Re: User-level Tasks in Hotplug Scripts?

[Jim Carter <jimc@math.ucla.edu>]

On Fri, 1 Feb 2002, Ryan Shaw wrote:
> I would like to have the script that is run
> when hotplug detects my camera launch nautilus
> as well, as it is my image browser of choice.
> ...
> Hotplugging scripts are run as root, so I have
> the following line to launch nautilus: [which won't start]
>
> su - ryan -c "nautilus --display=:0.0 > /home/ryan/nautilus.log 2>&1" &

I have a distantly related application which does security checksums (as
root) and displays the result to whoever happens to be logged in, piping it
to xmessage. Being root, with authority to read any file, I steal the
X-server's own authorization file.  Here's the code, leaving out two or
three details that bypass this if X happens to be turned off:

for f in /etc/X11/xdm/authdir/authfiles/A:0* ; do
    XAUTHORITY=$f
done
    export DISPLAY=:0.0
    export XAUTHORITY
    xmessage -title "Daily Housekeeping" -timeout 900 -file /tmp/report.txt

The loop is done because an accident might leave a stale auth file, and I'd
rather have it fail to auth than get a syntax error.

In your case, I'd suggest doing an imitation of xdm -- copy the auth file
to a file in /tmp owned by you and mode 600, and XAUTHORITY=/tmp/thatfile.
Then do the "su".  Then if your kid in middle school is using your machine,
he/she can plug in the camera and see the pics, but can't do much damage
through the X authorization.  (And, since the kid is the console user, the
auth file properly belongs to him, so essentially you've stolen it from
him, not him from you.)

I'm not suggesting this as a general solution, as for a Windoze-ish GUI to
select drivers and config parms, and particularly, the security
implications would have to be thought through *very* carefully in a public
lab environment, but for a single-user or family situation it's probably
sufficient.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA  90095-1555
Email: jimc@math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)


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