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Suppose the user's "real" X11 display on the host is Xorg or Xwayland listening on :42, but they also have an Xvfb server listening on :99. If we change the X11 display number to the arbitrary value :99, and the Flatpak sandbox shares its network namespace with the host, then clients inside the Flatpak sandbox will prefer to connect to the abstract socket @/tmp/.X11-unix/X99 (which is Xvfb), rather than the filesystem-backed socket /tmp/.X11-unix/X99 in the sandbox (which is really /tmp/.X11-unix/X42 on the host, i.e. Xorg or Xwayland). If they're relying on Xauthority (MIT-MAGIC-COOKIE-1) for access control (as many display managers do), then this will fail, because we gave the sandboxed app access to the cookies for Xorg/Xwayland (rewriting their display number from 42 to 99 as we did so), but Xvfb does not accept those cookies. If we're relying on `xhost +"si:localuser:$(id -nu)"` for access control (as gdm does), then the Flatpak app will successfully (!) connect to whatever is on :99, for example Xvfb or Xephyr, which is rarely what anyone wants either. Resolves: https://github.com/flatpak/flatpak/issues/3357 Signed-off-by: Simon McVittie <smcv@collabora.com>
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux.
See https://flatpak.org/ for more information.
Community discussion happens in #flatpak:matrix.org, on the mailing list, and on the Flathub Discourse.
Read documentation for Flatpak here.
Contributing
Flatpak welcomes contributions from anyone! Here are some ways you can help:
- Fix one of the issues and submit a PR
- Update flatpak's translations and submit a PR
- Improve flatpak's documentation, hosted at http://docs.flatpak.org and developed over in flatpak-docs
- Find a bug and submit a detailed report including your OS, flatpak version, and the steps to reproduce
- Add your favorite application to Flathub by writing a flatpak-builder manifest and submitting it
- Improve the Flatpak support in your favorite Linux distribution
Hacking
See CONTRIBUTING.md
Related Projects
Here are some notable projects in the Flatpak ecosystem:
- Flatseal: An app for managing permissions of Flatpak apps without using the CLI
- Flat-manager: A tool for managing Flatpak repositories