vpnshift

#!/bin/bash
#
# Copyright (c) 2016, crasm <crasm@vczf.io>
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


usage="usage: vpnshift -c <config> [<command> [<arg>...]]
optional:
	-u <user>      Execute <command> as <user>
	-d             Toggle namespace debug shell

if not otherwise specified:
	- The command defaults to the user's shell (${SHELL}).
	- The user must be inferred from sudo.
"

quick_die() {
	format="$1"; shift
	>&2 printf "${format}\n" "$@"
	exit 1
}

die() {
	format="$1"; shift
	>&2 printf "${format}\n" "$@"
	clean_exit 1
}

hush() {
	eval "$@" > /dev/null 2> /dev/null
}

must() {
	eval "$@" || die "failed: %s" "$*"
}

is_running() {
	local pid="$1"
	hush kill -s 0 "${pid}"
}

sig_kill() {
	local pid="$1"
	hush kill -s KILL "${pid}"
}

sig_term() {
	local pid="$1"
	hush kill -s TERM "${pid}"
}

clean_exit() {
	local exit_code="$1"

	if is_running "${openvpn_pid}"; then
		# Kill openvpn.
		sig_term "${openvpn_pid}"
		>&2 printf "stopping openvpn (pid = %d)." "${openvpn_pid}"
		for i in {1..100}; do
			if is_running "${openvpn_pid}"; then
				sleep 0.1
				printf "."
			else
				break
			fi
		done
		printf "\n"

		if is_running "${openvpn_pid}"; then
			>&2 echo "forced to kill openvpn"
			sig_kill "${openvpn_pid}"
		fi
	else
		>&2 echo "openvpn exited"
	fi

	# don't start cleaning up until openvpn is gone
	hush ip netns delete "${namespace}"
	hush rm --recursive --force "${namespace_dir}"
	hush sysctl --quiet net.ipv4.ip_forward="${forward}"
	if hush ps -C 'firewalld'; then
		echo "[firewalld] clearing firewalld state"
		hush systemctl restart firewalld
	else
		echo "${rules}" | hush iptables-restore
	fi

	# Sometimes there's a lag for the veths to be deleted by linux, so we
	# delete it manually.
	hush ip link delete "${veth_default}"
	hush ip link delete "${veth_vpn}"

	exit "${exit_code}"
}

nsdo() {
	ip netns exec "${namespace}" "$@"
}

_debug=0

main() {
	local config=
	local user="${SUDO_USER}"
	while getopts "hdc:u:" opt; do
		case "${opt}" in
			h) quick_die "${usage}" ;;
			d) _debug=1 ;;
			c) config="$(realpath "${OPTARG}")" ;;
			u) user="${OPTARG}" ;;
			*) quick_die "unknown option: %s" "${opt}" ;;
		esac
	done
	shift $(( OPTIND - 1 ))

	if [[ -z "${config}" ]]; then
		quick_die "openvpn config is required"
	fi

	if [[ -z "${user}" ]]; then
		quick_die "user must be provided explicitly via '-u' or implicitly via SUDO_USER"
	fi

	local cmd="$1"; shift

	if [[ -z "${cmd}" ]]; then
		cmd="${SHELL}"
	fi

	must ip netns add vpnshift
	must mkdir --parents "${namespace_dir}"

	# Set up loopback interface

	must nsdo ip address add '127.0.0.1/8' dev lo
	must nsdo ip address add '::1/128' dev lo
	must nsdo ip link set lo up

	# Set up veth tunnel

	must ip link add "${veth_vpn}" type veth peer name "${veth_default}"
	must ip link set "${veth_vpn}" netns "${namespace}"

	must ip link set "${veth_default}" up
	must nsdo ip link set "${veth_vpn}" up

	must ip address add "10.10.10.10/31" dev "${veth_default}"
	must nsdo ip \
		address add "10.10.10.11/31" dev "${veth_vpn}"

	must nsdo ip \
		route add default via "10.10.10.10" dev "${veth_vpn}"

	# Set up NAT and IP forwarding
	must sysctl --quiet net.ipv4.ip_forward=1

	# check if we need to enable masquerading via firewalld for veth_default
	if hush ps -C 'firewalld'; then
		echo "[firewalld] enabling firewalld based masquerading for ${veth_default}"

		if [[ $(firewall-cmd --get-zones | grep "${namespace}") != *"${namespace}"* ]]
		then
			echo "[firewalld] creating permanent new zone ${namespace} with target default"
			must firewall-cmd -q --permanent --new-zone="${namespace}"
			must firewall-cmd -q --permanent --zone="${namespace}" --set-target="default"
			must firewall-cmd -q --reload
		fi

		# add interface to our zone
		echo "[firewalld] adding ${veth_default} and ${veth_vpn} to zone ${namespace}"
		must firewall-cmd -q --zone="${namespace}" --change-interface="${veth_default}"

		# apply our source range to our zone
		echo "[firewalld] adding 10.10.10.10/31 as source for ${namespace}"
		must firewall-cmd -q --zone="${namespace}" --add-source=10.10.10.10/31

		# enable masquerading from our new source range on the default zone
		default_zone=$(firewall-cmd --get-default-zone)
		echo "[firewalld] enabling masquerading on default zone: ${default_zone}"
		must firewall-cmd -q --zone="${default_zone}" --add-masquerade
		must firewall-cmd -q --zone="${default_zone}"  --add-rich-rule=\'rule family="ipv4" source address="10.10.10.10/31" masquerade\'

		# optionally allow ports, services, etc. on our zone

		# enabling desired ports
		#echo "enabling all port traffic on zone ${namespace}"
		#must firewall-cmd -q --zone="${namespace}" --add-port=1025-65535/udp
		#must firewall-cmd -q --zone="${namespace}" --add-port=1025-65535/tcp

		# enable services
		#echo "enabling dns on zone ${namespace}"
		#must firewall-cmd -q --zone="${namespace}" --add-service=dns

	else
		must iptables --table "nat" --append "POSTROUTING" --jump "MASQUERADE" --source "10.10.10.10/31"
	fi

	# Set up DNS inside the new namespace
	printf > "${namespace_dir}/resolv.conf" \
		"nameserver %s\nnameserver %s\n" \
		"108.62.19.131" \
		"104.238.194.235"

	# drop in a shell to debug namespace connectivity ... the exit trap will catch exit from this and clean up
	if [[ "$_debug" == 1 ]]; then
		nsdo "${SHELL}"
	fi

	# Launch openvpn
	local tun="tunvpn"
	nsdo openvpn \
		--cd "$(dirname "${config}")" \
		--config "${config}" \
		--dev "${tun}" \
		--errors-to-stderr &

	openvpn_pid=$(ps --ppid "$!" \
		--format "pid" \
		--no-headers
	)

	>&2 printf "waiting for openvpn (pid = %d)\n" "${openvpn_pid}"

	while ! hush nsdo ip link show "${tun}"; do
		if ! is_running "${openvpn_pid}"; then
			clean_exit 1
		fi
		sleep 0.2
	done

	# Removing the default route protects from exposure if openvpn exits
	# prematurely.
	must nsdo ip \
		route delete default via "10.10.10.10" dev "${veth_vpn}"

	nsdo sudo -u "${user}" "${cmd}" "$@"
}

if [[ $# == 0 ]]; then
	quick_die "${usage}"
elif [[ "$(id -u)" != 0 ]]; then
	sudo "$0" "$@"
	exit "$?"
fi

# Stuff needed by clean_exit() to restore previous state.
namespace="vpnshift"
namespace_dir="/etc/netns/${namespace}"
forward="$(sysctl --values "net.ipv4.ip_forward")"
rules="$(iptables-save -t nat)"
veth_default="veth_default"
veth_vpn="veth_vpn"

openvpn_pid= # This is set later.

# Enable cleanup routine.
trap 'clean_exit 1' INT TERM
trap 'clean_exit $?' EXIT

main "$@"