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The Doctor
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PostPosted: Sat Jan 19, 2013 3:57 am    Post subject: Command line login to X Reply with quote

While login managers have their place, they do require running X as root, and hang out in the background. For more simple setups, it be convenient to have a lighter way to startx. This is particularly true if you are running openbox or similar which does not use the features of the login manager anyway.

This method assumes a bash shell.

To begin, one could simply edit the bashrc file to start X, but this is problematic. For everyday use, X is fine, but what about when (not if) X breaks? Switching to a console and using root might be an option unless the keyboard is dead as well. Also, an SSH login should not trigger X.

We can check /proc/cmdline to see if nox was entered as the boot parameter, then check the $DISPLAY variable and finally check the SSH status.

The result is something like this:

Code:
if [ "$(echo $DISPLAY | wc -w)" -eq "0" -a "$(cat /proc/cmdline | grep nox | wc -l) " -eq "0" ]; then
    if [ -n $SSH_CONNECTION ]; then
      exec startx
    fi
fi


This should simply be added to the end of the .bashrc file in your home directory.

ISSUES

The above script does not prevent an attacker from using ctr+alt+F1 to return to your shell and use ctr+c to kill X. To prevent that. It should be possible to replace the exec starx line with
Code:
exec nohup startx > /dev/null 2&>1 &
disown
exit
This will startx as your user and then log your user out of the session without killing X. Alternatively, vlock can be used. In that case, exec startx should be replaced by:
Code:
exec nohup startx > /dev/null 2&>1 &
vlock

Both methods work fine when I tested them. I prefer the vlock solution as it simply requires entering your password, instead of username and password, to recover access to the TTY session.

I hope someone else finds this useful. Please, enter any comments/criticism of this method.

EDIT: After thought: shutdown and reboot can be achieved using sudo with NOPASSWD options. Implantation will very by WM
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PaulBredbury
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PostPosted: Sat Jan 19, 2013 11:30 am    Post subject: Reply with quote

I use:
Code:
alias x='setsid /usr/bin/startx -- -nolisten tcp &> ~/.xorg.log & logout'

From previous discussion.

Dunno why you want nohup & disown :?:
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Ottre
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PostPosted: Sat Jan 19, 2013 12:11 pm    Post subject: Re: Command line login to X Reply with quote

The Doctor wrote:
and finally check the SSH status.

Code:

if [ -n $SSH_CONNECTION ]; then



What about serial console logins? A more robust check would be:

Code:

if [[ $(tty) =~ /dev/tty[1-6] ]]; then
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The Doctor
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PostPosted: Sun Jan 20, 2013 3:47 am    Post subject: Reply with quote

PaulBredbury wrote:
Dunno why you want nohup & disown :?:


Maybe I am misunderstanding the nohup command. As I understand it, it keeps the process running with the same priority as a foreground task while otherwise it have reduced priority and therefore run slower.

The disown is so the process is not killed by a logout on the terminal. Thanks for the link to the Arch forums. That one did not surface in my Google search.

Ottre wrote:
What about serial console logins? A more robust check would be:
Code:
if [[ $(tty) =~ /dev/tty[1-6] ]]; then
You are right! That is a much better check.

EDIT:
two more links that provide information, found vai the Arch thread:

[/url]http://en.gentoo-wiki.com/wiki/Non_Root_Xorg-Server[url]
http://www.gentoo-wiki.info/TIP_Fix_The_Login_Security_Hole

Looks like there is more on this that I realized originally started this thread or when I tried to do this myself. Oh well.
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krinn
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PostPosted: Sun Jan 20, 2013 10:26 am    Post subject: Reply with quote

I just want to know why you find that an issue ?

If your X is run under user "that" and someone ctrl+alt+f1 to stop X, he will now have a console log as "that". So what ? he could have just open a new console in X and have the same.
If your X is run under a user because you don't need a login manager, how an attacker that is not "root" or "that" exist ? If you have more than one user, i suppose you would have use a login manager no ?
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PaulBredbury
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PostPosted: Sun Jan 20, 2013 10:43 am    Post subject: Reply with quote

The Doctor wrote:
reduced priority

What documentation gives you that impression?

krinn wrote:
he could have just open a new console in X

Not if X is locked by a screensaver such as xscreensaver or i3lock.
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