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bpo-30570: fix an issubclass infinite recursion crash #29017

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bpo-30570: fix an issubclass infinite recursion crash #29017

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8 changes: 8 additions & 0 deletions Lib/test/test_isinstance.py
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,14 @@ def __bases__(self):
self.assertRaises(RecursionError, issubclass, int, X())
self.assertRaises(RecursionError, isinstance, 1, X())

def test_infinite_recursion_via_bases_tuple(self):
"""Regression test for bpo-30570."""
class Failure(object):
def __getattr__(self, attr):
return (self, None)

self.assertFalse(issubclass(Failure(), int))


def blowstack(fxn, arg, compare_to):
# Make sure that calling isinstance with a deeply nested tuple for its
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37 changes: 35 additions & 2 deletions Objects/abstract.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2525,7 +2525,8 @@ abstract_get_bases(PyObject *cls)


static int
abstract_issubclass(PyObject *derived, PyObject *cls)
_abstract_issubclass_inner(PyObject *derived, PyObject *cls,
PyObject* visited_set)
{
PyObject *bases = NULL;
Py_ssize_t i, n;
Expand Down Expand Up @@ -2558,7 +2559,24 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
continue;
}
for (i = 0; i < n; i++) {
r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
PyObject *borrowed_base = PyTuple_GET_ITEM(bases, i);
PyObject *visitor = PyLong_FromVoidPtr(borrowed_base);
if (visitor == NULL) {
Py_DECREF(bases);
return -1;
}
if (PySet_Contains(visited_set, visitor)) {
Py_DECREF(visitor);
continue;
}
if (PySet_Add(visited_set, visitor) < 0) {
Py_DECREF(visitor);
Py_DECREF(bases);
return -1;
}
Py_DECREF(visitor); // PySet_Add does its own INCREF.
r = _abstract_issubclass_inner(
borrowed_base, cls, visited_set);
if (r != 0)
break;
}
Expand All @@ -2567,6 +2585,21 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
}
}

static int
abstract_issubclass(PyObject *derived, PyObject *cls)
{
int result;
/* I would much rather use a C++ hash_map but we're stuck in C so
* we'll use our own high overhead for the purpose data structure. */
PyObject *visited_set = PySet_New(NULL);
if (visited_set == NULL) {
return -1;
}
result = _abstract_issubclass_inner(derived, cls, visited_set);
Py_DECREF(visited_set);
return result;
}

static int
check_class(PyObject *cls, const char *error)
{
Expand Down