Sandboxing Python

Mark Lawrence breamoreboy at yahoo.co.uk
Sun Aug 23 01:52:45 CEST 2015


On 23/08/2015 00:44, Chris Angelico wrote:
> On Sun, Aug 23, 2015 at 9:25 AM, Mark Lawrence <breamoreboy at yahoo.co.uk> wrote:
>> I was always led to believe that the subject was a difficult thing to do,
>> but here
>> https://www.reddit.com/r/learnpython/comments/3huz4x/how_to_do_math_inside_raw_input/
>> is a safe solution in only 23 characters, or are there any discernable flaws
>> in it?
>
>
> I'm sorry, I can't see which solution you're talking about there -
> maybe I just don't know how to read reddit properly. Can you paste the
> proposed code please?
>
> The best I can see there is "use eval but with no builtins". That's
> fundamentally flawed because you don't need builtins to break stuff.
> All you need is a literal, from which you can snag everything else via
> its attributes.
>
> However, for this situation, I would be recommending ast.literal_eval,
> which *is* safe. It's a lot more powerful than "split it into number,
> operator, number" as mentioned at the end, but still can't majorly
> break anything.
>
> ChrisA
>

<code>
 >>> import os
 >>> eval("os.system('rm -rf /')", {"__builtins__":None})
Traceback (most recent call last):
   File "<pyshell#8>", line 1, in <module>
     eval("os.system('rm -rf /')", {"__builtins__":None})
   File "<string>", line 1, in <module>
TypeError: 'NoneType' object is not subscriptable
</code>

<comment>
Surely I must I have missed your meaning because I needed just 23 
characters and zero extra lines to create a safe sandbox for this, but 
you've said that the core developers have tried and failed to do this. 
It appears that I didn't just wipe out my entire filesystem and you've 
stated quite matter-of-factly that there is no safe solution... so what 
happened here? Why didn't my filesystem just get wiped out?
</comment>

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence



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