[Python-Dev] Challenge: Please break this! (was: Reviving restricted mode)

[Brett Cannon]

On Mon, Feb 23, 2009 at 12:10, tav <tav at espians.com> wrote:

> Hey all,
>
> As an attempt to convince everyone of the merits of my functions-based
> approach to security, I've come up with a simple challenge. I've
> attached it as safelite.py
>
> The challenge is simple:
>
> * Open a fresh Python interpreter
> * Do: >>> from safelite import FileReader
> * You can use FileReader to read files on your filesystem
> * Now find a way to *write* to the filesystem from your interpreter
>
> Please note that the aim of this isn't to protect Python against
> crashes/segfaults or exhaustion of resources attacks, so those don't
> count.
>
> I'm keen to know your experiences even if you don't manage to write to
> the filesystem -- and especially if you do!
>
> Dinner and drinks on me for an evening -- when you are next in London
> or I am in your town -- to the first person who manages to break
> safelite.py and write to the filesystem.
>
> Good luck and thanks! =)
>
> > If you block __closure__ and __globals__ on function objects you will get
> a
> > semblance of a private namespace. That way you might (I have not thought
> > this one through like securing the interpreter for embedding) be able to
> get
> > what you need to safely pass in Python code through the globals of the
> code
> > being executed.
>
> Brett, this is exactly what I do.


Ah, OK. I just quickly looked at your patches on codereview and noticed that
neither __closure__ or __globals__  have been touched.


> You also need to restrict func_code.


I assume you are worried about getting a hold of the code type and
constructing code objects from scratch?


>
> The patch is simply for closing the other loopholes:
> type.__subclasses__, GeneratorType.gi_frame and gi_code. All possible
> in a patch of 6 lines of code thanks to Python's existing restricted
> framework in the interpreter.
>
> Please review and accept =)
>

I personally don't have the time. The feedback in this email is all I can
spare.

-Brett
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