Issue #18408: Fix PyErr_NormalizeException(), handle PyObject_IsSubclass() failure

PyObject_IsSubclass() can fail and raise a new exception!

1 files changed, 10 insertions, 1 deletions

diff --git a/Python/errors.c b/Python/errors.c
index 34445b65ea..53dd9a9650 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -227,12 +227,21 @@ PyErr_NormalizeException(PyObject **exc, PyObject **val, PyObject **tb)
        value will be an instance.
     */
     if (PyExceptionClass_Check(type)) {
+        int is_subclass;
+        if (inclass) {
+            is_subclass = PyObject_IsSubclass(inclass, type);
+            if (is_subclass < 0)
+                goto finally;
+        }
+        else
+            is_subclass = 0;
+
         /* if the value was not an instance, or is not an instance
            whose class is (or is derived from) type, then use the
            value as an argument to instantiation of the type
            class.
         */
-        if (!inclass || !PyObject_IsSubclass(inclass, type)) {
+        if (!inclass || !is_subclass) {
             PyObject *args, *res;
 
             if (value == Py_None)