ctypes callback functions only support 'fundamental' result types.

Check this and raise an error when something else is used - before
this change ctypes would hang or crash when such a callback was
called.  This is a partial fix for #1574584.

Will backport to release25-maint.

Lib/ctypes/test/test_callbacks.py

@@ -101,6 +101,19 @@ class Callbacks(unittest.TestCase):
             after = grc(o)
             self.failUnlessEqual((after, o), (before, o))
 
+    def test_unsupported_restype_1(self):
+        # Only "fundamental" result types are supported for callback
+        # functions, the type must have a non-NULL stgdict->setfunc.
+        # POINTER(c_double), for example, is not supported.
+
+        prototype = self.functype.im_func(POINTER(c_double))
+        # The type is checked when the prototype is called
+        self.assertRaises(TypeError, prototype, lambda: None)
+
+    def test_unsupported_restype_2(self):
+        prototype = self.functype.im_func(object)
+        self.assertRaises(TypeError, prototype, lambda: None)
+
 try:
     WINFUNCTYPE
 except NameError:

Misc/NEWS

@@ -81,6 +81,10 @@ Core and builtins
 Library
 -------
 
+- ctypes callback functions only support 'fundamental' data types as
+  result type.  Raise an error when something else is used.  This is a
+  partial fix for Bug #1574584.
+
 - Fix turtle so that time.sleep is imported for the entire library.  Allows
   the demo2 function to be executed on its own instead of only when the
   module is run as a script.

Modules/_ctypes/callbacks.c

@@ -293,8 +293,11 @@ ffi_info *AllocFunctionCallback(PyObject *callable,
 		p->restype = &ffi_type_void;
 	} else {
 		StgDictObject *dict = PyType_stgdict(restype);
-		if (dict == NULL)
-			goto error;
+		if (dict == NULL || dict->setfunc == NULL) {
+		  PyErr_SetString(PyExc_TypeError,
+				  "invalid result type for callback function");
+		  goto error;
+		}
 		p->setfunc = dict->setfunc;
 		p->restype = &dict->ffi_type_pointer;
 	}