#!/bin/bash
#
# Firewall Script - Version 0.9.0
# chkconfig: 2345 09 99
# description: firewall script for 2.2.x kernel
# Set for testing
# set -x
#
# NOTES:
#
# This script is written for RedHat 6.0 or better.
#
# This firewall script should work for most routers,
# dial-up or cable modem.
# It was written for RedHat distributions.
#
# Be careful about offering public
# services like web or ftp servers.
#
# INSTALLATION:
# 1. This file planned for a RedHat system.
# It would work on other distro's
# with perhaps no modification, but again...
# Who knows?!!?
# These instructions apply to RedHat systems.
#
# 2. place this file in /etc/rc.d/init.d
# (you'll have to be root..)
# call it something like "firewall" :-)
# make it root owned
# --> "chown root.root <filename>"
# make it executable
# --> "chmod 755 <filename>"
#
# 3. set the values for your network,
# internal interface, and DNS servers
# uncomment lines further down
# to enable optional in-bound services
# make sure "eth0" is your internal NIC
# (or change the value below)
# test it
# --> "/etc/rc.d/init.d/<filename> start"
# you can list the rules --> "ipchains -L -n"
# fix anything that broke... :-)
#
# 4. add the firewall
# to the RH init structure
# --> "chkconfig --add <filename>"
# next time the router boots,
# things should happen automagically!
# sleep better at night knowing you are
# *LESS* vulnerable than before...
#
# RELEASE NOTES
# 20 July, 1999 - initial writing -
# Anthony Ball <tony@LinuxSIG.org>
# 11 Dec, 1999 - updated by
# Mark Grennan <mark@grennan.com>
#
################################################
# Fill in the values below to match your
# local network.
PRIVATENET=xxx.xxx.xxx.xxx/xx
PUBLIC=ppp0
PRIVATE=eth0
# your dns servers
DNS1=xxx.xxx.xxx.xxx
DNS2=xxx.xxx.xxx.xxx
################################################
# some handy generic values to use
ANY=0.0.0.0/0
ALLONES=255.255.255.255
# Source function library.
. /etc/rc.d/init.d/functions
# Source networking configuration.
. /etc/sysconfig/network
# Check that networking is up.
[ ${NETWORKING} = "no" ] && exit 0
# See how we are called
case "$1" in
start)
# Start providing access
action "Starting firewall: " /bin/true
##
## Setup Envirement
##
# Flush all lists
/sbin/ipchains -F input
/sbin/ipchains -F output
/sbin/ipchains -F forward
# Plug up everything
/sbin/ipchains -I input 1 -j DENY
# set policy to deny (Default is ACCEPT)
/sbin/ipchains -P input DENY
/sbin/ipchains -P output ACCEPT
/sbin/ipchains -P forward ACCEPT
# Turn on packet forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
##
## Install Modules
##
# Insert the active ftp module.
# This will allow non-passive ftp to machines
# on the local network
# (but not to the router since it is not masq'd)
if ! ( /sbin/lsmod | /bin/grep masq_ftp > /dev/null ); \
then
/sbin/insmod ip_masq_ftp
fi
##
## Some Security Stuff
##
# turn on Source Address Verification
# and get spoof protection
# on all current and future interfaces.
if [ -e /proc/sys/net/ipv4/conf/all/rp_filter ]; then
for f in /proc/sys/net/ipv4/conf/*/rp_filter; do
echo 1 > $f
done
else
echo
echo "PROBLEMS SETTING UP IP SPOOFING PROTECTION"
echo "BE WORRIED."
echo
fi
# deny bcasts on remaining interfaces
/sbin/ipchains -A input -d 0.0.0.0 -j DENY
/sbin/ipchains -A input -d 255.255.255.255 -j DENY
# deny these without logging
# because there tend to be a lot...
# NetBIOS over IP
/sbin/ipchains -A input -p udp -d $ANY 137 -j DENY
# NetBIOS over IP
/sbin/ipchains -A input -p tcp -d $ANY 137 -j DENY
# NetBIOS over IP
/sbin/ipchains -A input -p udp -d $ANY 138 -j DENY
# NetBIOS over IP
/sbin/ipchains -A input -p tcp -d $ANY 138 -j DENY
# bootp
/sbin/ipchains -A input -p udp -d $ANY 67 -j DENY
# bootp
/sbin/ipchains -A input -p udp -d $ANY 68 -j DENY
# Multicast addresses
/sbin/ipchains -A input -s 224.0.0.0/8 -j DENY
##
## Allow private network out
##
# allow all packets on the loopback interface
/sbin/ipchains -A input -i lo -j ACCEPT
# allow all packets from the internal "trusted" interface
/sbin/ipchains -A input -i $PRIVATE -s $PRIVATENET \
-d $ANY -j ACCEPT
/sbin/ipchains -A input -i $PRIVATE \
-d $ALLONES -j ACCEPT
##
## Allow Outside Services into the firewall (if you dare)
##
# allow ICMP
/sbin/ipchains -A input -p icmp -j ACCEPT
# allow TCP
/sbin/ipchains -A input -p tcp ! -y -j ACCEPT
# allow lookups to DNS (on firewall)
/sbin/ipchains -A input -p udp -s $DNS1 domain \
-d $ANY 1023: -j ACCEPT
/sbin/ipchains -A input -p udp -s $DNS2 domain \
-d $ANY 1023: -j ACCEPT
# or (BETTER IDEA) run a caching DNS server
# on the router and use the
# following two/four lines instead...
# /sbin/ipchains -A input -p udp -s $DNS1 domain \
# -d $ANY domain -j ACCEPT
# /sbin/ipchains -A input -p udp -s $DNS2 domain \
# -d $ANY domain -j ACCEPT
# uncomment the following to allow ssh in
/sbin/ipchains -A input -p tcp -d $ANY 22 -j ACCEPT
# uncomment the following to allow telnet in (BAD IDEA!!)
/sbin/ipchains -A input -p tcp -d $ANY telnet -j ACCEPT
# uncomment to allow NTP
# (network time protocol) to router
# /sbin/ipchains -A input -p udp -d $ANY ntp -j ACCEPT
# uncomment to allow SMTP in
# (not for mail clients - only a server)
/sbin/ipchains -A input -p tcp -d $ANY smtp -j ACCEPT
# uncomment to allow POP3 in (for mail clients)
/sbin/ipchains -A input -p tcp -d $ANY 110 -j ACCEPT
# allow auth in for sending mail or doing ftp
/sbin/ipchains -A input -p tcp -d $ANY auth -j ACCEPT
# uncomment to allow HTTP in
# (only if you run a web server on the router)
/sbin/ipchains -A input -p tcp -d $ANY http -j ACCEPT
# uncomment to allow FTP in
/sbin/ipchains -A input -p tcp -d $ANY ftp -j ACCEPT
##
## Masquerading stuff
##
# masquerade packets forwarded from internal network
/sbin/ipchains -A forward -s $PRIVATENET -d $ANY -j MASQ
##
## deny EVERYthing else
## and log them to /var/log/messages
/sbin/ipchains -A input -l -j DENY
# Remove the Plug
/sbin/ipchains -D input 1
;;
stop)
action "Stoping firewall: " /bin/true
echo 0 > /proc/sys/net/ipv4/ip_forward
/sbin/ipchains -F input
/sbin/ipchains -F output
/sbin/ipchains -F forward
echo
;;
restart)
action "Restarting firewall: " /bin/true
$0 stop
$0 start
echo
;;
status)
# List out settings
/sbin/ipchains -L
;;
test)
##
## This is about as simple as it gets
## (This is not secure AT ALL)
action "WARNING Test Firewall: " /bin/true
/sbin/ipchains -F input
/sbin/ipchains -F output
/sbin/ipchains -F forward
echo 1 > /proc/sys/net/ipv4/ip_forward
/sbin/ipchains -A input -j ACCEPT
/sbin/ipchains -A output -j ACCEPT
/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -i $PUBLIC -j MASQ
echo
;;
*)
echo "Usage: $0 {start|stop|restart|status|test}"
exit 1
esac |