A qube with itself as GUI qube and no keyboard layout crashes qubesd

[DemiMarie]

Qubes OS version

R4.1

Are you using any testing repositories? If so, please list them AND where they are enabled (i.e., dom0, template, or standalone).

Testing enabled at least in dom0

Are you providing feedback about a specific package or packages in testing? (If so, please list the package(s) here and provide feedback in updates-status, linking to this issue.)

Affected component(s) or functionality

qubesd

Brief summary

If I set a qube’s GUI qube to be the qube itself, and do not set a keyboard layout, the keyboard_layout getter recurses forever, causing a stack overflow.

How Reproducible

100%

To Reproduce

Steps to reproduce the behavior:

1. Set a qube as its own GUI qube
2. Unset that qube’s keyboard_layout property
3. Try to start the qube

Expected behavior

A reasonable error message.

Actual behavior

Stack overflow in qubesd

Screenshots

Additional context

The network code already detects and prevents netvm cycles. The same should probably be done for guivm.

Solutions you've tried

Avoid creating the above nonsensical configuration.

Relevant documentation you've consulted

None

Related, non-duplicate issues

None that I am aware of.