minimum install & pickling

[Aaron "Castironpi" Brady]

On Sep 18, 5:20 am, Paul Boddie <p... at boddie.org.uk> wrote:
> On 17 Sep, 22:18, "Aaron \"Castironpi\" Brady" <castiro... at gmail.com>
> wrote:
>
> > On Sep 17, 4:43 am, Paul Boddie <p... at boddie.org.uk> wrote:
>
> > >http://wiki.python.org/moin/How_can_I_run_an_untrusted_Python_script_...)
>
> > These solutions have at least the same bugs that the bare bones
> > solution in the corresponding framework has.  Malicious code has fewer
> > options, but constructive code does too.  If you're running foreign
> > code, what do you want it to do?  What does it want to do?  The more
> > options it needs, the more code you have to trust.
>
> As I noted, instead of just forbidding access to external resources,
> what you'd want to do is to control access instead. This idea is not
> exactly new: although Brett Cannon was working on a sandbox capability
> for CPython, the underlying concepts involving different privilege
> domains have been around since Safe-Tcl, if not longer. The advantage
> of using various operating system features, potentially together with
> tools like fakechroot or, I believe, Plash, is that they should work
> for non-Python programs. Certainly, the chances of successfully
> introducing people to such capabilities are increased if you don't
> have to persuade the CPython core developers to incorporate your
> changes into their code.
>
> > The only way a Python script can return a value is with sys.exit, and
> > only an integer at that.  It is going to have output; maybe there's a
> > way to place a maximum limit on its consumption.  It's going to have
> > input, so that the output is relative to something.  You just make
> > copies to prevent it from destroying data.  Maybe command-line
> > parameters are enough.  IIRC if I recall correctly, Win32 has a way to
> > examine how much time a process has owned so far, and a way to
> > terminate it, which could be in Python's future.
>
> There is support for imposing limits on processes in the Python
> standard library:
>
> http://docs.python.org/lib/node521.html
>
> My experimental package, jailtools, relies on each process's sandbox
> being set up explicitly before the process is run, so you'd definitely
> want to copy data into the sandbox. Setting limits on the amount of
> data produced would probably require support from the operating
> system. Generally, when looking into these kinds of systems, most of
> the solutions ultimately come from the operating system: process
> control, resource utilisation, access control, and so on. (This is the
> amusing thing about Java: that Sun attempted to reproduce lots of
> things that a decent operating system would provide *and* insist on
> their use when deploying Java code in a controlled server environment,
> despite actually having a decent operating system to offer already.)
>
> > PyPy sandbox says:  "The C code generated by PyPy is not
> > segfaultable."  I find that to be a bold claim (whether it's true or
> > not).
>
> > I'm imagining in the general case, you want the foreign code to make
> > changes to objects in your particular context, such as exec x in
> > vars.  In that case, x can still be productive without any libraries,
> > just less productive.
>
> Defining an interface between trusted and untrusted code can be
> awkward. When I looked into this kind of thing for my undergraduate
> project, I ended up using something similar to CORBA, and my
> conclusion was that trusted code would need to expose an interface
> that untrusted "agents" would rely on to request operations outside
> the sandbox. That seems restrictive, but as the situation with rexec
> has shown, if you expose a broad interface to untrusted programs, it
> becomes increasingly difficult to verify whether or not the solution
> is actually secure.
>
> Paul

I think you could autogenerate a file with a copy of the data, then
run a bare bones Python installation with the foreign code that
imports the copy, or just concatenate the foreign code and copy.  At
least for input.  For output, you'd need a file that had an upper
bound on its size.

The problem with Python is that if an agent has access to a part of an
object, it has the whole thing.  Such as the trusted agents-- if they
can perform an operation, then anything with access to the agent can.
If they're just policy makers, then however an authorized agent
performs the action, is available to an unauthorized one.  You'd still
need a 'struct' instance to write your output, since memory is upper-
bounded, and you can't permit foreign code to store any form of Python
objects.