mdw@git.distorted.org.uk Git - firewall/blob - bookends.m4

   1 ### -*-sh-*-
   2 ###
   3 ### Initialization and finishing touches 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(30)m4_dnl
  25 ###--------------------------------------------------------------------------
  26 ### Clear existing firewall rules.
  27
  28 ## The main chains: set policy to drop, and then clear the rules.  For a
  29 ## while, incoming packets will be silently dropped, but we should have got
  30 ## everything going before anyone actually hits a timeout.
  31 ##
  32 ## We don't control some of the chains, so we should preserve them.  This
  33 ## introduces a whole bunch of problems.
  34
  35 ## Chains we're meant to preserve
  36 preserve_chains="filter:fail2ban filter:fail2ban-* $preserve_chains"
  37
  38 ## Take the various IP versions in turn.
  39 unref=nil
  40 for ip in ip ip6; do
  41   if [ "$FW_NOACT" ]; then break; fi
  42
  43   for table in $(cat /proc/net/${ip}_tables_names); do
  44
  45     ## Step 1: clear out the builtin chains.
  46     ${ip}tables -nL -t $table |
  47     sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
  48     while read chain; do
  49       case $table in
  50         nat) policy=ACCEPT ;;
  51         *) policy=DROP ;;
  52       esac
  53       run ${ip}tables -t $table -P $chain $policy
  54       run ${ip}tables -t $table -F $chain
  55     done
  56
  57     ## Step 2: clear out user chains.  Unfortunately, we can only clear
  58     ## chains which have no references to them, so work through picking off
  59     ## unreferenced chains which aren't meant to be preserved until there are
  60     ## none left.
  61     while :; do
  62       progress=nil
  63       ${ip}tables -nL -t $table |
  64       sed -n '/^Chain \([^ ]\+\) (0 references)$/ s//\1/p ' \
  65         >/var/run/firewall-chains.tmp
  66       while read chain; do
  67         match=nil
  68         for pat in $preserve_chains; do
  69           case "$table:$chain" in $pat) match=t ;; esac
  70         done
  71         case $match in
  72           nil)
  73             run ${ip}tables -t $table -F $chain
  74             run ${ip}tables -t $table -X $chain
  75             progress=t
  76             ;;
  77         esac
  78       done </var/run/firewall-chains.tmp
  79       case $progress in nil) break ;; esac
  80     done
  81
  82     ## Step 3: report on uncleared user chains.  This means that there's a
  83     ## serious problem.
  84     ${ip}tables -nL -t $table |
  85     sed -n '/^Chain \([^ ]\+\) (\([1-9][0-9]*\) references)$/ s//\1 \2/p ' \
  86       >/var/run/firewall-chains.tmp
  87     while read chain refs; do
  88       match=nil
  89       for pat in $preserve_chains; do
  90         case "$table:$chain" in $pat) match=t ;; esac
  91       done
  92       case $match in
  93         nil)
  94           echo >&2 "$0: can't clear referenced $ip chain \`$table:$chain'"
  95           unref=t
  96           ;;
  97       esac
  98     done </var/run/firewall-chains.tmp
  99   done
 100 done
 101 rm -f /var/run/firewall-chains.tmp
 102 case $unref in t) exit 1 ;; esac
 103
 104 m4_divert(32)m4_dnl
 105 ###--------------------------------------------------------------------------
 106 ### Set safe IP options.
 107
 108 ## Set forwarding options.  Apparently setting ip_forward clobbers other
 109 ## settings, so put this first.
 110 case $host_type_<::>FWHOST in
 111   router) forward=1 ;;
 112   *) forward=0 ;;
 113 esac
 114 setopt ip_forward $forward
 115 setdevopt forwarding $forward
 116 case $forward in
 117   0) inchains="INPUT" ;;
 118   1) inchains="INPUT FORWARD" ;;
 119 esac
 120
 121 ## Set dynamic port allocation.
 122 setopt ip_local_port_range $open_port_min $open_port_max
 123
 124 ## Deploy SYN-cookies if necessary.
 125 setopt tcp_syncookies 1
 126
 127 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
 128 setopt icmp_echo_ignore_broadcasts 0
 129
 130 ## Turn off iptables filtering for bridges.  We'll use ebtables if we need
 131 ## to; but right now the model is that we do filtering at the borders, and
 132 ## are tolerant of things which are local.
 133 if [ -x /sbin/brctl ]; then
 134   modprobe bridge || :
 135   if [ -d /proc/sys/net/bridge ]; then
 136     for filter in arptables iptables ip6tables; do
 137       run sysctl -q net.bridge.bridge-nf-call-$filter=0
 138     done
 139   fi
 140 fi
 141
 142 ## Turn off the reverse-path filter.  It's basically useless: the filter does
 143 ## nothing at all for single-homed hosts; and multi-homed hosts tend to have
 144 ## routing aysmmetries if there's any kind of cycle.
 145 setdevopt rp_filter 0
 146 setdevopt log_martians 0
 147
 148 ## Turn off things which can mess with our routing decisions.
 149 setdevopt accept_source_route 0
 150 setdevopt accept_redirects 0
 151
 152 ## If we're maent to stop the firewall, then now is the time to do it.
 153 $exit_after_clearing
 154
 155 m4_divert(34)m4_dnl
 156 ###--------------------------------------------------------------------------
 157 ### Establish error chains.
 158
 159 errorchain forbidden REJECT
 160 ## Generic `not allowed' chain.
 161
 162 errorchain tcp-fragment REJECT
 163 ## Chain for logging fragmented TCP segements.
 164
 165 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
 166 ## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.
 167
 168 errorchain mangle:bad-source-address DROP
 169 errorchain bad-source-address DROP
 170 ## Packet arrived on wrong interface for its source address.  Drops the
 171 ## packet, since there's nowhere sensible to send an error.
 172
 173 errorchain bad-destination-address REJECT
 174 ## Packet arrived on non-loopback interface with loopback destination.
 175
 176 errorchain interesting ACCEPT
 177 ## Not an error, just log interesting packets.
 178
 179 m4_divert(50)m4_dnl
 180 ###--------------------------------------------------------------------------
 181 ### Standard filtering.
 182
 183 ## Don't clobber local traffic
 184 run ip46tables -A INPUT -i lo -j ACCEPT
 185
 186 ## We really shouldn't see packets destined for localhost on any interface
 187 ## other than the loopback.
 188 run iptables -A INPUT -g bad-destination-address \
 189         -d 127.0.0.0/8
 190 run ip6tables -A INPUT -g bad-destination-address \
 191         -d ::1
 192
 193 ## We shouldn't be asked to forward things with link-local addresses.
 194 case $forward in
 195   1)
 196     run iptables -A FORWARD -g bad-source-address \
 197             -s 169.254.0.0/16
 198     run iptables -A FORWARD -g bad-destination-address \
 199             -d 169.254.0.0/16
 200     run ip6tables -A FORWARD -g bad-source-address \
 201             -s fe80::/10
 202     run ip6tables -A FORWARD -g bad-destination-address \
 203             -d fe80::/10
 204     ;;
 205 esac
 206
 207 ## Also, don't forward link-local broadcast or multicast.
 208 case $forward in
 209   1)
 210     run iptables -A FORWARD -g bad-destination-address \
 211             -d 255.255.255.255
 212     run iptables -A FORWARD -g bad-destination-address \
 213             -m addrtype --dst-type BROADCAST
 214     run iptables -A FORWARD -g bad-destination-address \
 215             -d 224.0.0.0/24
 216     clearchain check-fwd-multi
 217     for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 218       run ip6tables -A check-fwd-multi -g bad-destination-address \
 219             -d ff${x}2::/16
 220     done
 221     run ip6tables -A FORWARD -j check-fwd-multi -d ff00::/8
 222     ;;
 223 esac
 224
 225 ## Add a hook for fail2ban.
 226 clearchain fail2ban
 227 run ip46tables -A INPUT -j fail2ban
 228
 229 m4_divert(90)m4_dnl
 230 ###--------------------------------------------------------------------------
 231 ### Finishing touches.
 232
 233 m4_divert(94)m4_dnl
 234 ## Locally generated packets are all OK.
 235 run ip46tables -P OUTPUT ACCEPT
 236
 237 ## Other incoming things are forbidden.
 238 for chain in INPUT FORWARD; do
 239   run ip46tables -A $chain -g forbidden
 240 done
 241
 242 ## Allow stuff through unknown tables.
 243 for ip in ip ip6; do
 244   for table in $(cat /proc/net/${ip}_tables_names); do
 245     case $table in mangle | filter) continue ;; esac
 246     ${ip}tables -nL -t $table |
 247     sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
 248     while read chain; do
 249       run ${ip}tables -t $table -P $chain ACCEPT
 250     done
 251   done
 252 done
 253
 254 ## Dump the resulting configuration.
 255 if [ "$FW_DEBUG" ]; then
 256   for ip in ip ip6; do
 257     for table in mangle filter; do
 258       echo "----- $ip $table -----"
 259       echo
 260       ${ip}tables -t $table -nvL
 261       echo
 262     done
 263   done
 264 fi
 265
 266 m4_divert(-1)
 267 ###----- That's all, folks --------------------------------------------------