From: Oliver Hartkopp isotp_notify() unregisters the (RCU) CAN filters via can_rx_unregister() and clears so->bound without waiting for a grace period. isotp_release() uses so->bound to decide whether it needs to call synchronize_rcu() before cancelling so->rxtimer, so when NETDEV_UNREGISTER runs first it skips that synchronize_rcu() and can cancel the timer while an in-flight isotp_rcv() is still executing and about to re-arm it via isotp_send_fc(), leading to a use-after-free timer callback on the freed socket. sakisho-bot remarked a problem with rtnl_lock held in isotp_notify(), therefore make isotp_release() always call synchronize_rcu() before cancelling the timers, regardless of so->bound. This still closes the original race (isotp_notify() clearing so->bound without waiting for in-flight isotp_rcv() callers before isotp_release() cancels the RX timer) without adding any RCU wait to the netdevice notifier path. Fixes: 14a4696bc311 ("can: isotp: isotp_release(): omit unintended hrtimer restart on socket release") Closes: https://lore.kernel.org/linux-can/20260707085210.6B6C01F000E9@smtp.kernel.org/ Reported-by: Nico Yip Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260712-isotp-fixes-v10-1-793a1b1ce17f@hartkopp.net Cc: stable@kernel.org Signed-off-by: Marc Kleine-Budde --- net/can/isotp.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/can/isotp.c b/net/can/isotp.c index c48b4a818297..d30937345bcd 100644 --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -1237,11 +1237,18 @@ static int isotp_release(struct socket *sock) SINGLE_MASK(so->txid), isotp_rcv_echo, sk); dev_put(dev); - synchronize_rcu(); } } } + /* Always wait for a grace period before touching the timers below. + * A concurrent NETDEV_UNREGISTER may have already unregistered our + * filters and cleared so->bound in isotp_notify() without waiting + * for in-flight isotp_rcv() callers to finish, so this call must not + * be skipped just because so->bound is already 0 here. + */ + synchronize_rcu(); + hrtimer_cancel(&so->txfrtimer); hrtimer_cancel(&so->txtimer); hrtimer_cancel(&so->rxtimer); -- 2.53.0