From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 30 May 2018 20:43:15 +0200
Subject: [PATCH] netfilter: nf_flow_table: attach dst to skbs

Some drivers, such as vxlan and wireguard, use the skb's dst in order to
determine things like PMTU. They therefore loose functionality when flow
offloading is enabled. So, we ensure the skb has it before xmit'ing it
in the offloading path.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---

--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -220,7 +220,7 @@ nf_flow_offload_ip_hook(void *priv, stru
 	enum flow_offload_tuple_dir dir;
 	struct flow_offload *flow;
 	struct net_device *outdev;
-	const struct rtable *rt;
+	struct rtable *rt;
 	unsigned int thoff;
 	struct iphdr *iph;
 	__be32 nexthop;
@@ -241,7 +241,7 @@ nf_flow_offload_ip_hook(void *priv, stru
 
 	dir = tuplehash->tuple.dir;
 	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
-	rt = (const struct rtable *)flow->tuplehash[dir].tuple.dst_cache;
+	rt = (struct rtable *)flow->tuplehash[dir].tuple.dst_cache;
 
 	if (unlikely(nf_flow_exceeds_mtu(skb, flow->tuplehash[dir].tuple.mtu)) &&
 	    (ip_hdr(skb)->frag_off & htons(IP_DF)) != 0)
@@ -264,6 +264,7 @@ nf_flow_offload_ip_hook(void *priv, stru
 
 	skb->dev = outdev;
 	nexthop = rt_nexthop(rt, flow->tuplehash[!dir].tuple.src_v4.s_addr);
+	skb_dst_set_noref(skb, &rt->dst);
 	neigh_xmit(NEIGH_ARP_TABLE, outdev, &nexthop, skb);
 
 	return NF_STOLEN;
@@ -480,6 +481,7 @@ nf_flow_offload_ipv6_hook(void *priv, st
 
 	skb->dev = outdev;
 	nexthop = rt6_nexthop(rt, &flow->tuplehash[!dir].tuple.src_v6);
+	skb_dst_set_noref(skb, &rt->dst);
 	neigh_xmit(NEIGH_ND_TABLE, outdev, nexthop, skb);
 
 	return NF_STOLEN;