mdw@git.distorted.org.uk Git - firewall/blob - functions.m4

   1 ### -*-sh-*-
   2 ###
   3 ### Utility functions for firewall scripts
   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(20)m4_dnl
  25 ###--------------------------------------------------------------------------
  26 ### Utility functions.
  27
  28 ## doit COMMAND ARGS...
  29 ##
  30 ## If debugging, print the COMMAND and ARGS.  If serious, execute them.
  31 run () {
  32   set -e
  33   if [ "$FW_DEBUG" ]; then echo "* $*"; fi
  34   if ! [ "$FW_NOACT" ]; then "$@"; fi
  35 }
  36
  37 ## trace MESSAGE...
  38 ##
  39 ## If debugging, print the MESSAGE.
  40 trace () {
  41   set -e
  42   if [ "$FW_DEBUG" ]; then echo "$*"; fi
  43 }
  44
  45 ## defport NAME NUMBER
  46 ##
  47 ## Define $port_NAME to be NUMBER.
  48 defport () {
  49   name=$1 number=$2
  50   eval port_$name=$number
  51 }
  52
  53 ## defproto NAME NUMBER
  54 ##
  55 ## Define $proto_NAME to be NUMBER.
  56 defproto () {
  57   name=$1 number=$2
  58   eval proto_$name=$number
  59 }
  60
  61 ## addword VAR WORD
  62 ##
  63 ## Adds WORD to the value of the shell variable VAR, if it's not there
  64 ## already.  Words are separated by a single space; no leading or trailing
  65 ## spaces are introduced.
  66 addword () {
  67   var=$1 word=$2
  68   eval val=\$$var
  69   case " $val " in
  70     *" $word "*) ;;
  71     *) eval "$var=\${$var:+\$val }\$word" ;;
  72   esac
  73 }
  74
  75 m4_divert(38)m4_dnl
  76 ###--------------------------------------------------------------------------
  77 ### Utility chains (used by function definitions).
  78
  79 m4_divert(20)m4_dnl
  80 ###--------------------------------------------------------------------------
  81 ### Basic chain constructions.
  82
  83 ## ip46tables ARGS ...
  84 ##
  85 ## Do the same thing for `iptables' and `ip6tables'.
  86 ip46tables () {
  87   set -e
  88   iptables "$@"
  89   ip6tables "$@"
  90 }
  91
  92 ## clearchain CHAIN CHAIN ...
  93 ##
  94 ## Ensure that the named chains exist and are empty.
  95 clearchain () {
  96   set -e
  97   for chain; do
  98     case $chain in
  99       *:*) table=${chain%:*} chain=${chain#*:} ;;
 100       *) table=filter ;;
 101     esac
 102     run ip46tables -t $table -N $chain 2>/dev/null || :
 103   done
 104 }
 105
 106 ## makeset SET TYPE [PARAMS]
 107 ##
 108 ## Ensure that the named ipset exists.  Don't clear it.
 109 makeset () {
 110   set -e
 111   name=$1; shift
 112   if ipset -nL | grep -q "^Name: $name$"; then
 113     :
 114   else
 115     ipset -N "$name" "$@"
 116   fi
 117 }
 118
 119 ## errorchain CHAIN ACTION ARGS ...
 120 ##
 121 ## Make a chain which logs a message and then invokes some other action,
 122 ## typically REJECT.  Log messages are prefixed by `fw: CHAIN'.
 123 errorchain () {
 124   set -e
 125   chain=$1; shift
 126   case $chain in
 127     *:*) table=${chain%:*} chain=${chain#*:} ;;
 128     *) table=filter ;;
 129   esac
 130   clearchain $table:$chain
 131   run ip46tables -t $table -A $chain -j LOG \
 132           -m limit --limit 3/minute --limit-burst 10 \
 133           --log-prefix "fw: $chain " --log-level notice
 134   run ip46tables -t $table -A $chain -j "$@" \
 135           -m limit --limit 20/second --limit-burst 100
 136   run ip46tables -t $table -A $chain -j DROP
 137 }
 138
 139 m4_divert(20)m4_dnl
 140 ###--------------------------------------------------------------------------
 141 ### Basic option setting.
 142
 143 ## setopt OPTION VALUE
 144 ##
 145 ## Set an IP sysctl.
 146 setopt () {
 147   set -e
 148   opt=$1 val=$2
 149   any=nil
 150   for ver in ipv4 ipv6; do
 151     if [ -f /proc/sys/net/$ver/$opt ]; then
 152       run sysctl -q net/$ver/$opt="$val"
 153       any=t
 154     fi
 155   done
 156   case $any in
 157     nil) echo >&2 "$0: unknown IP option $opt"; exit 1 ;;
 158   esac
 159 }
 160
 161 ## setdevopt OPTION VALUE [INTERFACES ...]
 162 ##
 163 ## Set an IP interface-level sysctl.
 164 setdevopt () {
 165   set -e
 166   opt=$1 val=$2; shift 2
 167   case "$#,$1" in
 168     0, | 1,all)
 169       set -- $(
 170         seen=:
 171         for ver in ipv4 ipv6; do
 172           cd /proc/sys/net/$ver/conf
 173           for i in *; do
 174             [ -f $i/$opt ] || continue
 175             case "$seen" in (*:$i:*) continue ;; esac
 176             echo $i
 177           done
 178         done)
 179       ;;
 180   esac
 181   for i in "$@"; do
 182     any=nil
 183     for ver in ipv4 ipv6; do
 184       if [ -f /proc/sys/net/$ver/conf/$i/$opt ]; then
 185         any=t
 186         run sysctl -q net/ipv4/conf/$i/$opt="$val"
 187       fi
 188     done
 189     case $any in
 190       nil) echo >&2 "$0: unknown device option $opt"; exit 1 ;;
 191     esac
 192   done
 193 }
 194
 195 m4_divert(20)m4_dnl
 196 ###--------------------------------------------------------------------------
 197 ### Packet filter construction.
 198
 199 ## conntrack CHAIN
 200 ##
 201 ## Add connection tracking to CHAIN, and allow obvious stuff.
 202 conntrack () {
 203   set -e
 204   chain=$1
 205   run ip46tables -A $chain -p tcp -m state \
 206           --state ESTABLISHED,RELATED -j ACCEPT
 207   run ip46tables -A $chain -p tcp ! --syn -g bad-tcp
 208 }
 209
 210 ## commonrules CHAIN
 211 ##
 212 ## Add standard IP filtering rules to the CHAIN.
 213 commonrules () {
 214   set -e
 215   chain=$1
 216
 217   ## Pass fragments through, assuming that the eventual destination will sort
 218   ## things out properly.  Except for TCP, that is, which should never be
 219   ## fragmented.  This is an extra pain for ip6tables, which doesn't provide
 220   ## a pleasant way to detect non-initial fragments.
 221   run iptables -A $chain -p tcp -f -g tcp-fragment
 222   run iptables -A $chain -f -j ACCEPT
 223   run ip6tables -A $chain -p tcp -g tcp-fragment \
 224           -m ipv6header --soft --header frag
 225   run ip6tables -A $chain -j accept-non-init-frag
 226 }
 227
 228 m4_divert(38)m4_dnl
 229 ## Accept a non-initial fragment.  This is only needed by IPv6, to work
 230 ## around a deficiency in the option parser.
 231 run ip6tables -N accept-non-init-frag
 232 run ip6tables -A accept-non-init-frag -j RETURN \
 233         -m frag --fragfirst
 234 run ip6tables -A accept-non-init-frag -j ACCEPT
 235
 236 m4_divert(20)m4_dnl
 237 ## allowservices CHAIN PROTO SERVICE ...
 238 ##
 239 ## Add rules to allow the SERVICES on the CHAIN.
 240 allowservices () {
 241   set -e
 242   chain=$1 proto=$2; shift 2
 243   count=0
 244   list=
 245   for svc; do
 246     case $svc in
 247       *:*)
 248         n=2
 249         left=${svc%:*} right=${svc#*:}
 250         case $left in *[!0-9]*) eval left=\$port_$left ;; esac
 251         case $right in *[!0-9]*) eval right=\$port_$right ;; esac
 252         svc=$left:$right
 253         ;;
 254       *)
 255         n=1
 256         case $svc in *[!0-9]*) eval svc=\$port_$svc ;; esac
 257         ;;
 258     esac
 259     case $svc in
 260       *: | :* | "" | *[!0-9:]*)
 261         echo >&2 "Bad service name"
 262         exit 1
 263         ;;
 264     esac
 265     count=$(( $count + $n ))
 266     if [ $count -gt 15 ]; then
 267       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 268              --destination-ports ${list#,}
 269       list= count=$n
 270     fi
 271     list=$list,$svc
 272   done
 273   case $list in
 274     "")
 275       ;;
 276     ,*,*)
 277       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 278               --destination-ports ${list#,}
 279       ;;
 280     *)
 281       run ip46tables -A $chain -p $proto -j ACCEPT \
 282               --destination-port ${list#,}
 283       ;;
 284   esac
 285 }
 286
 287 ## ntpclient CHAIN NTPSERVER ...
 288 ##
 289 ## Add rules to CHAIN to allow NTP with NTPSERVERs.
 290 ntpclient () {
 291   set -e
 292   chain=$1; shift
 293   for ntp; do
 294     run iptables -A $chain -s $ntp -j ACCEPT \
 295             -p udp --source-port 123 --destination-port 123
 296   done
 297 }
 298
 299 ## dnsresolver CHAIN
 300 ##
 301 ## Add rules to allow CHAIN to be a DNS resolver.
 302 dnsresolver () {
 303   set -e
 304   chain=$1
 305   for p in tcp udp; do
 306     run ip46tables -A $chain -j ACCEPT \
 307              -m state --state ESTABLISHED \
 308              -p $p --source-port 53
 309   done
 310 }
 311
 312 ## openports CHAIN [MIN MAX]
 313 ##
 314 ## Add rules to CHAIN to allow the open ports.
 315 openports () {
 316   set -e
 317   chain=$1; shift
 318   [ $# -eq 0 ] && set -- $open_port_min $open_port_max
 319   run ip46tables -A $chain -p tcp -g interesting --destination-port $1:$2
 320   run ip46tables -A $chain -p udp -g interesting --destination-port $1:$2
 321 }
 322
 323 m4_divert(20)m4_dnl
 324 ###--------------------------------------------------------------------------
 325 ### Packet classification.
 326 ###
 327 ### See `classify.m4' for an explanation of how the firewall machinery for
 328 ### packet classification works.
 329 ###
 330 ### A list of all network names is kept in `allnets'.  For each network NET,
 331 ### shell variables are defined describing their properties.
 332 ###
 333 ### net_class_NET       The class of the network, as defined by
 334 ###                     `defnetclass'.
 335 ### net_inet_NET        List of IPv4 address ranges in the network.
 336 ### net_inet6_NET       List of IPv6 address ranges in the network.
 337 ### net_fwd_NET         List of other networks that this one forwards to.
 338 ### net_hosts_NET       List of hosts known to be in the network.
 339 ### host_inet_HOST      IPv4 address of the named HOST.
 340 ### host_inet6_HOST     IPv6 address of the named HOST.
 341 ###
 342 ### Similarly, a list of hosts is kept in `allhosts', and for each host HOST,
 343 ### a shell variables are defined:
 344 ###
 345 ### host_ifaces_HOST    List of interfaces for this host and the networks
 346 ###                     they attach to, in the form IFACE=NET.
 347
 348 ## defbitfield NAME WIDTH
 349 ##
 350 ## Defines MASK_NAME and BIT_NAME symbolic constants for dealing with
 351 ## bitfields: x << BIT_NAME yields the value x in the correct position, and
 352 ## ff & MASK_NAME extracts the corresponding value.
 353 defbitfield () {
 354   set -e
 355   name=$1 width=$2
 356   eval MASK_$name=$(( (1 << $width) - 1 << $bitindex ))
 357   eval BIT_$name=$bitindex
 358   bitindex=$(( $bitindex + $width ))
 359 }
 360
 361 ## Define the layout of the bitfield.
 362 bitindex=0
 363 defbitfield MASK 16
 364 defbitfield FROM 4
 365 defbitfield TO 4
 366
 367 ## defnetclass NAME FORWARD-TO...
 368 ##
 369 ## Defines a netclass called NAME, which is allowed to forward to the
 370 ## FORWARD-TO netclasses.
 371 ##
 372 ## For each netclass, constants from_NAME and to_NAME are defined as the
 373 ## appropriate values in the FROM and TO fields (i.e., not including any mask
 374 ## bits).
 375 ##
 376 ## This function also establishes mangle chains mark-from-NAME and
 377 ## mark-to-NAME for applying the appropriate mark bits to the packet.
 378 ##
 379 ## Because it needs to resolve forward references, netclasses must be defined
 380 ## in a two-pass manner, using a loop of the form
 381 ##
 382 ##   for pass in 1 2; do netclassindex=0; ...; done
 383 netclassess=
 384 defnetclass () {
 385   set -e
 386   name=$1; shift
 387   case $pass in
 388     1)
 389
 390       ## Pass 1.  Establish the from_NAME and to_NAME constants, and the
 391       ## netclass's mask bit.
 392       eval from_$name=$(( $netclassindex << $BIT_FROM ))
 393       eval to_$name=$(( $netclassindex << $BIT_TO ))
 394       eval _mask_$name=$(( 1 << ($netclassindex + $BIT_MASK) ))
 395       nets="$nets $name"
 396       ;;
 397     2)
 398
 399       ## Pass 2.  Compute the actual from and to values.  We're a little bit
 400       ## clever during source classification, and set the TO field to
 401       ## all-bits-one, so that destination classification needs only a single
 402       ## AND operation.
 403       from=$(( ($netclassindex << $BIT_FROM) + (0xf << $BIT_TO) ))
 404       for net; do
 405         eval bit=\$_mask_$net
 406         from=$(( $from + $bit ))
 407       done
 408       to=$(( ($netclassindex << $BIT_TO) + \
 409              (0xf << $BIT_FROM) + \
 410              (1 << ($netclassindex + $BIT_MASK)) ))
 411       trace "from $name --> set $(printf %x $from)"
 412       trace "  to $name --> and $(printf %x $from)"
 413
 414       ## Now establish the mark-from-NAME and mark-to-NAME chains.
 415       clearchain mangle:mark-from-$name mangle:mark-to-$name
 416       run ip46tables -t mangle -A mark-from-$name -j MARK --set-mark $from
 417       run ip46tables -t mangle -A mark-to-$name -j MARK --and-mark $to
 418       ;;
 419   esac
 420   netclassindex=$(( $netclassindex + 1 ))
 421 }
 422
 423 ## defnet NET CLASS
 424 ##
 425 ## Define a network.  Follow by calls to `addr', `forwards', etc. to define
 426 ## properties of the network.  Networks are processed in order, so if their
 427 ## addresses overlap then the more specific addresses should be defined
 428 ## earlier.
 429 defnet () {
 430   net=$1 class=$2
 431   addword allnets $net
 432   eval net_class_$1=\$class
 433 }
 434
 435 ## addr ADDRESS/LEN ...
 436 ##
 437 ## Define addresses for the network being defined.  ADDRESSes are in
 438 ## colon-separated IPv6 or dotted-quad IPv4 form.
 439 addr () {
 440   for i in "$@"; do
 441     case "$i" in
 442       *:*) addword net_inet6_$net $i ;;
 443       *) addword net_inet_$net $i ;;
 444     esac
 445   done
 446 }
 447
 448 ## forwards NET ...
 449 ##
 450 ## Declare that packets from this network are forwarded to the other NETs.
 451 forwards () {
 452   eval "net_fwd_$net=\"$*\""
 453 }
 454
 455 ## noxit NET ...
 456 ##
 457 ## Declare that packets from this network must not be forwarded to the other
 458 ## NETs.
 459 noxit () {
 460   eval "net_noxit_$net=\"$*\""
 461 }
 462
 463 ## host HOST ADDR ...
 464 ##
 465 ## Define the address of an individual host on the current network.  The
 466 ## ADDRs may be full IPv4 or IPv6 addresses, or offsets from the containing
 467 ## network address, which is a simple number for IPv4, or a suffix beginning
 468 ## with `::' for IPv6.  If an IPv6 base address is provided for the network
 469 ## but not for the host then the host's IPv4 address is used as a suffix.
 470 host () {
 471   name=$1; shift
 472
 473   ## Work out which addresses we've actually been given.
 474   unset a6
 475   for i in "$@"; do
 476     case "$i" in ::*) a6=$i ;; *) a=$i ;; esac
 477   done
 478   case "${a+t}" in
 479     t) ;;
 480     *) echo >&2 "$0: no address for $name"; exit 1 ;;
 481   esac
 482   case "${a6+t}" in t) ;; *) a6=::$a ;; esac
 483
 484   ## Work out the IPv4 address.
 485   eval nn=\$net_inet_$net
 486   for n in $nn; do
 487     addr=${n%/*}
 488     base=${addr%.*}
 489     offset=${addr##*.}
 490     case $a in *.*) aa=$a ;; *) aa=$base.$(( $offset + $a )) ;; esac
 491     eval host_inet_$name=$aa
 492   done
 493
 494   ## Work out the IPv6 address.
 495   eval nn=\$net_inet6_$net
 496   for n in $nn; do
 497     addr=${n%/*}
 498     base=${addr%::*}
 499     case $a in ::*) aa=$addr$a ;; *) aa=$a ;; esac
 500     eval host_inet6_$name=$aa
 501   done
 502
 503   ## Remember the host in the list.
 504   addword net_hosts_$net $name
 505 }
 506
 507 ## defhost NAME
 508 ##
 509 ## Define a new host.  Follow by calls to `iface' to define the host's
 510 ## interfaces.
 511 defhost () {
 512   host=$1
 513   addword allhosts $host
 514   eval host_type_$host=endsys
 515 }
 516
 517 ## router
 518 ##
 519 ## Declare the host to be a router, so it should forward packets and so on.
 520 router () {
 521   eval host_type_$host=router
 522 }
 523
 524 ## iface IFACE NET ...
 525 ##
 526 ## Define a host's interfaces.  Specifically, declares that the host has an
 527 ## interface IFACE attached to the listed NETs.
 528 iface () {
 529   name=$1; shift
 530   for net in "$@"; do
 531     addword host_ifaces_$host $name=$net
 532   done
 533 }
 534
 535 ## net_interfaces HOST NET
 536 ##
 537 ## Determine the interfaces on which packets may plausibly arrive from the
 538 ## named NET.  Returns `-' if no such interface exists.
 539 ##
 540 ## This algorithm is not very clever.  It's just about barely good enough to
 541 ## deduce transitivity through a simple routed network; with complicated
 542 ## networks, it will undoubtedly give wrong answers.  Check the results
 543 ## carefully, and, if necessary, list the connectivity explicitly; use the
 544 ## special interface `-' for networks you know shouldn't send packets to a
 545 ## host.
 546 net_interfaces () {
 547   host=$1 startnet=$2
 548
 549   ## Determine the locally attached networks.
 550   targets=:
 551   eval ii=\$host_ifaces_$host
 552   for i in $ii; do targets=$targets$i:; done
 553
 554   ## Determine the transitivity.
 555   seen=:
 556   nets=$startnet
 557   while :; do
 558
 559     ## First pass.  Determine whether any of the networks we're considering
 560     ## are in the target set.  If they are, then return the corresponding
 561     ## interfaces.
 562     found=""
 563     for net in $nets; do
 564       tg=$targets
 565       while :; do
 566         any=nil
 567         case $tg in
 568           *"=$net:"*)
 569             n=${tg%=$net:*}; tg=${n%:*}:; n=${n##*:}
 570             addword found $n
 571             any=t
 572             ;;
 573         esac
 574         case $any in nil) break ;; esac
 575       done
 576     done
 577     case "$found" in ?*) echo $found; return ;; esac
 578
 579     ## No joy.  Determine the set of networks which (a) these ones can
 580     ## forward to, and (b) that we've not considered already.  These are the
 581     ## nets we'll consider next time around.
 582     nextnets=""
 583     any=nil
 584     for net in $nets; do
 585       eval fwd=\$net_fwd_$net
 586       for n in $fwd; do
 587         case $seen in *":$n:"*) continue ;; esac
 588         seen=$seen$n:
 589         eval noxit=\$net_noxit_$n
 590         case " $noxit " in *" $startnet "*) continue ;; esac
 591         case " $nextnets " in
 592           *" $n "*) ;;
 593           *) addword nextnets $n; any=t ;;
 594         esac
 595       done
 596     done
 597
 598     ## If we've run out of networks then there's no reachability.  Return a
 599     ## failure.
 600     case $any in nil) echo -; return ;; esac
 601     nets=$nextnets
 602   done
 603 }
 604
 605 m4_divert(-1)
 606 ###----- That's all, folks --------------------------------------------------