Move per-host filtering to diversion 86 as promised.

[firewall] / classify.m4

### -*-sh-*-
###
### 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 ip46tables -t mangle -A in-classify -i lo -j ACCEPT

## Local broadcast and link-local multicast packets sometimes 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
run iptables -t mangle -A in-classify -j RETURN \
	-s 0.0.0.0 -d 224.0.0.0/24 \
	-p udp

## 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.  There are no
## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
## to worry about that.
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 ip6tables -t mangle -A local-source -j RETURN \
	-d ff00::/8
run ip46tables -t mangle -A local-source -g bad-source-address
run iptables -t mangle -A in-classify -j local-source \
	-m addrtype --src-type LOCAL
for addr in $host_6addrs; do
  run ip6tables -t mangle -A in-classify -j local-source \
	  -s $addr
done

## It's not valid to have a multicast address as a packet source: multicast
## routing is done away from the source, so a multicast address would make
## this impossible to do.  So discard these packets.  Also discard class-E
## IPv4 addresses, since they aren't assigned.
run iptables -t mangle -A in-classify -g bad-source-address \
	-s 224.0.0.0/3
run ip6tables -t mangle -A in-classify -g bad-source-address \
	-s ff00::/8

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

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## Build the input classification chains.  There's one chain `in-IFACE' for
## each local interface.  This chain does a further dispatch on the source
## address to the appropriate `mark-from-CLASS' chain for the source network
## class.
seen=:
for iface in $host_ifaces_<::>FWHOST; do
  ifname=${iface%=*}
  case $seen in *:$ifname:*) continue ;; esac
  seen=$seen$ifname:
  clearchain mangle:in-$ifname
  run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
done

## Now populate the `in-IFACE' and `out-classify' chains.  We iterate over
## the available networks and add addresses to the appropriate chains.  Also,
## build up a map of which interfaces receive from which address ranged so
## that we can finish the chains off properly later.  This contains entries
## of the form IFACE=:ADDR:ADDR:...:
ifnets=""
for net in $allnets; do

  ## Determine the addresses and class for this network, and populate the
  ## `out-classify' chains.
  eval addr=\$net_inet_$net addr6=\$net_inet6_$net class=\$net_class_$net
  case $class in virtual) continue ;; esac
  trace "$net : $class"
  for a in $addr; do
    run iptables -t mangle -A out-classify -g mark-to-$class -d $a
  done
  for a in $addr6; do
    run ip6tables -t mangle -A out-classify -g mark-to-$class -d $a
  done

  ## Now work through the interfaces.
  for iface in $(net_interfaces FWHOST $net); do
    nets=""
    case $iface in

      -)
	## A special `no interface' marker: we should not receive packets
	## from this network at all.
	continue
	;;

      *-+)
	## A special marker indicating a collection of point-to-point
	## interfaces.  We should match an address to a particular interface.
	## Later, we'll cap this chain off by rejecting all other traffic.
	eval hosts=\$net_hosts_$net
	for host in $hosts; do
	  eval ha=\$host_inet_$host ha6=\$host_inet6_$host
	  trace "$host : $class -> $iface"
	  for a in $ha; do
	    run iptables -t mangle -A in-$iface \
		    -i ${iface%+}$host -s $a -g mark-from-$class
	    nets=$nets$a:
	  done
	  for a in $ha6; do
	    run ip6tables -t mangle -A in-$iface \
		    -i ${iface%+}$host -s $a -g mark-from-$class
	    nets=$nets$a:
	  done
	done
	;;

      *)
	## A normal interface.  Classify incoming traffic according to the
	## source address.
	trace "$net : $class -> $iface"
	for a in $addr; do
	  run iptables -t mangle -A in-$iface -g mark-from-$class -s $a
	  nets=$nets$a:
	done
	for a in $addr6; do
	  run ip6tables -t mangle -A in-$iface -g mark-from-$class -s $a
	  nets=$nets$a:
	done
	case $net in default) nets=${nets}default: ;; esac
	;;
    esac

    ## Record that this interface receives traffic from this network.
    unset nifnets
    foundp=nil
    for ifnet in $ifnets; do
      case $ifnet in
	$iface=*:$net:*) addword nifnets $ifnet; foundp=t ;;
	$iface=*) addword nifnets $ifnet$nets; foundp=t ;;
	*) addword nifnets $ifnet ;;
      esac
    done
    case $foundp in nil) addword nifnets $iface=:$nets ;; esac
    ifnets=$nifnets

  done
done

## Wrap up all of the `in-IFACE' chains.  A chain which matches the `default'
## net should have unmatched but known networks blocked off, and then chain
## onto `in-default'.  Other chains should just chain onto
## `bad-source-address'.
trace "ifnets = $ifnets"
for ifnet in $ifnets; do
  iface=${ifnet%%=*} nets=${ifnet#*=}
  case $nets in
    *:default:*)
      for n in $allnets; do
	eval addr=\$net_inet_$n addr6=\$net_inet6_$n
	for a in $addr; do
	  case $nets in *:$a:*) continue ;; esac
	  nets=$nets$a
	  run iptables -t mangle -A in-$iface -s $a -g bad-source-address
	done
	for a in $addr6; do
	  case $nets in *:$a:*) continue ;; esac
	  nets=$nets$a
	  run ip6tables -t mangle -A in-$iface -s $a -g bad-source-address
	done
      done
      run ip46tables -t mangle -A in-$iface -g in-default
      ;;
    *)
      run ip46tables -t mangle -A in-$iface -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
for addr in \
	fc00::/7 \
	2001:0db8::/32
do
  run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
done
run ip46tables -t mangle -A in-default -g mark-from-$net_class_default

m4_divert(92)m4_dnl
## Put the final default decision on the in-default chain, and attach the
## classification chains to the PREROUTING hook.
for iface in $defaultifaces; do
  run ip46tables -t mangle -A in-$iface -g in-default
done
run ip46tables -t mangle -A out-classify -g mark-to-$net_class_default
run ip46tables -t mangle -A PREROUTING -j in-classify
run ip46tables -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 ip46tables -t mangle -P $i ACCEPT
done

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