netfilter: Update ip6_route_me_harder to consider L3 domain

The commit referenced below fixed packet re-routing if Netfilter mangles
a routing key property of a packet and the packet is routed in a VRF L3
domain. The fix, however, addressed IPv4 re-routing, only.

This commit applies the same behavior for IPv6. While at it, untangle
the nested ternary operator to make the code more readable.

Fixes: 6d8b49c3 ("netfilter: Update ip_route_me_harder to consider L3 domain")
Cc: stable@vger.kernel.org
Signed-off-by: Martin Willi <martin@strongswan.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv6/netfilter.c

@@ -24,14 +24,13 @@ int ip6_route_me_harder(struct net *net, struct sock *sk_partial, struct sk_buff
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	struct sock *sk = sk_to_full_sk(sk_partial);
+	struct net_device *dev = skb_dst(skb)->dev;
 	struct flow_keys flkeys;
 	unsigned int hh_len;
 	struct dst_entry *dst;
 	int strict = (ipv6_addr_type(&iph->daddr) &
 		      (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL));
 	struct flowi6 fl6 = {
-		.flowi6_oif = sk && sk->sk_bound_dev_if ? sk->sk_bound_dev_if :
-			strict ? skb_dst(skb)->dev->ifindex : 0,
 		.flowi6_mark = skb->mark,
 		.flowi6_uid = sock_net_uid(net, sk),
 		.daddr = iph->daddr,
@@ -39,6 +38,13 @@ int ip6_route_me_harder(struct net *net, struct sock *sk_partial, struct sk_buff
 	};
 	int err;
 
+	if (sk && sk->sk_bound_dev_if)
+		fl6.flowi6_oif = sk->sk_bound_dev_if;
+	else if (strict)
+		fl6.flowi6_oif = dev->ifindex;
+	else
+		fl6.flowi6_oif = l3mdev_master_ifindex(dev);
+
 	fib6_rules_early_flow_dissect(net, skb, &fl6, &flkeys);
 	dst = ip6_route_output(net, sk, &fl6);
 	err = dst->error;