malcontent

malcontent implements support for restricting the type of content accessible to non-administrator accounts on a Linux system. Typically, when this is used, a non-administrator account will be for a child using the system; and the administrator accounts will be for the parents; and the content being filtered will be apps which are not suitable for the child to use, due to (for example) being too violent.

It provides an accounts-service vendor extension for storing an app filter to restrict the child’s access to certain applications; a simple library for accessing and applying the app filter; and a UI program (malcontent-control) for viewing and changing the parental controls settings on users.

The parental controls policy is stored in /var/lib/AccountsService/users/${user}, which is a key file readable and writable only by the accounts-service daemon. Access to the data is mediated through accounts-service’s D-Bus interface, which libmalcontent is a client library for.

All the library APIs are currently unstable and are likely to change wildly.

Two kinds of policy are currently supported:

• A filter specifying whether installed applications are allowed to be run; this is typically set up to restrict access to a limited set of already-installed applications — but it can be set up to only allow access to a fixed list of applications and deny access to all others. Applications which are not currently installed are not subject to this filter.
• A set of mappings from OARS categories to the maximum ratings for those categories which are permissible for a user to install apps with. For example, a mapping of violence-realistic=mild would prevent any applications containing more than ‘mild’ violence from being installed. Applications which are already installed are not subject to this filter.

Additional policies may be added in future, such as filtering by content type or limiting the amount of time a user is allowed to use the system for.

Any application or service which provides the user with access to content which should be parentally filtered is responsible for querying the user’s parental controls filter and refusing to provide the content if not permitted by the filter. This could mean refusing to launch a flatpak app, hiding a search result in gnome-shell, or hiding an app in gnome-software because of its high OARS rating.

A sufficiently technically advanced user may always work around these parental controls. malcontent is not a mandatory access control (MAC) system like AppArmor or SELinux. However, its correct use by applications should provide enough of an obstacle to prevent users easily or accidentally having access to content which they shouldn’t.

Example usage

malcontent ships a malcontent-client application which can be used to get and set parental controls policies for users.

$ # This sets the parental controls policy for user ‘philip’ to allow no \\
    installation of apps with anything more than ‘none’ for realistic violence, \\
    and to blocklist running the org.freedesktop.Bustle flatpak:
$ malcontent-client set philip \\
    violence-realistic=none \\
    app/org.freedesktop.Bustle/x86_64/stable
App filter for user 1000 set

With that policy in place, other applications which are aware of malcontent will apply the policy:

$ flatpak run org.freedesktop.Bustle
error: Running app/org.freedesktop.Bustle/x86_64/stable is not allowed by the policy set by your administrator

Development

When developing malcontent, you should be able to run an uninstalled version of malcontent-client or malcontent-control, as long as the polkit files from accounts-service/ and malcontent-control/org.freedesktop.MalcontentControl.policy.in have been installed system-wide (typically under /usr/share/polkit-1) where your system copy of polkitd can find them.

Dependencies

• accounts-service
• appstream-glib
• dbus-daemon
• flatpak
• gio-2.0 ≥ 2.60
• gio-unix-2.0 ≥ 2.60
• glib-2.0 ≥ 2.60
• gobject-2.0 ≥ 2.60
• gtk+-3.0
• polkit-gobject-1

Licensing

All code in the libraries in this project is licensed under LGPL-2.1+. Code in the malcontent-control application is licensed under GPL-2.0+. See COPYING and the copyright headers in individual files for more details.

Bugs

Bug reports and patches should be filed in GitLab.