Upon wake, the desktop was visible briefly before the lock screen showed

[LinuxOnTheDesktop]

Distribution

Mint 21.2

Package version

5.8.1

Graphics hardware in use

Intel onchip; Mesa

Frequency

Only occasionally

Bug description

The desktop - including icons, conky, dock (Plank) - was visible for approximately a third of a second upon wake and before the lock screen. This is a security problem as well as behaviour that throws the user.

Steps to reproduce

Unknown. I have not seen the problem before - except when I had an external monitor attached (which I did not have this time): see #406.

What trigged the problem this time was simply waking the laptop (by pressing a key on its keyboard). The machine has been asleep for some eighteen hours.

Expected behavior

The desktop should not be visible until one has unlocked the PC.

Additional information

$ cinnamon-screensaver --debug --hold
Fractional scaling active: False
Trying to connect to logind...
Starting screensaver...
Debug mode active
Cinnamon Screensaver support not found in current theme - adding some...
service: 'GetActive' received, poking application.
service: 'GetActive' received, poking application.
org.gnome.ScreenSaver is gone from the session bus
org.mate.ScreenSaver is gone from the session bus
service: 'GetActive' received, poking application.
login client: found session path for user '<me>' (session_id: c2): /org/freedesktop/login1/session/c2
Successfully using logind

An excerpt from .xsession-errors:

cinnamon-session[4122]: WARNING: t+731.43769s: Detected that screensaver has appeared on the bus
log_ksystemlog: Log manager is not yet initialized
cinnamon-session[4122]: WARNING: t+872.62203s: Detected that screensaver has left the bus
cinnamon-session[4122]: WARNING: t+878.17943s: Detected that screensaver has left the bus
** (csd-automount:4293): WARNING **: 01:47:04.868: Can't call GetActive() on the ScreenSaver object: Cannot invoke method; proxy is for the well-known name “org.cinnamon.ScreenSaver” without an owner, and proxy was constructed with the G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START flag
mint-common (WARN): Process remote: Server returned status 404: Not Found
cinnamon-session[4122]: WARNING: t+991.45039s: Detected that screensaver has appeared on the bus

$ cat /var/log/syslog grep ScreenSaver
[. . .]
Aug 20 01:42:15 x1 systemd[1]: systemd-suspend.service: Deactivated successfully.
Aug 20 01:42:15 x1 systemd[1]: Finished System Suspend.
Aug 20 01:42:15 x1 systemd[1]: Stopped target Sleep.
Aug 20 01:42:15 x1 systemd[1]: Reached target Suspend.
Aug 20 01:42:15 x1 systemd[1]: Stopped target Suspend.
Aug 20 01:42:15 x1 systemd-networkd[967]: lo: Reset carrier
[. . .]
Aug 20 01:42:16 x1 systemd-networkd[967]: enp0s31f6: Link UP
Aug 20 01:42:16 x1 systemd-networkd[967]: wlp2s0: Link UP
[. . .]
Aug 20 01:42:22 x1 cinnamon-screensaver-pam-helper: pam_ecryptfs: seteuid error
Aug 20 01:42:30 x1 systemd[1]: NetworkManager-dispatcher.service: Deactivated successfully.
Aug 20 01:42:45 x1 systemd[1]: systemd-localed.service: Deactivated successfully.
Aug 20 01:42:52 x1 cinnamon-session[4122]: WARNING: t+625.67715s: Detected that screensaver has left the bus
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Error in sys.excepthook:
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Original exception was:
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Error in sys.excepthook:
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Original exception was:
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Error in sys.excepthook:
Aug 20 01:42:52 x1 org.cinnamon.ScreenSaver[20202]: Original exception was:
Aug 20 01:44:38 x1 cinnamon-session[4122]: WARNING: t+731.43769s: Detected that screensaver has appeared on the bus
Aug 20 01:45:47 x1 dbus-daemon[628]: [system] Activating via systemd: service name='org.freedesktop.hostname1' unit='dbus-org.freedesktop.hostname1.service' requested by ':1.365' (uid=1000 pid=25247 comm="/opt/sublime_text/sublime_text --detached ")
Aug 20 01:45:47 x1 systemd[1]: Starting Hostname Service...
Aug 20 01:45:48 x1 dbus-daemon[628]: [system] Successfully activated service 'org.freedesktop.hostname1'
Aug 20 01:45:48 x1 systemd[1]: Started Hostname Service.
Aug 20 01:46:18 x1 systemd[1]: systemd-hostnamed.service: Deactivated successfully.

Kernel 6.2.16 . . generic.

[LinuxOnTheDesktop]

The frequency of the problem has become high: it occurs at least as often as things work as they should.

[LinuxOnTheDesktop]

I repeat: 'This is a security problem as well as behaviour that throws the user.'

[przadka]

I'd like to echo the sentiments of the original post. I'm also experiencing this issue and can confirm its occurrence on my system.

• System Details:
• Distribution: Mint 21.2
• Kernel Version: 5.15.0-86-generic
• Display Manager: LightDM
• Graphics Card: TigerLake-LP GT2 [Iris Xe Graphics]
• Driver: Mesa Intel(R) Xe Graphics (TGL GT2)

The brief exposure of the desktop contents before the lock screen appears is indeed a security concern. In my case, it happens when my laptop is connected to an external monitor. The duration of this exposure is brief, but it's sufficient for someone to potentially capture sensitive information using a camera.

[LinuxOnTheDesktop]

Apparently one can get 'xscreensaver' to work on Linux Mint. However, one has to either compile from source (EDIT: there are instructions within the README file within the download] or use a rather old repository version.

[LinuxOnTheDesktop]

I wrote instructions for getting xscreensaver working on Mint Cinnamon. Those instructions are here on PasteBin.

Drawbacks of using xscreensaver

• As its name suggests (and the man page confirms, xscreensaver does not work under Wayland.

• If one compiles from source, then updating is a pain. I note here that the author of xscreensaver has implored Linux distributions either to package recent versions of his software or else not package it at all.

• There is a lack of integration with Cinnamon.

• Xscreensaver lacks some of the functionality of Cinnamon's screensaver.

So, why consider using xscreensaver? Because it locks the screen promptly and securely (and offers entertaining graphics).

EDITED.

[MatzFan]

Same issue here on LMDE 6 (faye) installed on an old MacBook Air.

The problem actually seems more acute after installing the latest version (v6.2.1).

[LinuxOnTheDesktop]

Michael Webster says (here) that the problem has a chance of being solved only when Mint moves to Wayland. For, the fundamental problem is the X windowing system. Thus - as I have verified - even xscreensaver (a program mentioned above) shows the desktop for a tiny but (on my hardware anyway) just-about-noticeable fraction of a second.