[PATCH can-next v2 3/3] can: raw: take rtnl_lock() before leaving the notifier list

[Oliver Hartkopp <socketcan@hartkopp.net>]

raw_release() removes the socket from raw_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 raw_notify() and has to
remove its CAN filters itself.

For raw this is not harmful: raw_release() removes the filters with
dev_net(ro->dev) under RTNL, so they are found even when the bound
device has been moved to another network namespace in this window. The
receivers only remain on the moved device until raw_release() gets
RTNL.

Take rtnl_lock() before removing the socket from the notifier list, so
that raw, isotp and bcm use the same locking scheme in their release
functions. As the notifier chain is always invoked under RTNL,
raw_busy_notifier can not point to the released socket anymore. Replace
the now dead busy-wait loop with a WARN_ON_ONCE().

Link: https://lore.kernel.org/linux-can/CEA6A38A-2646-4ADA-95B4-CBAE2F301A8E@doyensec.com/
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/raw.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index 0acd4f6c6dd6..925c0c1d243f 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -420,20 +420,21 @@ static int raw_release(struct socket *sock)
 		return 0;
 
 	ro = raw_sk(sk);
 	net = sock_net(sk);
 
+	rtnl_lock();
+
+	/* The netdev notifier chain runs under RTNL, so raw_notifier() can't
+	 * be walking raw_notifier_list and point to this socket. The spinlock
+	 * is still needed as raw_init() adds sockets without holding RTNL.
+	 */
 	spin_lock(&raw_notifier_lock);
-	while (raw_busy_notifier == ro) {
-		spin_unlock(&raw_notifier_lock);
-		schedule_timeout_uninterruptible(1);
-		spin_lock(&raw_notifier_lock);
-	}
+	WARN_ON_ONCE(raw_busy_notifier == ro);
 	list_del(&ro->notifier);
 	spin_unlock(&raw_notifier_lock);
 
-	rtnl_lock();
 	lock_sock(sk);
 
 	/* remove current filters & unregister */
 	if (ro->bound) {
 		if (ro->dev) {
-- 
2.53.0