properly handle malloc failure (closes #24044)

Patch by Christian Heimes.

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.2.7?
 Core and Builtins
 -----------------
 
+- Issue #24044: Fix possible null pointer dereference in list.sort in out of
+  memory conditions.
+
 - Issue #23055: Fixed a buffer overflow in PyUnicode_FromFormatV.  Analysis
   and fix by Guido Vranken.
 

Objects/listobject.c

@@ -1924,8 +1924,10 @@ listsort(PyListObject *self, PyObject *args, PyObject *kwds)
             keys = &ms.temparray[saved_ob_size+1];
         else {
             keys = PyMem_MALLOC(sizeof(PyObject *) * saved_ob_size);
-            if (keys == NULL)
-                return NULL;
+            if (keys == NULL) {
+                PyErr_NoMemory();
+                goto keyfunc_fail;
+            }
         }
 
         for (i = 0; i < saved_ob_size ; i++) {