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Safely executing user-submitted python code on the server

Asked 2009-11-15T13:23:32.937
9

I am looking into starting a project which involves executing python code that the user enters via a HTML form. I know this can be potentially lethal (exec), but I have seen it done successfully in at least one instance.

I sent an email off to the developers of the Python Challenge and I was told they are using a solution they came up with themselves, and they only let on that they are using "security features provided by the operating system" and that "the operating system [Linux] provides most of the security you need if you know how to use it."

Would anyone know how a safe and secure way to go about doing this? I thought about spawning a new VM for every submission, but that would have way too much overhead and be pert-near impossible to implement efficiently.

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http://codepad.org/about has implemented such a system successfully (as a public code pasting/running service!)

codepad.org is an online compiler/interpreter, and a simple collaboration tool. It's a pastebin that executes code for you. [...]

How it works

Code execution is handled by a supervisor based on geordi. The strategy is to run everything under ptrace, with many system calls disallowed or ignored. Compilers and final executables are both executed in a chroot jail, with strict resource limits. The supervisor is written in Haskell.

[...]

When your app is remote code execution, you have to expect security problems. Rather than rely on just the chroot and ptrace supervisor, I've taken some additional precautions:

  • The supervisor processes run on virtual machines, which are firewalled such that they are incapable of making outgoing connections.

  • The machines that run the virtual machines are also heavily firewalled, and restored from their source images periodically.

answered 2010-01-12T20:59:08.993

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