#!/bin/sh
# /etc/rc.d/rc.firewall-lan

# start/stop/restart iptables firewall rules

# base script generated by Easy Firewall Generator
# copyright 2002 Timothy Scott Morizot
# http://easyfwgen.morizot.net/gen/
# slackware specific version available at
# http://www.slackware.com/~alien/efg/

# modified liberally thereafter

# modified for colorized screen messages and local needs
source /etc/functions-colors

###############################################################################
#
# Load Modules
#
# echo "Loading module support."

# Unless you have kernel module auto-loading disabled, you should not
# need to manually load each of these modules. Other than ip_tables,
# ip_conntrack, and some of the optional modules, I've left these
# commented by default. Uncomment if you have any problems or if
# you have disabled module autoload. Note that some modules must
# be loaded by another kernel module.

# core netfilter module
# $MODPROBE ip_tables

# filter table module
# $MODPROBE iptable_filter

# the stateful connection tracking module
# $MODPROBE ip_conntrack

# the module for full ftp connection tracking
# $MODPROBE ip_conntrack_ftp

# the module for full irc connection tracking
# $MODPROBE ip_conntrack_irc

# mangle table module
# $MODPROBE iptable_mangle

# nat table module
# $MODPROBE iptable_nat

# The ftp nat module is required for non-PASV ftp support
# $MODPROBE ip_nat_ftp

# The irc nat module
# $MODPROBE ip_nat_irc

# LOG target module
# $MODPROBE ipt_LOG

# This is used to limit the number of packets per sec/min/hr
# $MODPROBE ipt_limit

# This match checks against the TCP flags
# $MODPROBE ipt_state

# REJECT target drops the packet and returns an ICMP response.
# The response is configurable. By default, connection refused.
# $MODPROBE ipt_REJECT

# filter using owner as part of the match
# $MODPROBE ipt_owner

# masquerade target module
# $MODPROBE ipt_MASQUERADE

# This target allows packets to be marked in the mangle table
# $MODPROBE ipt_mark

# This target affects the TCP MSS
# $MODPROBE ipt_tcpmss

# This match allows multiple ports instead of a single port or range
# $MODPROBE multiport

# This match catches packets with invalid flags
# $MODPROBE ipt_unclean

###############################################################################
#
# Set Policies

$IPT -P INPUT DROP
$IPT -P OUTPUT DROP
$IPT -P FORWARD DROP

###############################################################################
#
# User-Specified Chains
#
# Create user chains to reduce the number of rules each packet
# must traverse.

echo -e "${BOLDWHITE}Creating and populating rule chains.${COLOR_RESET}"

# Create a chain to filter INVALID packets

$IPT -N bad_packets

# Create another chain to filter bad tcp packets

$IPT -N bad_tcp_packets

# Create separate chains for icmp, tcp (incoming and outgoing),
# and incoming udp packets.

$IPT -N icmp_packets

# Used for UDP packets inbound from the Internet
$IPT -N udp_inbound

# Used to block outbound UDP services from internal network
# Default to allow all
$IPT -N udp_outbound

# Used to allow inbound services if desired
# Default fail except for established sessions
$IPT -N tcp_inbound

# Used to block outbound services from internal network
# Default to allow all
$IPT -N tcp_outbound

###############################################################################
#
# Populate User Chains
#
# bad_packets chain
#

# Drop INVALID packets immediately
$IPT -A bad_packets -p ALL -m state --state INVALID -j LOG --log-prefix "Invalid packet: "
$IPT -A bad_packets -p ALL -m state --state INVALID -j DROP

# Then check the tcp packets for additional problems
$IPT -A bad_packets -p tcp -j bad_tcp_packets

# All good, so return
$IPT -A bad_packets -p ALL -j RETURN

# bad_tcp_packets chain
#
# All tcp packets will traverse this chain.
# Every new connection attempt should begin with
# a syn packet. If it doesn't, it is likely a
# port scan. This drops packets in state
# NEW that are not flagged as syn packets.

# Return to the calling chain if the bad packets originate
# from the local interface. This maintains the approach
# throughout this firewall of a largely trusted internal
# network.
$IPT -A bad_tcp_packets -p tcp -i $LAN_IFACE -j RETURN

# However, I originally did apply this filter to the forward chain
# for packets originating from the internal network. While I have
# not conclusively determined its effect, it appears to have the
# interesting side effect of blocking some of the ad systems.
# Apparently some ad systems have the browser initiate a NEW
# connection that is not flagged as a syn packet to retrieve
# the ad image. If you wish to experiment further comment the
# rule above. If you try it, you may also wish to uncomment the
# rule below. It will keep those packets from being logged.
# There are a lot of them.
$IPT -A bad_tcp_packets -p tcp -i $LAN_IFACE ! --syn -m state --state NEW -j DROP

# $IPT -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn: "
$IPT -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j LOG --log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP

# All good, so return
$IPT -A bad_tcp_packets -p tcp -j RETURN

# icmp_packets chain
#
# This chain is for inbound (from the Internet) icmp packets only.
# Type 8 (Echo Request) is not accepted by default
# Enable it if you want remote hosts to be able to reach you.
# 11 (Time Exceeded) is the only one accepted
# that would not already be covered by the established
# connection rule. Applied to INPUT on the external interface.
#
# See: http://www.ee.siue.edu/~rwalden/networking/icmp.html
# for more info on ICMP types.
#
# Note that the stateful settings allow replies to ICMP packets.
# These rules allow new packets of the specified types.

# ICMP packets should fit in a Layer 2 frame, thus they should
# never be fragmented. Fragmented ICMP packets are a typical sign
# of a denial of service attack.
$IPT -A icmp_packets --fragment -p ICMP -j LOG --log-prefix "ICMP Fragment: "
$IPT -A icmp_packets --fragment -p ICMP -j DROP

# Echo - uncomment to allow your system to be pinged.
# Uncomment the LOG command if you also want to log PING attempts
#
# $IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j LOG --log-prefix "Ping detected: "
# $IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT

# By default, however, drop pings without logging. Blaster
# and other worms have infected systems blasting pings.
# Comment the line below if you want pings logged, but it
# will likely fill your logs.
# $IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j DROP

# Time Exceeded
$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

# Not matched, so return so it will be logged
$IPT -A icmp_packets -p ICMP -j RETURN

# TCP & UDP
# Identify ports at:
#  http://www.chebucto.ns.ca/~rakerman/port-table.html
#  http://www.iana.org/assignments/port-numbers

# udp_inbound chain
#
# This chain describes the inbound UDP packets it will accept.
# It's applied to INPUT on the external or Internet interface.
# Note that the stateful settings allow replies.
# These rules are for new requests.
# It drops netbios packets (windows) immediately without logging.

# Drop netbios calls
# Please note that these rules do not really change the way the firewall
# treats netbios connections. Connections from the localhost and
# internal interface (if one exists) are accepted by default.
# Responses from the Internet to requests initiated by or through
# the firewall are also accepted by default. To get here, the
# packets would have to be part of a new request received by the
# Internet interface. You would have to manually add rules to
# accept these. I added these rules because some network connections,
# such as those via cable modems, tend to be filled with noise from
# unprotected Windows machines. These rules drop those packets
# quickly and without logging them. This prevents them from traversing
# the whole chain and keeps the log from getting cluttered with
# chatter from Windows systems.
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 137 -j DROP
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 138 -j DROP

# Dynamic Address
# If DHCP, the initial request is a broadcast. The response
# doesn't exactly match the outbound packet. This explicitly
# allow the DHCP ports to alleviate this problem.
# If you receive your dynamic address by a different means, you
# can probably comment this line.
$IPT -A udp_inbound -p UDP -s 0/0 --sport 67 --destination-port 68 -j ACCEPT

# Not matched, so return for logging
$IPT -A udp_inbound -p UDP -j RETURN

# udp_outbound chain
#
# This chain is used with a private network to prevent forwarding for
# UDP requests on specific protocols. Applied to the FORWARD rule from
# the internal network. Ends with an ACCEPT

# No match, so ACCEPT
$IPT -A udp_outbound -p UDP -s 0/0 -j ACCEPT

# tcp_inbound chain
#
# This chain is used to allow inbound connections to the
# system/gateway. Use with care. It defaults to none.
# It's applied on INPUT from the external or Internet interface.

# Not matched, so return so it will be logged
$IPT -A tcp_inbound -p TCP -j RETURN

# tcp_outbound chain
#
# This chain is used with a private network to prevent forwarding for
# requests on specific protocols. Applied to the FORWARD rule from
# the internal network. Ends with an ACCEPT

# No match, so ACCEPT
$IPT -A tcp_outbound -p TCP -s 0/0 -j ACCEPT

###############################################################################
#
# INPUT Chain
#

echo "Processing INPUT chain."

# Allow all on localhost interface
$IPT -A INPUT -p ALL -i $LO_IFACE -j ACCEPT

# Drop bad packets
$IPT -A INPUT -p ALL -j bad_packets

# DOCSIS compliant cable modems
# Some DOCSIS compliant cable modems send IGMP multicasts to find
# connected PCs. The multicast packets have the destination address
# 224.0.0.1. You can accept them. If you choose to do so,
# Uncomment the rule to ACCEPT them and comment the rule to DROP
# them  The firewall will drop them here by default to avoid
# cluttering the log. The firewall will drop all multicasts
# to the entire subnet (224.0.0.1) by default. To only affect
# IGMP multicasts, change '-p ALL' to '-p 2'. Of course,
# if they aren't accepted elsewhere, it will only ensure that
# multicasts on other protocols are logged.
# Drop them without logging.
$IPT -A INPUT -p ALL -d 224.0.0.1 -j DROP
# The rule to accept the packets.
# $IPT -A INPUT -p ALL -d 224.0.0.1 -j ACCEPT

# Rules for the private network (accessing gateway system itself)
$IPT -A INPUT -p ALL -i $LAN_IFACE -s $LAN_NET -j ACCEPT
$IPT -A INPUT -p ALL -i $LAN_IFACE -d $LAN_BCAST -j ACCEPT

# Allow DHCP client request packets inbound from internal network
if [ "$DHCP_SERVER" = "yes" ] ; then
  echo -e "${BOLDYELLOW}Allowing DHCP services on local network.${COLOR_RESET}"
  $IPT -A INPUT -p UDP -i $LAN_IFACE --sport 68 --dport 67 -j ACCEPT
fi

# Inbound Internet Packet Rules

# Accept Established Connections
$IPT -A INPUT -p ALL -i $INET_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT

# Route the rest to the appropriate user chain
$IPT -A INPUT -p TCP -i $INET_IFACE -j tcp_inbound
$IPT -A INPUT -p UDP -i $INET_IFACE -j udp_inbound
$IPT -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets

# Drop without logging broadcasts that get this far.
# Cuts down on log clutter.
# Comment this line if testing new rules that impact
# broadcast protocols.
$IPT -A INPUT -m pkttype --pkt-type broadcast -j DROP

# Log packets that still don't match
$IPT -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-prefix "INPUT packet died: "

# Drop and log all other traffic
# $IPT -A INPUT -j LOGDROP --log-level debug

###############################################################################
#
# FORWARD Chain
#

# Used when forwarding for a private network

if [ "$IP_FORWARD" = "1" ];then
  echo "Processing FORWARD chain."

  # Drop bad packets
  $IPT -A FORWARD -p ALL -j bad_packets

  # Accept TCP packets we want to forward from internal sources
  $IPT -A FORWARD -p tcp -i $LAN_IFACE -j tcp_outbound

  # Accept UDP packets we want to forward from internal sources
  $IPT -A FORWARD -p udp -i $LAN_IFACE -j udp_outbound

  # If not blocked, accept any other packets from the internal interface
  $IPT -A FORWARD -p ALL -i $LAN_IFACE -j ACCEPT

  # Deal with responses from the internet
  $IPT -A FORWARD -i $INET_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT

  # Log packets that still don't match
  $IPT -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG --log-prefix "FORWARD packet died: "
fi

###############################################################################
#
# OUTPUT Chain
#

echo "Processing OUTPUT chain."

# Generally trust the firewall on output

# However, invalid icmp packets need to be dropped
# to prevent a possible exploit.
$IPT -A OUTPUT -m state -p icmp --state INVALID -j DROP

# Localhost
$IPT -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPT -A OUTPUT -p ALL -o $LO_IFACE -j ACCEPT

# To internal network
$IPT -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT
$IPT -A OUTPUT -p ALL -o $LAN_IFACE -j ACCEPT

# To internet
$IPT -A OUTPUT -p ALL -s $INET_IP -j ACCEPT
$IPT -A OUTPUT -p ALL -o $INET_IFACE -j ACCEPT

# Log packets that still don't match
$IPT -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-prefix "OUTPUT packet died: "