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Disconnecting a video output can cause XScreenSaver to crash (QSB-068, CVE-2021-34557) #6595

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@mcku

Description

@mcku

Qubes OS version

4.0.4

Affected component(s) or functionality

Screensaver, locking with Ctrl-Alt-L

Brief summary

Nothing happens when trying to lock the screen. No logs. Screensaver IS set to autostart already. And it works for some time. But after some time, (not sure about the exact cause), inactivity timer does not lock the screen, nor the screen lock shortcut works. When I open the Xfce Screensaver panel, it complains about the screensaver daemon being not running. Even after starting the daemon, same thing happens after some time.
As there is no log at all, I cannot trace the cause.

How Reproducible

This started a few days ago, probably after applying a UEFI firmware update. The bug is always present since then, I guess.

To Reproduce

Steps to reproduce the behavior:

  1. boot the system
  2. log in. do some work.
  3. the computer won't lock when you expect it to lock its screen

Expected behavior

The lock should work.

Actual behavior

Lock is disabled

Screenshots

Additional context

It might be considered a security issue as well, I did not notice that the screen was not locked but had the impression that it was.

Solutions you've tried

starting the xscreensaver using the respective xfce settings panel

Relevant documentation you've consulted

Found some basic info that suggests to restart the screensaver, to put it into autostart (which already appears in session and startup panel as a ticked item)

Related, non-duplicate issues

(could not find any)

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    C: desktop-linuxThis issue pertains to dom0's desktop in Qubes OS.P: blockerPriority: blocker. Prevents release (or would have prevented release if known prior to release).diagnosedTechnical diagnosis of this issue has been performed.securityThis issue pertains to the security of Qubes OS.

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