proto: add pseudo th protocol to match d/sport in generic way

Problem: Its not possible to easily match both udp and tcp in a single
rule.

... input ip protocol { tcp,udp } dport 53

will not work, as bison expects "tcp dport" or "sctp dport", or any
other transport protocol name.

Its possible to match the sport and dport via raw payload expressions,
e.g.:
... input ip protocol { tcp,udp } @th,16,16 53

but its not very readable.
Furthermore, its not possible to use this for set definitions:

table inet filter {
        set myset {
                type ipv4_addr . inet_proto . inet_service
        }

        chain forward {
                type filter hook forward priority filter; policy accept;
                ip daddr . ip protocol . @th,0,16 @myset
        }
}
 # nft -f test
 test:7:26-35: Error: can not use variable sized data types (integer) in concat expressions

During the netfilter workshop Pablo suggested to add an alias to do raw
sport/dport matching more readable, and make it use the inet_service
type automatically.

So, this change makes @th,0,16 work for the set definition case by
setting the data type to inet_service.

A new "th s|dport" syntax is provided as readable alternative:

ip protocol { tcp, udp } th dport 53

As "th" is an alias for the raw expression, no dependency is
generated -- its the users responsibility to add a suitable test to
select the l4 header types that should be matched.

Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/proto.h b/include/proto.h
index 92b25edb..fab48c1b 100644
--- a/include/proto.h
+++ b/include/proto.h
@@ -310,6 +310,12 @@ enum sctp_hdr_fields {
 	SCTPHDR_CHECKSUM,
 };
 
+enum th_hdr_fields {
+	THDR_INVALID,
+	THDR_SPORT,
+	THDR_DPORT,
+};
+
 extern const struct proto_desc proto_icmp;
 extern const struct proto_desc proto_igmp;
 extern const struct proto_desc proto_ah;
@@ -320,6 +326,7 @@ extern const struct proto_desc proto_udplite;
 extern const struct proto_desc proto_tcp;
 extern const struct proto_desc proto_dccp;
 extern const struct proto_desc proto_sctp;
+extern const struct proto_desc proto_th;
 extern const struct proto_desc proto_icmp6;
 
 extern const struct proto_desc proto_ip;