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http://blog.osdev.org/git/2014/02/13/using-git-on-a-synology-nas.html#!/bin/bash
# $Id: alcasar-watchdog.sh 1500 2014-11-27 08:09:43Z richard $

# alcasar-watchdog.sh
# by Rexy
# This script is distributed under the Gnu General Public License (GPL)
# Ce script prévient les usagers de l'indisponibilité de l'accès Internet
# il déconnecte les usagers dont
# - les équipements réseau ne répondent plus
# - les adresses MAC sont usurpées
# This script tells users that Internet access is down
# it logs out users whose 
# - PCs are quiet
# - MAC address is used by other systems (usurped)

CONF_FILE="/usr/local/etc/alcasar.conf"
EXTIF=`grep ^EXTIF= $CONF_FILE|cut -d"=" -f2`                   # EXTernal InterFace
INTIF=`grep ^INTIF= $CONF_FILE|cut -d"=" -f2`                   # INTernal InterFace
private_ip_mask=`grep PRIVATE_IP= $CONF_FILE|cut -d"=" -f2`
private_ip_mask=${private_ip_mask:=192.168.182.1/24}
PRIVATE_IP=`echo "$private_ip_mask" |cut -d"/" -f1`      # @ip du portail (côté LAN)
PRIVATE_IP=${PRIVATE_IP:=192.168.182.1}
tmp_file="/tmp/watchdog.txt"
DIR_WEB="/var/www/html"
Index_Page="$DIR_WEB/index.php"
IPTABLES="/sbin/iptables"
TUNIF="tun0"                                            # listen device for chilli daemon
OLDIFS=$IFS
IFS=$'\n'

function lan_down_alert ()
# users are redirected on ALCASAR IP address if a LAN problem is detected
{
        case $LAN_DOWN in
        "1")
                logger "$EXTIF (WAN card) link down"
                echo "$EXTIF (WAN card) link down"
                /bin/sed -i "s?diagnostic =.*?diagnostic = \"$EXTIF (WAN card) link down\";?g" $Index_Page
                ;;
        "2")
                logger "can't contact the default router"
                echo "can't contact the default router"
                /bin/sed -i "s?diagnostic =.*?diagnostic = \"can't contact the default router\";?g" $Index_Page
                ;;
        esac
        net_pb=`grep "network_pb = True;" $Index_Page|wc -l`
        if [ $net_pb = "0" ] # user alert (only the first time)  
                then
                /bin/sed -i "s?^\$network_pb.*?\$network_pb = True;?g" $Index_Page
                $IPTABLES -I PREROUTING -t nat -i $TUNIF -p udp --dport domain -j REDIRECT --to-port 56
        fi
}

function lan_test ()
# LAN connectiivity testing
{
        watchdog_process=`ps -C alcasar-watchdog.sh|wc -l`
        if [[ $(expr $watchdog_process) -gt 3 ]]
                then
                echo "ALCASAR watchdog is already running"
                exit 0
        fi
        # EXTIF testing
        LAN_DOWN="0"
        if [ `/sbin/ip link | grep $EXTIF|grep "NO-CARRIER" | wc -l` -eq "1" ]
                then
                LAN_DOWN="1"
        fi
        # Default GW testing
        if [ $LAN_DOWN -eq "0" ]
                then
                IP_GW=`/sbin/ip route list|grep ^default|cut -d" " -f3`
                arp_reply=`/usr/sbin/arping -I$EXTIF -c1 $IP_GW|grep response|cut -d" " -f2`
                if [ $arp_reply -eq "0" ]
                        then
                        LAN_DOWN="2"
                fi
        fi
        # if LAN pb detected, users are warned
        if [ $LAN_DOWN != "0" ]
                then
                        lan_down_alert
        # else switch in normal mode
        else
                echo "Internet access is OK for now"
                net_pb=`grep "network_pb = True;" $Index_Page|wc -l`
                if [ $net_pb != "0" ]
                        then
                        /bin/sed -i "s?^\$network_pb.*?\$network_pb = False;?g" $Index_Page
                        $IPTABLES -D PREROUTING -t nat -i $TUNIF -p udp --dport domain -j REDIRECT --to-port 56
                fi
        fi
}

usage="Usage: alcasar-watchdog.sh {-lt --lan_test}"
case $1 in
        -\? | -h* | --h*)
                echo "$usage"
                exit 0
                ;;
        -lt | --lan_test)
                lan_test
                exit 0
                ;;
        *)
                lan_test
                # read file that contains IP address of quiet equipments
                if [ -e $tmp_file ]; then
                        cat $tmp_file | while read noresponse
                        do
                                noresponse_ip=`echo $noresponse | cut -d" " -f1`
                                noresponse_mac=`echo $noresponse | cut -d" " -f2`
                                noresponse_user=`echo $noresponse | cut -d" " -f3`
                                arp_reply=`/usr/sbin/arping -b -I$INTIF -s$PRIVATE_IP -c1 -w4 $noresponse_ip|grep "Unicast reply"|wc -l`
                                if [[ $(expr $arp_reply) -eq 0 ]]
                                        then
                                        logger "alcasar-watchdog $noresponse_ip ($noresponse_mac) can't be contact. Alcasar disconnects the user ($noresponse_user)."
                                        /usr/sbin/chilli_query logout $noresponse_mac
                                        /usr/sbin/chilli_query dhcp-release $noresponse_mac  # release dhcp for mac_auth equipment 
                                fi
                        done
                        rm $tmp_file
                fi
# process each equipment known by chilli
                for system in `/usr/sbin/chilli_query list |grep -v "\.0\.0\.0"`
                do
                        active_ip=`echo $system |cut -d" " -f2`
                        active_session=`echo $system |cut -d" " -f5`
                        active_mac=`echo $system | cut -d" " -f1`
                        active_user=`echo $system |cut -d" " -f6`
# process only equipment with an authenticated user
                        if [[ $(expr $active_session) -eq 1 ]]
                        then
                                arp_reply=`/usr/sbin/arping -b -I$INTIF -s$PRIVATE_IP -c2 -w4 $active_ip|grep "Unicast reply"|wc -l`
# store @IP of quiet equipments
                                if [[ $(expr $arp_reply) -eq 0 ]]
                                        then
                                        PTN='^[[:xdigit:]][[:xdigit:]]-[[:xdigit:]][[:xdigit:]]-[[:xdigit:]][[:xdigit:]]-[[:xdigit:]][[:xdigit:]]-[[:xdigit:]][[:xdigit:]]-[[:xdigit:]][[:xdigit:]]$'
                                        if [[ $(expr $active_user : $PTN) -eq 0 ]] # don't process @mac auth equipments
                                        then
                                                echo "$active_ip $active_mac $active_user" >> $tmp_file
                                        fi
                                fi
# disconnect users whose equipement is usurped (@MAC)
                                if [[ $(expr $arp_reply) -gt 2 ]]
                                        then 
                                        echo "$(date "+[%x-%X] : ")alcasar-watchdog : $active_ip is usurped ($active_mac). Alcasar disconnect the user ($active_user)." >> /var/Save/security/watchdog.log
                                        logger "alcasar-watchdog : $active_ip is usurped ($active_mac). Alcasar disconnect the user ($active_user)."
                                        /usr/sbin/chilli_query logout $active_mac
                                        chmod 644 /var/Save/security/watchdog.log
                                fi
                        fi
                done
                ;;
esac    
IFS=$OLDIFS