netfilter: nf_tables: don't drop IPv6 packets that cannot parse transport

This is overly conservative and not flexible at all, so better let them
go through and let the filtering policy decide what to do with them. We
use skb_header_pointer() all over the place so we would just fail to
match when trying to access fields from malformed traffic.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables_ipv6.h

@@ -4,7 +4,7 @@
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <net/ipv6.h>
 
-static inline int
+static inline void
 nft_set_pktinfo_ipv6(struct nft_pktinfo *pkt,
 		     struct sk_buff *skb,
 		     const struct nf_hook_state *state)
@@ -17,15 +17,13 @@ nft_set_pktinfo_ipv6(struct nft_pktinfo *pkt,
 	protohdr = ipv6_find_hdr(pkt->skb, &thoff, -1, &frag_off, NULL);
 	if (protohdr < 0) {
 		nft_set_pktinfo_proto_unspec(pkt, skb);
-		return -1;
+		return;
 	}
 
 	pkt->tprot_set = true;
 	pkt->tprot = protohdr;
 	pkt->xt.thoff = thoff;
 	pkt->xt.fragoff = frag_off;
-
-	return 0;
 }
 
 static inline int

net/ipv6/netfilter/nf_tables_ipv6.c

@@ -22,9 +22,7 @@ static unsigned int nft_do_chain_ipv6(void *priv,
 {
 	struct nft_pktinfo pkt;
 
-	/* malformed packet, drop it */
-	if (nft_set_pktinfo_ipv6(&pkt, skb, state) < 0)
-		return NF_DROP;
+	nft_set_pktinfo_ipv6(&pkt, skb, state);
 
 	return nft_do_chain(&pkt, priv);
 }

net/ipv6/netfilter/nft_chain_route_ipv6.c

@@ -32,9 +32,7 @@ static unsigned int nf_route_table_hook(void *priv,
 	u_int8_t hop_limit;
 	u32 mark, flowlabel;
 
-	/* malformed packet, drop it */
-	if (nft_set_pktinfo_ipv6(&pkt, skb, state) < 0)
-		return NF_DROP;
+	nft_set_pktinfo_ipv6(&pkt, skb, state);
 
 	/* save source/dest address, mark, hoplimit, flowlabel, priority */
 	memcpy(&saddr, &ipv6_hdr(skb)->saddr, sizeof(saddr));