leds: trigger: netdev: fix refcnt leak on interface rename

[ Upstream commit 4cb6560514fa19d556954b88128f3846fee66a03 ]

Renaming a netdev-trigger-tracked interface was resulting in an
unbalanced dev_hold().

Example:
> iw phy phy0 interface add foo type __ap
> echo netdev > trigger
> echo foo > device_name
> ip link set foo name bar
> iw dev bar del
[  237.355366] unregister_netdevice: waiting for bar to become free. Usage count = 1
[  247.435362] unregister_netdevice: waiting for bar to become free. Usage count = 1
[  257.545366] unregister_netdevice: waiting for bar to become free. Usage count = 1

Above problem was caused by trigger checking a dev->name which obviously
changes after renaming an interface. It meant missing all further events
including the NETDEV_UNREGISTER which is required for calling dev_put().

This change fixes that by:
1) Comparing device struct *address* for notification-filtering purposes
2) Dropping unneeded NETDEV_CHANGENAME code (no behavior change)

Fixes: 06f502f5 ("leds: trigger: Introduce a NETDEV trigger")
Signed-off-by: NRafał Miłecki <rafal@milecki.pl>
Acked-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NJacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: NSasha Levin (Microsoft) <sashal@kernel.org>

drivers/leds/trigger/ledtrig-netdev.c

@@ -301,11 +301,11 @@ static int netdev_trig_notify(struct notifier_block *nb,
 		container_of(nb, struct led_netdev_data, notifier);
 
 	if (evt != NETDEV_UP && evt != NETDEV_DOWN && evt != NETDEV_CHANGE
-	    && evt != NETDEV_REGISTER && evt != NETDEV_UNREGISTER
-	    && evt != NETDEV_CHANGENAME)
+	    && evt != NETDEV_REGISTER && evt != NETDEV_UNREGISTER)
 		return NOTIFY_DONE;
 
-	if (strcmp(dev->name, trigger_data->device_name))
+	if (!(dev == trigger_data->net_dev ||
+	      (evt == NETDEV_REGISTER && !strcmp(dev->name, trigger_data->device_name))))
 		return NOTIFY_DONE;
 
 	cancel_delayed_work_sync(&trigger_data->work);
@@ -320,12 +320,9 @@ static int netdev_trig_notify(struct notifier_block *nb,
 		dev_hold(dev);
 		trigger_data->net_dev = dev;
 		break;
-	case NETDEV_CHANGENAME:
 	case NETDEV_UNREGISTER:
-		if (trigger_data->net_dev) {
 		dev_put(trigger_data->net_dev);
 		trigger_data->net_dev = NULL;
-		}
 		break;
 	case NETDEV_UP:
 	case NETDEV_CHANGE: