void ip_rt_get_source(u8 *addr, struct sk_buff *skb, struct rtable *rt)
{
	__be32 src;

	if (rt_is_output_route(rt))
		src = ip_hdr(skb)->saddr;
	else {
		struct fib_result res;
		struct flowi4 fl4;
		struct iphdr *iph;

		iph = ip_hdr(skb);

		memset(&fl4, 0, sizeof(fl4));
		fl4.daddr = iph->daddr;
		fl4.saddr = iph->saddr;
		fl4.flowi4_tos = RT_TOS(iph->tos);
		fl4.flowi4_oif = rt->dst.dev->ifindex;
		fl4.flowi4_iif = skb->dev->ifindex;
		fl4.flowi4_mark = skb->mark;

		rcu_read_lock();
		if (fib_lookup(dev_net(rt->dst.dev), &fl4, &res, 0) == 0)
			src = FIB_RES_PREFSRC(dev_net(rt->dst.dev), res);
		else
			src = inet_select_addr(rt->dst.dev,
					       rt_nexthop(rt, iph->daddr),
					       RT_SCOPE_UNIVERSE);
		rcu_read_unlock();
	}
	memcpy(addr, &src, 4);
}

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