#!/bin/bash
# adhoc_wifi_gateway
# (c) Paul Mansfield July 2009
# release under GNU Public License Latest Revision
# 
# History
#   20090719
#	PM
#	first release into the wild
#

##### CONSTANTS ####

# these are all you should need to change
WIFI=wlan0
WIFI_ESSID=My_Temporary_Access_Point
WIFI_WEP=DEADBEEFDEAFBEEFDEADBEEFDE
WAN=ppp0

# if DHCP daemon is running chroot, all files could be under here
DHCP_ROOT=/var/lib/dhcp/
DHCP_CONFIG=/etc/dhcpd.adhoc-wifi-ap.conf
DHCP_USER=dhcpd
DHCP_GROUP=nogroup
DHCP_LEASES=/db/dhcpd.wlan0.leases
DHCP_PID=/db/dhcpd.wlan0.pid

# shouldn't need to change these unless you're already using 172.16.31.0/24
WIFI_IP=172.16.31.1
WIFI_MASK=255.255.255.0
WIFI_NET=172.16.31.0
WIFI_DHCP="172.16.31.2 172.16.31.254"


## ROUTING ##

# set up routing
echo 1 > /proc/sys/net/ipv4/ip_forward

# need to NAT outbound packets
iptables -t nat -F					# kill existing NAT
iptables -t nat -I POSTROUTING -o $WAN -j MASQUERADE	# nat to WAN IP



## SECURITY ##

# need to permit input so DHCP works
iptables -I INPUT	-i $WIFI		-j ACCEPT

# permit forwarding
iptables -I FORWARD	-i $WIFI -o $WAN	-j ACCEPT
iptables -I FORWARD				-m state --state established,related -j ACCEPT



## WIRELESS ##

# set up ad-hoc wifi "access point"
iwconfig $WIFI mode ad-hoc
iwconfig $WIFI essid $WIFI_ESSID
iwconfig $WIFI enc $WIFI_WEP

ifconfig $WIFI $WIFI_IP netmask 255.255.255.0



## SERVICES ##


# test if already running a DHCP server
ps -ef | grep -v grep | grep "/usr/sbin/dhcpd -cf /etc/dhcpd.adhoc-wifi-ap.conf" > /dev/null
if [ $? -ne 0 ] ; then
	# set up a DHCP server

	# some dhcp servers need their leases file initialising
	touch		$DHCP_ROOT/$DHCP_LEASES
	chown dhcpd	$DHCP_ROOT/$DHCP_LEASES

	# create a DHCP server config
	cat > $DHCP_ROOT/$DHCP_CONFIG << EOF 
option domain-name-servers 154.32.105.18,154.32.107.18,154.32.109.18;
default-lease-time 86400;
ddns-update-style none;
subnet $WIFI_NET netmask $WIFI_MASK {
	range			dynamic-bootp	$WIFI_DHCP;
	option	routers		$WIFI_IP;
	default-lease-time	86400;
	max-lease-time		172800;
}
EOF

	# fire up DHCP daemon with the config
	/usr/sbin/dhcpd	-chroot $DHCP_ROOT	\
			-cf	$DHCP_CONFIG	\
			-pf	$DHCP_PID	\
			-lf	$DHCP_LEASES	\
			-user	$DHCP_USER	\
			-group	$DHCP_GROUP	\
			$WIFI
else
	echo "dhcpd appears to be already running on wifi, not started"
fi