netfilter: nft_fib: Fix for rpath check with VRF devices

Analogous to commit b575b24b ("netfilter: Fix rpfilter
dropping vrf packets by mistake") but for nftables fib expression:
Add special treatment of VRF devices so that typical reverse path
filtering via 'fib saddr . iif oif' expression works as expected.

Fixes: f6d0cbcf ("netfilter: nf_tables: add fib expression")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/ipv4/netfilter/nft_fib_ipv4.c

@@ -83,6 +83,9 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	else
 		oif = NULL;
 
+	if (priv->flags & NFTA_FIB_F_IIF)
+		fl4.flowi4_oif = l3mdev_master_ifindex_rcu(oif);
+
 	if (nft_hook(pkt) == NF_INET_PRE_ROUTING &&
 	    nft_fib_is_loopback(pkt->skb, nft_in(pkt))) {
 		nft_fib_store_result(dest, priv, nft_in(pkt));

net/ipv6/netfilter/nft_fib_ipv6.c

@@ -41,6 +41,9 @@ 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;
 	}
 
 	if (ipv6_addr_type(&fl6->saddr) & IPV6_ADDR_UNICAST)
@@ -197,7 +200,8 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	if (rt->rt6i_flags & (RTF_REJECT | RTF_ANYCAST | RTF_LOCAL))
 		goto put_rt_err;
 
-	if (oif && oif != rt->rt6i_idev->dev)
+	if (oif && oif != rt->rt6i_idev->dev &&
+	    l3mdev_master_ifindex_rcu(rt->rt6i_idev->dev) != oif->ifindex)
 		goto put_rt_err;
 
 	nft_fib_store_result(dest, priv, rt->rt6i_idev->dev);