gh-78878: Fix crash when creating an instance of _ctypes.CField

Lib/test/test_ctypes/test_struct_fields.py

@@ -54,6 +54,12 @@ class X(Structure):
  x.char = b'a\0b\0'
  self.assertEqual(bytes(x), b'a\x00###')
 
+ def test_6(self):
+ class X(Structure):
+ _fields_ = [("x", c_int)]
+ CField = type(X.x)
+ self.assertRaises(TypeError, CField)
+
  def test_gh99275(self):
  class BrokenStructure(Structure):
  def __init_subclass__(cls, **kwargs):

Misc/NEWS.d/next/Core and Builtins/2022-12-18-19-07-29.gh-issue-78878.00QOp1.rst

@@ -0,0 +1 @@
+Remove the ``PyCField_new`` which user cannot call it directly.

Modules/_ctypes/cfield.c

@@ -30,13 +30,6 @@ static void pymem_destructor(PyObject *ptr)
 /*
  PyCField_Type
 */
-static PyObject *
-PyCField_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
-{
- CFieldObject *obj;
- obj = (CFieldObject *)type->tp_alloc(type, 0);
- return (PyObject *)obj;
-}
 
 /*
  * Expects the size, index and offset for the current field in *psize and
@@ -68,7 +61,7 @@ PyCField_FromDesc(PyObject *desc, Py_ssize_t index,
 #define CONT_BITFIELD 2
 #define EXPAND_BITFIELD 3
 
- self = (CFieldObject *)_PyObject_CallNoArgs((PyObject *)&PyCField_Type);
+ self = (CFieldObject *)PyCField_Type.tp_alloc((PyTypeObject *)&PyCField_Type, 0);
  if (self == NULL)
  return NULL;
  dict = PyType_stgdict(desc);
@@ -341,7 +334,7 @@ PyTypeObject PyCField_Type = {
  0, /* tp_dictoffset */
  0, /* tp_init */
  0, /* tp_alloc */
- PyCField_new, /* tp_new */
+ 0,  /* tp_new */
  0, /* tp_free */
 };
 

Modules/_ctypes/stgdict.c

@@ -257,7 +257,7 @@ MakeFields(PyObject *type, CFieldObject *descr,
  }
  continue;
  }
- new_descr = (CFieldObject *)_PyObject_CallNoArgs((PyObject *)&PyCField_Type);
+ new_descr = (CFieldObject *)PyCField_Type.tp_alloc((PyTypeObject *)&PyCField_Type, 0);
  if (new_descr == NULL) {
  Py_DECREF(fdescr);
  Py_DECREF(fieldlist);