Graphically isolating Guix containers with Xpra.

[Rutger Helling]

Hey Guix,

Here's a small tip for how you can create graphically isolated containers with Guix and Xpra.

First we create a Xpra server, with no clipboard access.
$ xpra start --clipboard=no :200

Next we switch to an empty tmp directory, and start a Guix container that has access to the X200 socket only.
$ cd tmp
$ guix environment -C --ad-hoc coreutils gedit --expose=/home/$USER/.Xauthority --expose=/tmp/.X11-unix/X200 -- env DISPLAY=:200 XAUTHORITY=/home/$USER/.Xauthority gedit

On a different terminal (or over SSH) you can now access the Xpra server.
$ xpra attach :200

Note that in order to be fully isolated the container should not be able to access even abstract sockets.
You can either run the container without the -N switch, or create a new network namespace with a veth or something like that.

With the following command you can check the sockets. No X11 sockets other than the Xpra one should be shown.
$ ss | grep X11

Once Wayland becomes widely used this will probably be redundant, since the isolation in Wayland is far better than X11. But this might still be useful.

[Ludovic Courtès]

Hello Rutger,

Post by Rutger Helling
Here's a small tip for how you can create graphically isolated containers with Guix and Xpra.
First we create a Xpra server, with no clipboard access.
$ xpra start --clipboard=no :200
Next we switch to an empty tmp directory, and start a Guix container that has access to the X200 socket only.
$ cd tmp
$ guix environment -C --ad-hoc coreutils gedit --expose=/home/$USER/.Xauthority --expose=/tmp/.X11-unix/X200 -- env DISPLAY=:200 XAUTHORITY=/home/$USER/.Xauthority gedit
On a different terminal (or over SSH) you can now access the Xpra server.
$ xpra attach :200

Nice trick!

Did you see the discussion at
<https://lists.gnu.org/archive/html/help-guix/2018-01/msg00056.html>?

This is something we could directly add to ‘guix run’ or similar.

Ludo’.

[Rutger Helling]

Hi Ludo,

I've tried 'guix run' for a little bit and I think it has a lot of
potential! One of the problems with guix environment containers is that
it can take quite a while to build. 'guix run' could solve that.

Adding Xpra to 'guix run' and/or 'guix environment' in some way could
definitely be handy for isolation purposes. For the most part it would
just consist of starting up a Xpra socket and exposing that to the
container, then maybe automatically attaching to it.

I've pushed a change to Xpra to start Xvfb with '-nolisten local'. This
disables abstract sockets for the Xorg server that gets started with
Xpra. As a result, using the commands below, you should be isolated even
on the same network namespace.

I can also write something for the Guix documentation, though i'm not
sure if that's considered out-of-scope.

On Fri, 16 Feb 2018 17:55:46 +0100

Post by Ludovic Courtès
Hello Rutger,

Post by Rutger Helling
Here's a small tip for how you can create graphically isolated
containers with Guix and Xpra.
First we create a Xpra server, with no clipboard access.
$ xpra start --clipboard=no :200
Next we switch to an empty tmp directory, and start a Guix
container that has access to the X200 socket only. $ cd tmp
$ guix environment -C --ad-hoc coreutils gedit
--expose=/home/$USER/.Xauthority --expose=/tmp/.X11-unix/X200 --
env DISPLAY=:200 XAUTHORITY=/home/$USER/.Xauthority gedit
On a different terminal (or over SSH) you can now access the Xpra
server. $ xpra attach :200

Nice trick!
Did you see the discussion at
<https://lists.gnu.org/archive/html/help-guix/2018-01/msg00056.html>?
This is something we could directly add to ‘guix run’ or similar.
Ludo’.