static struct tun_struct *__tun_get(struct tun_file *tfile)
{
	struct tun_struct *tun;

	rcu_read_lock();
	tun = rcu_dereference(tfile->tun);
	if (tun)
		dev_hold(tun->dev);
	rcu_read_unlock();

	return tun;
}

The product dereferences a pointer that it expects to be valid but is NULL.