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 for t in mangle filter; do
  32   for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
  33     run ip46tables -t $t -P $i DROP 2>/dev/null || :
  34     run ip46tables -t $t -F $i 2>/dev/null || :
  35   done
  36   run ip46tables -t $t -F
  37   run ip46tables -t $t -X
  38 done
  39
  40 m4_divert(32)m4_dnl
  41 ###--------------------------------------------------------------------------
  42 ### Set safe IP options.
  43
  44 ## Set forwarding options.  Apparently setting ip_forward clobbers other
  45 ## settings, so put this first.
  46 setopt ip_forward $forward
  47 setdevopt forwarding $forward
  48
  49 ## Set dynamic port allocation.
  50 setopt ip_local_port_range $open_port_min $open_port_max
  51
  52 ## Deploy SYN-cookies if necessary.
  53 setopt tcp_syncookies 1
  54
  55 ## Allow broadcast and multicast ping, because it's a useful diagnostic tool.
  56 setopt icmp_echo_ignore_broadcasts 0
  57
  58 ## Turn off iptables filtering for bridges.  We'll use ebtables if we need
  59 ## to; but right now the model is that we do filtering at the borders, and
  60 ## are tolerant of things which are local.
  61 if [ -x /sbin/brctl ]; then
  62   modprobe bridge || :
  63   if [ -d /proc/sys/net/bridge ]; then
  64     for filter in arptables iptables ip6tables; do
  65       run sysctl -q net.bridge.bridge-nf-call-$filter=0
  66     done
  67   fi
  68 fi
  69
  70 ## Turn on the reverse-path filter, and log weird things.
  71 setdevopt rp_filter $rp_filter
  72 setdevopt log_martians $log_martians
  73
  74 ## Turn off things which can mess with our routing decisions.
  75 setdevopt accept_source_route 0
  76 setdevopt accept_redirects 0
  77
  78 ## If we're maent to stop the firewall, then now is the time to do it.
  79 $exit_after_clearing
  80
  81 m4_divert(34)m4_dnl
  82 ###--------------------------------------------------------------------------
  83 ### Establish error chains.
  84
  85 errorchain forbidden REJECT
  86 ## Generic `not allowed' chain.
  87
  88 errorchain tcp-fragment REJECT
  89 ## Chain for logging fragmented TCP segements.
  90
  91 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
  92 ## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.
  93
  94 errorchain mangle:bad-source-address DROP
  95 errorchain bad-source-address DROP
  96 ## Packet arrived on wrong interface for its source address.  Drops the
  97 ## packet, since there's nowhere sensible to send an error.
  98
  99 errorchain bad-destination-address REJECT
 100 ## Packet arrived on non-loopback interface with loopback destination.
 101
 102 errorchain interesting ACCEPT
 103 ## Not an error, just log interesting packets.
 104
 105 m4_divert(36)m4_dnl
 106 ###--------------------------------------------------------------------------
 107 ### Standard loopback stuff.
 108
 109 ## Don't clobber local traffic
 110 run ip46tables -A INPUT -i lo -j ACCEPT
 111
 112 ## We really shouldn't see packets destined for localhost on any interface
 113 ## other than the loopback.
 114 run iptables -A INPUT -g bad-destination-address \
 115         -d 127.0.0.0/8
 116 run ip6tables -A INPUT -g bad-destination-address \
 117         -d ::1
 118
 119 ## We shouldn't be asked to forward things with link-local addresses.
 120 run iptables -A FORWARD -g bad-source-address \
 121         -s 169.254.0.0/16
 122 run iptables -A FORWARD -g bad-destination-address \
 123         -d 169.254.0.0/16
 124 run ip6tables -A FORWARD -g bad-source-address \
 125         -s fe80::/10
 126 run ip6tables -A FORWARD -g bad-destination-address \
 127         -d fe80::/10
 128
 129 ## Also, don't forward link-local broadcast or multicast.
 130 run iptables -A FORWARD -g bad-destination-address \
 131         -d 255.255.255.255
 132 run iptables -A FORWARD -g bad-destination-address \
 133         -m addrtype --dst-type BROADCAST
 134 run iptables -A FORWARD -g bad-destination-address \
 135         -d 224.0.0.0/24
 136 for x in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
 137   run ip6tables -A FORWARD -g bad-destination-address \
 138         -d fe${x}2::/16
 139 done
 140
 141 m4_divert(90)m4_dnl
 142 ###--------------------------------------------------------------------------
 143 ### Finishing touches.
 144
 145 m4_divert(94)m4_dnl
 146 ## Locally generated packets are all OK.
 147 run iptables -P OUTPUT ACCEPT
 148
 149 ## Other incoming things are forbidden.
 150 for chain in INPUT FORWARD; do
 151   run iptables -A $chain -g forbidden
 152 done
 153
 154 m4_divert(-1)
 155 ###----- That's all, folks --------------------------------------------------