netfilter: nft_fib_ipv6: skip ipv6 packets from any to link-local

The ip6tables rpfilter match has an extra check to skip packets with
"::" source address.

Extend this to ipv6 fib expression.  Else ipv6 duplicate address detection
packets will fail rpf route check -- lookup returns -ENETUNREACH.

While at it, extend the prerouting check to also cover the ingress hook.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1543
Fixes: f6d0cbcf ("netfilter: nf_tables: add fib expression")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv6/netfilter/nft_fib_ipv6.c

@@ -135,6 +135,17 @@ void nft_fib6_eval_type(const struct nft_expr *expr, struct nft_regs *regs,
 }
 EXPORT_SYMBOL_GPL(nft_fib6_eval_type);
 
+static bool nft_fib_v6_skip_icmpv6(const struct sk_buff *skb, u8 next, const struct ipv6hdr *iph)
+{
+	if (likely(next != IPPROTO_ICMPV6))
+		return false;
+
+	if (ipv6_addr_type(&iph->saddr) != IPV6_ADDR_ANY)
+		return false;
+
+	return ipv6_addr_type(&iph->daddr) & IPV6_ADDR_LINKLOCAL;
+}
+
 void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 		   const struct nft_pktinfo *pkt)
 {
@@ -163,10 +174,13 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 
 	lookup_flags = nft_fib6_flowi_init(&fl6, priv, pkt, oif, iph);
 
-	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));
-		return;
+	if (nft_hook(pkt) == NF_INET_PRE_ROUTING ||
+	    nft_hook(pkt) == NF_INET_INGRESS) {
+		if (nft_fib_is_loopback(pkt->skb, nft_in(pkt)) ||
+		    nft_fib_v6_skip_icmpv6(pkt->skb, pkt->tprot, iph)) {
+			nft_fib_store_result(dest, priv, nft_in(pkt));
+			return;
+		}
 	}
 
 	*dest = 0;