[Bug 2148637] [NEW] update-notifier: GTK notification bypasses lockscreen

[Zayd]

Public bug reported:

## Problem

When the system is locked, check-new-release-gtk (launched by update-
notifier-release.service) attempts to display a GTK window, causing
GNOME Shell lockscreen to be incorrectly reset. Screen unlocks without
password.

## Steps to Reproduce

1. Login to Ubuntu desktop
2. Lock screen with Super+L
3. Wait for update-notifier-release.service to trigger
4. Lockscreen is bypassed

## Expected Behavior

Program should detect lockscreen and delay notification

## Actual Behavior

Lockscreen shield state is reset, screen unlocks automatically

## Logs

Apr 17 06:00:44 update-notifier: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
Apr 17 06:02:27 systemd: Starting update-notifier-release.service
Apr 17 06:02:48 check-new-release-gtk: timeout reached, exiting
Apr 17 06:02:48 systemd: Finished update-notifier-release.service

## Security Impact

Local attacker can bypass lockscreen via physical access

** Affects: update-notifier (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2148637

Title:
  update-notifier: GTK notification bypasses lockscreen

Status in update-notifier package in Ubuntu:
  New

Bug description:
  ## Problem

  When the system is locked, check-new-release-gtk (launched by update-
  notifier-release.service) attempts to display a GTK window, causing
  GNOME Shell lockscreen to be incorrectly reset. Screen unlocks without
  password.

  ## Steps to Reproduce

  1. Login to Ubuntu desktop
  2. Lock screen with Super+L
  3. Wait for update-notifier-release.service to trigger
  4. Lockscreen is bypassed

  ## Expected Behavior

  Program should detect lockscreen and delay notification

  ## Actual Behavior

  Lockscreen shield state is reset, screen unlocks automatically

  ## Logs

  Apr 17 06:00:44 update-notifier: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
  Apr 17 06:02:27 systemd: Starting update-notifier-release.service
  Apr 17 06:02:48 check-new-release-gtk: timeout reached, exiting
  Apr 17 06:02:48 systemd: Finished update-notifier-release.service

  ## Security Impact

  Local attacker can bypass lockscreen via physical access

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