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 ## An unpleasant hack.  We can't reject packets from the mangle table, so
  69 ## we mark packets with a bad destination and then detect this in the
  70 ## filter table.
  71 clearchain mangle:bad-destination-address
  72 BAD_DEST=0xf6f377d2
  73 run ip46tables -t mangle -A bad-destination-address \
  74   -j MARK --set-mark $BAD_DEST
  75 run ip46tables -t mangle -A bad-destination-address -j ACCEPT
  76 for i in $inchains; do
  77   run ip46tables -A $i -m mark --mark $BAD_DEST -g bad-destination-address
  78 done
  79
  80 ## Packets over the loopback interface are automatically trusted.  All manner
  81 ## of weird stuff happens on lo, and it's best not to second-guess it.
  82 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
  83
  84 ## Local broadcast and link-local multicast packets sometimes have bizarre
  85 ## addresses.  Don't block them just because of this.
  86 run iptables -t mangle -A in-classify -j RETURN \
  87         -s 0.0.0.0 -d 255.255.255.255 \
  88         -p udp
  89 run iptables -t mangle -A in-classify -j RETURN \
  90         -s 0.0.0.0 -d 224.0.0.0/24 \
  91         -p udp
  92
  93 ## Since packets with source and destination addresses both local will go
  94 ## over the loopback interface, I shouldn't see a packet from me over any
  95 ## other interface.  Except that I will if I sent a broadcast or multicast.
  96 ## Allow the broadcasts, and remember not to trust them.  There are no
  97 ## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
  98 ## to worry about that.
  99 run iptables -t mangle -A local-source -j RETURN \
 100         -m addrtype --dst-type BROADCAST
 101 run iptables -t mangle -A local-source -j RETURN \
 102         -m addrtype --dst-type MULTICAST
 103 run ip6tables -t mangle -A local-source -j RETURN \
 104         -d ff00::/8
 105 run ip46tables -t mangle -A local-source -g bad-source-address
 106 run iptables -t mangle -A in-classify -j local-source \
 107         -m addrtype --src-type LOCAL
 108 for addr in $host_6addrs; do
 109   run ip6tables -t mangle -A in-classify -j local-source \
 110           -s $addr
 111 done
 112
 113 m4_divert(41)m4_dnl
 114 ## Define the important networks.
 115 for pass in 1 2; do
 116   netclassindex=0
 117 m4_divert(42)m4_dnl
 118 done
 119
 120 m4_divert(46)m4_dnl
 121 ## Special IPv4 source addresses.  Forbid broadcast and multicast sources.
 122 ## Mark the special zero address and link-local addresses as such.  (This
 123 ## also matches class-E addresses, which are probably permanently invalid.)
 124 for i in 0.0.0.0 169.254.0.0/16; do
 125   run iptables -t mangle -A in-classify -g mark-from-link -s $i
 126 done
 127 run iptables -t mangle -A in-classify -g bad-source-address \
 128         -s 224.0.0.0/3
 129 run iptables -t mangle -A in-classify -g bad-source-address \
 130         -m addrtype --src-type BROADCAST \
 131
 132 ## Special IPv6 addresses.  Format multicast sources, and mark zero and
 133 ## link local addresses.
 134 for i in :: fe80::/10; do
 135   run ip6tables -t mangle -A in-classify -g mark-from-link -s $i
 136 done
 137 run ip6tables -t mangle -A in-classify -g bad-source-address \
 138         -s ff00::/8
 139
 140 ## Special IPv4 destination addresses.  The zero address is invalid; mark
 141 ## link-local and recognized broadcast addresses as link-local.  We leave
 142 ## multicast for later.
 143 for i in 0.0.0.0 240.0.0.0/4; do
 144   run iptables -t mangle -A out-classify -g bad-destination-address -d $i
 145 done
 146 run iptables -t mangle -A out-classify -g mark-to-link -d 169.254.0.0/16
 147 run iptables -t mangle -A out-classify -g mark-to-link \
 148         -m addrtype --dst-type BROADCAST
 149
 150 ## Special IPv6 destination addressses.  The zero address is again invalid;
 151 ## mark link local addresses.  We do multicast later.
 152 run ip6tables -t mangle -A out-classify -g bad-destination-address \
 153         -d ::
 154 run ip6tables -t mangle -A out-classify -g mark-to-link -d fe80::/10
 155
 156 ## Now deal with multicast.  Link-local multicast is detected as being
 157 ## link-local, so that we can prevent it being forwarded correctly.
 158 clearchain mangle:out-classify-mcast
 159 run iptables -t mangle -A out-classify-mcast -g mark-to-link \
 160         -d 224.0.0.0/24
 161 for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 162   run ip6tables -t mangle -A out-classify-mcast -g mark-to-link \
 163           -d ff${i}2::/16
 164 done
 165 run ip46tables -t mangle -A out-classify-mcast -g mark-to-mcast
 166 run iptables -t mangle -A out-classify -g out-classify-mcast \
 167         -d 224.0.0.0/4
 168 run ip6tables -t mangle -A out-classify -g out-classify-mcast \
 169         -d ff00::/8
 170
 171 ## Build the input classification chains.  There's one chain `in-IFACE' for
 172 ## each local interface.  This chain does a further dispatch on the source
 173 ## address to the appropriate `mark-from-CLASS' chain for the source network
 174 ## class.
 175 seen=:
 176 for iface in $host_ifaces_<::>FWHOST; do
 177   ifname=${iface%=*}
 178   case $seen in *:$ifname:*) continue ;; esac
 179   seen=$seen$ifname:
 180   clearchain mangle:in-$ifname
 181   run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
 182 done
 183
 184 ## Now populate the `in-IFACE' and `out-classify' chains.  We iterate over
 185 ## the available networks and add addresses to the appropriate chains.  Also,
 186 ## build up a map of which interfaces receive from which address ranged so
 187 ## that we can finish the chains off properly later.  This contains entries
 188 ## of the form IFACE=:ADDR:ADDR:...:
 189 ifnets=""
 190 for net in $allnets; do
 191
 192   ## Determine the addresses and class for this network, and populate the
 193   ## `out-classify' chains.
 194   eval addr=\$net_inet_$net addr6=\$net_inet6_$net class=\$net_class_$net
 195   case $class in virtual) continue ;; esac
 196   trace "$net : $class"
 197   for a in $addr; do
 198     run iptables -t mangle -A out-classify -g mark-to-$class -d $a
 199   done
 200   for a in $addr6; do
 201     run ip6tables -t mangle -A out-classify -g mark-to-$class -d $a
 202   done
 203
 204   ## Now work through the interfaces.
 205   for iface in $(net_interfaces FWHOST $net); do
 206     nets=""
 207     case $iface in
 208
 209       -)
 210         ## A special `no interface' marker: we should not receive packets
 211         ## from this network at all.
 212         continue
 213         ;;
 214
 215       *-+)
 216         ## A special marker indicating a collection of point-to-point
 217         ## interfaces.  We should match an address to a particular interface.
 218         ## Later, we'll cap this chain off by rejecting all other traffic.
 219         eval hosts=\$net_hosts_$net
 220         for host in $hosts; do
 221           eval ha=\$host_inet_$host ha6=\$host_inet6_$host
 222           trace "$host : $class -> $iface"
 223           for a in $ha; do
 224             run iptables -t mangle -A in-$iface \
 225                     -i ${iface%+}$host -s $a -g mark-from-$class
 226             nets=$nets$a:
 227           done
 228           for a in $ha6; do
 229             run ip6tables -t mangle -A in-$iface \
 230                     -i ${iface%+}$host -s $a -g mark-from-$class
 231             nets=$nets$a:
 232           done
 233         done
 234         ;;
 235
 236       *)
 237         ## A normal interface.  Classify incoming traffic according to the
 238         ## source address.
 239         trace "$net : $class -> $iface"
 240         for a in $addr; do
 241           run iptables -t mangle -A in-$iface -g mark-from-$class -s $a
 242           nets=$nets$a:
 243         done
 244         for a in $addr6; do
 245           run ip6tables -t mangle -A in-$iface -g mark-from-$class -s $a
 246           nets=$nets$a:
 247         done
 248         case $net in default) nets=${nets}default: ;; esac
 249         ;;
 250     esac
 251
 252     ## Record that this interface receives traffic from this network.
 253     unset nifnets
 254     foundp=nil
 255     for ifnet in $ifnets; do
 256       case $ifnet in
 257         $iface=*:$net:*) addword nifnets $ifnet; foundp=t ;;
 258         $iface=*) addword nifnets $ifnet$nets; foundp=t ;;
 259         *) addword nifnets $ifnet ;;
 260       esac
 261     done
 262     case $foundp in nil) addword nifnets $iface=:$nets ;; esac
 263     ifnets=$nifnets
 264
 265   done
 266 done
 267
 268 ## Wrap up all of the `in-IFACE' chains.  A chain which matches the `default'
 269 ## net should have unmatched but known networks blocked off, and then chain
 270 ## onto `in-default'.  Other chains should just chain onto
 271 ## `bad-source-address'.
 272 trace "ifnets = $ifnets"
 273 for ifnet in $ifnets; do
 274   iface=${ifnet%%=*} nets=${ifnet#*=}
 275   case $nets in
 276     *:default:*)
 277       for n in $allnets; do
 278         eval addr=\$net_inet_$n addr6=\$net_inet6_$n
 279         for a in $addr; do
 280           case $nets in *:$a:*) continue ;; esac
 281           nets=$nets$a
 282           run iptables -t mangle -A in-$iface -s $a -g bad-source-address
 283         done
 284         for a in $addr6; do
 285           case $nets in *:$a:*) continue ;; esac
 286           nets=$nets$a
 287           run ip6tables -t mangle -A in-$iface -s $a -g bad-source-address
 288         done
 289       done
 290       run ip46tables -t mangle -A in-$iface -g in-default
 291       ;;
 292     *)
 293       run ip46tables -t mangle -A in-$iface -g bad-source-address
 294       ;;
 295   esac
 296 done
 297
 298 ## Fill in the black holes in the network.
 299 for addr in \
 300         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 301         127.0.0.0/8 \
 302         192.0.2.0/24 198.51.100.0/24 203.0.113.0/24
 303 do
 304   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 305 done
 306 for addr in \
 307         fc00::/7 \
 308         2001:db8::/32
 309 do
 310   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 311 done
 312 run ip46tables -t mangle -A in-default -g mark-from-$net_class_default
 313
 314 m4_divert(92)m4_dnl
 315 ## Put the final default decision on the in-default chain, and attach the
 316 ## classification chains to the PREROUTING hook.
 317 for iface in $defaultifaces; do
 318   run ip46tables -t mangle -A in-$iface -g in-default
 319 done
 320 run ip46tables -t mangle -A out-classify -g mark-to-$net_class_default
 321 run ip46tables -t mangle -A PREROUTING -j in-classify
 322 run ip46tables -t mangle -A PREROUTING -j out-classify
 323
 324 ## Incoming stuff to or from a link-local address is OK.
 325 run ip46tables -t mangle -A INPUT \
 326         -m mark --mark $to_link/$MASK_TO \
 327         -j MARK --or-mark $fwd_link
 328 run ip46tables -t mangle -A INPUT \
 329         -m mark --mark $from_link/$MASK_FROM \
 330         -j MARK --or-mark $fwd_link
 331
 332 ## Now it's safe to let stuff through.
 333 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 334   run ip46tables -t mangle -P $i ACCEPT
 335 done
 336
 337 m4_divert(-1)
 338 ###----- That's all, folks --------------------------------------------------