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