From f5452aff708ae9010a4d4efaa36307c61402fda1 Mon Sep 17 00:00:00 2001
From: MonocleAI <54963236+monocle-ai@users.noreply.github.com>
Date: Wed, 14 Oct 2020 06:58:26 -0700
Subject: [PATCH 1/3] Fixed unchecked return in Objects/typeobject.c

Unchecked return in Objects/typeobject.c and possible uninitialized variables in cls and new_mro
---
 Objects/typeobject.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 3bb2c338fe0b530..d0bbe40722824a1 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -823,8 +823,10 @@ type_set_bases(PyTypeObject *type, PyObject *new_bases, void *context)
         PyTypeObject *cls;
         PyObject *new_mro, *old_mro = NULL;
 
-        PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
-                          "", 2, 3, &cls, &new_mro, &old_mro);
+        if(!PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
+                          "", 2, 3, &cls, &new_mro, &old_mro)) {
+           return NULL;
+        }
         /* Do not rollback if cls has a newer version of MRO.  */
         if (cls->tp_mro == new_mro) {
             Py_XINCREF(old_mro);

From 0a13d68e339efc2265211b634a2e0856d11838f8 Mon Sep 17 00:00:00 2001
From: MonocleAI <54963236+monocle-ai@users.noreply.github.com>
Date: Thu, 15 Oct 2020 06:22:35 -0700
Subject: [PATCH 2/3] Update typeobject.c

Removed return to call cleanup on temp in all the cases
---
 Objects/typeobject.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index d0bbe40722824a1..dab57147cf28956 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -823,16 +823,15 @@ type_set_bases(PyTypeObject *type, PyObject *new_bases, void *context)
         PyTypeObject *cls;
         PyObject *new_mro, *old_mro = NULL;
 
-        if(!PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
+        if(PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
                           "", 2, 3, &cls, &new_mro, &old_mro)) {
-           return NULL;
-        }
-        /* Do not rollback if cls has a newer version of MRO.  */
-        if (cls->tp_mro == new_mro) {
-            Py_XINCREF(old_mro);
-            cls->tp_mro = old_mro;
-            Py_DECREF(new_mro);
-        }
+           /* Do not rollback if cls has a newer version of MRO.  */
+           if (cls->tp_mro == new_mro) {
+               Py_XINCREF(old_mro);
+               cls->tp_mro = old_mro;
+               Py_DECREF(new_mro);
+           }
+        } 
     }
     Py_DECREF(temp);
 

From a196e6a12f923ebd2fefe0f3950c7205a2f3c0f3 Mon Sep 17 00:00:00 2001
From: MonocleAI <54963236+monocle-ai@users.noreply.github.com>
Date: Thu, 15 Oct 2020 06:29:16 -0700
Subject: [PATCH 3/3] Create 2020-10-15-06-28-50.bpo-42034.MonocleAI.rst

---
 .../next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst     | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst

diff --git a/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst b/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst
new file mode 100644
index 000000000000000..f78f1b2b1a5a140
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst
@@ -0,0 +1 @@
+Fix unchecked return in Objects/typeobject.c. The return value of a function that is potentially used to initialize a local variable is not checked. Therefore, reading the local variable may result in undefined behavior.