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

[Wes Turner]

On Mon, Apr 11, 2016 at 8:08 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
wrote:

> Jon Ribbens wrote:
>
>> So far it looks like blocking "_*" and the frame object attributes
>> appears to be sufficient.
>>
>
> Even if your sandbox as it currently exists is secure, it's
> only an extremely restricted subset. You seem to be assuming
> that if your technique works so far, then it can be extended
> to cover a larger subset, but I don't think that's certain.
>

How would you test that?


> One problem that's been raised is how to prevent untrusted
> code from monkeypatching imported modules. Possibly that
> could be addressed by giving the untrusted code a copy of
> the module, but I'm not entirely sure -- accidentally
> importing two copies of the same source file is a well-known
> source of bugs, after all.
>

https://en.wikipedia.org/wiki/Monkey_patch#Pitfalls

*
https://pypi.python.org/pypi?%3Aaction=search&term=monkeypatch&submit=search

  * https://pypi.python.org/pypi/apparmor_monkeys
  *
http://eventlet.net/doc/patching.html#monkeypatching-the-standard-library
  * http://www.gevent.org/gevent.monkey.html
  * https://docs.python.org/3/library/asyncio-sync.html#locks
  * https://docs.python.org/2/library/threading.html#lock-objects
  *
https://docs.python.org/2/library/sets.html?highlight=immutable#sets.ImmutableSet
  * http://doc.pypy.org/en/latest/stm.html#locks
   - " Infinite recursion just segfaults for now."
  * https://github.com/tobgu/pyrsistent #justfoundthis
    - https://github.com/tobgu/pyrsistent#invariants
    - https://github.com/tobgu/pyrsistent#freeze-and-thaw
      - freeze, thaw

  * define a @property (and no @propname.setter)
    - https://docs.python.org/2/howto/descriptor.html#properties
    - https://docs.python.org/2/library/functions.html#property


> A related, but more difficult problem is that if we allow
> the untrusted code to import any pure-Python classes, it
> will be able to monkeypatch them. So it seems like it will
> need its own copy of those classes as well --


* https://docs.python.org/3/library/importlib.html#importlib.__import__
*


> and having
> two copies of the same class around is *another* well
> known source of bugs.


One way to reduce the likelihood of this is to
bundle all dependencies into a self-contained
PEX ZIP package
and specify entry points.

* http://legacy.python.org/dev/peps/pep-0441/
*
https://pex.readthedocs.org/en/stable/buildingpex.html#specifying-entry-points
*
https://pex.readthedocs.org/en/stable/buildingpex.html#tailoring-pex-execution-at-build-time


>
>
> --
> Greg
>
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