[PATCH 6.18 20/60] rose: fix notifier unregistered too early in rose_exit()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bernard Pidoux <bernard.f6bvp@gmail.com>

commit f71a8a1edc14dba746edde38adddd654ba202b4d upstream.

rose_exit() called unregister_netdevice_notifier() before the loop that
calls unregister_netdev() on each ROSE virtual device.  As a result,
the NETDEV_DOWN event fired by unregister_netdev() was never delivered
to rose_device_event(), so rose_kill_by_device() never ran.

Every socket whose rose->device pointed at a ROSE device therefore kept
its netdev_tracker entry live until free_netdev() destroyed the
ref_tracker_dir, at which point the kernel reported all of them as
leaked references (165 entries in a typical FPAC setup).  Worse, those
sockets retained stale device pointers and live timers that could fire
into freed module text after module unload, causing a silent system
freeze with no kernel panic logged.

Fix by moving unregister_netdevice_notifier() to after the device-
unregistration loop.  unregister_netdev() then delivers NETDEV_DOWN
while the notifier is still registered, rose_kill_by_device() runs for
each device, releases all netdev references held by open sockets, and
calls rose_disconnect() which stops the per-socket timers.

Signed-off-by: Bernard Pidoux <bernard.f6bvp@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/rose/af_rose.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -1669,19 +1669,28 @@ static void __exit rose_exit(void)
 #ifdef CONFIG_SYSCTL
 	rose_unregister_sysctl();
 #endif
-	unregister_netdevice_notifier(&rose_dev_notifier);
-
 	sock_unregister(PF_ROSE);
 
 	for (i = 0; i < rose_ndevs; i++) {
 		struct net_device *dev = dev_rose[i];
 
 		if (dev) {
+			/* unregister_netdev() fires NETDEV_DOWN, which -- while the
+			 * notifier is still registered below -- invokes
+			 * rose_kill_by_device(dev).  That releases every socket's
+			 * netdev reference and disconnects all active circuits.
+			 * Unregistering the notifier before this loop was the
+			 * original bug: NETDEV_DOWN was never delivered, leaving
+			 * 165 netdev_tracker entries leaked and stale timers live.
+			 */
 			unregister_netdev(dev);
 			free_netdev(dev);
 		}
 	}
 
+	/* Now safe to remove the notifier -- all ROSE devices are gone. */
+	unregister_netdevice_notifier(&rose_dev_notifier);
+
 	kfree(dev_rose);
 	proto_unregister(&rose_proto);
 }