[pypy-dev] using python-ldap under pypy

[Elmir Jagudin]

On Mon, Dec 14, 2015 at 10:01 AM, Armin Rigo <arigo at tunes.org> wrote:

> Hi Elmir,
>
> On Sun, Dec 13, 2015 at 10:19 PM, Elmir Jagudin <elmir at unity3d.com> wrote:
> > The error happens in the python-ldap C code that converts ["uid", "cn"]
> > array to char **.
> >
> > In this file:
> >
> http://python-ldap.cvs.sourceforge.net/viewvc/python-ldap/python-ldap/Modules/LDAPObject.c?revision=1.91&view=markup
> >
> > in function attrs_from_List() there is this code (lines 289-290):
> >
> > 289:     attrs[i] = PyString_AsString(item);
> > 290:      Py_DECREF(item);
> >
> > On line 289 the assigned string is correct, however after executing line
> > 290, the string will be corrupted.
> >
> > I have noticed that under cpython, the refcount for 'item' is larger
> then 1.
> > However under pypy it is always 1, and I guess after decreasing it, the
> > 'item' is freed, and attrs[i] pointer becomes invalid.
>
> Ok.  However the sentence "under CPython the refcount for 'item' is
> larger than 1" is not true in all cases.  It is true for simple lists
> or tuples, but not for more complex types.  That means that you can
> probably get already-freed strings under CPython too.  Try for
> example:
>
> class CustomSeq(object):
>     def __getitem__(self, i):
>         return str(i)     # returns a refcount=1 result
>     def __len__(self):
>         return 2
>
> res = l.search_s(BASE_DN,
>                  ldap.SCOPE_SUBTREE,
>                  FILTER,
>                  CustomSeq())
>
>
> So it means it's really a bug of python-ldap, which just happens to
> crash more often on PyPy than on CPython.  It should be fixed there.
>

Yepp, you are right. Following version of the code above clearly shows that
it's broken under CPython as well:

class CustomSeq(object):
    def __getitem__(self, i):
        return str(i)     # returns a refcount=1 result
    def __len__(self):
        return 20

The resulting query send over network will be wrong.

Thanks for clarification.

/Elmir
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