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   for table in $(cat /proc/net/${ip}_tables_names); do
  42
  43     ## Step 1: clear out the builtin chains.
  44     ${ip}tables -nL -t $table |
  45     sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
  46     while read chain; do
  47       case $table in
  48         nat) policy=ACCEPT ;;
  49         *) policy=DROP ;;
  50       esac
  51       run ${ip}tables -t $table -P $chain $policy
  52       run ${ip}tables -t $table -F $chain
  53     done
  54
  55     ## Step 2: clear out user chains.  Unfortunately, we can only clear
  56     ## chains which have no references to them, so work through picking off
  57     ## unreferenced chains which aren't meant to be preserved until there are
  58     ## none left.
  59     while :; do
  60       progress=nil
  61       ${ip}tables -nL -t $table |
  62       sed -n '/^Chain \([^ ]\+\) (0 references)$/ s//\1/p ' \
  63         >/var/run/firewall-chains.tmp
  64       while read chain; do
  65         match=nil
  66         for pat in $preserve_chains; do
  67           case "$table:$chain" in $pat) match=t ;; esac
  68         done
  69         case $match in
  70           nil)
  71             run ${ip}tables -t $table -F $chain
  72             run ${ip}tables -t $table -X $chain
  73             progress=t
  74             ;;
  75         esac
  76       done </var/run/firewall-chains.tmp
  77       case $progress in nil) break ;; esac
  78     done
  79
  80     ## Step 3: report on uncleared user chains.  This means that there's a
  81     ## serious problem.
  82     ${ip}tables -nL -t $table |
  83     sed -n '/^Chain \([^ ]\+\) (\([1-9][0-9]*\) references)$/ s//\1 \2/p ' \
  84       >/var/run/firewall-chains.tmp
  85     while read chain refs; do
  86       match=nil
  87       for pat in $preserve_chains; do
  88         case "$table:$chain" in $pat) match=t ;; esac
  89       done
  90       case $match in
  91         nil)
  92           echo >&2 "$0: can't clear referenced $ip chain \`$table:$chain'"
  93           unref=t
  94           ;;
  95       esac
  96     done </var/run/firewall-chains.tmp
  97   done
  98 done
  99 rm -f /var/run/firewall-chains.tmp
 100 case $unref in t) exit 1 ;; esac
 101
 102 m4_divert(32)m4_dnl
 103 ###--------------------------------------------------------------------------
 104 ### Set safe IP options.
 105
 106 ## Set forwarding options.  Apparently setting ip_forward clobbers other
 107 ## settings, so put this first.
 108 setopt ip_forward $forward
 109 setdevopt forwarding $forward
 110
 111 ## Set dynamic port allocation.
 112 setopt ip_local_port_range $open_port_min $open_port_max
 113
 114 ## Deploy SYN-cookies if necessary.
 115 setopt tcp_syncookies 1
 116
 117 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
 118 setopt icmp_echo_ignore_broadcasts 0
 119
 120 ## Turn off iptables filtering for bridges.  We'll use ebtables if we need
 121 ## to; but right now the model is that we do filtering at the borders, and
 122 ## are tolerant of things which are local.
 123 if [ -x /sbin/brctl ]; then
 124   modprobe bridge || :
 125   if [ -d /proc/sys/net/bridge ]; then
 126     for filter in arptables iptables ip6tables; do
 127       run sysctl -q net.bridge.bridge-nf-call-$filter=0
 128     done
 129   fi
 130 fi
 131
 132 ## Turn on the reverse-path filter, and log weird things.
 133 setdevopt rp_filter $rp_filter
 134 setdevopt log_martians $log_martians
 135
 136 ## Turn off things which can mess with our routing decisions.
 137 setdevopt accept_source_route 0
 138 setdevopt accept_redirects 0
 139
 140 ## If we're maent to stop the firewall, then now is the time to do it.
 141 $exit_after_clearing
 142
 143 m4_divert(34)m4_dnl
 144 ###--------------------------------------------------------------------------
 145 ### Establish error chains.
 146
 147 errorchain forbidden REJECT
 148 ## Generic `not allowed' chain.
 149
 150 errorchain tcp-fragment REJECT
 151 ## Chain for logging fragmented TCP segements.
 152
 153 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
 154 ## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.
 155
 156 errorchain mangle:bad-source-address DROP
 157 errorchain bad-source-address DROP
 158 ## Packet arrived on wrong interface for its source address.  Drops the
 159 ## packet, since there's nowhere sensible to send an error.
 160
 161 errorchain bad-destination-address REJECT
 162 ## Packet arrived on non-loopback interface with loopback destination.
 163
 164 errorchain interesting ACCEPT
 165 ## Not an error, just log interesting packets.
 166
 167 m4_divert(36)m4_dnl
 168 ###--------------------------------------------------------------------------
 169 ### Standard filtering.
 170
 171 ## Don't clobber local traffic
 172 run ip46tables -A INPUT -i lo -j ACCEPT
 173
 174 ## We really shouldn't see packets destined for localhost on any interface
 175 ## other than the loopback.
 176 run iptables -A INPUT -g bad-destination-address \
 177         -d 127.0.0.0/8
 178 run ip6tables -A INPUT -g bad-destination-address \
 179         -d ::1
 180
 181 ## We shouldn't be asked to forward things with link-local addresses.
 182 run iptables -A FORWARD -g bad-source-address \
 183         -s 169.254.0.0/16
 184 run iptables -A FORWARD -g bad-destination-address \
 185         -d 169.254.0.0/16
 186 run ip6tables -A FORWARD -g bad-source-address \
 187         -s fe80::/10
 188 run ip6tables -A FORWARD -g bad-destination-address \
 189         -d fe80::/10
 190
 191 ## Also, don't forward link-local broadcast or multicast.
 192 run iptables -A FORWARD -g bad-destination-address \
 193         -d 255.255.255.255
 194 run iptables -A FORWARD -g bad-destination-address \
 195         -m addrtype --dst-type BROADCAST
 196 run iptables -A FORWARD -g bad-destination-address \
 197         -d 224.0.0.0/24
 198 for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 199   run ip6tables -A FORWARD -g bad-destination-address \
 200         -d fe${x}2::/16
 201 done
 202
 203 ## Add a hook for fail2ban.
 204 clearchain fail2ban
 205 run ip46tables -A INPUT -j fail2ban
 206
 207 m4_divert(90)m4_dnl
 208 ###--------------------------------------------------------------------------
 209 ### Finishing touches.
 210
 211 m4_divert(94)m4_dnl
 212 ## Locally generated packets are all OK.
 213 run ip46tables -P OUTPUT ACCEPT
 214
 215 ## Other incoming things are forbidden.
 216 for chain in INPUT FORWARD; do
 217   run ip46tables -A $chain -g forbidden
 218 done
 219
 220 m4_divert(-1)
 221 ###----- That's all, folks --------------------------------------------------