[PATCH] can: isotp: fix filter removal race between release and netns change

[Oliver Hartkopp <socketcan@hartkopp.net>]

isotp_release() removes the socket from isotp_notifier_list before it
takes rtnl_lock(). As the netdev notifier chain runs under RTNL, a
socket that leaves the list in this window is skipped by isotp_notify()
and has to remove its CAN filters itself.

This fails when the bound device is moved to another network namespace
in this window: isotp_release() passes sock_net(sk) to
can_rx_unregister(), which silently returns when this namespace does not
match dev_net(dev) anymore. As can_rx_register() stores rcv->sk without
taking a reference, the remaining receivers point to the freed socket
and travel with the device into the new namespace:

  BUG: KASAN: use-after-free in isotp_rcv+0x1570/0x24d0
  Read of size 1 at addr ffff888118130552 by task isotp_ns_uaf/578
   can_rcv_filter+0x4af/0x8c0
   can_receive+0x28d/0x3c0
   can_rcv+0x2a9/0x310
   __netif_receive_skb_one_core+0x21a/0x260
   process_backlog+0x210/0x760

Take rtnl_lock() before removing the socket from the notifier list, so
that isotp_release() and isotp_notify() can not both skip the removal.

As the notifier chain is always invoked under RTNL (see ASSERT_RTNL() in
call_netdevice_notifiers_info()), isotp_busy_notifier can not point to
the released socket anymore. Replace the now dead busy-wait loop with a
WARN_ON_ONCE(). isotp_notifier_lock is still needed, as isotp_init()
adds new sockets to isotp_notifier_list without holding RTNL.

Additionally use dev_net(so->dev) for the can_rx_unregister() calls, as
the CAN filters live in the device's namespace. With the new locking
both namespaces are equal there, but dev_net(so->dev) is stable under
RTNL and always names the correct namespace.

Fixes: 20bab8b88baa ("can: isotp: fix use-after-free race with concurrent NETDEV_UNREGISTER")
Reported-by: Norbert Szetei <norbert@doyensec.com>
Link: https://lore.kernel.org/linux-can/CEA6A38A-2646-4ADA-95B4-CBAE2F301A8E@doyensec.com/
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index f5dc9d04bd68..186daa818647 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1477,32 +1477,33 @@ static int isotp_release(struct socket *sock)
 	WRITE_ONCE(so->rx.state, ISOTP_IDLE);
 
 	/* forced SHUTDOWN may have skipped IDLE (gave up on a signal) */
 	wake_up_interruptible(&so->wait);
 
+	rtnl_lock();
+
+	/* The netdev notifier chain runs under RTNL, so isotp_notifier() can't
+	 * be walking isotp_notifier_list and point to this socket. The spinlock
+	 * is still needed as isotp_init() adds sockets without holding RTNL.
+	 */
 	spin_lock(&isotp_notifier_lock);
-	while (isotp_busy_notifier == so) {
-		spin_unlock(&isotp_notifier_lock);
-		schedule_timeout_uninterruptible(1);
-		spin_lock(&isotp_notifier_lock);
-	}
+	WARN_ON_ONCE(isotp_busy_notifier == so);
 	list_del(&so->notifier);
 	spin_unlock(&isotp_notifier_lock);
 
-	rtnl_lock();
 	lock_sock(sk);
 
 	/* remove current filters & unregister
 	 * tracked reference so->dev is taken at bind() time with rtnl_lock
 	 */
 	if (so->bound && so->dev) {
 		if (isotp_register_rxid(so))
-			can_rx_unregister(net, so->dev, so->rxid,
+			can_rx_unregister(dev_net(so->dev), so->dev, so->rxid,
 					  SINGLE_MASK(so->rxid),
 					  isotp_rcv, sk);
 
-		can_rx_unregister(net, so->dev, so->txid,
+		can_rx_unregister(dev_net(so->dev), so->dev, so->txid,
 				  SINGLE_MASK(so->txid),
 				  isotp_rcv_echo, sk);
 		netdev_put(so->dev, &so->dev_tracker);
 	}
 
-- 
2.53.0