Hiding Shutdown/reboot in logout dialog and possible security issue

[Nio Wiklund]

Hi Anders,

You can also ask in the Server Platforms Forum at

http://ubuntuforums.org/forumdisplay.php?f=339

where some real server guys will probably help you.

Best regards/Nio

2014-07-10 16:07, Anders Bruun Olsen skrev:
> Hi,
> 
> Ehm.. a graphical desktop environment is sort of the point of a terminal
> server. It provides remote desktops to users. It isn't for running a
> graphical desktop on a locally attached screen :)
> The issue here is two-fold:
> 
> 1. If the graphical login-manager (lightdm) is running, all users who
> login to a desktop remotely can shut down the entire machine. This is
> not a good thing, but can be circumvented by killing off lightdm. This
> is fine when you use something like Nomachine, which takes care of
> spinning up a desktop session. But with LTSP you would probably run into
> problems, since it depends on having a DM handling login and spinning up
> desktop sessions. Although lightdm may be intelligent enough to actually
> know when users are remote on LTSP, and will refuse to allow them to
> shutdown the machine without proper rights. This may be a none-issue for
> LTSP. I don't use LTSP, so I can't say for sure. With Nomachine it is an
> issue.
> 
> 2. Users can get confused when sitting in front of a thin client running
> the nomachine client. They want to shut down for the day and choose the
> shutdown menu on their Lubuntu desktop. Here the correct process is to
> choose logout and then shut down the thin client when logout has
> happened. But users don't usually think about the fact that this
> connects to a remote desktop, so pressing the shutdown button in the
> shutdown menu seems logical. They want to shut down their local machine.
> Unfortunately that button is meant to shut down the terminal server.
> When that does not work (they get the "access denied" message), most
> users get confused and go ask it-support for help. I just want to
> prevent this confusion, if possible :)
> 
> 
> 
> 2014-07-10 14:53 GMT+02:00 Nio Wiklund <nio.wiklund at gmail.com
> <mailto:nio.wiklund at gmail.com>>:
> 
>     2014-07-10 14:21, Anders Bruun Olsen skrev:
>     > Hi,
>     >
>     > I am looking to build a new terminal server for remote desktops which
>     > will be accessed through NoMachine Enterprise. Lubuntu and LXDE looks
>     > like a nice fit, but I have run into a couple of issues.
>     >
>     > I have a default install of Lubuntu 14.04 64-bit. I have created a
>     > non-privileged user (no sudo rights). I have also installed NoMachine
>     > Enterprise Server. First thing I discovered was what I would
>     almost call
>     > a security issue. When my non-privileged user is logged in remotely
>     > (with Nomachine Enterprise Client), choosing shutdown in the logout
>     > dialog actually does shut down the server. How can this user shut down
>     > the server, without root access? I found out, that if I ensure lightdm
>     > isn't running (nobody will login locally), my unprivileged user can't
>     > shut down the server, but will be asked for the password to a
>     privileged
>     > user, so I guess this is an issue with lightdm. Is this really
>     intended
>     > behavior?
> 
>     I think it is made for desktop installation, where any user should be
>     able to shut down the computer. But it is not suitable for a server. I'm
>     glad you found a way to stop shutting it down with superuser privileges.
> 
>     But, many people will discourage the use of a graphical desktop
>     environment for a server. Do you really need it? Or maybe a simple
>     window manager like Openbox or Fluxbox would do?
> 
>     >
>     > Next up, I would like to hide the shutdown and reboot buttons in the
>     > logout dialog. The only way I have been able to find by searching,
>     is to
>     > actually change the source code for lxsession-logout and recompile. Is
>     > there really no other way to hide those buttons?
> 
>     Sorry, I don't know this, but think other people can help you with it.
> 
>     > --
>     > Anders Bruun Olsen
>     > It-ansvarlig
>     > Det Danske Sprog- og Litteraturselskab
>     > (Society for Danish Language and Literature)
>     >
>     >
> 
> 
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> 
> 
> 
> -- 
> Anders Bruun Olsen
> It-ansvarlig
> Det Danske Sprog- og Litteraturselskab
> (Society for Danish Language and Literature)