bpo-41909: Enable previously disabled recursion checks. (GH-22536)
Enable recursion checks which were disabled when get __bases__ of non-type objects in issubclass() and isinstance() and when intern strings. It fixes a stack overflow when getting __bases__ leads to infinite recursion. Originally recursion checks was disabled for PyDict_GetItem() which silences all errors including the one raised in case of detected recursion and can return incorrect result. But now the code uses PyDict_GetItemWithError() and PyDict_SetDefault() instead.
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@ -303,6 +303,16 @@ class TestIsInstanceIsSubclass(unittest.TestCase):
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self.assertEqual(True, issubclass(B(), int))
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def test_infinite_recursion_in_bases(self):
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class X:
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@property
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def __bases__(self):
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return self.__bases__
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self.assertRaises(RecursionError, issubclass, X(), int)
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self.assertRaises(RecursionError, issubclass, int, X())
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self.assertRaises(RecursionError, isinstance, 1, X())
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def blowstack(fxn, arg, compare_to):
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# Make sure that calling isinstance with a deeply nested tuple for its
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@ -0,0 +1,2 @@
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Fixed stack overflow in :func:`issubclass` and :func:`isinstance` when
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getting the ``__bases__`` attribute leads to infinite recursion.
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@ -2336,9 +2336,7 @@ abstract_get_bases(PyObject *cls)
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_Py_IDENTIFIER(__bases__);
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PyObject *bases;
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Py_ALLOW_RECURSION
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(void)_PyObject_LookupAttrId(cls, &PyId___bases__, &bases);
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Py_END_ALLOW_RECURSION
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if (bases != NULL && !PyTuple_Check(bases)) {
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Py_DECREF(bases);
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return NULL;
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@ -15734,9 +15734,7 @@ PyUnicode_InternInPlace(PyObject **p)
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}
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PyObject *t;
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Py_ALLOW_RECURSION
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t = PyDict_SetDefault(interned, s, s);
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Py_END_ALLOW_RECURSION
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if (t == NULL) {
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PyErr_Clear();
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