Shellbox

Shellbox is a library for command execution, and also a server and client for remote command execution. It was primarily implemented to sandbox lilypond (used by the Score extension) and provide a way for MediaWiki to utilize external binaries without needing to run them in the same container. It was designed and approved via RFC: PHP microservice for containerized shell execution. Shellbox is usable starting with MediaWiki 1.36.

Information about using Shellbox in MediaWiki is available at Manual:BoxedCommand.

Server setup
It is recommended that you set up Shellbox to run as an unprivileged user inside an isolated container with no external network access. Wikimedia uses Kubernetes for this purpose and has a Helm chart that may be reusable.

The following packages should be installed inside the container: Apache2 (httpd), PHP-FPM, and whatever commands you need to shell out to (e.g. lilypond, imagemagick, etc.).

In the following examples we use shellbox.internal as the container hostname.

Get the Shellbox source and its dependencies:

Create an unprivileged user for Shellbox: useradd -r shellbox Create a temporary directory: install -o shellbox -g shellbox -d /var/tmp/shellbox Create the Shellbox configuration file :

Generate a secret key: php -r 'print bin2hex(fread(fopen("/dev/urandom","r"),16))."\n";' Create the Apache configuration

Protect the secret key against unprivileged reads: chown root:root /etc/apache2/sites-available/shellbox.internal.conf chmod 600 /etc/apache2/sites-available/shellbox.internal.conf Create the PHP-FPM pool configuration: [shellbox] user = shellbox group = shellbox listen = /run/php/shellbox.sock listen.owner = www-data listen.group = www-data pm = static pm.max_children = 1 When configured in this way, Shellbox does not have permission to connect to the PHP-FPM socket.

Pre-built containers
Wikimedia has pre-built containers that contain Shellbox, it's dependencies, and PHP-FPM: https://docker-registry.wikimedia.org/wikimedia/mediawiki-libs-shellbox/tags/

These images currently have no stability guarantee/versioning (help wanted on figuring this out).

Routes
Shellbox exposes a  route for manual and automated health checks. It also has a PHP-RPC interface for executing sandboxed PHP code.