#3643 add more checks to _testcapi to prevent segfaults

Author: Victor Stinner
Reviewer: Benjamin Peterson

Misc/NEWS

@@ -17,6 +17,12 @@ Core and Builtins
 Library
 -------
 
+Extension Modules
+-----------------
+
+- Issue #3643: Added a few more checks to _testcapi to prevent segfaults by
+  exploitation of poor argument checking.
+
 
 What's new in Python 3.0b3?
 ===========================

Modules/_testcapimodule.c

@@ -961,6 +961,10 @@ exception_print(PyObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "O:exception_print",
 				&value))
 		return NULL;
+	if (!PyExceptionInstance_Check(value)) {
+		PyErr_Format(PyExc_TypeError, "an exception instance is required");
+		return NULL;
+	}
 
 	tb = PyException_GetTraceback(value);
 	PyErr_Display((PyObject *) Py_TYPE(value), value, tb);