Fix for

[ 784825 ] fix obscure crash in descriptor handling

Should be applied to release23-maint and in all likelyhood
release22-maint, too.

Certainly doesn't apply to release21-maint.

2 files changed, 17 insertions, 5 deletions

diff --git a/Objects/object.c b/Objects/object.c
index 93057c0..8c4bd0e 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1412,12 +1412,15 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
 		}
 	}
 
+	Py_XINCREF(descr);
+
 	f = NULL;
 	if (descr != NULL &&
 	    PyType_HasFeature(descr->ob_type, Py_TPFLAGS_HAVE_CLASS)) {
 		f = descr->ob_type->tp_descr_get;
 		if (f != NULL && PyDescr_IsData(descr)) {
 			res = f(descr, obj, (PyObject *)obj->ob_type);
+			Py_DECREF(descr);
 			goto done;
 		}
 	}
@@ -1445,6 +1448,7 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
 			res = PyDict_GetItem(dict, name);
 			if (res != NULL) {
 				Py_INCREF(res);
+				Py_XDECREF(descr);
 				goto done;
 			}
 		}
@@ -1452,12 +1456,13 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
 
 	if (f != NULL) {
 		res = f(descr, obj, (PyObject *)obj->ob_type);
+		Py_DECREF(descr);
 		goto done;
 	}
 
 	if (descr != NULL) {
-		Py_INCREF(descr);
 		res = descr;
+		/* descr was already increfed above */
 		goto done;
 	}
 
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 5c0f73a..af255f1 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -2010,6 +2010,7 @@ type_getattro(PyTypeObject *type, PyObject *name)
 			return meta_get(meta_attribute, (PyObject *)type,
 					(PyObject *)metatype);
 		}
+		Py_INCREF(meta_attribute);
 	}
 
 	/* No data descriptor found on metatype. Look in tp_dict of this
@@ -2018,6 +2019,9 @@ type_getattro(PyTypeObject *type, PyObject *name)
 	if (attribute != NULL) {
 		/* Implement descriptor functionality, if any */
 		descrgetfunc local_get = attribute->ob_type->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)  */
@@ -2031,13 +2035,16 @@ type_getattro(PyTypeObject *type, PyObject *name)
 
 	/* No attribute found in local __dict__ (or bases): use the
 	 * descriptor from the metatype, if any */
-	if (meta_get != NULL)
-		return meta_get(meta_attribute, (PyObject *)type,
-				(PyObject *)metatype);
+	if (meta_get != NULL) {
+		PyObject *res;
+		res = meta_get(meta_attribute, (PyObject *)type,
+			       (PyObject *)metatype);
+		Py_DECREF(meta_attribute);
+		return res;
+	}
 
 	/* If an ordinary attribute was found on the metatype, return it now */
 	if (meta_attribute != NULL) {
-		Py_INCREF(meta_attribute);
 		return meta_attribute;
 	}