[Python-Dev] Challenge: Please break this! (a.k.a restricted mode revisited)

Paul Moore p.f.moore at gmail.com
Tue Apr 12 04:17:28 EDT 2016

On 11 April 2016 at 17:53, Jon Ribbens <jon+python-dev at unequivocal.co.uk> wrote:
>> You're limiting the subset of Python that people can use,
>> understood. And you're trying to ensure that people can't do "bad
>> things". Again, understood. But what subset are you actually allowing,
>> and what things are you trying to protect against? (For example, I
>> can't calculate sin(1.2) using the math module - why is that not
>> alllowed?
> It wasn't allowed in the earlier version because I wasn't allowing
> import at all, because this is just an experiment. As it happens,
> I added 'import' yesterday so yes you can use math.sin.

Well, I'll ask the obvious question, then. In allowing "import" did
you allow "import ctypes"? If so, then I win :-) Or did you explicitly
whitelist certain modules? And if so, which ones are they, and did I
succeed if I manage to import a module you hadn't whitelisted?

>> It feels at the moment as if I'm playing a game where I don't know the
>> rules, and every time I think I scored a point, the rules are changed
>> to retroactively disallow it.
> The challenge is to show some code that will escape from the sandbox,
> in a way that is not trivially fixable with a tiny patch, or in a way
> that demonstrates that such a large number of tiny patches would be
> required as to be unworkable.

But I'm still not clear when I count as "outside the sandbox", given
that I don't know what the rules of what is allowed *in* the sandbox


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