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[2.7] bpo-25750: fix refcounts in type_getattro() (GH-6118) #9091

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Merged
vstinner merged 1 commit into from
Sep 7, 2018
Merged

[2.7] bpo-25750: fix refcounts in type_getattro() (GH-6118) #9091

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2018-03-14-21-42-17.bpo-25750.lxgkQz.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix rare Python crash due to bad refcounting in ``type_getattro()`` if a
descriptor deletes itself from the class. Patch by Jeroen Demeyer.
20 changes: 13 additions & 7 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2611,6 +2611,7 @@ type_getattro(PyTypeObject *type, PyObject *name)
PyTypeObject *metatype = Py_TYPE(type);
PyObject *meta_attribute, *attribute;
descrgetfunc meta_get;
PyObject* res;

if (!PyString_Check(name)) {
PyErr_Format(PyExc_TypeError,
Expand All @@ -2632,36 +2633,41 @@ type_getattro(PyTypeObject *type, PyObject *name)
meta_attribute = _PyType_Lookup(metatype, name);

if (meta_attribute != NULL) {
Py_INCREF(meta_attribute);
meta_get = Py_TYPE(meta_attribute)->tp_descr_get;

if (meta_get != NULL && PyDescr_IsData(meta_attribute)) {
/* Data descriptors implement tp_descr_set to intercept
* writes. Assume the attribute is not overridden in
* type's tp_dict (and bases): call the descriptor now.
*/
return meta_get(meta_attribute, (PyObject *)type,
(PyObject *)metatype);
res = meta_get(meta_attribute, (PyObject *)type,
(PyObject *)metatype);
Py_DECREF(meta_attribute);
return res;
}
Py_INCREF(meta_attribute);
}

/* No data descriptor found on metatype. Look in tp_dict of this
* type and its bases */
attribute = _PyType_Lookup(type, name);
if (attribute != NULL) {
/* Implement descriptor functionality, if any */
descrgetfunc local_get = Py_TYPE(attribute)->tp_descr_get;
descrgetfunc local_get;
Py_INCREF(attribute);
local_get = Py_TYPE(attribute)->tp_descr_get;

Py_XDECREF(meta_attribute);

if (local_get != NULL) {
/* NULL 2nd argument indicates the descriptor was
* found on the target object itself (or a base) */
return local_get(attribute, (PyObject *)NULL,
(PyObject *)type);
res = local_get(attribute, (PyObject *)NULL,
(PyObject *)type);
Py_DECREF(attribute);
return res;
}

Py_INCREF(attribute);
return attribute;
}

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