Flatpak on Debian

Posted on 06/06/2016 by Simon McVittie

Quite a lot has happened in xdg-app since last time I blogged about it. Most noticeably, it isn't called xdg-app any more, having been renamed to Flatpak. It is now available in Debian experimental under that name, and the xdg-app package that was briefly there has been removed. I'm currently in the process of updating Flatpak to the latest version 0.6.4.

The privileged part has also spun off into a separate project, Bubblewrap, which recently had its first release (0.1.0). This is intended as a common component with which unprivileged users can start a container in a way that won't let them escalate privileges, like a more flexible version of linux-user-chroot.

Bubblewrap has also been made available in Debian, maintained by Laszlo Boszormenyi (also maintainer of linux-user-chroot). Yesterday I sent a patch to update Laszlo's packaging for 0.1.0. I'm hoping to become a co-maintainer to upload that myself, since I suspect Flatpak and Bubblewrap might need to track each other quite closely. For the moment, Flatpak still uses its own internal copy of Bubblewrap, but I consider that to be a bug and I'd like to be able to fix it soon.

At some point I also want to experiment with using Bubblewrap to sandbox some of the game engines that are packaged in Debian: networked games are a large attack surface, and typically consist of the sort of speed-optimized C or C++ code that is an ideal home for security vulnerabilities. I've already made some progress on jailing game engines with AppArmor, but making sensitive files completely invisible to the game engine seems even better than preventing them from being opened.

Next weekend I'm going to be heading to Toronto for the GTK Hackfest, primarily to to talk to GNOME and Flatpak developers about their plans for sandboxing, portals and Flatpak. Hopefully we can make some good progress there: the more I know about the state of software security, the less happy I am with random applications all being equally privileged. Newer display technologies like Wayland and Mir represent an opportunity to plug one of the largest holes in typical application containerization, which is a major step in bringing sandboxes like Flatpak and Snap from proof-of-concept to a practical improvement in security.

Other next steps for Flatpak in Debian:

• To get into the next stable release (Debian 9), Flatpak needs to move from experimental into unstable and testing. I've taken the first step towards that by uploading libgsystem to unstable. Before Flatpak can follow, OSTree also needs to move.
• Now that it's in Debian, please report bugs in the usual Debian way or send patches to fix bugs: Flatpak, OSTree, libgsystem.
• In particular, there are some OSTree bugs tagged help. I'd appreciate contributions to the OSTree packaging from people who are interested in using it to deploy dpkg-based operating systems - I'm primarily looking at it from the Flatpak perspective, so the boot/OS side of it isn't so well tested. Red Hat have rpm-ostree, and I believe Endless do something analogous to build OS images with dpkg, but I haven't had a chance to look into that in detail yet.
• Co-maintainers for Flatpak, OSTree, libgsystem would also be very welcome.

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