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=$number
  59 }
  60
  61 m4_divert(38)m4_dnl
  62 ###--------------------------------------------------------------------------
  63 ### Utility chains (used by function definitions).
  64
  65 m4_divert(22)m4_dnl
  66 ###--------------------------------------------------------------------------
  67 ### Basic chain constructions.
  68
  69 ## ip46tables ARGS ...
  70 ##
  71 ## Do the same thing for `iptables' and `ip6tables'.
  72 ip46tables () {
  73   set -e
  74   iptables "$@"
  75   ip6tables "$@"
  76 }
  77
  78 ## clearchain CHAIN CHAIN ...
  79 ##
  80 ## Ensure that the named chains exist and are empty.
  81 clearchain () {
  82   set -e
  83   for chain; do
  84     case $chain in
  85       *:*) table=${chain%:*} chain=${chain#*:} ;;
  86       *) table=filter ;;
  87     esac
  88     run ip46tables -t $table -N $chain
  89   done
  90 }
  91
  92 ## errorchain CHAIN ACTION ARGS ...
  93 ##
  94 ## Make a chain which logs a message and then invokes some other action,
  95 ## typically REJECT.  Log messages are prefixed by `fw: CHAIN'.
  96 errorchain () {
  97   set -e
  98   chain=$1; shift
  99   case $chain in
 100     *:*) table=${chain%:*} chain=${chain#*:} ;;
 101     *) table=filter ;;
 102   esac
 103   clearchain $table:$chain
 104   run ip46tables -t $table -A $chain -j LOG \
 105           -m limit --limit 3/minute --limit-burst 10 \
 106           --log-prefix "fw: $chain " --log-level notice
 107   run ip46tables -t $table -A $chain -j "$@" \
 108           -m limit --limit 20/second --limit-burst 100
 109   run ip46tables -t $table -A $chain -j DROP
 110 }
 111
 112 m4_divert(24)m4_dnl
 113 ###--------------------------------------------------------------------------
 114 ### Basic option setting.
 115
 116 ## setopt OPTION VALUE
 117 ##
 118 ## Set an IP sysctl.
 119 setopt () {
 120   set -e
 121   opt=$1 val=$2
 122   any=nil
 123   for ver in ipv4 ipv6; do
 124     if [ -f /proc/sys/net/$ver/$opt ]; then
 125       run sysctl -q net/$ver/$opt="$val"
 126       any=t
 127     fi
 128   done
 129   case $any in
 130     nil) echo >&2 "$0: unknown IP option $opt"; exit 1 ;;
 131   esac
 132 }
 133
 134 ## setdevopt OPTION VALUE [INTERFACES ...]
 135 ##
 136 ## Set an IP interface-level sysctl.
 137 setdevopt () {
 138   set -e
 139   opt=$1 val=$2; shift 2
 140   case "$#,$1" in
 141     0, | 1,all)
 142       set -- $(
 143         seen=:
 144         for ver in ipv4 ipv6; do
 145           cd /proc/sys/net/$ver/conf
 146           for i in *; do
 147             [ -f $i/$opt ] || continue
 148             case "$seen" in (*:$i:*) continue ;; esac
 149             echo $i
 150           done
 151         done)
 152       ;;
 153   esac
 154   for i in "$@"; do
 155     any=nil
 156     for ver in ipv4 ipv6; do
 157       if [ -f /proc/sys/net/$ver/conf/$i/$opt ]; then
 158         any=t
 159         run sysctl -q net/ipv4/conf/$i/$opt="$val"
 160       fi
 161     done
 162     case $any in
 163       nil) echo >&2 "$0: unknown device option $opt"; exit 1 ;;
 164     esac
 165   done
 166 }
 167
 168 m4_divert(26)m4_dnl
 169 ###--------------------------------------------------------------------------
 170 ### Packet filter construction.
 171
 172 ## conntrack CHAIN
 173 ##
 174 ## Add connection tracking to CHAIN, and allow obvious stuff.
 175 conntrack () {
 176   set -e
 177   chain=$1
 178   run ip46tables -A $chain -p tcp -m state \
 179           --state ESTABLISHED,RELATED -j ACCEPT
 180   run ip46tables -A $chain -p tcp ! --syn -g bad-tcp
 181 }
 182
 183 ## commonrules CHAIN
 184 ##
 185 ## Add standard IP filtering rules to the CHAIN.
 186 commonrules () {
 187   set -e
 188   chain=$1
 189
 190   ## Pass fragments through, assuming that the eventual destination will sort
 191   ## things out properly.  Except for TCP, that is, which should never be
 192   ## fragmented.  This is an extra pain for ip6tables, which doesn't provide
 193   ## a pleasant way to detect non-initial fragments.
 194   run iptables -A $chain -p tcp -f -g tcp-fragment
 195   run iptables -A $chain -f -j ACCEPT
 196   run ip6tables -A $chain -p tcp -g tcp-fragment \
 197           -m ipv6header --soft --header frag
 198   run ip6tables -A $chain -j accept-non-init-frag
 199 }
 200
 201 m4_divert(38)m4_dnl
 202 ## Accept a non-initial fragment.  This is only needed by IPv6, to work
 203 ## around a deficiency in the option parser.
 204 run ip6tables -N accept-non-init-frag
 205 run ip6tables -A accept-non-init-frag -j RETURN \
 206         -m frag --fragfirst
 207 run ip6tables -A accept-non-init-frag -j ACCEPT
 208
 209 m4_divert(26)m4_dnl
 210 ## allowservices CHAIN PROTO SERVICE ...
 211 ##
 212 ## Add rules to allow the SERVICES on the CHAIN.
 213 allowservices () {
 214   set -e
 215   chain=$1 proto=$2; shift 2
 216   count=0
 217   list=
 218   for svc; do
 219     case $svc in
 220       *:*)
 221         n=2
 222         left=${svc%:*} right=${svc#*:}
 223         case $left in *[!0-9]*) eval left=\$port_$left ;; esac
 224         case $right in *[!0-9]*) eval right=\$port_$right ;; esac
 225         svc=$left:$right
 226         ;;
 227       *)
 228         n=1
 229         case $svc in *[!0-9]*) eval svc=\$port_$svc ;; esac
 230         ;;
 231     esac
 232     case $svc in
 233       *: | :* | "" | *[!0-9:]*)
 234         echo >&2 "Bad service name"
 235         exit 1
 236         ;;
 237     esac
 238     count=$(( $count + $n ))
 239     if [ $count -gt 15 ]; then
 240       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 241              --destination-ports ${list#,}
 242       list= count=$n
 243     fi
 244     list=$list,$svc
 245   done
 246   case $list in
 247     "")
 248       ;;
 249     ,*,*)
 250       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 251               --destination-ports ${list#,}
 252       ;;
 253     *)
 254       run ip46tables -A $chain -p $proto -j ACCEPT \
 255               --destination-port ${list#,}
 256       ;;
 257   esac
 258 }
 259
 260 ## ntpclient CHAIN NTPSERVER ...
 261 ##
 262 ## Add rules to CHAIN to allow NTP with NTPSERVERs.
 263 ntpclient () {
 264   set -e
 265   chain=$1; shift
 266   for ntp; do
 267     run iptables -A $chain -s $ntp -j ACCEPT \
 268             -p udp --source-port 123 --destination-port 123
 269   done
 270 }
 271
 272 ## dnsresolver CHAIN
 273 ##
 274 ## Add rules to allow CHAIN to be a DNS resolver.
 275 dnsresolver () {
 276   set -e
 277   chain=$1
 278   for p in tcp udp; do
 279     run ip46tables -A $chain -j ACCEPT \
 280              -m state --state ESTABLISHED \
 281              -p $p --source-port 53
 282   done
 283 }
 284
 285 ## openports CHAIN [MIN MAX]
 286 ##
 287 ## Add rules to CHAIN to allow the open ports.
 288 openports () {
 289   set -e
 290   chain=$1; shift
 291   [ $# -eq 0 ] && set -- $open_port_min $open_port_max
 292   run ip46tables -A $chain -p tcp -g interesting --destination-port $1:$2
 293   run ip46tables -A $chain -p udp -g interesting --destination-port $1:$2
 294 }
 295
 296 m4_divert(28)m4_dnl
 297 ###--------------------------------------------------------------------------
 298 ### Packet classification.
 299
 300 ## defbitfield NAME WIDTH
 301 ##
 302 ## Defines MASK_NAME and BIT_NAME symbolic constants for dealing with
 303 ## bitfields: x << BIT_NAME yields the value x in the correct position, and
 304 ## ff & MASK_NAME extracts the corresponding value.
 305 defbitfield () {
 306   set -e
 307   name=$1 width=$2
 308   eval MASK_$name=$(( (1 << $width) - 1 << $bitindex ))
 309   eval BIT_$name=$bitindex
 310   bitindex=$(( $bitindex + $width ))
 311 }
 312
 313 ## Define the layout of the bitfield.
 314 bitindex=0
 315 defbitfield MASK 16
 316 defbitfield FROM 4
 317 defbitfield TO 4
 318
 319 ## defnetclass NAME FORWARD-TO...
 320 ##
 321 ## Defines a netclass called NAME, which is allowed to forward to the
 322 ## FORWARD-TO netclasses.
 323 ##
 324 ## For each netclass, constants from_NAME and to_NAME are defined as the
 325 ## appropriate values in the FROM and TO fields (i.e., not including any mask
 326 ## bits).
 327 ##
 328 ## This function also establishes mangle chains mark-from-NAME and
 329 ## mark-to-NAME for applying the appropriate mark bits to the packet.
 330 ##
 331 ## Because it needs to resolve forward references, netclasses must be defined
 332 ## in a two-pass manner, using a loop of the form
 333 ##
 334 ##   for pass in 1 2; do netclassindex=0; ...; done
 335 netclassess=
 336 defnetclass () {
 337   set -e
 338   name=$1; shift
 339   case $pass in
 340     1)
 341
 342       ## Pass 1.  Establish the from_NAME and to_NAME constants, and the
 343       ## netclass's mask bit.
 344       eval from_$name=$(( $netclassindex << $BIT_FROM ))
 345       eval to_$name=$(( $netclassindex << $BIT_TO ))
 346       eval _mask_$name=$(( 1 << ($netclassindex + $BIT_MASK) ))
 347       nets="$nets $name"
 348       ;;
 349     2)
 350
 351       ## Pass 2.  Compute the actual from and to values.  We're a little bit
 352       ## clever during source classification, and set the TO field to
 353       ## all-bits-one, so that destination classification needs only a single
 354       ## AND operation.
 355       from=$(( ($netclassindex << $BIT_FROM) + (0xf << $BIT_TO) ))
 356       for net; do
 357         eval bit=\$_mask_$net
 358         from=$(( $from + $bit ))
 359       done
 360       to=$(( ($netclassindex << $BIT_TO) + \
 361              (0xf << $BIT_FROM) + \
 362              (1 << ($netclassindex + $BIT_MASK)) ))
 363       trace "from $name --> set $(printf %x $from)"
 364       trace "  to $name --> and $(printf %x $from)"
 365
 366       ## Now establish the mark-from-NAME and mark-to-NAME chains.
 367       clearchain mangle:mark-from-$name mangle:mark-to-$name
 368       run ip46tables -t mangle -A mark-from-$name -j MARK --set-mark $from
 369       run ip46tables -t mangle -A mark-to-$name -j MARK --and-mark $to
 370       ;;
 371   esac
 372   netclassindex=$(( $netclassindex + 1 ))
 373 }
 374
 375 ## defiface NAME[,NAME,...] NETCLASS:NETWORK/MASK...
 376 ##
 377 ## Declares network interfaces with the given NAMEs and associates with them
 378 ## a number of reachable networks.  During source classification, a packet
 379 ## arriving on interface NAME from an address in NETWORK/MASK is classified
 380 ## as coming from to NETCLASS.  During destination classification, all
 381 ## packets going to NETWORK/MASK are classified as going to NETCLASS,
 382 ## regardless of interface (which is good, because the outgoing interface
 383 ## hasn't been determined yet).
 384 ##
 385 ## As a special case, the NETWORK/MASK can be the string `default', which
 386 ## indicates that all addresses not matched elsewhere should be considered.
 387 ifaces=:
 388 defaultifaces=""
 389 allnets= allnets6=
 390 defiface () {
 391   set -e
 392   names=$1; shift
 393   seen=:
 394   for name in $(echo $names | sed 'y/,/ /'); do
 395     case $seen in *:"$name":*) continue ;; esac
 396     seen=$seen$name:
 397     case $ifaces in
 398       *:"$name":*) ;;
 399       *)
 400         clearchain mangle:in-$name
 401         run ip46tables -t mangle -A in-classify -i $name -g in-$name
 402         ;;
 403     esac
 404     ifaces=$ifaces$name:
 405     for item; do
 406       netclass=${item%:*} addr=${item#*:}
 407       case $addr in
 408         default)
 409           case "$defaultifaces,$defaultclass" in
 410             ,* | *,$netclass)
 411               defaultifaces="$defaultifaces $name"
 412               defaultclass=$netclass
 413               ;;
 414             *)
 415               echo >&2 "$0: inconsistent default netclasses"
 416               exit 1
 417               ;;
 418           esac
 419           ;;
 420         *:*)
 421           run ip6tables -t mangle -A in-$name -g mark-from-$netclass \
 422                 -s $addr
 423           run ip6tables -t mangle -A out-classify -g mark-to-$netclass \
 424                 -d $addr
 425           allnets6="$allnets6 $name:$addr"
 426           ;;
 427         *)
 428           run iptables -t mangle -A in-$name -g mark-from-$netclass \
 429                 -s $addr
 430           run iptables -t mangle -A out-classify -g mark-to-$netclass \
 431                 -d $addr
 432           allnets="$allnets $name:$addr"
 433           ;;
 434       esac
 435     done
 436   done
 437 }
 438
 439 ## defvpn IFACE CLASS NET HOST:ADDR ...
 440 ##
 441 ## Defines a VPN interface.  If the interface has the form `ROOT+' (i.e., a
 442 ## netfilter wildcard) then define a separate interface ROOTHOST routing to
 443 ## ADDR; otherwise just write a blanket rule allowing the whole NET.  All
 444 ## addresses concerned are put in the named CLASS.
 445 defvpn () {
 446   set -e
 447   iface=$1 class=$2 net=$3; shift 3
 448   case $iface in
 449     *-+)
 450       root=${iface%+}
 451       for host; do
 452         name=${host%%:*} addr=${host#*:}
 453         defiface $root$name $class:$addr
 454       done
 455       ;;
 456     *)
 457       defiface $iface $class:$net
 458       ;;
 459   esac
 460 }
 461
 462 m4_divert(-1)
 463 ###----- That's all, folks --------------------------------------------------