syncdnsblocks

#!/bin/sh

# Synchronizes DNS blocklist from master dns server
#
# Universe is running a DNS server which blocks certain domains.
# Elsewhere, we don't have access to universe's DNS server
# yet we still want to have those domains blocked.
#
# Solution: dynamically update hosts file depending on location
#
# If the nameserver we're using is the universe's nameserver,
# remove all hosts entries (these are mapped to a special IP
# inside universe) but make a list of all current entries
# and save them locally.
#
# If the nameserver we're using is not universe's, take the
# hosts that would be blocked in universe and install them into
# the hosts file.

DNS_MASTER="10.0.0.254"
BLOCKLIST_URL="http://${DNS_MASTER}/cgi-bin/dnsblocklist"
BLOCKLIST_CACHE="/var/state/dnsblocklist"

if [ -n "$NAMESERVER" ]; then
    nameserver="$NAMESERVER"
else
    nameserver=$(cat /etc/resolv.conf | grep ^nameserver | awk '{ print $2 }')
fi

cp /etc/hosts.master /etc/hosts

if [ "$nameserver" == "$DNS_MASTER" ]; then
    wget -O $BLOCKLIST_CACHE $BLOCKLIST_URL
elif [ -f $DNSBLOCKLIST ]; then
    for host in $(cat $BLOCKLIST_CACHE); do
        echo 127.0.0.1 $host >> /etc/hosts
    done
fi