-socketcan@hartkopp.net
Reported-by: syzbot+2339c27f5c66c652843e@syzkaller.appspotmail.com
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/isotp.c

@@ -906,6 +906,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	struct canfd_frame *cf;
 	int ae = (so->opt.flags & CAN_ISOTP_EXTEND_ADDR) ? 1 : 0;
 	int wait_tx_done = (so->opt.flags & CAN_ISOTP_WAIT_TX_DONE) ? 1 : 0;
+	s64 hrtimer_sec = 0;
 	int off;
 	int err;
 
@@ -1004,7 +1005,9 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 		isotp_create_fframe(cf, so, ae);
 
 		/* start timeout for FC */
-		hrtimer_start(&so->txtimer, ktime_set(1, 0), HRTIMER_MODE_REL_SOFT);
+		hrtimer_sec = 1;
+		hrtimer_start(&so->txtimer, ktime_set(hrtimer_sec, 0),
+			      HRTIMER_MODE_REL_SOFT);
 	}
 
 	/* send the first or only CAN frame */
@@ -1017,6 +1020,11 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (err) {
 		pr_notice_once("can-isotp: %s: can_send_ret %pe\n",
 			       __func__, ERR_PTR(err));
+
+		/* no transmission -> no timeout monitoring */
+		if (hrtimer_sec)
+			hrtimer_cancel(&so->txtimer);
+
 		goto err_out_drop;
 	}