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 invoke 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-DEFAULT (usually `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
  65 ### match.
  66
  67 clearchain mangle:in-classify mangle:in-default mangle:out-classify
  68 clearchain mangle:local-source
  69
  70 ## An unpleasant hack.  We can't reject packets from the mangle table, so
  71 ## we mark packets with a bad destination and then detect this in the
  72 ## filter table.
  73 clearchain mangle:bad-destination-address
  74 BAD_DEST=0xf6f377d2
  75 run ip46tables -t mangle -A bad-destination-address \
  76   -j MARK --set-mark $BAD_DEST
  77 run ip46tables -t mangle -A bad-destination-address -j ACCEPT
  78 for i in $inchains; do
  79   run ip46tables -A $i -m mark --mark $BAD_DEST -g bad-destination-address
  80 done
  81
  82 ## Packets over the loopback interface are automatically trusted.  All manner
  83 ## of weird stuff happens on lo, and it's best not to second-guess it.
  84 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
  85
  86 ## Local broadcast and link-local multicast packets sometimes have bizarre
  87 ## addresses.  Don't block them just because of this.
  88 run iptables -t mangle -A in-classify -j RETURN \
  89         -s 0.0.0.0 -d 255.255.255.255 \
  90         -p udp
  91 run iptables -t mangle -A in-classify -j RETURN \
  92         -s 0.0.0.0 -d 224.0.0.0/24 \
  93         -p udp
  94
  95 ## Since packets with source and destination addresses both local will go
  96 ## over the loopback interface, I shouldn't see a packet from me over any
  97 ## other interface.  Except that I will if I sent a broadcast or multicast.
  98 ## Allow the broadcasts, and remember not to trust them.  There are no
  99 ## broadcast addresses in IPv6 (only link-local multicast) so we don't have
 100 ## to worry about that.
 101 run iptables -t mangle -A local-source -j RETURN \
 102         -m addrtype --dst-type BROADCAST
 103 run iptables -t mangle -A local-source -j RETURN \
 104         -m addrtype --dst-type MULTICAST
 105 run ip6tables -t mangle -A local-source -j RETURN \
 106         -d ff00::/8
 107 run ip46tables -t mangle -A local-source -g bad-source-address
 108 run iptables -t mangle -A in-classify -j local-source \
 109         -m addrtype --src-type LOCAL
 110 for addr in $host_6addrs; do
 111   run ip6tables -t mangle -A in-classify -j local-source \
 112           -s $addr
 113 done
 114
 115 m4_divert(41)m4_dnl
 116 ## Define the important networks.
 117 for pass in 1 2; do
 118   netclassindex=0
 119 m4_divert(42)m4_dnl
 120 done
 121
 122 m4_divert(46)m4_dnl
 123 ## Special IPv4 source addresses.  Forbid broadcast and multicast sources.
 124 ## Mark the special zero address and link-local addresses as such.  (This
 125 ## also matches class-E addresses, which are probably permanently invalid.)
 126 for i in 0.0.0.0 169.254.0.0/16; do
 127   run iptables -t mangle -A in-classify -g mark-from-link -s $i
 128 done
 129 run iptables -t mangle -A in-classify -g bad-source-address \
 130         -s 224.0.0.0/3
 131 run iptables -t mangle -A in-classify -g bad-source-address \
 132         -m addrtype --src-type BROADCAST \
 133
 134 ## Special IPv6 addresses.  Forbid multicast sources, and mark zero and
 135 ## link local addresses.
 136 for i in :: fe80::/10; do
 137   run ip6tables -t mangle -A in-classify -g mark-from-link -s $i
 138 done
 139 run ip6tables -t mangle -A in-classify -g bad-source-address \
 140         -s ff00::/8
 141
 142 ## Special IPv4 destination addresses.  The zero address is invalid; mark
 143 ## link-local and recognized broadcast addresses as link-local.  We leave
 144 ## multicast for later.
 145 for i in 0.0.0.0 240.0.0.0/4; do
 146   run iptables -t mangle -A out-classify -g bad-destination-address -d $i
 147 done
 148 run iptables -t mangle -A out-classify -g mark-to-link -d 169.254.0.0/16
 149 run iptables -t mangle -A out-classify -g mark-to-link -d 255.255.255.255
 150 run iptables -t mangle -A out-classify -g mark-to-link \
 151         -m addrtype --dst-type BROADCAST
 152
 153 ## Special IPv6 destination addressses.  The zero address is again invalid;
 154 ## mark link local addresses.  We do multicast later.
 155 run ip6tables -t mangle -A out-classify -g bad-destination-address \
 156         -d ::
 157 run ip6tables -t mangle -A out-classify -g mark-to-link -d fe80::/10
 158
 159 ## Now deal with multicast.  Link-local multicast is detected as being
 160 ## link-local, so that we can prevent it being forwarded correctly.
 161 clearchain mangle:out-classify-mcast
 162 run iptables -t mangle -A out-classify-mcast -g mark-to-link \
 163         -d 224.0.0.0/24
 164 for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 165   run ip6tables -t mangle -A out-classify-mcast -g mark-to-link \
 166           -d ff${i}2::/16
 167 done
 168 run ip46tables -t mangle -A out-classify-mcast -g mark-to-mcast
 169 run iptables -t mangle -A out-classify -g out-classify-mcast \
 170         -d 224.0.0.0/4
 171 run ip6tables -t mangle -A out-classify -g out-classify-mcast \
 172         -d ff00::/8
 173
 174 ## Build the input classification chains.  There's one chain `in-IFACE' for
 175 ## each local interface.  This chain does a further dispatch on the source
 176 ## address to the appropriate `mark-from-CLASS' chain for the source network
 177 ## class.  We also build a table mapping interface names to numbers (since
 178 ## the names are so unhelpful).
 179 seen=:
 180 ifq=0
 181 ifmap=""
 182 for iface in $host_ifaces_<::>FWHOST; do
 183   ifname=${iface%=*}
 184   case $seen in *:$ifname:*) continue ;; esac
 185   seen=$seen$ifname:
 186   addword ifmap $ifname=$ifq
 187   ifq=$(( $ifq + 1 ))
 188   clearchain mangle:in-$ifname
 189   run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
 190 done
 191
 192 ## We do a first pass over nets first, and then the interfaces which those
 193 ## networks reach.  During this pass, we populate the `out-classify' chains,
 194 ## and we also build some lists so that we can do later passes over
 195 ## interfaces first and then reaching networks.  This is complicated by
 196 ## interface names being unhelpful.
 197 ##
 198 ## Here are the variables we maintain.
 199 ##
 200 ## ifmap                A list of entries IFACE=N mapping interface names to
 201 ##                      numbers.
 202 ##
 203 ## ifnets_N             A space-separated list of networks reaching interface
 204 ##                      number N.  This is used for building the matching
 205 ##                      chains.
 206 ##
 207 ## ifaddrs_N            A bang-separated list of address ranges reaching
 208 ##                      interface number N.  This is used for filtering out
 209 ##                      known networks if the default network reaches the
 210 ##                      interface.
 211 for net in $allnets; do
 212
 213   ## Work through the interfaces that this network reaches.
 214   for iface in $(net_interfaces FWHOST $net); do
 215     case $iface in -) break ;; esac
 216
 217     ## Find a sequence number for this interface.
 218     q=nil
 219     for i in $ifmap; do
 220       case "$i" in "$iface"=*) q=${i##*=}; break ;; esac
 221     done
 222     case $q in
 223       nil)
 224         echo >&2 "$0 INTERNAL ERROR: missing interface \`$iface'!"
 225         exit 1
 226         ;;
 227     esac
 228
 229     ## Remember the reachability information.
 230     addword ifnets_$q $net
 231   done
 232 done
 233
 234 ## Build the `ifaddr_N' map and an `all-addresses' list.
 235 alladdrs=!
 236 trace "ifmap = $ifmap"
 237 for entry in $ifmap; do
 238   iface=${entry%=*} q=${entry##*=}
 239   eval nets=\$ifnets_$q
 240   aa=!
 241   for n in $nets; do
 242     eval "addrs=\"\$net_inet_$n \$net_inet6_$n\""
 243     trace "$iface $n addrs = $addrs"
 244     for a in $addrs; do
 245       case $aa in *!$a!*) ;; *) aa=$aa$a! ;; esac
 246       case $alladdrs in *!$a!*) ;; *) alladdrs=$alladdrs$a! ;; esac
 247     done
 248   done
 249   eval ifaddrs_$q=\$aa
 250   trace "iface $q = $iface; nets = $nets; addrs = $aa"
 251 done
 252 trace "alladdrs = $alladdrs"
 253
 254 ## Populate the `out-classify' chain, matching networks.
 255 prepare_to () { mode=goto fail=mark-to-$net_class_default; }
 256 matchnets -d mark-to : prepare_to out-classify "" 0 $allnets
 257
 258 ## A `finish' hook for rejecting known address ranges arriving on a
 259 ## default-reachable interface.
 260 finish_from_default () {
 261   q=$1 chain=$2
 262   eval addrs=\$ifaddrs_$q
 263
 264   for n in $allnets; do
 265     eval addr=\$net_inet_$n addr6=\$net_inet6_$n
 266     for a in $addr; do
 267       case $a in !*) continue ;; esac
 268       case $addrs in *"!$a!"*) continue ;; esac
 269       run iptables -t mangle -A $chain -s $a -g bad-source-address
 270     done
 271     for a in $addr6; do
 272       case $a in !*) continue ;; esac
 273       case $addrs in *"!$a!"*) continue ;; esac
 274       run ip6tables -t mangle -A $chain -s $a -g bad-source-address
 275     done
 276   done
 277   run ip46tables -t mangle -A $chain -g in-default
 278 }
 279
 280 ## A `prepare' hook for input classification.  If the interface is
 281 ## default-reachable, then we need to reject known address ranges before
 282 ## dispatching to the default chain; otherwise just reject the packet.
 283 prepare_from () {
 284   q=$1 flags=$2
 285   case $flags in
 286     *:default:*) mode=call finish="finish_from_default $q" ;;
 287     *) mode=goto fail=bad-source-address ;;
 288   esac
 289 }
 290
 291 ## Populate the `in-IFACE' chains.
 292 for entry in $ifmap; do
 293   iface=${entry%=*} q=${entry##*=}
 294   eval nets=\$ifnets_$q
 295
 296   case $iface in
 297     *-+)
 298       ## A special marker indicating a collection of point-to-point
 299       ## interfaces.  We should match an address to a particular interface.
 300       chains=""
 301       for net in $nets; do
 302         eval hosts=\$net_hosts_$net class=\$net_class_$net
 303         for host in $hosts; do
 304           eval ha=\$host_inet_$host ha6=\$host_inet6_$host
 305           trace "$host : $class -> $iface"
 306           for a in $ha; do
 307             run iptables -t mangle -A in-$iface \
 308                     -i ${iface%+}$host -s $a -g mark-from-$class
 309           done
 310           for a in $ha6; do
 311             run ip6tables -t mangle -A in-$iface \
 312                     -i ${iface%+}$host -s $a -g mark-from-$class
 313           done
 314         done
 315       done
 316       run ip46tables -t mangle -A in-$iface -g bad-source-address
 317       ;;
 318     *)
 319       matchnets -s mark-from : "prepare_from $q" in-$iface "" 0 $nets
 320       ;;
 321   esac
 322 done
 323
 324 ## Fill in the black holes in the network.  Some of these might actually be
 325 ## known networks, so don't fill those in again.  See RFC5735 and RFC4291,
 326 ## and their successors.
 327 for addr in \
 328         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 329         127.0.0.0/8 \
 330         192.0.2.0/24 198.51.100.0/24 203.0.113.0/24
 331 do
 332   case $alladdrs in *!$addr!*) continue ;; esac
 333   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 334 done
 335 for addr in \
 336         fc00::/7 fec0::/10 \
 337         ::0:0/96 ::ffff:0:0/96 \
 338         2001:db8::/32
 339 do
 340   case $alladdrs in *!$addr!*) continue ;; esac
 341   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 342 done
 343 run ip46tables -t mangle -A in-default -g mark-from-$net_class_default
 344
 345 m4_divert(92)m4_dnl
 346 ## Put the final default decision on the in-default chain, and attach the
 347 ## classification chains to the INPUT and (maybe) FORWARD hooks.
 348 for iface in $defaultifaces; do
 349   run ip46tables -t mangle -A in-$iface -g in-default
 350 done
 351 chains="INPUT"
 352 case $forward in 1) chains="$chains FORWARD" ;; esac
 353 for c in $chains; do
 354   run ip46tables -t mangle -A $c -j in-classify
 355   run ip46tables -t mangle -A $c -j out-classify
 356 done
 357
 358 ## Incoming stuff to or from a link-local address is OK.
 359 run ip46tables -t mangle -A INPUT \
 360         -m mark --mark $to_link/$MASK_TO \
 361         -j MARK --or-mark $fwd_link
 362 run ip46tables -t mangle -A INPUT \
 363         -m mark --mark $from_link/$MASK_FROM \
 364         -j MARK --or-mark $fwd_link
 365
 366 ## Now it's safe to let stuff through.
 367 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 368   run ip46tables -t mangle -P $i ACCEPT
 369 done
 370
 371 m4_divert(-1)
 372 ###----- That's all, folks --------------------------------------------------