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