[PATCH nft] meta: skip protocol context update for nfproto with same table family

[Pablo Neira Ayuso <pablo@netfilter.org>]

Inefficient bytecode crashes ruleset listing:

[ meta load nfproto => reg 1 ]
[ cmp eq reg 1 0x00000002 ] <-- this specifies NFPROTO_IPV4 but table family is IPv4!
[ payload load 4b @ network header + 12 => reg 1 ]
[ cmp gte reg 1 0x1000000a ]
[ cmp lte reg 1 0x1f00000a ]
[ masq ]

This IPv4 table obviously only see IPv4 traffic, but bytecode specifies
a redundant match on NFPROTO_IPV4.

After this patch, listing works:

 # nft list ruleset
 table ip crash {
        chain crash {
                type nat hook postrouting priority srcnat; policy accept;
                ip saddr 10.0.0.16-10.0.0.31 masquerade
        }
 }

Skip protocol context update in case that this information is redundant.

Fixes: https://bugzilla.netfilter.org/show_bug.cgi?id=1562
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 src/meta.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/meta.c b/src/meta.c
index dcf971a5dd62..3be270a4253c 100644
--- a/src/meta.c
+++ b/src/meta.c
@@ -773,6 +773,11 @@ static void meta_expr_pctx_update(struct proto_ctx *ctx,
 		break;
 	case NFT_META_NFPROTO:
 		protonum = mpz_get_uint8(right->value);
+		if (protonum == NFPROTO_IPV4 && h->desc == &proto_ip)
+			break;
+		else if (protonum == NFPROTO_IPV6 && h->desc == &proto_ip6)
+			break;
+
 		desc = proto_find_upper(h->desc, protonum);
 		if (desc == NULL) {
 			desc = &proto_unknown;
-- 
2.30.2