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OpenVPN 3 Linux client
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Signed-off-by: David Sommerseth <davids@openvpn.net>
Latest commit 346098a Jun 3, 2019

README.md

OpenVPN 3 Linux client

This is the next generation OpenVPN client for Linux. This project is very different from the more classic OpenVPN 2.x versions. First, this is currently only a pure client-only implementation.

The biggest change from the classic OpenVPN 2.x generation is that it does not need to be started by a root or otherwise privileged account any more. By default, all users on the system will have access to start and manage their own VPN tunnels. It will also support configuring DNS out-of-the-box.

The same OpenVPN 3 Core library which is used in the OpenVPN Connect clients is also used in this OpenVPN 3 client. This implementation does not support all options OpenVPN 2.x does, but if you have a functional configuration with OpenVPN Connect (typically on Android or iOS devices) it will work with this client. In general OpenVPN 3 supports routed TUN configurations; TAP and bridged setups are unsupported and will not work.

On a more technical level, this client builds on D-Bus and does also ship with a Python 3 module which can also be used to implement your own OpenVPN client front-end. Any language which supports D-Bus bindings can also be used.

Pre-built binaries

See the instructions on https://community.openvpn.net/openvpn/wiki/OpenVPN3Linux how to install pre-built OpenVPN 3 Linux packages on Debian, Ubuntu, Fedora, Red Hat Enterprise Linux, CentOS and Scientific Linux.

Quick start: Using the openvpn2 front-end

The openvpn2 front-end is a command line interface which tries to be similar to the old and classic openvpn-2.x generation. It supports most of the options used by clients and will ignore unsupported options which does not impact the ability to get a connection running.

  • Starting a VPN session:

    $ openvpn2 --config my-vpn-config.conf
    

If the provided configuration contains the --daemon option, it will provide the session path related to this session and return to the command line again. From this point of, this session needs to be managed via the openvpn3 front-end.

For more information, see the openvpn2(1) and openvpn3-session-manage(1) man-pages.

Using the openvpn3 front-end

The openvpn3 program is the main and preferred command line user interface.

  • Starting a VPN session: Single-shot approach

    $ openvpn3 session-start --config my-vpn-config.conf
    

    This will import the configuration and start a new session directly

  • Starting a VPN session: Multi-step approach

    1. Import the configuration file:

      $ openvpn3 config-import --config my-vpn-config.conf
      

      This will return a configuration path. This path is a unique reference to this specific configuration profile.

    2. (Optional) Display all imported configuration profiles

      $ openvpn3 configs-list
      
    3. Start a new VPN session

      $ openvpn3 session-start --config my-vpn-config.conf
      

      or

      $ openvpn3 session-start --config-path /net/openvpn/v3/configuration/d45d4263x42b8x4669xa8b2x583bcac770b2
      
  • Listing established sessions

       $ openvpn3 sessions-list
    
  • Getting tunnel statistics For already running tunnels, it is possible to extract live statistics of each VPN session individually

    $ openvpn3 session-stats --config my-vpn-config.conf
    

    or

    $ openvpn3 session-stats --path /net/openvpn/v3/sessions/46fff369sd155s41e5sb97fsbb9d54738124
    
  • Managing VPN sessions For running VPN sessions, you manage them using the openvpn3 session-manage command, again by providing the session path. For example, to restart a connection:

    $ openvpn3 session-manage --config my-vpn-config.conf --restart
    

    or

    $ openvpn3 session-manage --path /net/openvpn/v3/sessions/46fff369sd155s41e5sb97fsbb9d54738124 --restart
    

    Other actions can be --pause, --resume, and --disconnect.

All the openvpn3 operations are also described via the --help option.

   $ openvpn3 --help
   $ openvpn3 session-start --help

For more information, see the openvpn3(1), openvpn3-session-start(1), openvpn3-session-manage(1) and openvpn3-config-import(1) man-pages.

Auto-loading/starting VPN tunnels

The openvpn3-autoload utility is used to pre-load configuration profiles and possibly also start tunnels. This requires a little bit of preparations. When starting it via systemctl start openvpn3-autoload it will look for configuration profiles found inside /etc/openvpn3/autoload which has a corresponding .autoload configuration present in addition. This tells both the Configuration Manager and Session Manager how to process the VPN configuration profile.

For more details, look at the openvpn3-autoload(8) man-page.

Introduction to the OpenVPN 3 Linux architecture

To interact with the various OpenVPN 3 services running in the background, three different utilities are provided.

  • openvpn2 (man page)

    This is an interface which tries to look and behave a bit more like the classic OpenVPN 2.x versions. It does only allow options which are supported by the OpenVPN 3 Core Library, plus there are a handful options which are ignored as it is possible to establish connections without those options active.

    When running openvpn2 with --daemon it will return a D-Bus path to the VPN session. This path can be used by the openvpn3 utility to further manage this session.

  • openvpn3 (man page)

    This is a brand new command line interface which does not look like OpenVPN 2.x at all. It can be used to start, stop, pause, resume tunnels and retrieve tunnel statistics. It can also be used as import, retrieve and manage configurations stored in the configuration manager, as well as handling access control lists for VPN configuration profiles and running VPN sessions.

  • openvpn3-admin (man page)

    This will mostly only work when run as root. This is used to adjust some settings or retrieve information from some of the backend services.

The OpenVPN 3 Linux project is built on D-Bus. This means it is possible to build your own tools instead of using these tools, all which is required is to access the various OpenVPN 3 D-Bus services. In reality all the front-ends mentioned are just specialized D-Bus clients for the OpenVPN 3 D-Bus services. This resolves the challenges with proper privilege separation between users and the various operations running a VPN tunnel requires.

As mentioned, there are various D-Bus services running behind the scenes. There are six services which is good to beware of. All of these services will normally start automatically. And when they are idle for a while with no data to maintain, they will shutdown automatically.

  • openvpn3-service-configmgr (man page | D-Bus documentation)

    This is the configuration manager. All configuration profiles will be uploaded and managed by this service before a tunnel is started. This service also ensures only users granted access to VPN various profiles has the proper access to them. By default this process is started as the openvpn user.

  • openvpn3-service-sessionmgr (man page | D-Bus documentation)

    This manages all VPN tunnels which are about to start or has started. It takes care of communicating with the VPN backend processes and ensures only users with the right access levels can manage the various tunnels. This service is started as the openvpn user.

  • openvpn3-service-backendstart (man page | D-Bus documentation)

    This is a helper service and is only used by the session manager. The only task this service has is to start a new VPN client backend processes (the VPN tunnel instances). By default this is also started as the openvpn user.

  • openvpn3-service-client (man page | D-Bus documentation)

    This is to be started by the openvpn3-service-backendstart only. One such process is started per VPN client. Once it has started, it registers itself with the session manager and the session manager provides it with the needed details so it can retrieve the proper configuration profile from the configuration manager. This service will depend on the openvpn3-service-netcfg to manage the tun interface and related configuration. This service is also running as the openvpn users by default.

  • openvpn3-service-netcfg (man page | D-Bus documentation)

    This provides a service similar to a VPN API on other platforms. It is responsible for creating, managing and destroying of TUN interfaces, configure them as well as handle the DNS configuration provided by the VPN server. This is the most privileged process which only have a few capabilities enabled (such as CAP_NET_ADMIN and possibly CAP_DAC_OVERRIDE or CAP_NET_RAW) by default. With these capabilities, the service can run as the openvpn user.

    Currently DNS configuration is done by manipulating /etc/resolv.conf directly, but can be extended to support better methods (systemd-resolved and NetworkManager are being investigated as potential solutions). When integrating with other services, the CAP_DAC_OVERRIDE privilege might not be needed. The CAP_NET_RAW capability is only needed when using --redirect-method bind-device.

  • openvpn3-service-logger (man page | D-Bus documentation)

    This service will listen for log events happening from all the various OpenVPN 3 D-Bus services. It supports writing these events to the console (stdout), files or redirect to syslog. This is also automatically started when needed, if it isn't already running.

More information can be found in the openvpn3-linux(7) man page and OpenVPN 3 D-Bus overview.

How to build openvpn3-linux locally

The following dependencies are needed:

  • A C++ compiler capable of at least -std=c++11. The ./configure script will try to detect if -std=c++14 is available and switch to that if possible, otherwise it will test for -std=c++11. If support for neither is found, it will fail.

  • mbed TLS 2.4 or newer (not needed if building with OpenSSL)

    https://tls.mbed.org/

  • OpenSSL 1.0.2 or newer (not needed if building with mbed TLS)

    https://www.openssl.org/

  • GLib2 2.50 or newer

    http://www.gtk.org This dependency is due to the GDBus library, which is the D-Bus implementation being used.

  • jsoncpp 0.10.5 or newer

    https://github.com/open-source-parsers/jsoncpp

  • libcap-ng 0.7.5 or newer

    http://people.redhat.com/sgrubb/libcap-ng

  • liblz4 1.7.3 or newer

    https://lz4.github.io/lz4

  • libuuid 2.23.2 or newer

    https://en.wikipedia.org/wiki/Util-linux

  • (optional) Python 3.4 or newer

    If Python 3.4 or newer is found, the openvpn2, openvpn3-autoload utilities and an openvpn3 Python module will be built and installed.

  • (optional) Python docutils

    http://docutils.sourceforge.net/ This is needed for the rst2man utility, used to generate the man pages.

  • (optional) selinux-policy-devel

    For Linux distributions running with SELinux in enforced mode (like Red Hat Enterprise Linux and Fedora), this is required.

In addition, this git repository will pull in two git submodules:

  • openvpn3

    https://github.com/OpenVPN/openvpn3 This is the OpenVPN 3 Core library. This is where the core VPN implementation is done.

  • ASIO

    https://github.com/chriskohlhoff/asio The OpenVPN 3 Core library depends on some bleeding edge features in ASIO, so we need to do a build against the ASIO git repository.

    This openvpn3-linux git repository will pull in the appropriate ASIO library as a git submodule.

First install the package dependencies needed to run the build.

Debian/Ubuntu:

  • Building with mbed TLS:

    # apt-get install libmbedtls-dev
    
  • Building with OpenSSL:

    For newer Debian and Ubuntu releases shipping with OpenSSL 1.1 or newer:

    # apt-get install libssl-dev libssl1.1
    

    For Ubuntu 16.04 LTS, which ships with OpenSSL 1.0:

    # apt-get install libssl-dev libssl1.0.0
    
  • Generic build requirements:

    # apt-get install build-essential git pkg-config autoconf autoconf-archive libglib2.0-dev libjsoncpp-dev uuid-dev liblz4-dev libcap-ng-dev
    

Fedora:

  • Building with mbed TLS:

    # dnf install mbedtls-devel
    
  • Building with OpenSSL:

    # dnf install openssl-devel
    
  • Generic build requirements:

    # dnf install gcc-c++ git autoconf autoconf-archive automake make pkgconfig glib2-devel jsoncpp-devel libuuid-devel libcap-ng-devel selinux-policy-devel lz4-devel zlib-devel libxml2 python3-dbus python3-pyOpenSSL
    

Red Hat Enterprise Linux / CentOS / Scientific Linux

First install the epel-release repository if that is not yet installed. Then you can run:

  • Building with mbed TLS:

    # yum install mbedtls-devel
    
  • Building with OpenSSL

    # yum install openssl-devel
    
  • Generic build requirements:

    # yum install gcc-c++ git autoconf autoconf-archive automake make pkgconfig glib2-devel jsoncpp-devel libuuid-devel lz4-devel libcap-ng-devel selinux-policy-devel lz4-devel zlib-devel libxml2 python36 python36-dbus python36-gobject python36-pyOpenSSL
    

Preparations building from git

  • Clone this git repository: git clone git://github.com/OpenVPN/openvpn3-linux
  • Enter the openvpn3-linux directory: cd openvpn3-linux
  • Run: ./bootstrap.sh

Completing these steps will provide you with a ./configure script.

Adding the openvpn user and group accounts

The default configuration for the services assumes a service account openvpn to be present. If it does not exist you should add one, e.g. by:

# groupadd -r openvpn
# useradd -r -s /sbin/nologin -g openvpn openvpn

Building OpenVPN 3 Linux client

If you already have a ./configure script or have retrieved an openvpn3-linux-*.tar.xz tarball generated by make dist, the following steps will build the client.

  • Run: ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
  • Run: make
  • Run: make install

By default, OpenVPN 3 Linux is built using the OpenSSL library. If you want to compile against mbed TLS, add the --with-crypto-library=mbedtls argument to ./configure.

You might need to also reload D-Bus configuration to make D-Bus aware of the newly installed service. On most system this happens automatically but occasionally a manual operation is needed:

# systemctl reload dbus

The --prefix can be changed, but beware that you will then need to add --datarootdir=/usr/share instead. This is related to the D-Bus auto-start feature. The needed D-Bus service profiles will otherwise be installed in a directory the D-Bus message service does not know of. The same is for the --sysconfdir path. It will install a needed OpenVPN 3 D-Bus policy into /etc/dbus-1/system.d/.

With everything built and installed, it should be possible to run both the openvpn2 and openvpn3 command line tools - even as an unprivileged user.

Auto-completion helper for bash/zsh

The openvpn3 front-end provides an interface for bash-completion to retrieve valid sub-commands, options and arguments - including valid D-Bus paths. To enable this feature, copy src/shell/bash-completion/openvpn3 to either /etc/bash_completion.d or /usr/share/bash-completion/completions (depending on the Linux distribution).

SELinux

The openvpn3-service-netcfg service depends on being able to pass a file descriptor to the tun device it has created on behalf of the openvpn3-service-client service (where each of these processes represents a single VPN session). This is done via D-Bus. But on systems with SELinux, the D-Bus daemon is not allowed to pass file descriptors related to /dev/net/tun.

The openvpn3-linux project ships an SELinux policy module, which will be installed in /etc/openvpn3/selinux if the ./configure script can locate the SELinux policy development files. On RHEL/Fedora the development files are located under /usr/share/selinux/devel and provided by the selinux-policy-devel package.

If the selinux-policy-devel package has been detected by ./configure, running make install will install the openvpn3.pp policy package, typically in /etc/openvpn3/selinux.

This policy package adds a SELinux boolean, dbus_access_tuntap_device, which grants processes, such as dbus-daemon running under the system_dbusd_t security context access to files labelled as tun_tap_device_t; which matches the label of /dev/net/tun.

To install and activate this SELinux security module, as root run:

     # semodule -i /etc/openvpn3/selinux/openvpn3.pp
     # semanage boolean --m --on dbus_access_tuntap_device

On Red Hat Enterprise Linux and Fedora, the openvpn3-service-netcfg will stop running and the OpenVPN 3 Linux client will be non-functional if this has not been done. The source code of the policy package can be found in src/selinux/openvpn3.te.

For users installing the pre-built RPM binaries, this is handled by the RPM scriptlet during package install.

Logging

Logging happens via openvpn3-service-logger. If not started manually, it will automatically be started by the backend processes needing it. The default configuration sends log data to syslog. This service can be started manually and must run as the openvpn user. If being started as root, it will automatically switch to the openvpn user. See openvpn3-service-logger --help for more details. Unless --syslog or --log-file is provided, it will log to the console (stdout).

This log service can also be managed (even though fairly few options to tweak) via openvpn3-admin log-service. The most important feature here is probably to modify the log level.

For more information about logging, see the openvpn3-service-logger(8), man page, D-Bus Logging and net.openvpn.v3.log D-Bus service documentation.

General debugging

Ensure you have done a build using --enable-debug-options when running ./configure. This ensures the most crucial debug options are available.

Most of the backend services (openvpn3-service-logger, openvpn3-service-configmgr, openvpn3-service-sessionmgr and openvpn3-service-backendstart) can be run in a console. All with the exception of openvpn3-service-netcfg should be started as the openvpn user. openvpn3-service-netcfg must be started as root but will as soon as possible drop its privileges to the openvpn user as well, after it has acquired the CAP_NET_ADMIN capability and possibly a few others. See their corresponding --help screen for details. Most of these programs can be forced to provide more log data by setting --log-level. And they can all provide logging to the console.

For more information about debugging, please see docs/debugging.md

D-Bus debugging

To debug what is happening, busctl, gdbus and dbus-send utilities are useful. The service destinations these tools need to move forward are:

  • net.openvpn.v3.configuration (Configuration manager)
  • net.openvpn.v3.sessions (Session manager)

Both of these services allows introspection.

There exists also a net.openvpn.v3.backends service, but that is restricted to be accessible only by the openvpn user - and even that users access is locked-down by default and introspection is not possible without modifying the D-Bus policy.

Looking at the D-Bus log messages can be also helpful, for example with:

$ journalctl --since today -u dbus

For more information about debugging, please see docs/debugging.md

Contribution

  • Code contributions Code contributions are most welcome. Please submit patches for review to the openvpn-devel@lists.sourceforge.net mailing list. All patches must carry a Signed-off-by line and must be reviewed publicly before acceptance. Pull requests are not acceptable unless it is for early reviews and patch discussions. Final patches MUST go to the mailing list.

  • Testing This code is quite new, but has been used a lot in various setups. Please reach out on FreeNode @ #openvpn for help and discussing issues you encounter, or subscribe to and ask on the openvpn-users@lists.sourceforge.net mailing list.

  • Packagers We are beginning to targeting packaging in Linux distributions. The Fedora Copr repository is one which is currently available. We are looking for people willing to package this in other Linux distributions as well.

DISCLAIMER

The OpenVPN 3 Linux project is BETA quality. It is fully functional and so far we have few reports about instabilities.

The OpenVPN 3 Core library this project builds on is used by the OpenVPN Connect and Private Tunnel clients in addition to the OpenVPN for Android client (need to explicitly enable the OpenVPN 3 backend), so the pure VPN tunnel implementation should be good to use.

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