local.mk: Introduce new target for testing.

[firewall] / classify.m4

### -*-m4-*-
###
### Classify packets according to source and destination networks.
###
### (c) 2008 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

m4_divert(40)m4_dnl
###--------------------------------------------------------------------------
### Address classification.
###
### The objective of address classification is to work out what kind of
### networks a packet is travelling between, in order to make filtering
### decisions easier.
###
### Address classification is done in the mangle table, by attaching
### appropriate marks to the packet.  We split the Internet into a number of
### address classes, and make forwarding decisions based on the classes of
### the source and destination addresses.
###
### The mark word is split into three fields: the FROM and TO fields simply
### record the source and destination classes numerically; the MASK field is
### used to determine whether forwarding should occur.  There is a mask bit
### for each address class.  Source classification sets mask bits according
### to the forwarding policy for the source address class.  Destination
### classification clears all of the mask bits except for the one
### corresponding to the actual destination class.  Therefore, forwarding is
### permitted if and only if the mask bits are not all zero.
###
### The mangle chains are arranged as follows.
###
### The PREROUTING hook simply invokes in-classify and out-classify chains as
### subroutines.  These will tail-call appropriate classification chains.
###
### The in-classify chain is responsible for both source address
### classification and verifying that the packet arrived from the correct
### interface.  It does an initial dispatch on the source interface, to
### in-IFACE.  The in-IFACE chain dispatches to mark-from-CLASS when it
### recognizes an address belonging to the CLASS; if no matches succeed, it
### goes to bad-source-address, which logs a message and drops the packet.
### The default interface is special.  If no explicit matches are found, it
### dispatches to in-default which forbids a few obviously evil things and
### finally dispatches to mark-from-untrusted.
###
### The out-classify is simpler because it doesn't care about the interface.
### It simply checks each network range in turn, dispatching to mark-to-CLASS
### on a match or mark-to-DEFAULT (probably untrusted) if there is no match.

clearchain mangle:in-classify mangle:in-default mangle:out-classify
clearchain mangle:local-source

## Packets over the loopback interface are automatically trusted.  All manner
## of weird stuff happens on lo, and it's best not to second-guess it.
run iptables -t mangle -A in-classify -i lo -j ACCEPT

## Local bootp packets have bizarre addresses.  Don't block them just because
## of this.
run iptables -t mangle -A in-classify -j RETURN \
	-s 0.0.0.0 -d 255.255.255.255 \
	-p udp --source-port $port_bootpc --destination-port $port_bootps

## Since packets with source and destination addresses both local will go
## over the loopback interface, I shouldn't see a packet from me over any
## other interface.  Except that I will if I sent a broadcast or multicast.
## Allow the broadcasts, and remember not to trust them.
run iptables -t mangle -A local-source -j RETURN \
	-m addrtype --dst-type BROADCAST
run iptables -t mangle -A local-source -j RETURN \
	-m addrtype --dst-type MULTICAST
run iptables -t mangle -A local-source -g bad-source-address
run iptables -t mangle -A in-classify -j local-source \
	-m addrtype --src-type LOCAL

m4_divert(41)m4_dnl
## Define the important networks.
for pass in 1 2; do
  netclassindex=0
m4_divert(42)m4_dnl
done

m4_divert(46)m4_dnl
## Mark addresses reachable on non-default interfaces as not reachable on the
## default interface.
trace "nets = $allnets"
for net in $allnets; do
  case $net in
    "$defaultiface":*)
      ;;
    *)
      run iptables -t mangle -A in-$defaultiface \
	      -s ${net#*:} -g bad-source-address
      ;;
  esac
done

## Fill in the black holes in the network.
for addr in \
	10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
	127.0.0.0/8 192.0.2.0/24
do
  run iptables -t mangle -A in-default -s $addr -g bad-source-address
done

m4_divert(92)m4_dnl
## Put the final default decision on the in-default chain, and attach the
## classification chains to the PREROUTING hook.
run iptables -t mangle -A in-$defaultiface -g mark-from-$defaultclass
run iptables -t mangle -A PREROUTING -j in-classify
run iptables -t mangle -A PREROUTING -j out-classify

## Now it's safe to let stuff through.
for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
  run iptables -t mangle -P $i ACCEPT
done

m4_divert(-1)
###----- That's all, folks --------------------------------------------------