Re: Disabling dangerous commands

[David Bateman]

Søren Hauberg wrote:
> lør, 29 05 2010 kl. 21:51 +1000, skrev Thomas Karpiniec:
>   
> > I'm trying to come up with a way of disabling commands such as
> > system(), fopen(), plot(), dlmwrite(), etc., which can spawn
> > subprocesses or interact with the rest of the system.
> >
> > The reason I want to do this is that I have written an octave IRC bot
> > for GNU/Linux which allows you to do maths in-channel by forwarding
> > the input to an octave process and reading results back out to the
> > channel. Obviously I need to somehow lock it down so that users can't
> > wreak havoc on my system via octave. :)
> >
> > I'm open to broader suggestions but my current feeling is that a list
> > of restricted commands within octave would provide the best
> > protection. I've searched online and through the manual and I haven't
> > been able to find a way to do that.
> >
> > I could always patch octave, of course. Does anyone know if there is
> > a neater way?
> >     
>
> There was a thread on something similar a while back (related to
> creating a web interface to Octave); you might want to find that.
>
> In general, if you disable system commands than many other functions
> will stop working (example: if you disable the 'system' function, then
> you wont be able to start gnuplot, i.e. no plotting). So, I really think
> you need to follow Sergei's advice and go with the virtual machine.
>
> Søren
>
>   

You should also think about using PAM to limit the number of processes 
that can be spawned by octave as anything in octave that can be used to 
spawn an external process or thread can be used as a fork bomb... For 
example "i=0; while(true); figure(++i); plot(1:10); endwhile" will fork 
a new gnuplot process for each figure.

Running an octave command that will take an extremely long time might 
also be used to deny the use of your octave process to someone else (or 
do you have different process for each user), and you might not even be 
able to limit this with the ulimit command. For example "while (true), 
sleep(1000); endwhile" won't use much processor time but will lockup the 
octave process doing nothing useful..

D.