Issue #5939: Add additional runtime checking to ensure a valid capsule

in Modules/_ctypes/callproc.c.  Reviewed by Benjamin P.  My first commit!

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.2 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #5939: Add additional runtime checking to ensure a valid capsule
+  in Modules/_ctypes/callproc.c.
+
 - Issue #7309: Fix unchecked attribute access when converting
   UnicodeEncodeError, UnicodeDecodeError, and UnicodeTranslateError to
   strings.

Modules/_ctypes/callproc.c

@@ -139,8 +139,14 @@ _ctypes_get_errobj(int **pspace)
 			return NULL;
 	}
 	errobj = PyDict_GetItem(dict, error_object_name);
-	if (errobj)
+	if (errobj) {
+		if (!PyCapsule_IsValid(errobj, CTYPES_CAPSULE_NAME_PYMEM)) {
+			PyErr_SetString(PyExc_RuntimeError,
+				"ctypes.error_object is an invalid capsule");
+			return NULL;
+		}
 		Py_INCREF(errobj);
+	}
 	else {
 		void *space = PyMem_Malloc(sizeof(int) * 2);
 		if (space == NULL)