Hiding Shutdown/reboot in logout dialog and possible security issue

[Anders Bruun Olsen]

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>:

> 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)
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