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 $i
 147 done
 148 run iptables -t mangle -A out-classify -g mark-to-link -d 169.254.0.0/16
 149 run iptables -t mangle -A out-classify -g mark-to-link \
 150         -m addrtype --dst-type BROADCAST
 151
 152 ## Special IPv6 destination addressses.  The zero address is again invalid;
 153 ## mark link local addresses.  We do multicast later.
 154 run ip6tables -t mangle -A out-classify -g bad-destination-address \
 155         -d ::
 156 run ip6tables -t mangle -A out-classify -g mark-to-link -d fe80::/10
 157
 158 ## Now deal with multicast.  Link-local multicast is detected as being
 159 ## link-local, so that we can prevent it being forwarded correctly.
 160 clearchain mangle:out-classify-mcast
 161 run iptables -t mangle -A out-classify-mcast -g mark-to-link \
 162         -d 224.0.0.0/24
 163 for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 164   run ip6tables -t mangle -A out-classify-mcast -g mark-to-link \
 165           -d ff${i}2::/16
 166 done
 167 run ip46tables -t mangle -A out-classify-mcast -g mark-to-mcast
 168 run iptables -t mangle -A out-classify -g out-classify-mcast \
 169         -d 224.0.0.0/4
 170 run ip6tables -t mangle -A out-classify -g out-classify-mcast \
 171         -d ff00::/8
 172
 173 ## Build the input classification chains.  There's one chain `in-IFACE' for
 174 ## each local interface.  This chain does a further dispatch on the source
 175 ## address to the appropriate `mark-from-CLASS' chain for the source network
 176 ## class.  We also build a table mapping interface names to numbers (since
 177 ## the names are so unhelpful).
 178 seen=:
 179 ifq=0
 180 ifmap=""
 181 for iface in $host_ifaces_<::>FWHOST; do
 182   ifname=${iface%=*}
 183   case $seen in *:$ifname:*) continue ;; esac
 184   seen=$seen$ifname:
 185   addword ifmap $ifname=$ifq
 186   ifq=$(( $ifq + 1 ))
 187   clearchain mangle:in-$ifname
 188   run ip46tables -t mangle -A in-classify -i $ifname -g in-$ifname
 189 done
 190
 191 ## We do a first pass over nets first, and then the interfaces which those
 192 ## networks reach.  During this pass, we populate the `out-classify' chains,
 193 ## and we also build some lists so that we can do later passes over
 194 ## interfaces first and then reaching networks.  This is complicated by
 195 ## interface names being unhelpful.
 196 ##
 197 ## Here are the variables we maintain.
 198 ##
 199 ## ifmap                A list of entries IFACE=N mapping interface names to
 200 ##                      numbers.
 201 ##
 202 ## ifnets_N             A space-separated list of networks reaching interface
 203 ##                      number N.  This is used for building the matching
 204 ##                      chains.
 205 ##
 206 ## ifaddrs_N            A bang-separated list of address ranges reaching
 207 ##                      interface number N.  This is used for filtering out
 208 ##                      known networks if the default network reaches the
 209 ##                      interface.
 210 for net in $allnets; do
 211
 212   ## Work through the interfaces that this network reaches.
 213   for iface in $(net_interfaces FWHOST $net); do
 214     case $iface in -) break ;; esac
 215
 216     ## Find a sequence number for this interface.
 217     q=nil
 218     for i in $ifmap; do
 219       case "$i" in "$iface"=*) q=${i##*=}; break ;; esac
 220     done
 221     case $q in
 222       nil)
 223         echo >&2 "$0 INTERNAL ERROR: missing interface \`$iface'!"
 224         exit 1
 225         ;;
 226     esac
 227
 228     ## Remember the reachability information.
 229     addword ifnets_$q $net
 230   done
 231 done
 232
 233 ## Build the `ifaddr_N' map and an `all-addresses' list.
 234 alladdrs=!
 235 trace "ifmap = $ifmap"
 236 for entry in $ifmap; do
 237   iface=${entry%=*} q=${entry##*=}
 238   eval nets=\$ifnets_$q
 239   aa=!
 240   for n in $nets; do
 241     eval "addrs=\"\$net_inet_$n \$net_inet6_$n\""
 242     trace "$iface $n addrs = $addrs"
 243     for a in $addrs; do
 244       case $aa in *!$a!*) ;; *) aa=$aa$a! ;; esac
 245       case $alladdrs in *!$a!*) ;; *) alladdrs=$alladdrs$a! ;; esac
 246     done
 247   done
 248   eval ifaddrs_$q=\$aa
 249   trace "iface $q = $iface; nets = $nets; addrs = $aa"
 250 done
 251 trace "alladdrs = $alladdrs"
 252
 253 ## Populate the `out-classify' chain, matching networks.
 254 prepare_to () { mode=goto fail=mark-to-$net_class_default; }
 255 matchnets -d mark-to : prepare_to out-classify "" 0 $allnets
 256
 257 ## A `finish' hook for rejecting known address ranges arriving on a
 258 ## default-reachable interface.
 259 finish_from_default () {
 260   q=$1 chain=$2
 261   eval addrs=\$ifaddrs_$q
 262
 263   for n in $allnets; do
 264     eval addr=\$net_inet_$n addr6=\$net_inet6_$n
 265     for a in $addr; do
 266       case $a in !*) continue ;; esac
 267       case $addrs in *"!$a!"*) continue ;; esac
 268       run iptables -t mangle -A $chain -s $a -g bad-source-address
 269     done
 270     for a in $addr6; do
 271       case $a in !*) continue ;; esac
 272       case $addrs in *"!$a!"*) continue ;; esac
 273       run ip6tables -t mangle -A $chain -s $a -g bad-source-address
 274     done
 275   done
 276   run ip46tables -t mangle -A $chain -g in-default
 277 }
 278
 279 ## A `prepare' hook for input classification.  If the interface is
 280 ## default-reachable, then we need to reject known address ranges before
 281 ## dispatching to the default chain; otherwise just reject the packet.
 282 prepare_from () {
 283   q=$1 flags=$2
 284   case $flags in
 285     *:default:*) mode=call finish="finish_from_default $q" ;;
 286     *) mode=goto fail=bad-source-address ;;
 287   esac
 288 }
 289
 290 ## Populate the `in-IFACE' chains.
 291 for entry in $ifmap; do
 292   iface=${entry%=*} q=${entry##*=}
 293   eval nets=\$ifnets_$q
 294
 295   case $iface in
 296     *-+)
 297       ## A special marker indicating a collection of point-to-point
 298       ## interfaces.  We should match an address to a particular interface.
 299       chains=""
 300       for net in $nets; do
 301         eval hosts=\$net_hosts_$net class=\$net_class_$net
 302         for host in $hosts; do
 303           eval ha=\$host_inet_$host ha6=\$host_inet6_$host
 304           trace "$host : $class -> $iface"
 305           for a in $ha; do
 306             run iptables -t mangle -A in-$iface \
 307                     -i ${iface%+}$host -s $a -g mark-from-$class
 308           done
 309           for a in $ha6; do
 310             run ip6tables -t mangle -A in-$iface \
 311                     -i ${iface%+}$host -s $a -g mark-from-$class
 312           done
 313         done
 314       done
 315       run ip46tables -t mangle -A in-$iface -g bad-source-address
 316       ;;
 317     *)
 318       matchnets -s mark-from : "prepare_from $q" in-$iface "" 0 $nets
 319       ;;
 320   esac
 321 done
 322
 323 ## Fill in the black holes in the network.  Some of these might actually be
 324 ## known networks, so don't fill those in again.  See RFC5735 and RFC4291,
 325 ## and their successors.
 326 for addr in \
 327         10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
 328         127.0.0.0/8 \
 329         192.0.2.0/24 198.51.100.0/24 203.0.113.0/24
 330 do
 331   case $alladdrs in *!$addr!*) continue ;; esac
 332   run iptables -t mangle -A in-default -s $addr -g bad-source-address
 333 done
 334 for addr in \
 335         fc00::/7 fec0::/10 \
 336         ::0:0/96 ::ffff:0:0/96 \
 337         2001:db8::/32
 338 do
 339   case $alladdrs in *!$addr!*) continue ;; esac
 340   run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
 341 done
 342 run ip46tables -t mangle -A in-default -g mark-from-$net_class_default
 343
 344 m4_divert(92)m4_dnl
 345 ## Put the final default decision on the in-default chain, and attach the
 346 ## classification chains to the INPUT and (maybe) FORWARD hooks.
 347 for iface in $defaultifaces; do
 348   run ip46tables -t mangle -A in-$iface -g in-default
 349 done
 350 chains="INPUT"
 351 case $forward in 1) chains="$chains FORWARD" ;; esac
 352 for c in $chains; do
 353   run ip46tables -t mangle -A $c -j in-classify
 354   run ip46tables -t mangle -A $c -j out-classify
 355 done
 356
 357 ## Incoming stuff to or from a link-local address is OK.
 358 run ip46tables -t mangle -A INPUT \
 359         -m mark --mark $to_link/$MASK_TO \
 360         -j MARK --or-mark $fwd_link
 361 run ip46tables -t mangle -A INPUT \
 362         -m mark --mark $from_link/$MASK_FROM \
 363         -j MARK --or-mark $fwd_link
 364
 365 ## Now it's safe to let stuff through.
 366 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
 367   run ip46tables -t mangle -P $i ACCEPT
 368 done
 369
 370 m4_divert(-1)
 371 ###----- That's all, folks --------------------------------------------------