Nameserver setup script for OpenVPN in combination with Ubuntu's NetworkManager and dnsmasq

update-dnsmasq

#!/bin/bash
# 
# Parses DHCP options from openvpn to send to dnsmasq via dbus
# To use set as 'up' and 'down' script in your openvpn *.conf:
# up /etc/openvpn/update-dnsmasq
# down /etc/openvpn/update-dnsmasq
#
# Used snippets of resolvconf script by Thomas Hood and Chris Hanson.
# Licensed under the GNU GPL.  See /usr/share/common-licenses/GPL. 
# 
# Example envs set from openvpn:
#
#     foreign_option_1='dhcp-option DNS 193.43.27.132'
#     foreign_option_2='dhcp-option DNS 193.43.27.133'
#     foreign_option_3='dhcp-option DOMAIN be.bnc.ch'
#

DEV_DIR="/etc/openvpn/devices"

[ "$script_type" ] || exit 0
[ "$dev" ] || exit 0



if [ ! -d $DEV_DIR ]; then
    mkdir $DEV_DIR;
fi

split_into_parts()
{
	part1="$1"
	part2="$2"
	part3="$3"
}

inet_aton() {
    local count=3
    local int=0
    for num in $(echo $1 | sed -e 's/\./ /g'); do
	let "int+=$num*256**$count"
	let "count-=1"
    done
    echo $int
}

update_dnsmasq() {
    PARAMS=
    for file in $DEV_DIR/*.openvpn; do
	ns=$(cat $file | sed -n -e 's/^[[:space:]]*nameserver[[:space:]]\+//p')
	PARAMS+="uint32:$(inet_aton $ns) "
	domain=$(cat $file | sed -n -e 's/^[[:space:]]*search[[:space:]]\+//p')
	PARAMS+="string:$domain "
    done
    # load default nameservers from network manager
    for nameserver in $(nmcli device show | grep DNS | awk '{print $2}' | grep -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'); do
	PARAMS+="uint32:$(inet_aton $nameserver) string: "
    done
    dbus-send --system --print-reply --dest='org.freedesktop.NetworkManager.dnsmasq' \
	          /uk/org/thekelleys/dnsmasq uk.org.thekelleys.SetServers $PARAMS
}

case "$script_type" in
  up)
	NMSRVRS=""
	SRCHS=""
	for optionvarname in ${!foreign_option_*} ; do
		option="${!optionvarname}"
		echo "$option"
		split_into_parts $option
		if [ "$part1" = "dhcp-option" ] ; then
			if [ "$part2" = "DNS" ] ; then
				NMSRVRS="${NMSRVRS:+$NMSRVRS }$part3"
			elif [ "$part2" = "DOMAIN" ] ; then
				SRCHS="${SRCHS:+$SRCHS }$part3"
			fi
		fi
	done
	R=""
	[ "$SRCHS" ] && R="search $SRCHS
"
	for NS in $NMSRVRS ; do
        	R="${R}nameserver $NS
"
	done
	echo -n "$R" > "$DEV_DIR/${dev}.openvpn"
	update_dnsmasq
	;;
  down)
	rm -fv "$DEV_DIR/${dev}.openvpn"
	update_dnsmasq
	;;
esac