static struct tun_flow_entry *tun_flow_find(struct hlist_head *head, u32 rxhash)
{
	struct tun_flow_entry *e;

	hlist_for_each_entry_rcu(e, head, hash_link) {
		if (e->rxhash == rxhash)
			return e;
	}
	return NULL;
}

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