Re: Python from Wise Guy's Viewpoint

From: Pascal Costanza (costanza_at_web.de)
Date: 10/27/03 

Date: Mon, 27 Oct 2003 20:07:48 +0100

Alexander Schmolck wrote:

> Pascal Costanza <costanza@web.de> writes:
>
>
>>>>What's the problem?!?
>>>
>>>Maybe something like this?
>>> (* 10000000000000000000000000000000000000000000000000000000
>>> 10000000000000000000000000000000000000000000000 etc.)
>>
>>I don't get the point.
>
>
> Sorry for being unclear. I was just asking whether something along the lines
> of your safe eval wouldn't still be vulnerable to a DoS attack.

Welcome to Macintosh Common Lisp Version 5.0!
? (defun fac (x)
     (if (= x 0) 1
         (* x (fac (- x 1)))))
fac
? (fac 100000)
> Error: Stack overflow on control stack.
> To globally increase stack space,
> increase *minimum-stack-overflow-size*
> While executing: "Unknown"
> Type Command-/ to continue, Command-. to abort.
> If continued: Continue with a larger stack
See the Restarts… menu item for further choices.
1 >

...now add an exception handler around calls to myeval that handles
stack overflow, and don't allow the user code access to functions and
variables that can manipulate these settings. (With an appropriate
exception handler, the user wouldn't see the error as printed above and
wouldn't be able to issue the possible restarts.)

I know this doesn't completely answer your question, but it might give
you a clue about what is possible in modern Common Lisp implementations,
and how one could approach these things.

Pascal

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