[Python-Dev] The pysandbox project is broken

[Trent Nelson]

On Tue, Nov 12, 2013 at 01:16:55PM -0800, Victor Stinner wrote:
> pysandbox cannot be used in practice
> ====================================
> 
> To protect the untrusted namespace, pysandbox installs a lot of
> different protections. Because of all these protections, it becomes
> hard to write Python code. Basic features like "del dict[key]" are
> denied. Passing an object to a sandbox is not possible to sandbox,
> pysandbox is unable to proxify arbitary objects.
> 
> For something more complex than evaluating "1+(2*3)", pysandbox cannot
> be used in practice, because of all these protections. Individual
> protections cannot be disabled, all protections are required to get a
> secure sandbox.

    This sounds a lot like the work I initially did with PyParallel to
    try and intercept/prevent parallel threads mutating main-thread
    objects.

    I ended up arriving at a much better solution by just relying on
    memory protection; main thread pages are set read-only prior to
    parallel threads being able to run.  If a parallel thread attempts
    to mutate a main thread object; a SEH is raised (SIGSEV on POSIX),
    which I catch in the ceval loop and convert into an exception.

    See slide 138 of this: https://speakerdeck.com/trent/pyparallel-how-we-removed-the-gil-and-exploited-all-cores-1

    I'm wondering if this sort of an approach (which worked surprisingly
    well) could be leveraged to also provide a sandbox environment?  The
    goals are the same: robust protection against mutation of memory
    allocated outside of the sandbox.

    (I'm purely talking about memory mutation; haven't thought about how
     that could be extended to prevent file system interaction as well.)


        Trent.