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

Jon Ribbens jon+python-dev at unequivocal.co.uk
Fri Apr 8 10:55:36 EDT 2016

On Fri, Apr 08, 2016 at 03:37:45PM +0100, Paul Moore wrote:

On 8 April 2016 at 15:18, Jon Ribbens <jon+python-dev at unequivocal.co.uk> wrote: > I would be very interested to see if anyone can manage to break it. > Bugs which are trivially fixable are of course welcomed, but the real > question is: is this approach basically sound, or is it fundamentally > unworkable?

What are the limitations? It seems to even block "import" which seems over-zealous (no import math?)

The restrictions are:

Of the builtins, import, compile, globals, input, locals, memoryview, open, print, type and vars are unavailable (and some of the exceptions, but mostly because they're irrelevant).

You cannot access any name or attribute which starts with "_", or is called "gi_frame" or "gi_code".

You cannot use the "with" statement (although it's possible it might be safe for me to add that back in if I also disallow access to attributes called "tb_frame").

Importing modules is fundamentally unsafe because the untrusted code might alter the module, and the altered version would then be used by the containing application. My code has a "_copy_module" function which copies (some of) the contents of modules, so some sort of import functionality of a white-list of modules could be added using this, but there's no point in me going through working out which modules are safe to white-list until I'm vaguely confident that my approach isn't fundamentally broken in the first place.

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