bpo-46347: Fix PyEval_EvalCodeEx to correctly cleanup in error paths (#30553)

Author: 1st1

Python/ceval.c

@@ -5090,7 +5090,7 @@ PyEval_EvalCodeEx(PyObject *_co, PyObject *globals, PyObject *locals,
                   PyObject *kwdefs, PyObject *closure)
 {
     PyThreadState *tstate = _PyThreadState_GET();
-    PyObject *res;
+    PyObject *res = NULL;
     PyObject *defaults = _PyTuple_FromArray(defs, defcount);
     if (defaults == NULL) {
         return NULL;
@@ -5103,23 +5103,19 @@ PyEval_EvalCodeEx(PyObject *_co, PyObject *globals, PyObject *locals,
     if (locals == NULL) {
         locals = globals;
     }
-    PyObject *kwnames;
+    PyObject *kwnames = NULL;
     PyObject *const *allargs;
-    PyObject **newargs;
+    PyObject **newargs = NULL;
     if (kwcount == 0) {
         allargs = args;
-        kwnames = NULL;
     }
     else {
         kwnames = PyTuple_New(kwcount);
         if (kwnames == NULL) {
-            res = NULL;
             goto fail;
         }
         newargs = PyMem_Malloc(sizeof(PyObject *)*(kwcount+argcount));
         if (newargs == NULL) {
-            res = NULL;
-            Py_DECREF(kwnames);
             goto fail;
         }
         for (int i = 0; i < argcount; i++) {
@@ -5149,11 +5145,9 @@ PyEval_EvalCodeEx(PyObject *_co, PyObject *globals, PyObject *locals,
     res = _PyEval_Vector(tstate, &constr, locals,
                          allargs, argcount,
                          kwnames);
-    if (kwcount) {
-        Py_DECREF(kwnames);
-        PyMem_Free(newargs);
-    }
 fail:
+    Py_XDECREF(kwnames);
+    PyMem_Free(newargs);
     Py_DECREF(defaults);
     return res;
 }