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 case $host_type_<::>FWHOST in
 109   router) forward=1 ;;
 110   *) forward=0 ;;
 111 esac
 112 setopt ip_forward $forward
 113 setdevopt forwarding $forward
 114 case $forward in
 115   0) inchains="INPUT" ;;
 116   1) inchains="INPUT FORWARD" ;;
 117 esac
 118
 119 ## Set dynamic port allocation.
 120 setopt ip_local_port_range $open_port_min $open_port_max
 121
 122 ## Deploy SYN-cookies if necessary.
 123 setopt tcp_syncookies 1
 124
 125 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
 126 setopt icmp_echo_ignore_broadcasts 0
 127
 128 ## Turn off iptables filtering for bridges.  We'll use ebtables if we need
 129 ## to; but right now the model is that we do filtering at the borders, and
 130 ## are tolerant of things which are local.
 131 if [ -x /sbin/brctl ]; then
 132   modprobe bridge || :
 133   if [ -d /proc/sys/net/bridge ]; then
 134     for filter in arptables iptables ip6tables; do
 135       run sysctl -q net.bridge.bridge-nf-call-$filter=0
 136     done
 137   fi
 138 fi
 139
 140 ## Turn off the reverse-path filter.  It's basically useless: the filter does
 141 ## nothing at all for single-homed hosts; and multi-homed hosts tend to have
 142 ## routing aysmmetries if there's any kind of cycle.
 143 setdevopt rp_filter 0
 144 setdevopt log_martians 0
 145
 146 ## Turn off things which can mess with our routing decisions.
 147 setdevopt accept_source_route 0
 148 setdevopt accept_redirects 0
 149
 150 ## If we're maent to stop the firewall, then now is the time to do it.
 151 $exit_after_clearing
 152
 153 m4_divert(34)m4_dnl
 154 ###--------------------------------------------------------------------------
 155 ### Establish error chains.
 156
 157 errorchain forbidden REJECT
 158 ## Generic `not allowed' chain.
 159
 160 errorchain tcp-fragment REJECT
 161 ## Chain for logging fragmented TCP segements.
 162
 163 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
 164 ## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.
 165
 166 errorchain mangle:bad-source-address DROP
 167 errorchain bad-source-address DROP
 168 ## Packet arrived on wrong interface for its source address.  Drops the
 169 ## packet, since there's nowhere sensible to send an error.
 170
 171 errorchain bad-destination-address REJECT
 172 ## Packet arrived on non-loopback interface with loopback destination.
 173
 174 errorchain interesting ACCEPT
 175 ## Not an error, just log interesting packets.
 176
 177 m4_divert(50)m4_dnl
 178 ###--------------------------------------------------------------------------
 179 ### Standard filtering.
 180
 181 ## Don't clobber local traffic
 182 run ip46tables -A INPUT -i lo -j ACCEPT
 183
 184 ## We really shouldn't see packets destined for localhost on any interface
 185 ## other than the loopback.
 186 run iptables -A INPUT -g bad-destination-address \
 187         -d 127.0.0.0/8
 188 run ip6tables -A INPUT -g bad-destination-address \
 189         -d ::1
 190
 191 ## We shouldn't be asked to forward things with link-local addresses.
 192 case $forward in
 193   1)
 194     run iptables -A FORWARD -g bad-source-address \
 195             -s 169.254.0.0/16
 196     run iptables -A FORWARD -g bad-destination-address \
 197             -d 169.254.0.0/16
 198     run ip6tables -A FORWARD -g bad-source-address \
 199             -s fe80::/10
 200     run ip6tables -A FORWARD -g bad-destination-address \
 201             -d fe80::/10
 202     ;;
 203 esac
 204
 205 ## Also, don't forward link-local broadcast or multicast.
 206 case $forward in
 207   1)
 208     run iptables -A FORWARD -g bad-destination-address \
 209             -d 255.255.255.255
 210     run iptables -A FORWARD -g bad-destination-address \
 211             -m addrtype --dst-type BROADCAST
 212     run iptables -A FORWARD -g bad-destination-address \
 213             -d 224.0.0.0/24
 214     clearchain check-fwd-multi
 215     for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 216       run ip6tables -A check-fwd-multi -g bad-destination-address \
 217             -d ff${x}2::/16
 218     done
 219     ip6tables -A FORWARD -j check-fwd-multi -d ff00::/8
 220     ;;
 221 esac
 222
 223 ## Add a hook for fail2ban.
 224 clearchain fail2ban
 225 run ip46tables -A INPUT -j fail2ban
 226
 227 m4_divert(90)m4_dnl
 228 ###--------------------------------------------------------------------------
 229 ### Finishing touches.
 230
 231 m4_divert(94)m4_dnl
 232 ## Locally generated packets are all OK.
 233 run ip46tables -P OUTPUT ACCEPT
 234
 235 ## Other incoming things are forbidden.
 236 for chain in INPUT FORWARD; do
 237   run ip46tables -A $chain -g forbidden
 238 done
 239
 240 ## Allow stuff through unknown tables.
 241 for ip in ip ip6; do
 242   for table in $(cat /proc/net/${ip}_tables_names); do
 243     case $table in mangle | filter) continue ;; esac
 244     ${ip}tables -nL -t $table |
 245     sed -n '/^Chain \([^ ]\+\) (policy .*$/ s//\1/p ' |
 246     while read chain; do
 247       run ${ip}tables -t $table -P $chain ACCEPT
 248     done
 249   done
 250 done
 251
 252 ## Dump the resulting configuration.
 253 if [ "$FW_DEBUG" ]; then
 254   for ip in ip ip6; do
 255     for table in mangle filter; do
 256       echo "----- $ip $table -----"
 257       echo
 258       ${ip}tables -t $table -nvL
 259       echo
 260     done
 261   done
 262 fi
 263
 264 m4_divert(-1)
 265 ###----- That's all, folks --------------------------------------------------