[3.12] gh-105375: Harden pyexpat initialisation (#105606) (#105669)

erlend-aasland · web-flow · commit d310fc776ee4 · 2023-06-11T21:35:13.000Z
(cherry picked from commit 20a56d8) Add proper error handling to add_errors_module() to prevent exceptions from possibly being overwritten.
diff --git a/Misc/NEWS.d/next/Library/2023-06-09-23-00-13.gh-issue-105605.YuwqxY.rst b/Misc/NEWS.d/next/Library/2023-06-09-23-00-13.gh-issue-105605.YuwqxY.rst
@@ -0,0 +1,3 @@
+Harden :mod:`pyexpat` error handling during module initialisation to prevent
+exceptions from possibly being overwritten, and objects from being
+dereferenced twice.
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
@@ -1775,14 +1775,18 @@ add_error(PyObject *errors_module, PyObject *codes_dict,
 static int
 add_errors_module(PyObject *mod)
 {
+    // add_submodule() returns a borrowed ref.
     PyObject *errors_module = add_submodule(mod, MODULE_NAME ".errors");
     if (errors_module == NULL) {
         return -1;
     }
 
     PyObject *codes_dict = PyDict_New();
+    if (codes_dict == NULL) {
+        return -1;
+    }
     PyObject *rev_codes_dict = PyDict_New();
-    if (codes_dict == NULL || rev_codes_dict == NULL) {
+    if (rev_codes_dict == NULL) {
         goto error;
     }
 
@@ -1803,17 +1807,17 @@ add_errors_module(PyObject *mod)
         goto error;
     }
 
-    if (PyModule_AddObject(errors_module, "codes", Py_NewRef(codes_dict)) < 0) {
-        Py_DECREF(codes_dict);
+    int rc = PyModule_AddObjectRef(errors_module, "codes", codes_dict);
+    Py_CLEAR(codes_dict);
+    if (rc < 0) {
         goto error;
     }
-    Py_CLEAR(codes_dict);
 
-    if (PyModule_AddObject(errors_module, "messages", Py_NewRef(rev_codes_dict)) < 0) {
-        Py_DECREF(rev_codes_dict);
+    rc = PyModule_AddObjectRef(errors_module, "messages", rev_codes_dict);
+    Py_CLEAR(rev_codes_dict);
+    if (rc < 0) {
         goto error;
     }
-    Py_CLEAR(rev_codes_dict);
 
     return 0;
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Harden :mod:`pyexpat` error handling during module initialisation to prevent
	`2`	`+exceptions from possibly being overwritten, and objects from being`
	`3`	`+dereferenced twice.`