[3.13] gh-132747: Fix NULL dereference when calling a method's __get__ manually (GH-132772) (#132786)

ZeroIntensity · web-flow · commit bb59fdec7184 · 2025-04-21T21:38:51.000Z
(cherry picked from commit fa70bf8) Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
diff --git a/Lib/test/test_types.py b/Lib/test/test_types.py
@@ -631,6 +631,25 @@ def test_method_descriptor_types(self):
         self.assertIsInstance(int.from_bytes, types.BuiltinMethodType)
         self.assertIsInstance(int.__new__, types.BuiltinMethodType)
 
+    def test_method_descriptor_crash(self):
+        # gh-132747: The default __get__() implementation in C was unable
+        # to handle a second argument of None when called from Python
+        import _io
+        import io
+        import _queue
+
+        to_check = [
+            # (method, instance)
+            (_io._TextIOBase.read, io.StringIO()),
+            (_queue.SimpleQueue.put, _queue.SimpleQueue()),
+            (str.capitalize, "nobody expects the spanish inquisition")
+        ]
+
+        for method, instance in to_check:
+            with self.subTest(method=method, instance=instance):
+                bound = method.__get__(instance)
+                self.assertIsInstance(bound, types.BuiltinMethodType)
+
     def test_ellipsis_type(self):
         self.assertIsInstance(Ellipsis, types.EllipsisType)
 
diff --git a/Misc/NEWS.d/next/Core and Builtins/2025-04-21-07-39-59.gh-issue-132747.L-cnej.rst b/Misc/NEWS.d/next/Core and Builtins/2025-04-21-07-39-59.gh-issue-132747.L-cnej.rst
@@ -0,0 +1,2 @@
+Fix a crash when calling :meth:`~object.__get__` of a :term:`method` with a
+:const:`None` second argument.
diff --git a/Objects/descrobject.c b/Objects/descrobject.c
@@ -144,7 +144,7 @@ method_get(PyObject *self, PyObject *obj, PyObject *type)
         return NULL;
     }
     if (descr->d_method->ml_flags & METH_METHOD) {
-        if (PyType_Check(type)) {
+        if (type == NULL || PyType_Check(type)) {
             return PyCMethod_New(descr->d_method, obj, NULL, descr->d_common.d_type);
         } else {
             PyErr_Format(PyExc_TypeError,

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fix a crash when calling :meth:`~object.__get__` of a :term:`method` with a
	`2`	+:const:`None` second argument.
Original file line number	Diff line number	Diff line change
`@@ -144,7 +144,7 @@ method_get(PyObject self, PyObject obj, PyObject *type)`
`144`	`144`	`return NULL;`
`145`	`145`	`}`
`146`	`146`	`if (descr->d_method->ml_flags & METH_METHOD) {`
`147`		`- if (PyType_Check(type)) {`
	`147`	`+ if (type == NULL \|\| PyType_Check(type)) {`
`148`	`148`	`return PyCMethod_New(descr->d_method, obj, NULL, descr->d_common.d_type);`
`149`	`149`	`} else {`
`150`	`150`	`PyErr_Format(PyExc_TypeError,`