[Python-Dev] Re: Capabilities (original) (raw)

Samuele Pedroni pedronis@bluewin.ch
Sun, 9 Mar 2003 20:09:33 +0100

From: "Samuele Pedroni" <pedronis@bluewin.ch>

From: "Jim Fulton" <jim@zope.com> > For example, you can't proxy exceptions without > breaking exception handling. In Zope, we rely on restricted execution to prevent > certian kinds of introspection on exceptions and exception classes. In Zope, we > also don't proxy None, because None is usually checked for identity. We also don't > proxy strings, and numbers. > That was a question I was asking myself about proxies: exception handling. But I never had the time to play with it to check.

Does that mean that restricted code can get unproxied instances of classic classes as caught exceptions?

maybe the question was unclear, but it was serious, what I was asking is whether some restricted code can do:

try: deliberate code to force exception except Exception,e: ...

so that e is caught unproxied. Looking at zope/security/_proxy.c it seems this can be the case...

then to be (likely) on the safe side, all exception class definitions for possible e classes: like e.g.

class MyExc(Exception): ...

ought to be executed in restricted mode, or be "trivial/empty": something like

class MyExc(Exception): def init(self, msg): self.message = msg Exception.init(self, msg)

def __str__(self):
    return self.message

is already too much rope.

Although it seems not to have the "nice" two-level-of-calls behavior of Bastion instances, an unproxied instance of MyExc if MyExc was defined outside of restricted execution, can be used to break out of restricted execution.

regards.