[PATCH] can: isotp: omit unintended hrtimer restart on socket release

[Oliver Hartkopp <socketcan@hartkopp.net>]

When closing the isotp socket the potentially running hrtimers are
canceled before removing the subscription for CAN idendifiers via
can_rx_unregister().

This may lead to an unintended (re)start of a hrtimer in isotp_rcv_cf()
and isotp_rcv_fc() in the case that a CAN frame is received by
isotp_rcv() while the subscription removal is processed.

However, isotp_rcv() is called under RCU protection, so after calling
can_rx_unregister, we may call synchronize_rcu in order to wait for any
RCU read-side critical sections to finish. This prevents the reception
of CAN frames after hrtimer_cancel() and therefore the unintended
(re)start of the hrtimers.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index be6183f8ca11..234cc4ad179a 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1026,13 +1026,10 @@ static int isotp_release(struct socket *sock)
 	list_del(&so->notifier);
 	spin_unlock(&isotp_notifier_lock);
 
 	lock_sock(sk);
 
-	hrtimer_cancel(&so->txtimer);
-	hrtimer_cancel(&so->rxtimer);
-
 	/* remove current filters & unregister */
 	if (so->bound && (!(so->opt.flags & CAN_ISOTP_SF_BROADCAST))) {
 		if (so->ifindex) {
 			struct net_device *dev;
 
@@ -1040,14 +1037,18 @@ static int isotp_release(struct socket *sock)
 			if (dev) {
 				can_rx_unregister(net, dev, so->rxid,
 						  SINGLE_MASK(so->rxid),
 						  isotp_rcv, sk);
 				dev_put(dev);
+				synchronize_rcu();
 			}
 		}
 	}
 
+	hrtimer_cancel(&so->txtimer);
+	hrtimer_cancel(&so->rxtimer);
+
 	so->ifindex = 0;
 	so->bound = 0;
 
 	sock_orphan(sk);
 	sock->sk = NULL;
-- 
2.30.2