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

   1 ### -*-m4-*-
   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 iptables -t $t -P $i DROP 2>/dev/null || :
  34     run iptables -t $t -F $i 2>/dev/null || :
  35   done
  36   run iptables -t $t -F
  37   run iptables -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 ## Turn on the reverse-path filter, and log weird things.
  56 setdevopt rp_filter 1
  57 setdevopt log_martians 1
  58
  59 ## Turn off things which can mess with our routing decisions.
  60 setdevopt accept_source_route 0
  61 setdevopt accept_redirects 0
  62
  63 ## If we're maent to stop the firewall, then now is the time to do it.
  64 $exit_after_clearing
  65
  66 m4_divert(34)m4_dnl
  67 ###--------------------------------------------------------------------------
  68 ### Establish error chains.
  69
  70 errorchain forbidden REJECT --reject-with icmp-host-prohibited
  71 ## Generic `not allowed' chain.  Rejects with ICMP host-prohibited.
  72
  73 errorchain tcp-fragment REJECT --reject-with icmp-host-prohibited
  74 ## Chain for logging fragmented TCP segements.  Rejects with ICMP
  75 ## host-prohibited.
  76
  77 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
  78 ## Bad TCP segments (e.g., for unknown connections).  Sends a TCP reset.
  79
  80 errorchain mangle:bad-source-address DROP
  81 ## Packet arrived on wrong interface for its source address.  Drops the
  82 ## packet, since there's nowhere sensible to send an error.
  83
  84 errorchain bad-destination-address REJECT --reject-with icmp-host-prohibited
  85 ## Packet arrived on non-loopback interface with loopback destination.  Sends
  86 ## a rude note back.
  87
  88 errorchain interesting ACCEPT
  89 ## Not an error, just log interesting packets.
  90
  91 m4_divert(36)m4_dnl
  92 ###--------------------------------------------------------------------------
  93 ### Standard loopback stuff.
  94
  95 ## Don't clobber local traffic
  96 run iptables -A INPUT -i lo -j ACCEPT
  97
  98 ## We really shouldn't see packets destined for localhost on any interface
  99 ## other than the loopback.
 100 run iptables -A INPUT -g bad-destination-address \
 101         -d 127.0.0.0/8
 102
 103 m4_divert(90)m4_dnl
 104 ###--------------------------------------------------------------------------
 105 ### Finishing touches.
 106
 107 m4_divert(94)m4_dnl
 108 ## Locally generated packets are all OK.
 109 run iptables -P OUTPUT ACCEPT
 110
 111 ## Other incoming things are forbidden.
 112 for chain in INPUT FORWARD; do
 113   run iptables -A $chain -g forbidden
 114 done
 115
 116 m4_divert(-1)
 117 ###----- That's all, folks --------------------------------------------------