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=$number
  51 }
  52
  53 m4_divert(38)m4_dnl
  54 ###--------------------------------------------------------------------------
  55 ### Utility chains (used by function definitions).
  56
  57 m4_divert(22)m4_dnl
  58 ###--------------------------------------------------------------------------
  59 ### Basic chain constructions.
  60
  61 ## ip46tables ARGS ...
  62 ##
  63 ## Do the same thing for `iptables' and `ip6tables'.
  64 ip46tables () {
  65   set -e
  66   iptables "$@"
  67   ip6tables "$@"
  68 }
  69
  70 ## clearchain CHAIN CHAIN ...
  71 ##
  72 ## Ensure that the named chains exist and are empty.
  73 clearchain () {
  74   set -e
  75   for chain; do
  76     case $chain in
  77       *:*) table=${chain%:*} chain=${chain#*:} ;;
  78       *) table=filter ;;
  79     esac
  80     run ip46tables -t $table -N $chain
  81   done
  82 }
  83
  84 ## errorchain CHAIN ACTION ARGS ...
  85 ##
  86 ## Make a chain which logs a message and then invokes some other action,
  87 ## typically REJECT.  Log messages are prefixed by `fw: CHAIN'.
  88 errorchain () {
  89   set -e
  90   chain=$1; shift
  91   case $chain in
  92     *:*) table=${chain%:*} chain=${chain#*:} ;;
  93     *) table=filter ;;
  94   esac
  95   clearchain $table:$chain
  96   run ip46tables -t $table -A $chain -j LOG \
  97           -m limit --limit 3/minute --limit-burst 10 \
  98           --log-prefix "fw: $chain " --log-level notice
  99   run ip46tables -t $table -A $chain -j "$@"
 100 }
 101
 102 m4_divert(24)m4_dnl
 103 ###--------------------------------------------------------------------------
 104 ### Basic option setting.
 105
 106 ## setopt OPTION VALUE
 107 ##
 108 ## Set an IP sysctl.
 109 setopt () {
 110   set -e
 111   opt=$1 val=$2
 112   any=nil
 113   for ver in ipv4 ipv6; do
 114     if [ -f /proc/sys/net/$ver/$opt ]; then
 115       run sysctl -q net/$ver/$opt="$val"
 116       any=t
 117     fi
 118   done
 119   case $any in
 120     nil) echo >&2 "$0: unknown IP option $opt"; exit 1 ;;
 121   esac
 122 }
 123
 124 ## setdevopt OPTION VALUE [INTERFACES ...]
 125 ##
 126 ## Set an IP interface-level sysctl.
 127 setdevopt () {
 128   set -e
 129   opt=$1 val=$2; shift 2
 130   case "$#,$1" in
 131     0, | 1,all)
 132       set -- $(
 133         seen=:
 134         for ver in ipv4 ipv6; do
 135           cd /proc/sys/net/$ver/conf
 136           for i in *; do
 137             [ -f $i/$opt ] || continue
 138             case "$seen" in (*:$i:*) continue ;; esac
 139             echo $i
 140           done
 141         done)
 142       ;;
 143   esac
 144   for i in "$@"; do
 145     any=nil
 146     for ver in ipv4 ipv6; do
 147       if [ -f /proc/sys/net/$ver/conf/$i/$opt ]; then
 148         any=t
 149         run sysctl -q net/ipv4/conf/$i/$opt="$val"
 150       fi
 151     done
 152     case $any in
 153       nil) echo >&2 "$0: unknown device option $opt"; exit 1 ;;
 154     esac
 155   done
 156 }
 157
 158 m4_divert(26)m4_dnl
 159 ###--------------------------------------------------------------------------
 160 ### Packet filter construction.
 161
 162 ## conntrack CHAIN
 163 ##
 164 ## Add connection tracking to CHAIN, and allow obvious stuff.
 165 conntrack () {
 166   set -e
 167   chain=$1
 168   run ip46tables -A $chain -p tcp -m state \
 169           --state ESTABLISHED,RELATED -j ACCEPT
 170   run ip46tables -A $chain -p tcp ! --syn -g bad-tcp
 171 }
 172
 173 ## commonrules CHAIN
 174 ##
 175 ## Add standard IP filtering rules to the CHAIN.
 176 commonrules () {
 177   set -e
 178   chain=$1
 179
 180   ## Pass fragments through, assuming that the eventual destination will sort
 181   ## things out properly.  Except for TCP, that is, which should never be
 182   ## fragmented.  This is an extra pain for ip6tables, which doesn't provide
 183   ## a pleasant way to detect non-initial fragments.
 184   run iptables -A $chain -p tcp -f -g tcp-fragment
 185   run iptables -A $chain -f -j ACCEPT
 186   run ip6tables -A $chain -p tcp -g tcp-fragment \
 187           -m ipv6header --soft --header frag
 188   run ip6tables -A $chain -j accept-non-init-frag
 189 }
 190
 191 m4_divert(38)m4_dnl
 192 ## Accept a non-initial fragment.  This is only needed by IPv6, to work
 193 ## around a deficiency in the option parser.
 194 run ip6tables -N accept-non-init-frag
 195 run ip6tables -A accept-non-init-frag -j RETURN \
 196         -m frag --fragfirst
 197 run ip6tables -A accept-non-init-frag -j ACCEPT
 198
 199 m4_divert(26)m4_dnl
 200 ## allowservices CHAIN PROTO SERVICE ...
 201 ##
 202 ## Add rules to allow the SERVICES on the CHAIN.
 203 allowservices () {
 204   set -e
 205   chain=$1 proto=$2; shift 2
 206   count=0
 207   list=
 208   for svc; do
 209     case $svc in
 210       *:*)
 211         n=2
 212         left=${svc%:*} right=${svc#*:}
 213         case $left in *[!0-9]*) eval left=\$port_$left ;; esac
 214         case $right in *[!0-9]*) eval right=\$port_$right ;; esac
 215         svc=$left:$right
 216         ;;
 217       *)
 218         n=1
 219         case $svc in *[!0-9]*) eval svc=\$port_$svc ;; esac
 220         ;;
 221     esac
 222     case $svc in
 223       *: | :* | "" | *[!0-9:]*)
 224         echo >&2 "Bad service name"
 225         exit 1
 226         ;;
 227     esac
 228     count=$(( $count + $n ))
 229     if [ $count -gt 15 ]; then
 230       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 231              --destination-ports ${list#,}
 232       list= count=$n
 233     fi
 234     list=$list,$svc
 235   done
 236   case $list in
 237     "")
 238       ;;
 239     ,*,*)
 240       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 241               --destination-ports ${list#,}
 242       ;;
 243     *)
 244       run ip46tables -A $chain -p $proto -j ACCEPT \
 245               --destination-port ${list#,}
 246       ;;
 247   esac
 248 }
 249
 250 ## ntpclient CHAIN NTPSERVER ...
 251 ##
 252 ## Add rules to CHAIN to allow NTP with NTPSERVERs.
 253 ntpclient () {
 254   set -e
 255   chain=$1; shift
 256   for ntp; do
 257     run iptables -A $chain -s $ntp -j ACCEPT \
 258             -p udp --source-port 123 --destination-port 123
 259   done
 260 }
 261
 262 ## dnsresolver CHAIN
 263 ##
 264 ## Add rules to allow CHAIN to be a DNS resolver.
 265 dnsresolver () {
 266   set -e
 267   chain=$1
 268   for p in tcp udp; do
 269     run ip46tables -A $chain -j ACCEPT \
 270              -m state --state ESTABLISHED \
 271              -p $p --source-port 53
 272   done
 273 }
 274
 275 ## openports CHAIN [MIN MAX]
 276 ##
 277 ## Add rules to CHAIN to allow the open ports.
 278 openports () {
 279   set -e
 280   chain=$1; shift
 281   [ $# -eq 0 ] && set -- $open_port_min $open_port_max
 282   run ip46tables -A $chain -p tcp -g interesting --destination-port $1:$2
 283   run ip46tables -A $chain -p udp -g interesting --destination-port $1:$2
 284 }
 285
 286 m4_divert(28)m4_dnl
 287 ###--------------------------------------------------------------------------
 288 ### Packet classification.
 289
 290 ## defbitfield NAME WIDTH
 291 ##
 292 ## Defines MASK_NAME and BIT_NAME symbolic constants for dealing with
 293 ## bitfields: x << BIT_NAME yields the value x in the correct position, and
 294 ## ff & MASK_NAME extracts the corresponding value.
 295 defbitfield () {
 296   set -e
 297   name=$1 width=$2
 298   eval MASK_$name=$(( (1 << $width) - 1 << $bitindex ))
 299   eval BIT_$name=$bitindex
 300   bitindex=$(( $bitindex + $width ))
 301 }
 302
 303 ## Define the layout of the bitfield.
 304 bitindex=0
 305 defbitfield MASK 16
 306 defbitfield FROM 4
 307 defbitfield TO 4
 308
 309 ## defnetclass NAME FORWARD-TO...
 310 ##
 311 ## Defines a netclass called NAME, which is allowed to forward to the
 312 ## FORWARD-TO netclasses.
 313 ##
 314 ## For each netclass, constants from_NAME and to_NAME are defined as the
 315 ## appropriate values in the FROM and TO fields (i.e., not including any mask
 316 ## bits).
 317 ##
 318 ## This function also establishes mangle chains mark-from-NAME and
 319 ## mark-to-NAME for applying the appropriate mark bits to the packet.
 320 ##
 321 ## Because it needs to resolve forward references, netclasses must be defined
 322 ## in a two-pass manner, using a loop of the form
 323 ##
 324 ##   for pass in 1 2; do netclassindex=0; ...; done
 325 netclassess=
 326 defnetclass () {
 327   set -e
 328   name=$1; shift
 329   case $pass in
 330     1)
 331
 332       ## Pass 1.  Establish the from_NAME and to_NAME constants, and the
 333       ## netclass's mask bit.
 334       eval from_$name=$(( $netclassindex << $BIT_FROM ))
 335       eval to_$name=$(( $netclassindex << $BIT_TO ))
 336       eval _mask_$name=$(( 1 << ($netclassindex + $BIT_MASK) ))
 337       nets="$nets $name"
 338       ;;
 339     2)
 340
 341       ## Pass 2.  Compute the actual from and to values.  We're a little bit
 342       ## clever during source classification, and set the TO field to
 343       ## all-bits-one, so that destination classification needs only a single
 344       ## AND operation.
 345       from=$(( ($netclassindex << $BIT_FROM) + (0xf << $BIT_TO) ))
 346       for net; do
 347         eval bit=\$_mask_$net
 348         from=$(( $from + $bit ))
 349       done
 350       to=$(( ($netclassindex << $BIT_TO) + \
 351              (0xf << $BIT_FROM) + \
 352              (1 << ($netclassindex + $BIT_MASK)) ))
 353       trace "from $name --> set $(printf %x $from)"
 354       trace "  to $name --> and $(printf %x $from)"
 355
 356       ## Now establish the mark-from-NAME and mark-to-NAME chains.
 357       clearchain mangle:mark-from-$name mangle:mark-to-$name
 358       run ip46tables -t mangle -A mark-from-$name -j MARK --set-mark $from
 359       run ip46tables -t mangle -A mark-to-$name -j MARK --and-mark $to
 360       ;;
 361   esac
 362   netclassindex=$(( $netclassindex + 1 ))
 363 }
 364
 365 ## defiface NAME[,NAME,...] NETCLASS:NETWORK/MASK...
 366 ##
 367 ## Declares network interfaces with the given NAMEs and associates with them
 368 ## a number of reachable networks.  During source classification, a packet
 369 ## arriving on interface NAME from an address in NETWORK/MASK is classified
 370 ## as coming from to NETCLASS.  During destination classification, all
 371 ## packets going to NETWORK/MASK are classified as going to NETCLASS,
 372 ## regardless of interface (which is good, because the outgoing interface
 373 ## hasn't been determined yet).
 374 ##
 375 ## As a special case, the NETWORK/MASK can be the string `default', which
 376 ## indicates that all addresses not matched elsewhere should be considered.
 377 ifaces=:
 378 defaultifaces=""
 379 allnets= allnets6=
 380 defiface () {
 381   set -e
 382   names=$1; shift
 383   seen=:
 384   for name in $(echo $names | sed 'y/,/ /'); do
 385     case $seen in *:"$name":*) continue ;; esac
 386     seen=$seen$name:
 387     case $ifaces in
 388       *:"$name":*) ;;
 389       *)
 390         clearchain mangle:in-$name
 391         run ip46tables -t mangle -A in-classify -i $name -g in-$name
 392         ;;
 393     esac
 394     ifaces=$ifaces$name:
 395     for item; do
 396       netclass=${item%:*} addr=${item#*:}
 397       case $addr in
 398         default)
 399           case "$defaultifaces,$defaultclass" in
 400             ,* | *,$netclass)
 401               defaultifaces="$defaultifaces $name"
 402               defaultclass=$netclass
 403               ;;
 404             *)
 405               echo >&2 "$0: inconsistent default netclasses"
 406               exit 1
 407               ;;
 408           esac
 409           ;;
 410         *:*)
 411           run ip6tables -t mangle -A in-$name -g mark-from-$netclass \
 412                 -s $addr
 413           run ip6tables -t mangle -A out-classify -g mark-to-$netclass \
 414                 -d $addr
 415           allnets6="$allnets6 $name:$addr"
 416           ;;
 417         *)
 418           run iptables -t mangle -A in-$name -g mark-from-$netclass \
 419                 -s $addr
 420           run iptables -t mangle -A out-classify -g mark-to-$netclass \
 421                 -d $addr
 422           allnets="$allnets $name:$addr"
 423           ;;
 424       esac
 425     done
 426   done
 427 }
 428
 429 ## defvpn IFACE CLASS NET HOST:ADDR ...
 430 ##
 431 ## Defines a VPN interface.  If the interface has the form `ROOT+' (i.e., a
 432 ## netfilter wildcard) then define a separate interface ROOTHOST routing to
 433 ## ADDR; otherwise just write a blanket rule allowing the whole NET.  All
 434 ## addresses concerned are put in the named CLASS.
 435 defvpn () {
 436   set -e
 437   iface=$1 class=$2 net=$3; shift 3
 438   case $iface in
 439     *-+)
 440       root=${iface%+}
 441       for host; do
 442         name=${host%%:*} addr=${host#*:}
 443         defiface $root$name $class:$addr
 444       done
 445       ;;
 446     *)
 447       defiface $iface $class:$net
 448       ;;
 449   esac
 450 }
 451
 452 m4_divert(-1)
 453 ###----- That's all, folks --------------------------------------------------