src: Add tproxy support

This patch adds support for transparent proxy functionality which is
supported in ip, ip6 and inet tables.

The syntax is the following:
	tproxy [{|ip|ip6}] to {<ip address>|:<port>|<ip address>:<port>}

It looks for a socket listening on the specified address or port and
assigns it to the matching packet.

In an inet table, a packet matches for both families until address is
specified.
Network protocol family has to be specified **only** in inet tables if
address is specified.

As transparent proxy support is implemented for sockets with layer 4
information, a transport protocol header criterion has to be set in the
same rule. eg. 'meta l4proto tcp' or 'udp dport 4444'

Example ruleset:
	table ip x {
		chain y {
			type filter hook prerouting priority -150; policy accept;
			tcp dport ntp tproxy to 1.1.1.1
			udp dport ssh tproxy to :2222
		}
	}
	table ip6 x {
		chain y {
			type filter hook prerouting priority -150; policy accept;
			tcp dport ntp tproxy to [dead::beef]
			udp dport ssh tproxy to :2222
		}
	}
	table inet x {
		chain y {
			type filter hook prerouting priority -150; policy accept;
			tcp dport 321 tproxy to :ssh
			tcp dport 99 tproxy ip to 1.1.1.1:999
			udp dport 155 tproxy ip6 to [dead::beef]:smux
		}
	}

Signed-off-by: Máté Eckl <ecklm94@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/scanner.l b/src/scanner.l
index ed01b5e7..703700fe 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -261,6 +261,8 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "socket"		{ return SOCKET; }
 "transparent"		{ return TRANSPARENT;}
 
+"tproxy"		{ return TPROXY; }
+
 "accept"		{ return ACCEPT; }
 "drop"			{ return DROP; }
 "continue"		{ return CONTINUE; }