this post was submitted on 13 Jan 2024
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Wayland running GUI program as another user (lemmy.world)
submitted 10 months ago* (last edited 6 months ago) by shadowintheday2@lemmy.world to c/linux@lemmy.ml
4 comments fedilink hide all child comments
 

I use https://github.com/slingamn/namespaced-openvpn to have a isolated namespace and VPN connection

On X, these two steps would allow me to run a GUI program in the protected namespace. So I could have .e.g an IDE configuration for my main user/personal projects, and another entirely different instance of the same IDE for work because they use different users

sudo xhost '+si:localuser:user'
sudo ip netns exec protected sudo -u user -i

On Wayland, although the protected shell is created fine, GUI programs don't start. E.g fgor Dolphin

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
Failed to create wl_display (No such file or directory)

I've tried to preserve the env without success:


sudo -E ip netns exec protected sudo -u user -i

It seems that I access to the wayland socket is a must for this to work

This discussion has a nuke option - giving 777 access to the dir where the wayland socket is, and another less permissive approach adding the users to a group and giving access to a new location where the wayland socket is created

https://stackoverflow.com/questions/41736528/linux-wayland-display-multiple-user

Is this second approach secure? If not, which other steps could I take to achieve what I did in X?

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[–] vole@lemmy.world 7 points 10 months ago* (last edited 10 months ago) (1 children)

I got interested, so I spent some time looking into what's going on here. I'm not intimately familiar with X11 or Wayland, but I figured out some stuff.

Why sudo ip netns exec protected sudo -u user -i doesn't work for X11 apps

Short answer: file permissions and abstract unix sockets (which I didn't know were a thing before now).

File permissions: when I start an X11 login session, the DISPLAY is :0 and /tmp/.X11-unix/ has only 1 file X0. This file has 777 access. When I start my wayland session with Xwayland, the DISPLAY is :1 and /tmp/.X11-unix/ has 2 files X0 (777) and X1 (755). I can't figure out how to connect to display :0, so I guess I'm stuck with :1. When you change to a different (non-root) user, the user no longer has access to /tmp/.X11-unix/X1.

Abstract unix sockets: When I start my wayland/xwayland session, it creates abstract unix sockets with ids @/tmp/.X11-unix/X0 and @/tmp/.X11-unix/X1. See ss -lnp | grep Xwayland. The network namespace also sandboxes these abstract unix sockets. Compare socat ABSTRACT-CONNECT:/tmp/.X11-unix/X1 STDIN and sudo ip netns exec private socat ABSTRACT-CONNECT:/tmp/.X11-unix/X1 STDIN.

When you do sudo ip netns exec protected su - user, you loose access to both the filesystem unix socket /tmp/.X11-unix/X1 and the abstract unix socket @/tmp/.X11-unix/X1. You need access to one or the other for X11 applications to work.

I tried using socat to forward X1 such that it works in the network namespace... and it kinda works. sudo ip netns exec protected socat ABSTRACT-LISTEN:/tmp/.X11-unix/X1,fork UNIX-CONNECT:/tmp/.X11-unix/X1. It appears having ABSTRACT-LISTEN before UNIX-CONNECT is important, I guess it would be worth it to properly learn socat. With this sudo ip netns exec protected su - testuser -c 'env DISPLAY=:1 xmessage hi' works, but sudo ip netns exec protected su - testuser -c 'env DISPLAY=:1 QT_QPA_PLATFORM=xcb kcalc' does not work. 😞

Changing the file permissions on /tmp/.X11-unix/X1 to give the user access seems to work better.

Wayland waypipe

Waypipe works as advertised. But it's still a little bit tricky because you need to have two separate processes for the waypipe client and server, wait for the waypipe socket to be created, adjust file permissions for the waypipe socket file, and set (and probably mkdir) XDG_RUNTIME_DIR.

waypipe -s /tmp/mywaypipe client &
sleep 0.1
chgrp shared-display /tmp/mywaypipe
chmod g+w /tmp/mywaypipe
sudo ip netns exec protected su - testuser -c 'mkdir -p -m 0700 /tmp/runtime-testuser && env XDG_RUNTIME_DIR=/tmp/runtime-testuser waypipe -s /tmp/mywaypipe server -- env QT_QPA_PLATFORM=wayland kcalc'
kill -SIGINT %1

Combined

into this script https://github.com/vole-dev/grabbag/blob/main/run-netns-user-wayland.bash

[–] shadowintheday2@lemmy.world 2 points 10 months ago

Sir, you're awesome! Thank you a lot for taking your time and explaining what you have found I will try these steps when I have some free time to tinker, and the info and script you have provided has cleared a lot of questions that I had