static void tun_net_init(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);

	switch (tun->flags & TUN_TYPE_MASK) {
	case IFF_TUN:
		dev->netdev_ops = &tun_netdev_ops;

		/* Point-to-Point TUN Device */
		dev->hard_header_len = 0;
		dev->addr_len = 0;
		dev->mtu = 1500;

		/* Zero header length */
		dev->type = ARPHRD_NONE;
		dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
		break;

	case IFF_TAP:
		dev->netdev_ops = &tap_netdev_ops;
		/* Ethernet TAP Device */
		ether_setup(dev);
		dev->priv_flags &= ~IFF_TX_SKB_SHARING;
		dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;

		eth_hw_addr_random(dev);

		break;
	}

	dev->min_mtu = MIN_MTU;
	dev->max_mtu = MAX_MTU - dev->hard_header_len;
}

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