openvpn-netns

Start OpenVPN connection inside Linux network namespace.

These scripts allow some programs to use the VPN connection while the rest of the system uses the normal network connection. For programs inside the namespace, the only network connection to the outside world is through the VPN tunnel. This prevents VPN leaks. Multiple VPN connections can be opened at the same time each in its separate namespace.

This is based on https://github.com/pekman/openvpn-netns and modified to work with systemd and Debian Jessie OpenVPN package, and to setup an exta bridged interface inside the VPN namespace (careful of leaks in that case!!!) if desired.

Installing

sudo ln -s "$PWD"/systemd/system/netns@.service /etc/systemd/system/netns@.service
sudo ln -s "$PWD"/systemd/system/netns-bridge@.service /etc/systemd/system/netns-bridge@.service
sudo ln -s "$PWD"/openvpn/netns /etc/openvpn/netns

Then see the example folder for using it, all of the subfolders and files are meant to be put under /etc.

Configuration

In Debian, an OpenVPN tunnel configured in the file /etc/openvpn/foovpn.conf is started using:

sudo systemctl start openvpn-client@foovpn.service

To setup such a tunnel inside its own namespace (named foovpn, based on the openvpn configuration filename):

1. Add the following into the drop-in configuration file /etc/systemd/system/openvpn-client@foovpn.service.d/netns.conf:

[Unit]
Requires=netns@foovpn.service
After=netns@foovpn.service

[Service]
CapabilityBoundingSet=CAP_SYS_ADMIN

2. Modify /etc/openvpn/foovpn.conf to add the following:

# ensure there is no up/down for the openvpn resolvconf script
script-security 2
route-noexec
ifconfig-noexec
up /etc/openvpn/netns
route-up /etc/openvpn/netns
down /etc/openvpn/netns

Normally, DNS settings received from OpenVPN server are used inside the namespace. To override them, create the file /etc/netns/foovpn/resolv.conf, which will be bind mounted into /etc/resolv.conf inside the namespace (see man ip-netns). If the file doesn't exist, it is automatically generated from DNS settings from the server when the connection is started and deleted when the connection is terminated.

Then to run a command inside the foovpn network namespace, use:

sudo ip netns exec foovpn /usr/bin/command...

To setup a systemd service (e.g., foo.service) to be run inside the foovpn network namespace:

1. Add the following into the drop-in configuration file /etc/systemd/system/foo.service.d/netns.conf:

[Unit]
Requires=netns@foovpn.service openvpn-client@foovpn.service
After=netns@foovpn.service openvpn-client@foovpn.service

2. Modify the foo.service file (put it in /etc/systemd/system if it is coming from a Debian package) to have the following:

[Service]
# Run as root, user/group is setup in the ExecStart
User=root
# this needs to be wrapped in netns exec and runuser to work
ExecStart=/bin/ip netns exec foovpn runuser -g group -u user -- /usr/bin/DAEMON --DAEMON-ARGUMENTS

To setup such a systemd service but with an extra interface bridged to one of the existing interface of the host system (useful if you need the service to listen to a local interface on top of using the openvpn network):

1. Modify the drop-in configuration file /etc/systemd/system/foo.service.d/netns.conf to be as following instead:

[Unit]
Requires=netns@foovpn.service netns-bridge@foovpn.service openvpn-client@foovpn.service
After=netns@foovpn.service netns-bridge@foovpn.service openvpn-client@foovpn.service

2. Add a configuration file /etc/netns/foovpn/bridge.env containing the following:

INTERFACE=eth0
ADDRESS=192.168.0.50/24

It will setup an interface named mv.eth0 (mv is for macvlan) inside the namespace with the address 192.168.0.50/24. Note that it would make most sense to use an address available in the same network as the original eth0 interface. Then eth0 will be able to connect to 192.168.0.50 as well as any machine on the network of eth0.