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 2>/dev/null || :
  89   done
  90 }
  91
  92 ## makeset SET TYPE [PARAMS]
  93 ##
  94 ## Ensure that the named ipset exists.  Don't clear it.
  95 makeset () {
  96   set -e
  97   name=$1; shift
  98   if ipset -nL | grep -q "^Name: $name$"; then
  99     :
 100   else
 101     ipset -N "$name" "$@"
 102   fi
 103 }
 104
 105 ## errorchain CHAIN ACTION ARGS ...
 106 ##
 107 ## Make a chain which logs a message and then invokes some other action,
 108 ## typically REJECT.  Log messages are prefixed by `fw: CHAIN'.
 109 errorchain () {
 110   set -e
 111   chain=$1; shift
 112   case $chain in
 113     *:*) table=${chain%:*} chain=${chain#*:} ;;
 114     *) table=filter ;;
 115   esac
 116   clearchain $table:$chain
 117   run ip46tables -t $table -A $chain -j LOG \
 118           -m limit --limit 3/minute --limit-burst 10 \
 119           --log-prefix "fw: $chain " --log-level notice
 120   run ip46tables -t $table -A $chain -j "$@" \
 121           -m limit --limit 20/second --limit-burst 100
 122   run ip46tables -t $table -A $chain -j DROP
 123 }
 124
 125 m4_divert(24)m4_dnl
 126 ###--------------------------------------------------------------------------
 127 ### Basic option setting.
 128
 129 ## setopt OPTION VALUE
 130 ##
 131 ## Set an IP sysctl.
 132 setopt () {
 133   set -e
 134   opt=$1 val=$2
 135   any=nil
 136   for ver in ipv4 ipv6; do
 137     if [ -f /proc/sys/net/$ver/$opt ]; then
 138       run sysctl -q net/$ver/$opt="$val"
 139       any=t
 140     fi
 141   done
 142   case $any in
 143     nil) echo >&2 "$0: unknown IP option $opt"; exit 1 ;;
 144   esac
 145 }
 146
 147 ## setdevopt OPTION VALUE [INTERFACES ...]
 148 ##
 149 ## Set an IP interface-level sysctl.
 150 setdevopt () {
 151   set -e
 152   opt=$1 val=$2; shift 2
 153   case "$#,$1" in
 154     0, | 1,all)
 155       set -- $(
 156         seen=:
 157         for ver in ipv4 ipv6; do
 158           cd /proc/sys/net/$ver/conf
 159           for i in *; do
 160             [ -f $i/$opt ] || continue
 161             case "$seen" in (*:$i:*) continue ;; esac
 162             echo $i
 163           done
 164         done)
 165       ;;
 166   esac
 167   for i in "$@"; do
 168     any=nil
 169     for ver in ipv4 ipv6; do
 170       if [ -f /proc/sys/net/$ver/conf/$i/$opt ]; then
 171         any=t
 172         run sysctl -q net/ipv4/conf/$i/$opt="$val"
 173       fi
 174     done
 175     case $any in
 176       nil) echo >&2 "$0: unknown device option $opt"; exit 1 ;;
 177     esac
 178   done
 179 }
 180
 181 m4_divert(26)m4_dnl
 182 ###--------------------------------------------------------------------------
 183 ### Packet filter construction.
 184
 185 ## conntrack CHAIN
 186 ##
 187 ## Add connection tracking to CHAIN, and allow obvious stuff.
 188 conntrack () {
 189   set -e
 190   chain=$1
 191   run ip46tables -A $chain -p tcp -m state \
 192           --state ESTABLISHED,RELATED -j ACCEPT
 193   run ip46tables -A $chain -p tcp ! --syn -g bad-tcp
 194 }
 195
 196 ## commonrules CHAIN
 197 ##
 198 ## Add standard IP filtering rules to the CHAIN.
 199 commonrules () {
 200   set -e
 201   chain=$1
 202
 203   ## Pass fragments through, assuming that the eventual destination will sort
 204   ## things out properly.  Except for TCP, that is, which should never be
 205   ## fragmented.  This is an extra pain for ip6tables, which doesn't provide
 206   ## a pleasant way to detect non-initial fragments.
 207   run iptables -A $chain -p tcp -f -g tcp-fragment
 208   run iptables -A $chain -f -j ACCEPT
 209   run ip6tables -A $chain -p tcp -g tcp-fragment \
 210           -m ipv6header --soft --header frag
 211   run ip6tables -A $chain -j accept-non-init-frag
 212 }
 213
 214 m4_divert(38)m4_dnl
 215 ## Accept a non-initial fragment.  This is only needed by IPv6, to work
 216 ## around a deficiency in the option parser.
 217 run ip6tables -N accept-non-init-frag
 218 run ip6tables -A accept-non-init-frag -j RETURN \
 219         -m frag --fragfirst
 220 run ip6tables -A accept-non-init-frag -j ACCEPT
 221
 222 m4_divert(26)m4_dnl
 223 ## allowservices CHAIN PROTO SERVICE ...
 224 ##
 225 ## Add rules to allow the SERVICES on the CHAIN.
 226 allowservices () {
 227   set -e
 228   chain=$1 proto=$2; shift 2
 229   count=0
 230   list=
 231   for svc; do
 232     case $svc in
 233       *:*)
 234         n=2
 235         left=${svc%:*} right=${svc#*:}
 236         case $left in *[!0-9]*) eval left=\$port_$left ;; esac
 237         case $right in *[!0-9]*) eval right=\$port_$right ;; esac
 238         svc=$left:$right
 239         ;;
 240       *)
 241         n=1
 242         case $svc in *[!0-9]*) eval svc=\$port_$svc ;; esac
 243         ;;
 244     esac
 245     case $svc in
 246       *: | :* | "" | *[!0-9:]*)
 247         echo >&2 "Bad service name"
 248         exit 1
 249         ;;
 250     esac
 251     count=$(( $count + $n ))
 252     if [ $count -gt 15 ]; then
 253       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 254              --destination-ports ${list#,}
 255       list= count=$n
 256     fi
 257     list=$list,$svc
 258   done
 259   case $list in
 260     "")
 261       ;;
 262     ,*,*)
 263       run ip46tables -A $chain -p $proto -m multiport -j ACCEPT \
 264               --destination-ports ${list#,}
 265       ;;
 266     *)
 267       run ip46tables -A $chain -p $proto -j ACCEPT \
 268               --destination-port ${list#,}
 269       ;;
 270   esac
 271 }
 272
 273 ## ntpclient CHAIN NTPSERVER ...
 274 ##
 275 ## Add rules to CHAIN to allow NTP with NTPSERVERs.
 276 ntpclient () {
 277   set -e
 278   chain=$1; shift
 279   for ntp; do
 280     run iptables -A $chain -s $ntp -j ACCEPT \
 281             -p udp --source-port 123 --destination-port 123
 282   done
 283 }
 284
 285 ## dnsresolver CHAIN
 286 ##
 287 ## Add rules to allow CHAIN to be a DNS resolver.
 288 dnsresolver () {
 289   set -e
 290   chain=$1
 291   for p in tcp udp; do
 292     run ip46tables -A $chain -j ACCEPT \
 293              -m state --state ESTABLISHED \
 294              -p $p --source-port 53
 295   done
 296 }
 297
 298 ## openports CHAIN [MIN MAX]
 299 ##
 300 ## Add rules to CHAIN to allow the open ports.
 301 openports () {
 302   set -e
 303   chain=$1; shift
 304   [ $# -eq 0 ] && set -- $open_port_min $open_port_max
 305   run ip46tables -A $chain -p tcp -g interesting --destination-port $1:$2
 306   run ip46tables -A $chain -p udp -g interesting --destination-port $1:$2
 307 }
 308
 309 m4_divert(28)m4_dnl
 310 ###--------------------------------------------------------------------------
 311 ### Packet classification.
 312
 313 ## defbitfield NAME WIDTH
 314 ##
 315 ## Defines MASK_NAME and BIT_NAME symbolic constants for dealing with
 316 ## bitfields: x << BIT_NAME yields the value x in the correct position, and
 317 ## ff & MASK_NAME extracts the corresponding value.
 318 defbitfield () {
 319   set -e
 320   name=$1 width=$2
 321   eval MASK_$name=$(( (1 << $width) - 1 << $bitindex ))
 322   eval BIT_$name=$bitindex
 323   bitindex=$(( $bitindex + $width ))
 324 }
 325
 326 ## Define the layout of the bitfield.
 327 bitindex=0
 328 defbitfield MASK 16
 329 defbitfield FROM 4
 330 defbitfield TO 4
 331
 332 ## defnetclass NAME FORWARD-TO...
 333 ##
 334 ## Defines a netclass called NAME, which is allowed to forward to the
 335 ## FORWARD-TO netclasses.
 336 ##
 337 ## For each netclass, constants from_NAME and to_NAME are defined as the
 338 ## appropriate values in the FROM and TO fields (i.e., not including any mask
 339 ## bits).
 340 ##
 341 ## This function also establishes mangle chains mark-from-NAME and
 342 ## mark-to-NAME for applying the appropriate mark bits to the packet.
 343 ##
 344 ## Because it needs to resolve forward references, netclasses must be defined
 345 ## in a two-pass manner, using a loop of the form
 346 ##
 347 ##   for pass in 1 2; do netclassindex=0; ...; done
 348 netclassess=
 349 defnetclass () {
 350   set -e
 351   name=$1; shift
 352   case $pass in
 353     1)
 354
 355       ## Pass 1.  Establish the from_NAME and to_NAME constants, and the
 356       ## netclass's mask bit.
 357       eval from_$name=$(( $netclassindex << $BIT_FROM ))
 358       eval to_$name=$(( $netclassindex << $BIT_TO ))
 359       eval _mask_$name=$(( 1 << ($netclassindex + $BIT_MASK) ))
 360       nets="$nets $name"
 361       ;;
 362     2)
 363
 364       ## Pass 2.  Compute the actual from and to values.  We're a little bit
 365       ## clever during source classification, and set the TO field to
 366       ## all-bits-one, so that destination classification needs only a single
 367       ## AND operation.
 368       from=$(( ($netclassindex << $BIT_FROM) + (0xf << $BIT_TO) ))
 369       for net; do
 370         eval bit=\$_mask_$net
 371         from=$(( $from + $bit ))
 372       done
 373       to=$(( ($netclassindex << $BIT_TO) + \
 374              (0xf << $BIT_FROM) + \
 375              (1 << ($netclassindex + $BIT_MASK)) ))
 376       trace "from $name --> set $(printf %x $from)"
 377       trace "  to $name --> and $(printf %x $from)"
 378
 379       ## Now establish the mark-from-NAME and mark-to-NAME chains.
 380       clearchain mangle:mark-from-$name mangle:mark-to-$name
 381       run ip46tables -t mangle -A mark-from-$name -j MARK --set-mark $from
 382       run ip46tables -t mangle -A mark-to-$name -j MARK --and-mark $to
 383       ;;
 384   esac
 385   netclassindex=$(( $netclassindex + 1 ))
 386 }
 387
 388 ## defiface NAME[,NAME,...] NETCLASS:NETWORK/MASK...
 389 ##
 390 ## Declares network interfaces with the given NAMEs and associates with them
 391 ## a number of reachable networks.  During source classification, a packet
 392 ## arriving on interface NAME from an address in NETWORK/MASK is classified
 393 ## as coming from to NETCLASS.  During destination classification, all
 394 ## packets going to NETWORK/MASK are classified as going to NETCLASS,
 395 ## regardless of interface (which is good, because the outgoing interface
 396 ## hasn't been determined yet).
 397 ##
 398 ## As a special case, the NETWORK/MASK can be the string `default', which
 399 ## indicates that all addresses not matched elsewhere should be considered.
 400 ifaces=:
 401 defaultifaces=""
 402 allnets= allnets6=
 403 defiface () {
 404   set -e
 405   names=$1; shift
 406   seen=:
 407   for name in $(echo $names | sed 'y/,/ /'); do
 408     case $seen in *:"$name":*) continue ;; esac
 409     seen=$seen$name:
 410     case $ifaces in
 411       *:"$name":*) ;;
 412       *)
 413         clearchain mangle:in-$name
 414         run ip46tables -t mangle -A in-classify -i $name -g in-$name
 415         ;;
 416     esac
 417     ifaces=$ifaces$name:
 418     for item; do
 419       netclass=${item%:*} addr=${item#*:}
 420       case $addr in
 421         default)
 422           case "$defaultifaces,$defaultclass" in
 423             ,* | *,$netclass)
 424               defaultifaces="$defaultifaces $name"
 425               defaultclass=$netclass
 426               ;;
 427             *)
 428               echo >&2 "$0: inconsistent default netclasses"
 429               exit 1
 430               ;;
 431           esac
 432           ;;
 433         *:*)
 434           run ip6tables -t mangle -A in-$name -g mark-from-$netclass \
 435                 -s $addr
 436           run ip6tables -t mangle -A out-classify -g mark-to-$netclass \
 437                 -d $addr
 438           allnets6="$allnets6 $name:$addr"
 439           ;;
 440         *)
 441           run iptables -t mangle -A in-$name -g mark-from-$netclass \
 442                 -s $addr
 443           run iptables -t mangle -A out-classify -g mark-to-$netclass \
 444                 -d $addr
 445           allnets="$allnets $name:$addr"
 446           ;;
 447       esac
 448     done
 449   done
 450 }
 451
 452 ## defvpn IFACE CLASS NET HOST:ADDR ...
 453 ##
 454 ## Defines a VPN interface.  If the interface has the form `ROOT+' (i.e., a
 455 ## netfilter wildcard) then define a separate interface ROOTHOST routing to
 456 ## ADDR; otherwise just write a blanket rule allowing the whole NET.  All
 457 ## addresses concerned are put in the named CLASS.
 458 defvpn () {
 459   set -e
 460   iface=$1 class=$2 net=$3; shift 3
 461   case $iface in
 462     *-+)
 463       root=${iface%+}
 464       for host; do
 465         name=${host%%:*} addr=${host#*:}
 466         defiface $root$name $class:$addr
 467       done
 468       ;;
 469     *)
 470       defiface $iface $class:$net
 471       ;;
 472   esac
 473 }
 474
 475 m4_divert(-1)
 476 ###----- That's all, folks --------------------------------------------------