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 broadcast and link-local multicast packets sometimes have bizarre
  73 ## addresses.  Don't block them just because 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
  77 run iptables -t mangle -A in-classify -j RETURN \
  78         -s 0.0.0.0 -d 224.0.0.0/24 \
  79         -p udp
  80
  81 ## Since packets with source and destination addresses both local will go
  82 ## over the loopback interface, I shouldn't see a packet from me over any
  83 ## other interface.  Except that I will if I sent a broadcast or multicast.
  84 ## Allow the broadcasts, and remember not to trust them.  There are no
  85 ## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
  86 ## to worry about that.
  87 run iptables -t mangle -A local-source -j RETURN \
  88         -m addrtype --dst-type BROADCAST
  89 run iptables -t mangle -A local-source -j RETURN \
  90         -m addrtype --dst-type MULTICAST
  91 run ip6tables -t mangle -A local-source -j RETURN \
  92         -d ff00::/8
  93 run ip46tables -t mangle -A local-source -g bad-source-address
  94 run iptables -t mangle -A in-classify -j local-source \
  95         -m addrtype --src-type LOCAL
  96 for addr in $host_6addrs; do
  97   run ip6tables -t mangle -A in-classify -j local-source \
  98           -s $addr
  99 done
 100
 101 ## It's not valid to have a multicast address as a packet source: multicast
 102 ## routing is done away from the source, so a multicast address would make
 103 ## this impossible to do.  So discard these packets.  Also discard class-E
 104 ## IPv4 addresses, since they aren't assigned.
 105 run iptables -t mangle -A in-classify -g bad-source-address \
 106         -s 224.0.0.0/3
 107 run ip6tables -t mangle -A in-classify -g bad-source-address \
 108         -s ff00::/8
 109
 110 m4_divert(41)m4_dnl
 111 ## Define the important networks.
 112 for pass in 1 2; do
 113   netclassindex=0
 114 m4_divert(42)m4_dnl
 115 done
 116
 117 m4_divert(46)m4_dnl
 118 ## Build the input classification chains.  There's one chain `in-IFACE' for
 119 ## each local interface.  This chain does a further dispatch on the source
 120 ## address to the appropriate `mark-from-CLASS' chain for the source network
 121 ## class.
 122 seen=:
 123 for iface in $host_ifaces_<::>FWHOST; do
 124   ifname=${iface%=*}
 125   case $seen in *:$ifname:*) continue ;; esac
 126   seen=$seen$ifname:
 127   clearchain mangle:in-$ifname
 128   run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
 129 done
 130
 131 ## Now populate the `in-IFACE' and `out-classify' chains.  We iterate over
 132 ## the available networks and add addresses to the appropriate chains.  Also,
 133 ## build up a map of which interfaces receive from which address ranged so
 134 ## that we can finish the chains off properly later.  This contains entries
 135 ## of the form IFACE=:ADDR:ADDR:...:
 136 ifnets=""
 137 for net in $allnets; do
 138
 139   ## Determine the addresses and class for this network, and populate the
 140   ## `out-classify' chains.
 141   eval addr=\$net_inet_$net addr6=\$net_inet6_$net class=\$net_class_$net
 142   case $class in virtual) continue ;; esac
 143   trace "$net : $class"
 144   for a in $addr; do
 145     run iptables -t mangle -A out-classify -g mark-to-$class -d $a
 146   done
 147   for a in $addr6; do
 148     run ip6tables -t mangle -A out-classify -g mark-to-$class -d $a
 149   done
 150
 151   ## Now work through the interfaces.
 152   for iface in $(net_interfaces FWHOST $net); do
 153     nets=""
 154     case $iface in
 155
 156       -)
 157         ## A special `no interface' marker: we should not receive packets
 158         ## from this network at all.
 159         continue
 160         ;;
 161
 162       *-+)
 163         ## A special marker indicating a collection of point-to-point
 164         ## interfaces.  We should match an address to a particular interface.
 165         ## Later, we'll cap this chain off by rejecting all other traffic.
 166         eval hosts=\$net_hosts_$net
 167         for host in $hosts; do
 168           eval ha=\$host_inet_$host ha6=\$host_inet6_$host
 169           trace "$host : $class -> $iface"
 170           for a in $ha; do
 171             run iptables -t mangle -A in-$iface \
 172                     -i ${iface%+}$host -s $a -g mark-from-$class
 173             nets=$nets$a:
 174           done
 175           for a in $ha6; do
 176             run ip6tables -t mangle -A in-$iface \
 177                     -i ${iface%+}$host -s $a -g mark-from-$class
 178             nets=$nets$a:
 179           done
 180         done
 181         ;;
 182
 183       *)
 184         ## A normal interface.  Classify incoming traffic according to the
 185         ## source address.
 186         trace "$net : $class -> $iface"
 187         for a in $addr; do
 188           run iptables -t mangle -A in-$iface -g mark-from-$class -s $a
 189           nets=$nets$a:
 190         done
 191         for a in $addr6; do
 192           run ip6tables -t mangle -A in-$iface -g mark-from-$class -s $a
 193           nets=$nets$a:
 194         done
 195         case $net in default) nets=${nets}default: ;; esac
 196         ;;
 197     esac
 198
 199     ## Record that this interface receives traffic from this network.
 200     unset nifnets
 201     foundp=nil
 202     for ifnet in $ifnets; do
 203       case $ifnet in
 204         $iface=*:$net:*) addword nifnets $ifnet; foundp=t ;;
 205         $iface=*) addword nifnets $ifnet$nets; foundp=t ;;
 206         *) addword nifnets $ifnet ;;
 207       esac
 208     done
 209     case $foundp in nil) addword nifnets $iface=:$nets ;; esac
 210     ifnets=$nifnets
 211
 212   done
 213 done
 214
 215 ## Wrap up all of the `in-IFACE' chains.  A chain which matches the `default'
 216 ## net should have unmatched but known networks blocked off, and then chain
 217 ## onto `in-default'.  Other chains should just chain onto
 218 ## `bad-source-address'.
 219 trace "ifnets = $ifnets"
 220 for ifnet in $ifnets; do
 221   iface=${ifnet%%=*} nets=${ifnet#*=}
 222   case $nets in
 223     *:default:*)
 224       for n in $allnets; do
 225         eval addr=\$net_inet_$n addr6=\$net_inet6_$n
 226         for a in $addr; do
 227           case $nets in *:$a:*) continue ;; esac
 228           nets=$nets$a
 229           run iptables -t mangle -A in-$iface -s $a -g bad-source-address
 230         done
 231         for a in $addr6; do
 232           case $nets in *:$a:*) continue ;; esac
 233           nets=$nets$a
 234           run ip6tables -t mangle -A in-$iface -s $a -g bad-source-address
 235         done
 236       done
 237       run ip46tables -t mangle -A in-$iface -g in-default
 238       ;;
 239     *)
 240       run ip46tables -t mangle -A in-$iface -g bad-source-address
 241       ;;
 242   esac
 243 done
 244
 245 ## Fill in the black holes in the network.
 246 for addr in \
 247         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 248         127.0.0.0/8 \
 249         192.0.2.0/24 198.51.100.0/24 203.0.113.0/24
 250 do
 251   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 252 done
 253 for addr in \
 254         fc00::/7 \
 255         2001:0db8::/32
 256 do
 257   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 258 done
 259 run ip46tables -t mangle -A in-default -g mark-from-$net_class_default
 260
 261 m4_divert(92)m4_dnl
 262 ## Put the final default decision on the in-default chain, and attach the
 263 ## classification chains to the PREROUTING hook.
 264 for iface in $defaultifaces; do
 265   run ip46tables -t mangle -A in-$iface -g in-default
 266 done
 267 run ip46tables -t mangle -A out-classify -g mark-to-$net_class_default
 268 run ip46tables -t mangle -A PREROUTING -j in-classify
 269 run ip46tables -t mangle -A PREROUTING -j out-classify
 270
 271 ## Now it's safe to let stuff through.
 272 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 273   run ip46tables -t mangle -P $i ACCEPT
 274 done
 275
 276 m4_divert(-1)
 277 ###----- That's all, folks --------------------------------------------------