mdw@git.distorted.org.uk Git - firewall/blob - classify.m4

   1 ### -*-sh-*-
   2 ###
   3 ### Classify packets according to source and destination networks.
   4 ###
   5 ### (c) 2008 Mark Wooding
   6 ###
   7
   8 ###----- Licensing notice ---------------------------------------------------
   9 ###
  10 ### This program is free software; you can redistribute it and/or modify
  11 ### it under the terms of the GNU General Public License as published by
  12 ### the Free Software Foundation; either version 2 of the License, or
  13 ### (at your option) any later version.
  14 ###
  15 ### This program is distributed in the hope that it will be useful,
  16 ### but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ### GNU General Public License for more details.
  19 ###
  20 ### You should have received a copy of the GNU General Public License
  21 ### along with this program; if not, write to the Free Software Foundation,
  22 ### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  23
  24 m4_divert(40)m4_dnl
  25 ###--------------------------------------------------------------------------
  26 ### Address classification.
  27 ###
  28 ### The objective of address classification is to work out what kind of
  29 ### networks a packet is travelling between, in order to make filtering
  30 ### decisions easier.
  31 ###
  32 ### Address classification is done in the mangle table, by attaching
  33 ### appropriate marks to the packet.  We split the Internet into a number of
  34 ### address classes, and make forwarding decisions based on the classes of
  35 ### the source and destination addresses.
  36 ###
  37 ### The mark word is split into three fields: the FROM and TO fields simply
  38 ### record the source and destination classes numerically; the MASK field is
  39 ### used to determine whether forwarding should occur.  There is a mask bit
  40 ### for each address class.  Source classification sets mask bits according
  41 ### to the forwarding policy for the source address class.  Destination
  42 ### classification clears all of the mask bits except for the one
  43 ### corresponding to the actual destination class.  Therefore, forwarding is
  44 ### permitted if and only if the mask bits are not all zero.
  45 ###
  46 ### The mangle chains are arranged as follows.
  47 ###
  48 ### The PREROUTING hook simply invokes in-classify and out-classify chains as
  49 ### subroutines.  These will tail-call appropriate classification chains.
  50 ###
  51 ### The in-classify chain is responsible for both source address
  52 ### classification and verifying that the packet arrived from the correct
  53 ### interface.  It does an initial dispatch on the source interface, to
  54 ### in-IFACE.  The in-IFACE chain dispatches to mark-from-CLASS when it
  55 ### recognizes an address belonging to the CLASS; if no matches succeed, it
  56 ### goes to bad-source-address, which logs a message and drops the packet.
  57 ### The default interface is special.  If no explicit matches are found, it
  58 ### dispatches to in-default which forbids a few obviously evil things and
  59 ### finally dispatches to mark-from-untrusted.
  60 ###
  61 ### The out-classify is simpler because it doesn't care about the interface.
  62 ### It simply checks each network range in turn, dispatching to mark-to-CLASS
  63 ### on a match or mark-to-DEFAULT (probably untrusted) if there is no match.
  64
  65 clearchain mangle:in-classify mangle:in-default mangle:out-classify
  66 clearchain mangle:local-source
  67
  68 ## Packets over the loopback interface are automatically trusted.  All manner
  69 ## of weird stuff happens on lo, and it's best not to second-guess it.
  70 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
  71
  72 ## Local bootp packets have bizarre addresses.  Don't block them just because
  73 ## of this.
  74 run iptables -t mangle -A in-classify -j RETURN \
  75         -s 0.0.0.0 -d 255.255.255.255 \
  76         -p udp --source-port $port_bootpc --destination-port $port_bootps
  77
  78 ## Since packets with source and destination addresses both local will go
  79 ## over the loopback interface, I shouldn't see a packet from me over any
  80 ## other interface.  Except that I will if I sent a broadcast or multicast.
  81 ## Allow the broadcasts, and remember not to trust them.  There are no
  82 ## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
  83 ## to worry about that.
  84 run iptables -t mangle -A local-source -j RETURN \
  85         -m addrtype --dst-type BROADCAST
  86 run iptables -t mangle -A local-source -j RETURN \
  87         -m addrtype --dst-type MULTICAST
  88 run ip6tables -t mangle -A local-source -j RETURN \
  89         -d ff00::/8
  90 run ip46tables -t mangle -A local-source -g bad-source-address
  91 run iptables -t mangle -A in-classify -j local-source \
  92         -m addrtype --src-type LOCAL
  93 for addr in $host_6addrs; do
  94   run ip6tables -t mangle -A in-classify -j local-source \
  95           -s $addr
  96 done
  97
  98 ## It's not valid to have a multicast address as a packet source: multicast
  99 ## routing is done away from the source, so a multicast address would make
 100 ## this impossible to do.  So discard these packets.  Also discard class-E
 101 ## IPv4 addresses, since they aren't assigned.
 102 run iptables -t mangle -A in-classify -g bad-source-address \
 103         -s 224.0.0.0/3
 104 run ip6tables -t mangle -A in-classify -g bad-source-address \
 105         -s ff00::/8
 106
 107 m4_divert(41)m4_dnl
 108 ## Define the important networks.
 109 for pass in 1 2; do
 110   netclassindex=0
 111 m4_divert(42)m4_dnl
 112 done
 113
 114 m4_divert(46)m4_dnl
 115 ## Mark addresses reachable on non-default interfaces as not reachable on the
 116 ## default interface.
 117 trace "nets = $allnets $allnets6"
 118 for net in $allnets; do
 119   case $net in
 120     "$defaultiface":*)
 121       ;;
 122     *)
 123       run iptables -t mangle -A in-$defaultiface \
 124               -s ${net#*:} -g bad-source-address
 125       ;;
 126   esac
 127 done
 128 for net in $allnets6; do
 129   case $net in
 130     "$defaultiface":*)
 131       ;;
 132     *)
 133       run ip6tables -t mangle -A in-$defaultiface \
 134               -s ${net#*:} -g bad-source-address
 135       ;;
 136   esac
 137 done
 138
 139 ## Fill in the black holes in the network.
 140 for addr in \
 141         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 142         127.0.0.0/8 192.0.2.0/24
 143 do
 144   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 145 done
 146 for addr in \
 147         fc00::/7 \
 148         2001:0db8::/32
 149 do
 150   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 151 done
 152
 153 m4_divert(92)m4_dnl
 154 ## Put the final default decision on the in-default chain, and attach the
 155 ## classification chains to the PREROUTING hook.
 156 run ip46tables -t mangle -A in-$defaultiface -g mark-from-$defaultclass
 157 run ip46tables -t mangle -A PREROUTING -j in-classify
 158 run ip46tables -t mangle -A PREROUTING -j out-classify
 159
 160 ## Now it's safe to let stuff through.
 161 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 162   run ip46tables -t mangle -P $i ACCEPT
 163 done
 164
 165 m4_divert(-1)
 166 ###----- That's all, folks --------------------------------------------------