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