src: add TCP option matching

This patch enables nft to match against TCP options.

Currently these TCP options are supported:
* End of Option List (eol)
* No-Operation (noop)
* Maximum Segment Size (maxseg)
* Window Scale (window)
* SACK Permitted (sack_permitted)
* SACK (sack)
* Timestamps (timestamp)

Syntax: tcp options $option_name [$offset] $field_name
Example:

 # count all incoming packets with a specific maximum segment size `x`
 # nft add rule filter input tcp option maxseg size x counter

 # count all incoming packets with a SACK TCP option where the third
 # (counted from zero) left field is greater `x`.
 # nft add rule filter input tcp option sack 2 left \> x counter

If the offset (the `2` in the example above) is zero, it can optionally
be omitted.
For all non-SACK TCP options it is always zero, thus can be left out.

Option names and field names are parsed from templates, similar to meta
and ct options rather than via keywords to prevent adding more keywords
than necessary.

Signed-off-by: Manuel Messner <mm@skelett.io>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/exthdr.h b/include/exthdr.h
index 93a53f30..cdcc2b95 100644
--- a/include/exthdr.h
+++ b/include/exthdr.h
@@ -2,6 +2,7 @@
 #define NFTABLES_EXTHDR_H
 
 #include <proto.h>
+#include <tcpopt.h>
 
 /**
  * struct exthdr_desc - extension header description
@@ -78,6 +79,7 @@ enum mh_hdr_fields {
 	MHHDR_CHECKSUM,
 };
 
+extern const struct expr_ops exthdr_expr_ops;
 extern const struct exthdr_desc exthdr_hbh;
 extern const struct exthdr_desc exthdr_rt;
 extern const struct exthdr_desc exthdr_rt0;