src: ipv6: switch implicit dependencies to meta l4proto

when using rule like

ip6 filter input tcp dport 22
nft generates:
  [ payload load 1b @ network header + 6 => reg 1 ]
  [ cmp eq reg 1 0x00000006 ]
  [ payload load 2b @ transport header + 2 => reg 1 ]
  [ cmp eq reg 1 0x00001600 ]

which is: ip6 filter input ip6 nexthdr tcp dport 22
IOW, such a rule won't match if e.g. a fragment header is in place.

This changes ip6_proto to use 'meta l4proto' which is the protocol header
found by exthdr walk.

A side effect is that for bridge we get a shorter dependency chain as it
no longer needs to prepend 'ether proto ipv6' for old 'ip6 nexthdr' dep.

Only problem:

ip6 nexthdr tcp tcp dport 22
will now inject a (useless) meta l4 dependency as ip6 nexthdr is no
longer flagged as EXPR_F_PROTOCOL, to avoid this add a small helper
that skips the unneded meta dependency in that case.

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 18 insertions, 1 deletions

diff --git a/src/payload.c b/src/payload.c
index 31e5a024..38db15ee 100644
--- a/src/payload.c
+++ b/src/payload.c
@@ -117,6 +117,23 @@ static const struct expr_ops payload_expr_ops = {
 	.pctx_update	= payload_expr_pctx_update,
 };
 
+/*
+ * ipv6 is special case, we normally use 'meta l4proto' to fetch the last
+ * l4 header of the ipv6 extension header chain so we will also match
+ * tcp after a fragmentation header, for instance.
+ *
+ * If user specifically asks for nexthdr x, treat is as a full
+ * dependency rather than injecting another (useless) meta l4 one.
+ */
+static bool proto_key_is_protocol(const struct proto_desc *desc, unsigned int type)
+{
+	if (type == desc->protocol_key ||
+	    (desc == &proto_ip6 && type == IP6HDR_NEXTHDR))
+		return true;
+
+	return false;
+}
+
 struct expr *payload_expr_alloc(const struct location *loc,
 				const struct proto_desc *desc,
 				unsigned int type)
@@ -129,7 +146,7 @@ struct expr *payload_expr_alloc(const struct location *loc,
 	if (desc != NULL) {
 		tmpl = &desc->templates[type];
 		base = desc->base;
-		if (type == desc->protocol_key)
+		if (proto_key_is_protocol(desc, type))
 			flags = EXPR_F_PROTOCOL;
 	} else {
 		tmpl = &proto_unknown_template;