net: Do not route unicast IP packets twice

Packets marked with 'offload_l3_fwd_mark' were already forwarded by a
capable device and should not be forwarded again by the kernel.
Therefore, have the kernel consume them.

The check is performed in ip{,6}_forward_finish() in order to allow the
kernel to process such packets in ip{,6}_forward() and generate required
exceptions. For example, ICMP redirects.
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_forward.c

@@ -69,6 +69,13 @@ static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *s
 	__IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS);
 	__IP_ADD_STATS(net, IPSTATS_MIB_OUTOCTETS, skb->len);
 
+#ifdef CONFIG_NET_SWITCHDEV
+	if (skb->offload_l3_fwd_mark) {
+		consume_skb(skb);
+		return 0;
+	}
+#endif
+
 	if (unlikely(opt->optlen))
 		ip_forward_options(skb);
 

net/ipv6/ip6_output.c

@@ -378,6 +378,13 @@ static inline int ip6_forward_finish(struct net *net, struct sock *sk,
 	__IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTFORWDATAGRAMS);
 	__IP6_ADD_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTOCTETS, skb->len);
 
+#ifdef CONFIG_NET_SWITCHDEV
+	if (skb->offload_l3_fwd_mark) {
+		consume_skb(skb);
+		return 0;
+	}
+#endif
+
 	return dst_output(net, sk, skb);
 }