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gh-155452: Prevent recursion crash in dir() #155453

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9b0b726
gh-155452: Prevent recursion crash in dir()
BHUVANSH855 Aug 9, 2026
5308d8c
gh-155452: Skip dir recursion test on limited stacks
BHUVANSH855 Aug 10, 2026
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16 changes: 16 additions & 0 deletions Lib/test/test_builtin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -755,6 +755,22 @@ def __dir__(self):
# test that object has a __dir__()
self.assertEqual(sorted([].__dir__()), dir([]))

@support.skip_emscripten_stack_overflow()
@support.skip_wasi_stack_overflow()
def test_dir_cyclic_bases(self):
class Fake:
pass

a = Fake()
a.__bases__ = (a,)

class C:
@property
def __class__(self):
return a

self.assertRaises(RecursionError, dir, C())

def test___ne__(self):
self.assertFalse(None.__ne__(None))
self.assertIs(None.__ne__(0), NotImplemented)
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-08-09-21-24-08.gh-issue-155452.4mUzjM.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a crash in :func:`dir` when an object's ``__class__`` has cyclic
``__bases__``.
34 changes: 20 additions & 14 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
#include "Python.h"
#include "pycore_abstract.h" // _PySequence_IterSearch()
#include "pycore_call.h" // _PyObject_VectorcallTstate()
#include "pycore_ceval.h" // _Py_EnterRecursiveCall()
#include "pycore_code.h" // CO_FAST_FREE
#include "pycore_descrobject.h" // _PyMember_GetOffset()
#include "pycore_dict.h" // _PyDict_KeysSize()
Expand Down Expand Up @@ -6949,22 +6950,27 @@ merge_class_dict(PyObject *dict, PyObject *aclass)
Py_DECREF(bases);
return -1;
}
else {

@skirpichev skirpichev Aug 9, 2026

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You can reduce patch, leaving "else" branch. Just add _Py_EnterRecursiveCall/_Py_LeaveRecursiveCall calls.

for (i = 0; i < n; i++) {
int status;
PyObject *base = PySequence_GetItem(bases, i);
if (base == NULL) {
Py_DECREF(bases);
return -1;
}
status = merge_class_dict(dict, base);
Py_DECREF(base);
if (status < 0) {
Py_DECREF(bases);
return -1;
}
if (_Py_EnterRecursiveCall(" in __bases__")) {
Py_DECREF(bases);
return -1;
}
for (i = 0; i < n; i++) {
int status;
PyObject *base = PySequence_GetItem(bases, i);
if (base == NULL) {
_Py_LeaveRecursiveCall();
Py_DECREF(bases);
return -1;
}
status = merge_class_dict(dict, base);
Py_DECREF(base);
if (status < 0) {
_Py_LeaveRecursiveCall();
Py_DECREF(bases);
return -1;
}
}
_Py_LeaveRecursiveCall();
Py_DECREF(bases);
}
return 0;
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