From 7403e91630456ae2a495ac7621c2152d9a270400 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Sun, 26 Apr 2015 18:46:40 +0200
Subject: [PATCH] Issue #23996: Avoid a crash when a delegated generator raises
 an unnormalized StopIteration exception.  Patch by Stefan Behnel.

---
 Misc/NEWS           |  3 +++
 Objects/genobject.c | 27 ++++++++++++++++++++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/Misc/NEWS b/Misc/NEWS
index 2616bf7d932..e84e142857d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #23996: Avoid a crash when a delegated generator raises an
+  unnormalized StopIteration exception.  Patch by Stefan Behnel.
+
 - Issue #24022: Fix tokenizer crash when processing undecodable source code.
 
 - Issue #23309: Avoid a deadlock at shutdown if a daemon thread is aborted
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 08d30bf4b7b..f125847bd79 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -396,13 +396,30 @@ _PyGen_FetchStopIterationValue(PyObject **pvalue) {
 
     if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
         PyErr_Fetch(&et, &ev, &tb);
+        if (ev) {
+            /* exception will usually be normalised already */
+            if (Py_TYPE(ev) == (PyTypeObject *) et
+                || PyObject_IsInstance(ev, PyExc_StopIteration)) {
+                value = ((PyStopIterationObject *)ev)->value;
+                Py_INCREF(value);
+                Py_DECREF(ev);
+            } else if (et == PyExc_StopIteration) {
+                /* avoid normalisation and take ev as value */
+                value = ev;
+            } else {
+                /* normalisation required */
+                PyErr_NormalizeException(&et, &ev, &tb);
+                if (!PyObject_IsInstance(ev, PyExc_StopIteration)) {
+                    PyErr_Restore(et, ev, tb);
+                    return -1;
+                }
+                value = ((PyStopIterationObject *)ev)->value;
+                Py_INCREF(value);
+                Py_DECREF(ev);
+            }
+        }
         Py_XDECREF(et);
         Py_XDECREF(tb);
-        if (ev) {
-            value = ((PyStopIterationObject *)ev)->value;
-            Py_INCREF(value);
-            Py_DECREF(ev);
-        }
     } else if (PyErr_Occurred()) {
         return -1;
     }