VPN killswitch

killswitch.txt

cat /etc/udev/rules.d/81-vpn-firewall.rules
KERNEL=="tun0", ACTION=="add", RUN+="/usr/bin/forward.sh add"
KERNEL=="tun0", ACTION=="remove", RUN+="/usr/bin/forward.sh remove"

cat /usr/bin/forward.sh
#!/bin/bash
#
# forward.sh
# VER 0.1
#
# Reloads the ferm firewall ruleset and is invoked by
# the udev via /etc/udev/rules.d/81-vpn-firewall.rules.
#
#

LOGGER=/usr/bin/logger
LOGGER_TAG=$0

UDEV_ACTION=$1

MSG_FW_RULE_ADD="Enabling forwarding"
MSG_FW_RULE_REMOVE="Disabling forwarding"
MSG_UDEV_ACTION_UNKNOWN="dafuq"

case "$UDEV_ACTION" in
    add)
        $LOGGER -t $LOGGER_TAG $MSG_FW_RULE_ADD
        $FERM $FERM_CONF
        sysctl net.ipv4.ip_forward=1
        ;;
    remove)
        $LOGGER -t $LOGGER_TAG $MSG_FW_RULE_REMOVE
        sysctl net.ipv4.ip_forward=0
        $FERM $FERM_CONF
        ;;
    *)
        $LOGGER -t $LOGGER_TAG $MSG_UDEV_ACTION_UNKNOWN
        exit 1
esac