gh-128049: Fix type confusion bug with the return value of a custom ExceptionGroup split function (#128079)

1 files changed, 19 insertions, 2 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 3cf11b6..e92a11b 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2134,8 +2134,25 @@ _PyEval_ExceptionGroupMatch(PyObject* exc_value, PyObject *match_type,
         if (pair == NULL) {
             return -1;
         }
-        assert(PyTuple_CheckExact(pair));
-        assert(PyTuple_GET_SIZE(pair) == 2);
+
+        if (!PyTuple_CheckExact(pair)) {
+            PyErr_Format(PyExc_TypeError,
+                         "%.200s.split must return a tuple, not %.200s",
+                         Py_TYPE(exc_value)->tp_name, Py_TYPE(pair)->tp_name);
+            Py_DECREF(pair);
+            return -1;
+        }
+
+        // allow tuples of length > 2 for backwards compatibility
+        if (PyTuple_GET_SIZE(pair) < 2) {
+            PyErr_Format(PyExc_TypeError,
+                         "%.200s.split must return a 2-tuple, "
+                         "got tuple of size %zd",
+                         Py_TYPE(exc_value)->tp_name, PyTuple_GET_SIZE(pair));
+            Py_DECREF(pair);
+            return -1;
+        }
+
         *match = Py_NewRef(PyTuple_GET_ITEM(pair, 0));
         *rest = Py_NewRef(PyTuple_GET_ITEM(pair, 1));
         Py_DECREF(pair);