From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Since j1939_session_deactivate_activate_next() in j1939_tp_rxtimer() is
called only when the timer is enabled, we need to call
j1939_session_deactivate_activate_next() if we cancelled the timer.
Otherwise, refcount for j1939_session leaks, which will later appear as

| unregister_netdevice: waiting for vcan0 to become free. Usage count = 2.

problem.

Reported-by: syzbot <redacted>
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Link: https://patch.msgid.link/b1212653-8fa1-44e1-be9d-12f950fb3a07@I-love.SAKURA.ne.jp
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 net/can/j1939/transport.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 613a911dda10..8656ab388c83 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c

@@ -1695,8 +1695,16 @@ static int j1939_xtp_rx_rts_session_active(struct j1939_session *session,
 
 		j1939_session_timers_cancel(session);
 		j1939_session_cancel(session, J1939_XTP_ABORT_BUSY);
-		if (session->transmission)
+		if (session->transmission) {
 			j1939_session_deactivate_activate_next(session);
+		} else if (session->state == J1939_SESSION_WAITING_ABORT) {
+			/* Force deactivation for the receiver.
+			 * If we rely on the timer starting in j1939_session_cancel,
+			 * a second RTS call here will cancel that timer and fail
+			 * to restart it because the state is already WAITING_ABORT.
+			 */
+			j1939_session_deactivate_activate_next(session);
+		}
 
 		return -EBUSY;
 	}

-- 
2.51.0