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