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

Jon Ribbens jon+python-dev at unequivocal.co.uk
Sun Apr 10 12:51:13 EDT 2016

On Sun, Apr 10, 2016 at 02:51:23PM +1000, Nick Coghlan wrote:

On 9 April 2016 at 22:43, Victor Stinner <victor.stinner at gmail.com> wrote: > See pysandbox test suite for a lot of ways to escape a sandbox. CPython has > a list of know code to crash CPython (I don't recall the dieectory in > sources), even with the latest version of CPython.

They're at https://hg.python.org/cpython/file/tip/Lib/test/crashers

Thanks. I take your point that sandboxing Python requires CPython to free of code execution bugs. However I will note that none of the crashers in that directory will work inside my experiment (except "infinite_loop_re.py", which isn't a crasher just a long loop).

Even without those considerations though, there are system level denial of service attacks that untrusted code can perform without even trying to break out of the sandbox - the most naive is "while 1: pass", but there are more interesting ones like "from itertools import count; sum(count())", or even "sum(iter(int, 1))" and "list(iter(int, 1))".

Yes, of course. I have already explicitly noted that infinite loops and memory exhausation are not preventable.

Operating system level security sandboxes still aren't particularly easy to use correctly, but they're a lot more reliable than language runtime level sandboxes, can be used to defend against many more attack vectors, and even offer increased flexibility (e.g. "can write to these directories, but no others", "can read these files, but no others", "can contact these IP addresses, but no others").

I don't entirely trust operating system sandboxes either - I generally assume that if someone can execute arbitrary code on my machine, then they can do anything they want to that machine.

What I might trust, though, would be a "sandbox Python" that is itself running inside an operating system sandbox...

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