netfilter: rpfilter/fib: Populate flowic_l3mdev field

Use the introduced field for correct operation with VRF devices instead
of conditionally overwriting flowic_oif. This is a partial revert of
commit b575b24b ("netfilter: Fix rpfilter dropping vrf packets by
mistake"), implementing a simpler solution.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/ipv4/netfilter/ipt_rpfilter.c

@@ -77,7 +77,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
 	flow.flowi4_tos = iph->tos & IPTOS_RT_MASK;
 	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
-	flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));
+	flow.flowi4_l3mdev = l3mdev_master_ifindex_rcu(xt_in(par));
 
 	return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
 }

net/ipv4/netfilter/nft_fib_ipv4.c

@@ -84,7 +84,7 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
 		oif = NULL;
 
 	if (priv->flags & NFTA_FIB_F_IIF)
-		fl4.flowi4_oif = l3mdev_master_ifindex_rcu(oif);
+		fl4.flowi4_l3mdev = l3mdev_master_ifindex_rcu(oif);
 
 	if (nft_hook(pkt) == NF_INET_PRE_ROUTING &&
 	    nft_fib_is_loopback(pkt->skb, nft_in(pkt))) {

net/ipv6/netfilter/ip6t_rpfilter.c

@@ -37,6 +37,7 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 	bool ret = false;
 	struct flowi6 fl6 = {
 		.flowi6_iif = LOOPBACK_IFINDEX,
+		.flowi6_l3mdev = l3mdev_master_ifindex_rcu(dev),
 		.flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
 		.flowi6_proto = iph->nexthdr,
 		.daddr = iph->saddr,
@@ -55,9 +56,7 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 	if (rpfilter_addr_linklocal(&iph->saddr)) {
 		lookup_flags |= RT6_LOOKUP_F_IFACE;
 		fl6.flowi6_oif = dev->ifindex;
-	/* Set flowi6_oif for vrf devices to lookup route in l3mdev domain. */
-	} else if (netif_is_l3_master(dev) || netif_is_l3_slave(dev) ||
-		  (flags & XT_RPFILTER_LOOSE) == 0)
+	} else if ((flags & XT_RPFILTER_LOOSE) == 0)
 		fl6.flowi6_oif = dev->ifindex;
 
 	rt = (void *)ip6_route_lookup(net, &fl6, skb, lookup_flags);
@@ -72,9 +71,7 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 		goto out;
 	}
 
-	if (rt->rt6i_idev->dev == dev ||
-	    l3mdev_master_ifindex_rcu(rt->rt6i_idev->dev) == dev->ifindex ||
-	    (flags & XT_RPFILTER_LOOSE))
+	if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
 		ret = true;
  out:
 	ip6_rt_put(rt);

net/ipv6/netfilter/nft_fib_ipv6.c

@@ -41,9 +41,8 @@ static int nft_fib6_flowi_init(struct flowi6 *fl6, const struct nft_fib *priv,
 	if (ipv6_addr_type(&fl6->daddr) & IPV6_ADDR_LINKLOCAL) {
 		lookup_flags |= RT6_LOOKUP_F_IFACE;
 		fl6->flowi6_oif = get_ifindex(dev ? dev : pkt->skb->dev);
-	} else if ((priv->flags & NFTA_FIB_F_IIF) &&
-		   (netif_is_l3_master(dev) || netif_is_l3_slave(dev))) {
-		fl6->flowi6_oif = dev->ifindex;
+	} else if (priv->flags & NFTA_FIB_F_IIF) {
+		fl6->flowi6_l3mdev = l3mdev_master_ifindex_rcu(dev);
 	}
 
 	if (ipv6_addr_type(&fl6->saddr) & IPV6_ADDR_UNICAST)