#!/bin/sh

# A post-up/down hook to automatically create/delete a virtual subnet
# for IPSec (inet4 only).
# Copyright © 2016 Guilhem Moulin <guilhem@fripost.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

set -ue
PATH=/usr/sbin:/usr/bin:/sbin:/bin

# Ignore the loopback interface and non inet4 families.
[ "$IFACE" != lo -a "$ADDRFAM" = inet ] || exit 0

# Only the device with the default, globally-scoped route, is of
# interest here.
ip="$( ip -4 -o route show to default scope global \
     | sed -nr '/^default via (\S+) dev (\S+).*/ {s//\2 \1/p;q}' )"
[ "${ip% *}" = "$IFACE" ] || exit 0
ip="${ip##* }"

vip="{{ ipsec[inventory_hostname_short] }}"
vsubnet="{{ ipsec_subnet }}"

case "$MODE" in
    start) ip address add "$vip/32" dev "$IFACE" scope global || true
           # Nullroute the subnet used for IPSec to avoid data leaks
           # in the absence of xfrm lookup (i.e., when there is no
           # matching IPSec Security Association).
           ip route replace prohibit "$vsubnet" proto static || true
           ip route replace table 220 to "$vsubnet" via "$ip" dev "$IFACE" proto static src "$vip" || true
    ;;
    stop)  ip route del table 220 to "$vsubnet" via "$ip" dev "$IFACE" proto static src "$vip" || true
           ip route del prohibit "$vsubnet" proto static || true
           ip address del "$vip/32" dev "$IFACE" scope global || true
esac