What were you trying to do that didn't work?

Customer is setting up a kiosk using gnome-kiosk with polyinstantiation enabled, and gnome-kiosk fails to start with:

Failed to start X Wayland: Directory "/tmp/.X11-unix" is not writable

What is the impact of this issue to you?

That's a critical error so mutter dumps a core file and the session exits before it even started.

Please provide the package NVR for which the bug is seen:

mutter-40.9-24.el9

But also reproducible in F42 with mutter-48.2-1.fc42 so this issue is still present upstream presumably

How reproducible is this bug?:

Always

Steps to reproduce

1. Install gnome-kiosk and gnome-kiosk-search-appliance
2. sudo useradd -Z user_u kioskuser
3. sudo passwd kioskuser
4. Add following content in /etc/security/namespace.conf
   /tmp tmpfs tmpfs ~kioskuser
   /var/tmp tmpfs tmpfs ~kioskuser
   $HOME tmpfs tmpfs ~kioskuser
5. Enable SELinux polyinstantiation
   setsebool -P polyinstantiation_enabled on
6. Try to login in gnome-kiosk search appliance with the user kioskuser

Expected results

The GNOME Kiosk search appliance session start.

Actual results

The session does not start, back to the GDM login screen.