Desktop is not restored correctly after screen saver

[Reuben Thomas]

With the update to 3.28.3-0ubuntu0.18.04.4, on two separate machines, the screen saver stopped working properly.

When the screen is locked manually (by clicking the lock screen icon), the screen either freezes with the desktop still showing, or shows the same grey background as the login screen; it does not show the normal lock screen image.

When the screen saver is activated automatically, the screen turns off as normal, but when I press a key, the grey background as for the login screen is shown (in fact, it's the same as the login screen, but without the login widget; that is, the normal icons are shown at the top of the screen).

Pressing Ctrl+Alt+F1 switches to the login dialog.

I can then log in successfully, but all GNOME shell extensions are disabled.

(A simple workaround is then to restart gnome-shell with the "r" command from the "Enter a command" dialog.)

I am marking this bug as a security vulnerability because in the case that the screen simply freezes, confidential information may be displayed by the failure of the screen shield to activate.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-shell 3.28.3-0ubuntu0.18.04.4
ProcVersionSignature: Ubuntu 4.15.0-43.46-generic 4.15.18
Uname: Linux 4.15.0-43-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: GNOME
Date: Fri Jan 18 10:28:59 2019
DisplayManager: gdm3
InstallationDate: Installed on 2014-11-26 (1514 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: gnome-shell
UpgradeStatus: Upgraded to bionic on 2018-08-16 (155 days ago)

[Reuben Thomas (rrt)]

(The issue doesn't seem to me to be serious enough to warrant keeping the bug private.)

[Reuben Thomas (rrt)]

I tried building 3.28.3-0ubuntu0.18.04.3 and installing that, but that doesn't fix the problem, so it looks as though the cause may lie elsewhere, in some other update that has happened in the same period.

[Reuben Thomas (rrt)]

In case it was a kernel problem (I have also had a kernel update since I last rebooted, from 4.15.0-42 to -43), I installed the latest HWE 18.04 kernel, but that did not help.

I should note that in fact the screen shield *does* sometimes activate; but when it does, pressing a key reveals only the grey background, not the login dialog.

Another potential culprit might be gdm3, but of course there has been no update to that package recently.

[Reuben Thomas (rrt)]

I have updated the bug to reflect that it's related to the screen saver (desktop idleness), not specifically the lock screen.

[Reuben Thomas (rrt)]

I tried disabling the lock screen with

$ gsettings set org.gnome.desktop.lockdown disable-lock-screen true

and that makes no difference.

[Reuben Thomas (rrt)]

I notice that if I use the mouse to deactivate the screen saver, I do still see the screen shield, so that appears to be working normally. When the shield lifts, I get the "login screen without login widget" described above.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[isparnid (daniel-rapp)]

same symptoms for me after these two updates (same distribution as Reuben Thomas):
Start-Date: 2019-01-18 12:11:53
Commandline: aptdaemon role='role-commit-packages' sender=':1.1127'
Upgrade: libcups2:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), libcups2:i386 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), libzmq5:amd64 (4.2.5-1, 4.2.5-1ubuntu0.1), oracle-java8-unlimited-jce-policy:amd64 (8u191-1~webupd8~1, 8u201-1~webupd8~1), libcupsmime1:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), oracle-java8-set-default:amd64 (8u191-1~webupd8~1, 8u201-1~webupd8~1), oracle-java8-installer:amd64 (8u191-1~webupd8~1, 8u201-1~webupd8~1), libcupsppdc1:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), libcupsimage2:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), libcupscgi1:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3), cups-ipp-utils:amd64 (2.2.7-1ubuntu2.2, 2.2.7-1ubuntu2.3)
End-Date: 2019-01-18 12:12:13

Start-Date: 2019-01-18 18:51:12
Commandline: /usr/sbin/synaptic
Requested-By: daniel (1000)
Upgrade: fdisk:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), uuid-runtime:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libfdisk1:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), gvfs-backends:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), gvfs-bin:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), libmount1:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libmount1:i386 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), util-linux:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), mount:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libblkid1:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libblkid1:i386 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), gvfs-libs:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), gvfs-fuse:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), libuuid1:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libuuid1:i386 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), libsmartcols1:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), rfkill:amd64 (2.31.1-0.4ubuntu3.2, 2.31.1-0.4ubuntu3.3), bsdutils:amd64 (1:2.31.1-0.4ubuntu3.2, 1:2.31.1-0.4ubuntu3.3), gvfs:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), gvfs-common:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2), gvfs-daemons:amd64 (1.36.1-0ubuntu1.1, 1.36.1-0ubuntu1.2)
End-Date: 2019-01-18 18:51:23

[Daniel van Vugt (vanvugt)]

When you say "the grey background" of the login screen, that makes me curious. Why is it grey? It should be purple.

If it's grey because of changes you made then please try Ubuntu without changing the system in such a way that the login screen is grey. Does the bug still happen if you install Ubuntu without changing it?

[Reuben Thomas (rrt)]

It's always been grey on Ubuntu GNOME as far as I'm aware.

[isparnid (daniel-rapp)]

I confirm what Reuben says. I use "gnome on Xorg" at boot time. I just tried "ubuntu" and "gnome": I still have a grey startup screen.

[Daniel van Vugt (vanvugt)]

Ah, I see. You started with Ubuntu GNOME 14.04 and then upgraded. So you likely still have the upstream theme that is grey. And "grey" is not a problem.

I now think this might be one of the incarnations of bug 1769383. I think maybe a few related bugs have been grouped in there so first please wait for the fix for bug 1769383 to see if it improves things.

[Reuben Thomas (rrt)]

Thanks for the pointer; I've subscribed to that bug.

[Eugene Romanenko (eros2)]

Same here, after latest gjs/polkit bionic updates about once per day this issue happens. Syslog contains some .js blames about polkit (attached).

[Eugene Romanenko (eros2)]

Yesterday this happens again, symptoms exactly as described in Bug Description: "When the screen is locked manually (by clicking the lock screen icon), the screen either freezes with the desktop still showing".

Say again, this started after latest gjs/polkit updates was landed in bionic.

syslog at the moment of pressing Super-L attached.

[Reuben Thomas (rrt)]

@vanvugt: I had a look at the other bug and its proposed fix. I do not have the package gnome-shell-extension-ubuntu-dock installed, and the recent update's changelog suggests that the update fixes a bug in that package, so I'm not sure how it could be the cause of this bug?

[Daniel van Vugt (vanvugt)]

You are right. This can't be related to that bug if the ubuntu-dock extension is not installed.

[Daniel van Vugt (vanvugt)]

I may have forgotten to mention that installed extensions (even if disabled) can still cause bugs.

Please try uninstalling all of these:

'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'<email address hidden>'
'windowIsReady_Remover@<email address hidden>'
'<email address hidden>'
'<email address hidden>@gmail.com'
'<email address hidden>'
'<email address hidden>'

Or more simply you can try live booting:
  http://releases.ubuntu.com/18.04.1/ubuntu-18.04.1-desktop-amd64.iso
and tell us if that has the same bug.

[isparnid (daniel-rapp)]

In the list, I just have <email address hidden>@gmail.com installed. After deletion, the bug still persists.
But after that, the TaskBar@zpydr extension started to disappear and freeze the screen. I just do ctrl-alt-f1 to replay the session but no more taskbar.
After removing TaskBar@zpydr, no more bugs.
But I bitterly regret this extension which is really very useful (for me).

[Reuben Thomas (rrt)]

I had several of these extensions. I started by disabling them all. This fixed the problem (thanks!). I then re-enabled most of them one at a time (because they are all things I find extremely useful—I do not like to install extensions unless I have to!).

In the end, I was able to reinstall all but one of the extensions I need, namely

'<email address hidden>'

I had no problem with:

'<email address hidden>'
'<email address hidden>'
'<email address hidden>@gmail.com'
'windowIsReady_Remover@<email address hidden>'
'<email address hidden>'
'<email address hidden>'

I am interested in how you made the list, @vanvugt; is there some reason to suspect the other extensions listed are problematic too?

In any case, my immediate problem seems to be solved (thanks very much), and I now need to find a fix for using Project Hamster, as I rely on it to time work.

[Reuben Thomas (rrt)]

For anyone else having the same problem as me, a patched version of the Hamster time tracker extension is available; see https://github.com/projecthamster/hamster-shell-extension/issues/295

[Eugene Romanenko (eros2)]

I not have this extension, but have the issue...

But anyway, I dropped using gdm and use lightdm + gnome-screensaver + extension to fix lock button behaviour.
Looks like gnome shell behaves better without gdm.

[Daniel van Vugt (vanvugt)]

Reuben,

Great. In that case it would be a bug in '<email address hidden>' which is not installed from the Ubuntu archive (I think). So the status of this bug is then 'Invalid' for Ubuntu.

I generated that list from your attachment (at the top): 'GsettingsChanges.txt'

---

Eugene,

Please log your own bug by:

1. Removing lightdm and reverting back to gdm3
2. Run: ubuntu-bug gnome-shell

[Reuben Thomas (rrt)]

Thanks for the explanation, and I agree that the bug is "Invalid" for Ubuntu.