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[3.14] gh-132835: Add defensive NULL checks to MRO resolution (GH-134763) #140436

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Merged
merged 1 commit into from
Oct 22, 2025
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[3.14] gh-132835: Add defensive NULL checks to MRO resolution (GH-134763) #140436

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14 changes: 10 additions & 4 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1658,7 +1658,7 @@ static int recurse_down_subclasses(PyTypeObject *type, PyObject *name,
update_callback callback, void *data);

static int
mro_hierarchy(PyTypeObject *type, PyObject *temp)
mro_hierarchy_for_complete_type(PyTypeObject *type, PyObject *temp)
{
ASSERT_TYPE_LOCK_HELD();

Expand All @@ -1669,6 +1669,7 @@ mro_hierarchy(PyTypeObject *type, PyObject *temp)
return res;
}
PyObject *new_mro = lookup_tp_mro(type);
assert(new_mro != NULL);

PyObject *tuple;
if (old_mro != NULL) {
Expand Down Expand Up @@ -1713,7 +1714,7 @@ mro_hierarchy(PyTypeObject *type, PyObject *temp)
Py_ssize_t n = PyList_GET_SIZE(subclasses);
for (Py_ssize_t i = 0; i < n; i++) {
PyTypeObject *subclass = _PyType_CAST(PyList_GET_ITEM(subclasses, i));
res = mro_hierarchy(subclass, temp);
res = mro_hierarchy_for_complete_type(subclass, temp);
if (res < 0) {
break;
}
Expand Down Expand Up @@ -1795,7 +1796,7 @@ type_set_bases_unlocked(PyTypeObject *type, PyObject *new_bases)
if (temp == NULL) {
goto bail;
}
if (mro_hierarchy(type, temp) < 0) {
if (mro_hierarchy_for_complete_type(type, temp) < 0) {
goto undo;
}
Py_DECREF(temp);
Expand Down Expand Up @@ -3291,6 +3292,7 @@ mro_implementation_unlocked(PyTypeObject *type)
*/
PyTypeObject *base = _PyType_CAST(PyTuple_GET_ITEM(bases, 0));
PyObject *base_mro = lookup_tp_mro(base);
assert(base_mro != NULL);
Py_ssize_t k = PyTuple_GET_SIZE(base_mro);
PyObject *result = PyTuple_New(k + 1);
if (result == NULL) {
Expand Down Expand Up @@ -3325,9 +3327,12 @@ mro_implementation_unlocked(PyTypeObject *type)
return NULL;
}

PyObject *mro_to_merge;
for (Py_ssize_t i = 0; i < n; i++) {
PyTypeObject *base = _PyType_CAST(PyTuple_GET_ITEM(bases, i));
to_merge[i] = lookup_tp_mro(base);
mro_to_merge = lookup_tp_mro(base);
assert(mro_to_merge != NULL);
to_merge[i] = mro_to_merge;
}
to_merge[n] = bases;

Expand Down Expand Up @@ -8623,6 +8628,7 @@ type_ready_inherit(PyTypeObject *type)

// Inherit slots
PyObject *mro = lookup_tp_mro(type);
assert(mro != NULL);
Py_ssize_t n = PyTuple_GET_SIZE(mro);
for (Py_ssize_t i = 1; i < n; i++) {
PyObject *b = PyTuple_GET_ITEM(mro, i);
Expand Down
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