Override-redirect windows that are strictly contained in their parents should have no border

[arkenoi]

Qubes OS version

4.0

Affected component(s) or functionality

GUI lxde window decorations

Brief summary

Due to "hardwired" window decorations (which you may see as a security feature) MS Office windows get mis-rendered

How Reproducible

Always

To Reproduce

Steps to reproduce the behavior:

1. Make a Windows wm with MS Office and RDP enabled
2. Enable incoming connections to Windows WM from one Linux WM in sys-firewall
3. run a single MS Word app (outside of the windows desktop) via freerdp from a Linux wm

Expected behavior

Normal window frame around the whole window

Actual behavior

A lot of weird, thin, misplaced window frames around random GUI elements.

Screenshots

Additional context

I initially reported this as freerdp bug, but apparently, it is a Qubes issue

Solutions you've tried

/gdi:sw
+aero
-decorations
turning ms office hardware graphics acceleration off

possibly related:

#6199

[DemiMarie]

It’s hard to tell from the screenshot, but it looks like these decorations are from the GUI daemon. In that case, this is working as intended, as the borders are used to indicate trust.

That said, the user experience is poor. Wayland might fix this, as I am not sure if Wayland clients abuse windows the way X Window System clients do.

[marmarek]

I've seen similar things when running MS Office (but not any other windows application) through wine, so it's rather specific to MS Office not just FreeRDP. I guess it tries to draw some fancy shadows that technically are implemented as separate windows and thus gets forced colorful borders.

[marmarek]

Maybe we can add some heuristic on gui-agent side to ignore those specific "windows"?

[arkenoi]

Apparently they are from GUI daemon indeed (the effect is similar in any case: wine, freerdp or seamless mode). But it does not explain why it leaves artifacts on all virtual desktops. It would be great to have some workaround for this bug.

[marmarek]

But it does not explain why it leaves artifacts on all virtual desktops.

It kind of does. This uses override-redirect window type that is not controlled by window manager, and so is not affected by the workspace switch. This is yet another case of #4705 (although here it is "just" UX issue, not security one).

[arkenoi]

could be a quick fix be implemented on freerdp's side?

[marmarek]

maybe? I think it does have all the needed data to exclude such windows.

[DemiMarie]

I would prefer to fix this on the FreeRDP side, rather than the GUI daemon side. FreeRDP has more information about this, and is also already a more complex piece of software anyway.

[arkenoi]

FreeRDP/FreeRDP#6640

[DemiMarie]

That said, the user experience is poor. Wayland might fix this, as I am not sure if Wayland clients abuse windows the way X Window System clients do.

It turns out that the exact opposite is the case: even mundane Wayland clients (such as Firefox) make heavy use of surfaces. Therefore, fixing this problem in the GUI daemon is a hard requirement for Wayland support. While in theory this could be solved in the GUI agent, this would result in a substantial performance hit: compositing in the GUI agent happens on the CPU, while compositing in the GUI daemon happens on the GPU, which is faster and uses much less power.

[DemiMarie]

This is trickier than I thought it would be, as the size of the parent window can change at any time, in which case the size of the child window needs to be updated accordingly. I am not sure how to implement this in a glitch-free way on X11, although it is easy on Wayland. Nevermind! The X11 protocol guarantees that a child window will always be within its parent, so a border is never necessary.

[DemiMarie]

Turns out that child windows are useless for Wayland, or just about anything else for that matter. Instead, the Wayland compositor will do the compositing in software. @marmarek NACK’d hardware accelerating it using the RENDER extension.

[DemiMarie]

Not fixed.