PYTHON-5571 - Fix memory leak when raising InvalidDocument with C extensions

Author: NoahStapp

bson/_cbsonmodule.c

@@ -1657,10 +1657,10 @@ void handle_invalid_doc_error(PyObject* dict) {
     }
 
     if (evalue && PyErr_GivenExceptionMatches(etype, InvalidDocument)) {
-        PyObject *msg = PyObject_Str(evalue);
+        msg = PyObject_Str(evalue);
         if (msg) {
             // Prepend doc to the existing message
-            PyObject *dict_str = PyObject_Str(dict);
+            dict_str = PyObject_Str(dict);
             if (dict_str == NULL) {
                 goto cleanup;
             }
@@ -1672,15 +1672,17 @@ void handle_invalid_doc_error(PyObject* dict) {
             if (msg_utf8 == NULL) {
                 goto cleanup;
             }
-            PyObject *new_msg = PyUnicode_FromFormat("Invalid document %s | %s", dict_str_utf8, msg_utf8);
+            new_msg = PyUnicode_FromFormat("Invalid document %s | %s", dict_str_utf8, msg_utf8);
             Py_DECREF(evalue);
             Py_DECREF(etype);
             etype = InvalidDocument;
             InvalidDocument = NULL;
             if (new_msg) {
                 evalue = new_msg;
+                new_msg = NULL;
             } else {
                 evalue = msg;
+                msg = NULL;
             }
         }
         PyErr_NormalizeException(&etype, &evalue, &etrace);