Xscreen saver and lightdm prevent use of operating system (total lockout) after guest session screen lock

[Omadas]

Steps to reproduce bug:

1) Install xubuntu or mint xfce
2) download and set lightdm as desktop manager
3) sign in to a guest session and either close your laptop lid or allow timeout to start screen lock

Why this is a bug:

xscreensaver will not accept a blank/null password, and with a blank/null password assigned to the guest session, the xscreensaver client will not allow the user to continue their session or login as a new user (because you cannot login as a new user as xscreensaver does not support lightdm for this feature.

Why this is severe:

when xscreensaver locks the guest user out of their session, all other users are similarly locked out. Being so locked out, the computer most be hard-reset/rebooted and any documents and processes not saved prior to the guest session being logged in is lost.

Why this is a lightdm bug:

Because lightdm is not setting the gconf setting to disable the lock screen feature for guest sessions

Why this is a xscreensaver bug:

xscreensaver does not support any dm other than mdm

[Gunnar Hjalmarsson (gunnarhj)]

Hi Omadas,

lightdm tries to disable screen locking for a few cases, please see:

/usr/lib/lightdm/guest-session-auto.sh

Do you possibly know what's missing to make it effective for xscreensaver?

[Gunnar Hjalmarsson (gunnarhj)]

Started my Xubuntu system, and noticed that xscreensaver is not installed by default. The locking mechanism seems to be provided by light-locker. Also, xscreensaver's lock feature seems to be disabled by default. Hence it's not clear to me how this issue can be reproduced. Please clarify.

[Omadas (bsperger)]

...Now I am not so sure, the system i am using still has this problem: It is MintXFCE.
I will purge and reinstall and see if it is a config problem somewhere.

[Omadas (bsperger)]

After the reinstall xscreensaver is still locking by default. I can disable this feature in Settings and it is now fine (Because it does not lock). However, I wanted this locking feature, it is still a bug in that enabling this locking feature still locks the screen for the guest account, which uses a blank password to sign in (which then cannot be used by xscreensaver because it does not accept null/blank passwords.
   I would suggest that fresh installs of xscreensaver disable screenlock by default. I believe as far as light-dm is concerned, after a quick google search i found that the setting or flag it needs to enable to prevent screenlocking might be available in gconf... but i dont know the specific area where this would need to be implemented without looking...

[Omadas (bsperger)]

Some ideas for the guest session:
gsettings set org.gnome.desktop.lockdown disable-lock-screen 'true'
or
gsettings set org.gnome.desktop.screensaver ubuntu-lock-on-suspend 'false'

[Gunnar Hjalmarsson (gunnarhj)]

Well, if this only happens on Linux Mint, you are on the wrong bug tracker. I added the Linux Mint task to the report.

With that said, the lightdm developers are possibly willing to add whatever is required to address this issue, but in that case they need to know - really know - what would be required. Myself is working with Ubuntu and sometimes the official flavors, so I can't help there.

As regards your ideas in comment #5, the first one is already there in /usr/lib/lightdm/guest-session-auto.sh. When I had a quick look in Xubuntu, I got the impression that the xscreensaver settings are saved in ~/.xscreensaver rather than as gsettings values, but I may not have got the whole picture.

So the ball is in your court again. ;)

[Omadas (bsperger)]

Thanks for your help... for now I just disabled session locking. I will await the Mint team's responce.

[Gunnar Hjalmarsson (gunnarhj)]

On 2016-08-12 03:18, Omadas wrote:
> Thanks for your help... for now I just disabled session locking. I
> will await the Mint team's responce.

Ok, fine with me. Thank *you* for reporting the issue! ;)