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 INPUT and FORWARD hooks simply invokes in-classify and out-classify
  49 ### chains as subroutines.  These will tail-call appropriate classification
  50 ### chains.
  51 ###
  52 ### The in-classify chain is responsible for both source address
  53 ### classification and verifying that the packet arrived from the correct
  54 ### interface.  It does an initial dispatch on the source interface, to
  55 ### in-IFACE.  The in-IFACE chain dispatches to mark-from-CLASS when it
  56 ### recognizes an address belonging to the CLASS; if no matches succeed, it
  57 ### goes to bad-source-address, which logs a message and drops the packet.
  58 ### The default interface is special.  If no explicit matches are found, it
  59 ### dispatches to in-default which forbids a few obviously evil things and
  60 ### finally dispatches to mark-from-untrusted.
  61 ###
  62 ### The out-classify is simpler because it doesn't care about the interface.
  63 ### It simply checks each network range in turn, dispatching to mark-to-CLASS
  64 ### on a match or mark-to-DEFAULT (probably untrusted) if there is no match.
  65
  66 clearchain mangle:in-classify mangle:in-default mangle:out-classify
  67 clearchain mangle:local-source
  68
  69 ## An unpleasant hack.  We can't reject packets from the mangle table, so
  70 ## we mark packets with a bad destination and then detect this in the
  71 ## filter table.
  72 clearchain mangle:bad-destination-address
  73 BAD_DEST=0xf6f377d2
  74 run ip46tables -t mangle -A bad-destination-address \
  75   -j MARK --set-mark $BAD_DEST
  76 run ip46tables -t mangle -A bad-destination-address -j ACCEPT
  77 for i in $inchains; do
  78   run ip46tables -A $i -m mark --mark $BAD_DEST -g bad-destination-address
  79 done
  80
  81 ## Packets over the loopback interface are automatically trusted.  All manner
  82 ## of weird stuff happens on lo, and it's best not to second-guess it.
  83 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
  84
  85 ## Local broadcast and link-local multicast packets sometimes have bizarre
  86 ## addresses.  Don't block them just because of this.
  87 run iptables -t mangle -A in-classify -j RETURN \
  88         -s 0.0.0.0 -d 255.255.255.255 \
  89         -p udp
  90 run iptables -t mangle -A in-classify -j RETURN \
  91         -s 0.0.0.0 -d 224.0.0.0/24 \
  92         -p udp
  93
  94 ## Since packets with source and destination addresses both local will go
  95 ## over the loopback interface, I shouldn't see a packet from me over any
  96 ## other interface.  Except that I will if I sent a broadcast or multicast.
  97 ## Allow the broadcasts, and remember not to trust them.  There are no
  98 ## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
  99 ## to worry about that.
 100 run iptables -t mangle -A local-source -j RETURN \
 101         -m addrtype --dst-type BROADCAST
 102 run iptables -t mangle -A local-source -j RETURN \
 103         -m addrtype --dst-type MULTICAST
 104 run ip6tables -t mangle -A local-source -j RETURN \
 105         -d ff00::/8
 106 run ip46tables -t mangle -A local-source -g bad-source-address
 107 run iptables -t mangle -A in-classify -j local-source \
 108         -m addrtype --src-type LOCAL
 109 for addr in $host_6addrs; do
 110   run ip6tables -t mangle -A in-classify -j local-source \
 111           -s $addr
 112 done
 113
 114 m4_divert(41)m4_dnl
 115 ## Define the important networks.
 116 for pass in 1 2; do
 117   netclassindex=0
 118 m4_divert(42)m4_dnl
 119 done
 120
 121 m4_divert(46)m4_dnl
 122 ## Special IPv4 source addresses.  Forbid broadcast and multicast sources.
 123 ## Mark the special zero address and link-local addresses as such.  (This
 124 ## also matches class-E addresses, which are probably permanently invalid.)
 125 for i in 0.0.0.0 169.254.0.0/16; do
 126   run iptables -t mangle -A in-classify -g mark-from-link -s $i
 127 done
 128 run iptables -t mangle -A in-classify -g bad-source-address \
 129         -s 224.0.0.0/3
 130 run iptables -t mangle -A in-classify -g bad-source-address \
 131         -m addrtype --src-type BROADCAST \
 132
 133 ## Special IPv6 addresses.  Format multicast sources, and mark zero and
 134 ## link local addresses.
 135 for i in :: fe80::/10; do
 136   run ip6tables -t mangle -A in-classify -g mark-from-link -s $i
 137 done
 138 run ip6tables -t mangle -A in-classify -g bad-source-address \
 139         -s ff00::/8
 140
 141 ## Special IPv4 destination addresses.  The zero address is invalid; mark
 142 ## link-local and recognized broadcast addresses as link-local.  We leave
 143 ## multicast for later.
 144 for i in 0.0.0.0 240.0.0.0/4; do
 145   run iptables -t mangle -A out-classify -g bad-destination-address -d $i
 146 done
 147 run iptables -t mangle -A out-classify -g mark-to-link -d 169.254.0.0/16
 148 run iptables -t mangle -A out-classify -g mark-to-link \
 149         -m addrtype --dst-type BROADCAST
 150
 151 ## Special IPv6 destination addressses.  The zero address is again invalid;
 152 ## mark link local addresses.  We do multicast later.
 153 run ip6tables -t mangle -A out-classify -g bad-destination-address \
 154         -d ::
 155 run ip6tables -t mangle -A out-classify -g mark-to-link -d fe80::/10
 156
 157 ## Now deal with multicast.  Link-local multicast is detected as being
 158 ## link-local, so that we can prevent it being forwarded correctly.
 159 clearchain mangle:out-classify-mcast
 160 run iptables -t mangle -A out-classify-mcast -g mark-to-link \
 161         -d 224.0.0.0/24
 162 for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 163   run ip6tables -t mangle -A out-classify-mcast -g mark-to-link \
 164           -d ff${i}2::/16
 165 done
 166 run ip46tables -t mangle -A out-classify-mcast -g mark-to-mcast
 167 run iptables -t mangle -A out-classify -g out-classify-mcast \
 168         -d 224.0.0.0/4
 169 run ip6tables -t mangle -A out-classify -g out-classify-mcast \
 170         -d ff00::/8
 171
 172 ## Build the input classification chains.  There's one chain `in-IFACE' for
 173 ## each local interface.  This chain does a further dispatch on the source
 174 ## address to the appropriate `mark-from-CLASS' chain for the source network
 175 ## class.  We also build a table mapping interface names to numbers (since
 176 ## the names are so unhelpful).
 177 seen=:
 178 ifq=0
 179 ifmap=""
 180 for iface in $host_ifaces_<::>FWHOST; do
 181   ifname=${iface%=*}
 182   case $seen in *:$ifname:*) continue ;; esac
 183   seen=$seen$ifname:
 184   addword ifmap $ifname=$ifq
 185   ifq=$(( $ifq + 1 ))
 186   clearchain mangle:in-$ifname
 187   run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
 188 done
 189
 190 ## We do a first pass over nets first, and then the interfaces which those
 191 ## networks reach.  During this pass, we populate the `out-classify' chains,
 192 ## and we also build some lists so that we can do later passes over
 193 ## interfaces first and then reaching networks.  This is complicated by
 194 ## interface names being unhelpful.
 195 ##
 196 ## Here are the variables we maintain.
 197 ##
 198 ## ifmap                A list of entries IFACE=N mapping interface names to
 199 ##                      numbers.
 200 ##
 201 ## ifnets_N             A space-separated list of networks reaching interface
 202 ##                      number N.  This is used for building the matching
 203 ##                      chains.
 204 ##
 205 ## ifaddrs_N            A bang-separated list of address ranges reaching
 206 ##                      interface number N.  This is used for filtering out
 207 ##                      known networks if the default network reaches the
 208 ##                      interface.
 209 for net in $allnets; do
 210
 211   ## Work through the interfaces that this network reaches.
 212   for iface in $(net_interfaces FWHOST $net); do
 213     case $iface in -) break ;; esac
 214
 215     ## Find a sequence number for this interface.
 216     q=nil
 217     for i in $ifmap; do
 218       case "$i" in "$iface"=*) q=${i##*=}; break ;; esac
 219     done
 220     case $q in
 221       nil)
 222         echo >&2 "$0 INTERNAL ERROR: missing interface \`$iface'!"
 223         exit 1
 224         ;;
 225     esac
 226
 227     ## Remember the reachability information.
 228     addword ifnets_$q $net
 229   done
 230 done
 231
 232 ## Build the `ifaddr_N' map and an `all-addresses' list.
 233 alladdrs=!
 234 trace "ifmap = $ifmap"
 235 for entry in $ifmap; do
 236   iface=${entry%=*} q=${entry##*=}
 237   eval nets=\$ifnets_$q
 238   aa=!
 239   for n in $nets; do
 240     eval "addrs=\"\$net_inet_$n \$net_inet6_$n\""
 241     trace "$iface $n addrs = $addrs"
 242     for a in $addrs; do
 243       case $aa in *!$a!*) ;; *) aa=$aa$a! ;; esac
 244       case $alladdrs in *!$a!*) ;; *) alladdrs=$alladdrs$a! ;; esac
 245     done
 246   done
 247   eval ifaddrs_$q=\$aa
 248   trace "iface $q = $iface; nets = $nets; addrs = $aa"
 249 done
 250 trace "alladdrs = $alladdrs"
 251
 252 ## Populate the `out-classify' chain, matching networks.
 253 prepare_to () { mode=goto fail=mark-to-$net_class_default; }
 254 matchnets -d mark-to : prepare_to out-classify "" 0 $allnets
 255
 256 ## A `finish' hook for rejecting known address ranges arriving on a
 257 ## default-reachable interface.
 258 finish_from_default () {
 259   q=$1 chain=$2
 260   eval addrs=\$ifaddrs_$q
 261
 262   for n in $allnets; do
 263     eval addr=\$net_inet_$n addr6=\$net_inet6_$n
 264     for a in $addr; do
 265       case $a in !*) continue ;; esac
 266       case $addrs in *"!$a!"*) continue ;; esac
 267       run iptables -t mangle -A $chain -s $a -g bad-source-address
 268     done
 269     for a in $addr6; do
 270       case $a in !*) continue ;; esac
 271       case $addrs in *"!$a!"*) continue ;; esac
 272       run ip6tables -t mangle -A $chain -s $a -g bad-source-address
 273     done
 274   done
 275   run ip46tables -t mangle -A $chain -g in-default
 276 }
 277
 278 ## A `prepare' hook for input classification.  If the interface is
 279 ## default-reachable, then we need to reject known address ranges before
 280 ## dispatching to the default chain; otherwise just reject the packet.
 281 prepare_from () {
 282   q=$1 flags=$2
 283   case $flags in
 284     *:default:*) mode=call finish="finish_from_default $q" ;;
 285     *) mode=goto fail=bad-source-address ;;
 286   esac
 287 }
 288
 289 ## Populate the `in-IFACE' chains.
 290 for entry in $ifmap; do
 291   iface=${entry%=*} q=${entry##*=}
 292   eval nets=\$ifnets_$q
 293
 294   case $iface in
 295     *-+)
 296       ## A special marker indicating a collection of point-to-point
 297       ## interfaces.  We should match an address to a particular interface.
 298       chains=""
 299       for net in $nets; do
 300         eval hosts=\$net_hosts_$net class=\$net_class_$net
 301         for host in $hosts; do
 302           eval ha=\$host_inet_$host ha6=\$host_inet6_$host
 303           trace "$host : $class -> $iface"
 304           for a in $ha; do
 305             run iptables -t mangle -A in-$iface \
 306                     -i ${iface%+}$host -s $a -g mark-from-$class
 307           done
 308           for a in $ha6; do
 309             run ip6tables -t mangle -A in-$iface \
 310                     -i ${iface%+}$host -s $a -g mark-from-$class
 311           done
 312         done
 313       done
 314       run ip46tables -t mangle -A in-$iface -g bad-source-address
 315       ;;
 316     *)
 317       matchnets -s mark-from : "prepare_from $q" in-$iface "" 0 $nets
 318       ;;
 319   esac
 320 done
 321
 322 ## Fill in the black holes in the network.  Some of these might actually be
 323 ## known networks, so don't fill those in again.  See RFC5735 or its
 324 ## successors.
 325 for addr in \
 326         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 327         127.0.0.0/8 \
 328         192.0.2.0/24 198.51.100.0/24 203.0.113.0/24
 329 do
 330   case $alladdrs in *!$addr!*) continue ;; esac
 331   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 332 done
 333 for addr in \
 334         fc00::/7 \
 335         2001:db8::/32
 336 do
 337   case $alladdrs in *!$addr!*) continue ;; esac
 338   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 339 done
 340 run ip46tables -t mangle -A in-default -g mark-from-$net_class_default
 341
 342 m4_divert(92)m4_dnl
 343 ## Put the final default decision on the in-default chain, and attach the
 344 ## classification chains to the INPUT and (maybe) FORWARD hooks.
 345 for iface in $defaultifaces; do
 346   run ip46tables -t mangle -A in-$iface -g in-default
 347 done
 348 chains="INPUT"
 349 case $forward in 1) chains="$chains FORWARD" ;; esac
 350 for c in $chains; do
 351   run ip46tables -t mangle -A $c -j in-classify
 352   run ip46tables -t mangle -A $c -j out-classify
 353 done
 354
 355 ## Incoming stuff to or from a link-local address is OK.
 356 run ip46tables -t mangle -A INPUT \
 357         -m mark --mark $to_link/$MASK_TO \
 358         -j MARK --or-mark $fwd_link
 359 run ip46tables -t mangle -A INPUT \
 360         -m mark --mark $from_link/$MASK_FROM \
 361         -j MARK --or-mark $fwd_link
 362
 363 ## Now it's safe to let stuff through.
 364 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 365   run ip46tables -t mangle -P $i ACCEPT
 366 done
 367
 368 m4_divert(-1)
 369 ###----- That's all, folks --------------------------------------------------