tun: call dev_get_valid_name() before register_netdevice()

register_netdevice() could fail early when we have an invalid
dev name, in which case ->ndo_uninit() is not called. For tun
device, this is a problem because a timer etc. are already
initialized and it expects ->ndo_uninit() to clean them up.

We could move these initializations into a ->ndo_init() so
that register_netdevice() knows better, however this is still
complicated due to the logic in tun_detach().

Therefore, I choose to just call dev_get_valid_name() before
register_netdevice(), which is quicker and much easier to audit.
And for this specific case, it is already enough.

Fixes: 96442e42429e ("tuntap: choose the txq based on rxq")
Reported-by: Dmitry Alexeev <avekceeb@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
void netdev_run_todo(void)
{
	struct list_head list;

	/* Snapshot list, allow later requests */
	list_replace_init(&net_todo_list, &list);

	__rtnl_unlock();


	/* Wait for rcu callbacks to finish before next phase */
	if (!list_empty(&list))
		rcu_barrier();

	while (!list_empty(&list)) {
		struct net_device *dev
			= list_first_entry(&list, struct net_device, todo_list);
		list_del(&dev->todo_list);

		rtnl_lock();
		call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
		__rtnl_unlock();

		if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
			pr_err("network todo '%s' but state %d\n",
			       dev->name, dev->reg_state);
			dump_stack();
			continue;
		}

		dev->reg_state = NETREG_UNREGISTERED;

		netdev_wait_allrefs(dev);

		/* paranoia */
		BUG_ON(netdev_refcnt_read(dev));
		BUG_ON(!list_empty(&dev->ptype_all));
		BUG_ON(!list_empty(&dev->ptype_specific));
		WARN_ON(rcu_access_pointer(dev->ip_ptr));
		WARN_ON(rcu_access_pointer(dev->ip6_ptr));
		WARN_ON(dev->dn_ptr);

		if (dev->priv_destructor)
			dev->priv_destructor(dev);
		if (dev->needs_free_netdev)
			free_netdev(dev);

		/* Report a network device has been unregistered */
		rtnl_lock();
		dev_net(dev)->dev_unreg_count--;
		__rtnl_unlock();
		wake_up(&netdev_unregistering_wq);

		/* Free network device */
		kobject_put(&dev->dev.kobj);
	}
}

void netdev_run_todo(void)
{
	struct list_head list;

	/* Snapshot list, allow later requests */
	list_replace_init(&net_todo_list, &list);

	__rtnl_unlock();


	/* Wait for rcu callbacks to finish before next phase */
	if (!list_empty(&list))
		rcu_barrier();

	while (!list_empty(&list)) {
		struct net_device *dev
			= list_first_entry(&list, struct net_device, todo_list);
		list_del(&dev->todo_list);

		rtnl_lock();
		call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
		__rtnl_unlock();

		if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
			pr_err("network todo '%s' but state %d\n",
			       dev->name, dev->reg_state);
			dump_stack();
			continue;
		}

		dev->reg_state = NETREG_UNREGISTERED;

		netdev_wait_allrefs(dev);

		/* paranoia */
		BUG_ON(netdev_refcnt_read(dev));
		BUG_ON(!list_empty(&dev->ptype_all));
		BUG_ON(!list_empty(&dev->ptype_specific));
		WARN_ON(rcu_access_pointer(dev->ip_ptr));
		WARN_ON(rcu_access_pointer(dev->ip6_ptr));
		WARN_ON(dev->dn_ptr);

		if (dev->priv_destructor)
			dev->priv_destructor(dev);
		if (dev->needs_free_netdev)
			free_netdev(dev);

		/* Report a network device has been unregistered */
		rtnl_lock();
		dev_net(dev)->dev_unreg_count--;
		__rtnl_unlock();
		wake_up(&netdev_unregistering_wq);

		/* Free network device */
		kobject_put(&dev->dev.kobj);
	}
}
