Raise an error instead of crashing with a segfault when a NULL

function pointer is called.

Will backport to release25-maint.

Lib/ctypes/test/test_funcptr.py

@@ -123,5 +123,11 @@ class CFuncPtrTestCase(unittest.TestCase):
         self.failUnlessEqual(strtok(None, "\n"), "c")
         self.failUnlessEqual(strtok(None, "\n"), None)
 
+    def test_NULL_funcptr(self):
+        tp = CFUNCTYPE(c_int)
+        func = tp() # NULL function pointer
+        # raise a ValueError when we try to call it
+        self.assertRaises(ValueError, func)
+
 if __name__ == '__main__':
     unittest.main()

Modules/_ctypes/_ctypes.c

@@ -3312,6 +3312,11 @@ CFuncPtr_call(CFuncPtrObject *self, PyObject *inargs, PyObject *kwds)
 
 
 	pProc = *(void **)self->b_ptr;
+	if (pProc == NULL) {
+		PyErr_SetString(PyExc_ValueError,
+				"attempt to call NULL function pointer");
+		return NULL;
+	}
 #ifdef MS_WIN32
 	if (self->index) {
 		/* It's a COM method */