121 lines
5.0 KiB
Markdown
121 lines
5.0 KiB
Markdown
# OpenVPN for Docker
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OpenVPN server in a Docker container complete with an EasyRSA PKI CA.
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## Quick Start
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* Create the `$OVPN_DATA` volume container, i.e. `OVPN_DATA="ovpn-data"`
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docker run --name $OVPN_DATA -v /etc/openvpn busybox
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* Initalize the `$OVPN_DATA` container that will hold the configuration files and certificates
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docker run --volumes-from $OVPN_DATA --rm kylemanna/openvpn ovpn_genconfig -u udp://VPN.SERVERNAME.COM:1194
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docker run --volumes-from $OVPN_DATA --rm -it kylemanna/openvpn ovpn_initpki
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* Start OpenVPN server process
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docker run --volumes-from $OVPN_DATA -d -p 1194:1194/udp --privileged kylemanna/openvpn
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* Generate a client certificate without a passphrase
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docker run --volumes-from $OVPN_DATA --rm -it kylemanna/openvpn easyrsa build-client-full CLIENTNAME nopass
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* Retrieve the client configuration with embedded certificates
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docker run --volumes-from $OVPN_DATA --rm kylemanna/openvpn ovpn_getclient CLIENTNAME > CLIENTNAME.ovpn
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## How Does It Work?
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Initialize the volume container using the `kylemanna/openvpn` image with the
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included scripts to automatically generate:
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- Diffie-Hellman parameters
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- a private key
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- a self-certificate matching the private key for the OpenVPN server
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- an EasyRSA CA key and certificate
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- a TLS auth key from HMAC security
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The OpenVPN server is started with the default run cmd of `ovpn_run`
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The configuration is located in `/etc/openvpn`, and the Dockerfile
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declares that directory as a volume. It means that you can start another
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container with the `--volumes-from` flag, and access the configuration.
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The volume also holds the PKI keys and certs so that it could be backed up.
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To generate a client certificate, `kylemanna/openvpn` uses EasyRSA via the
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`easyrsa` command in the container's path. The `EASYRSA_*` environmental
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variables place the PKI CA under `/etc/opevpn/pki`.
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Conveniently, `kylemanna/openvpn` comes with a script called `ovpn_getclient`,
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which dumps an inline OpenVPN client configuration file. This single file can
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then be given to a client for access to the VPN.
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## OpenVPN Details
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We use `tun` mode, because it works on the widest range of devices.
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`tap` mode, for instance, does not work on Android, except if the device
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is rooted.
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The topology used is `net30`, because it works on the widest range of OS.
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`p2p`, for instance, does not work on Windows.
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The UDP server uses`192.168.255.0/24` for dynamic clients by default.
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The client profile specifies `redirect-gateway def1`, meaning that after
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establishing the VPN connection, all traffic will go through the VPN.
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This might cause problems if you use local DNS recursors which are not
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directly reachable, since you will try to reach them through the VPN
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and they might not answer to you. If that happens, use public DNS
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resolvers like those of Google (8.8.4.4 and 8.8.8.8) or OpenDNS
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(208.67.222.222 and 208.67.220.220).
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## Security Discussion
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The Docker container runs its own EasyRSA PKI Certificate Authority. This was
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chosen as a good way to compromise on security and convenience. The container
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runs under the assumption that the OpenVPN container is running on a secure
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host, that is to say that an adversary does not have access to the PKI files
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under `/etc/openvpn/pki`. This is a fairly reasonable compromise because if an
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adversary had access to these files, the adversary could manipulate the
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function of the OpenVPN server itself (sniff packets, create a new PKI CA, MITM
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packets, etc).
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* The certificate authority key is kept in the container by default for
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simplicity. It's highly recommended to secure the CA key with some
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passphrase to protect against a filesystem compromise. A more secure system
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would put the EasyRSA PKI CA on an offline system (can use the same Docker
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image to accomplish this).
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* It would be impossible for an adversary to sign bad or forged certificates
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without first cracking the key's passphase should the adversary have root
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access to the filesystem.
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* The EasyRSA `build-client-full` command will generate and leave keys on the
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server, again possible to compromise and steal the keys. The keys generated
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need to signed by the CA which the user hopefully configured with a passphrase
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as described above.
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* Assuming the rest of the Docker container's filesystem is secure, TLS + PKI
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security should prevent any malicious host from using the VPN.
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## Differences from jpetazzo/dockvpn
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* No longer uses serveconfig to distribute the configuration via https
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* Proper PKI support integrated into image
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* OpenVPN config files, PKI keys and certs are stored on a storage
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volume for re-use across containers
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* Only offer UDP support for now, I don't have a good use case for TCP
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* Addition of tls-auth for HMAC security
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## Tested On
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* Docker hosts:
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* server a Digitial Ocean Droplet with 512 MB RAM running Ubuntu 14.04
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* Clients
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* Android App OpenVPN Connect 1.1.14 (built 56)
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* OpenVPN core 3.0 android armv7a thumb2 32-bit
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* OS X Mavericks with Tunnelblick 3.4beta26 (build 3828) using openvpn-2.3.4
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* ArchLinux OpenVPN pkg 2.3.4-1
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