gh-101765: Fix SystemError / segmentation fault in iter `__reduce__` when internal access of `builtins.__dict__` exhausts the iterator (#101769)

1 files changed, 8 insertions, 3 deletions

diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index ba2c2e978c..657443f31f 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -3169,11 +3169,16 @@ PyDoc_STRVAR(length_hint_doc,
 static PyObject *
 striter_reduce(striterobject *it, PyObject *Py_UNUSED(ignored))
 {
+    PyObject *iter = _PyEval_GetBuiltin(&_Py_ID(iter));
+
+    /* _PyEval_GetBuiltin can invoke arbitrary code,
+     * call must be before access of iterator pointers.
+     * see issue #101765 */
+
     if (it->it_seq != NULL) {
-        return Py_BuildValue("N(O)n", _PyEval_GetBuiltin(&_Py_ID(iter)),
-                             it->it_seq, it->it_index);
+        return Py_BuildValue("N(O)n", iter, it->it_seq, it->it_index);
     } else {
-        return Py_BuildValue("N(())", _PyEval_GetBuiltin(&_Py_ID(iter)));
+        return Py_BuildValue("N(())", iter);
     }
 }