Preventing the use of a null pointer in mro_hierarchy

[smurav]

In some cases type->tp_mro can be NULL and the new_mro variable can get a null value from the lookup_tp_mro call in the mro_hierarchy function.

cpython/Objects/typeobject.c

Line 1654 in 5f50541

PyObject *new_mro = lookup_tp_mro(type);

In this case, there may be problems with calling the Py_NewRef and the Py_DECREF functions.

cpython/Objects/typeobject.c

Line 1658 in 5f50541

tuple = PyTuple_Pack(3, type, new_mro, old_mro);

cpython/Objects/typeobject.c

Line 1661 in 5f50541

tuple = PyTuple_Pack(2, type, new_mro);

cpython/Objects/typeobject.c

Line 1674 in 5f50541

Py_DECREF(new_mro);

Linked PRs

• gh-132835: Fix using a null pointer in mro_hierarchy #132836