Add Picture button in Background does not allow you to select wallpaper

[Sam Lane]

[ Impact ]

 * On Ubuntu Budgie 24.04 / 24.10, When trying to select a custom wallpaper to add to the Backgrounds page of Budgie Control Center, the "Add Picture" button will open a dialog to select an image file. However, there will be no thumbnail of the image displayed in this dialog, the "Open" button will remain insensitive, and double-clicking the file name will have no effect. The only option is to cancel out of the dialog. This prevents the user from adding a custom wallpaper. This is due to AppArmor changes preventing certain apps doing deemed security related issues in userspace. In this case libgnome-desktop is calling bwrap which is the deemed culprit.

 * The upload addresses this issue by using GdkPixbuf to create the thumbnail image, instead of gnome-desktop thumbnail creator.

[ Test Plan ]

 To reproduce:

 * On Ubuntu Budgie 24.04/24.10
 * Open Budgie Control Center
 * Navigate to the Background panel
 * Select the "Add Picture" option
 * Select an image file
 * The thumbnail is not updated to show the currently selected image
 * The "Open" button remains inactive, and the only option is to cancel the dialog

 * After this, the proposed fix can be applied.
 * Open Budgie Control Center and repeat the above
 * When a valid image is selected, the thumbnail is now properly shown and the "Open" button is enabled.
 * Open the selected image. The image is now properly added to Budgie Control Center and can selected as a background

[ Where problems could occur ]

  * It is possible that gnome-desktop thumbnail creator provided additional functionality or handled a wider range of images than GdkPixbuf.
  * Mitigating factors are that this is very specific to the Budgie desktop, and it only directly impacts users who set wallpapers. It improves functionality where it is currently not working.

[ Other Info ]

--- Original Report ---

Ubuntu Budgie 24.04
budgie-control-center 1.4.0-2build3

When trying to select a custom wallpaper to add to the Backgrounds page of Budgie Control Center, the "Add Picture" button will open a dialog to select an image file. However, there will be no thumbnail of the image displayed in this dialog, the "Open" button will remain insensitive, and double-clicking the file name will have no effect. The only option is to cancel out of the dialog.

Steps to reproduce:

On Ubuntu Budgie Noble / Oracular:
 - open Budgie Control Center
 - Navigate to the Backgrounds page and click the "Add Picture" button in the top right title bar.
 - When the file chooser dialog opens, select an image file.

What I would expect to happen:

I would expect the thumbnail to update in the lower right, and the "Open" button to become enabled.

What happened instead:

The "Open" button remains disabled, and the thumbnail is shown as a "?".

Additional information:

This is due to AppArmor changes preventing certain apps doing deemed security related issues in userspace.
Running budgie-control-center from the terminal illustrates the issue with thumbnails with the following output:
(budgie-control-center:38170): cc-background-chooser-WARNING **: 12:37:31.144: could not general thumbnail file:///home/sam/Pictures/flavors/Flavor-Ubuntu-Budgie.png (image/png) Child process exited with code 1

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: budgie-control-center 1.4.0-2build3
ProcVersionSignature: Ubuntu 6.8.0-31.31-generic 6.8.1
Uname: Linux 6.8.0-31-generic x86_64
ApportVersion: 2.28.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: Budgie:GNOME
Date: Tue May 14 12:38:19 2024
InstallationDate: Installed on 2024-05-08 (6 days ago)
InstallationMedia: Ubuntu-Budgie 24.04 LTS "Noble Numbat" - Release amd64 (20240424)
SourcePackage: budgie-control-center
UpgradeStatus: No upgrade log present (probably fresh install)

[Steve Langasek (vorlon)]

The proposed solution here deals with bubblewrap being broken by apparmor in noble by altogether eliminating the intended security benefits of the bubblewrap sandboxing of the thumbnailer.

I do not think this is an appropriate resolution of this issue. We need to fix bubblewrap to work with current apparmor, not downgrade the security of the desktop in noble.

I have reopened the bubblewrap task on LP: #2046844 and escalated to the AppArmor team.

[John Johansen (jjohansen)]

Agreed that, we don't want to remove sandboxing on the thumbnailer. We are looking at what we can do for a fix.

[John Johansen (jjohansen)]

I can report the bwrap-userns-restrict profile in Oneric makes this work for me. This fix migrated out of proposed this week, so it has only been available for a few days.

We will work on getting it SRUed to noble.

[John Johansen (jjohansen)]

@samlan00:

you should be able to revert your fix on Oneiric.

[John Johansen (jjohansen)]

Uhmmm sorry Oracular not Oneiric, seems I am a full 13 years out of sync