do safety checks on __qualname__ assignment

Lib/test/test_descr.py

@@ -4502,6 +4502,14 @@ order (MRO) for bases """
         self.assertEqual(float.real.__qualname__, 'float.real')
         self.assertEqual(int.__add__.__qualname__, 'int.__add__')
 
+        class X:
+            pass
+        with self.assertRaises(TypeError):
+            del X.__qualname__
+
+        self.assertRaises(TypeError, type.__dict__['__qualname__'].__set__,
+                          str, 'Oink')
+
     def test_qualname_dict(self):
         ns = {'__qualname__': 'some.name'}
         tp = type('Foo', (), ns)

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.3.1?
 Core and Builtins
 -----------------
 
+- Fix segfaults on setting __qualname__ on builtin types and attempting to
+  delete it on any type.
+
 - Issue #16271: Fix strange bugs that resulted from __qualname__ appearing in a
   class's __dict__ and on type.
 

Objects/typeobject.c

@@ -311,6 +311,8 @@ type_set_qualname(PyTypeObject *type, PyObject *value, void *context)
 {
     PyHeapTypeObject* et;
 
+    if (!check_set_special_type_attr(type, value, "__qualname__"))
+        return -1;
     if (!PyUnicode_Check(value)) {
         PyErr_Format(PyExc_TypeError,
                      "can only assign string to %s.__qualname__, not '%s'",