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[3.12] gh-123083: Fix a potential use-after-free in ``STORE_ATTR_WITH… #123237

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Merged
merged 1 commit into from
Aug 22, 2024
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[3.12] gh-123083: Fix a potential use-after-free in ``STORE_ATTR_WITH… #123237

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18 changes: 18 additions & 0 deletions Lib/test/test_dict.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1476,6 +1476,24 @@ def test_dict_items_result_gc_reversed(self):
gc.collect()
self.assertTrue(gc.is_tracked(next(it)))

def test_store_evilattr(self):
class EvilAttr:
def __init__(self, d):
self.d = d

def __del__(self):
if 'attr' in self.d:
del self.d['attr']
gc.collect()

class Obj:
pass

obj = Obj()
obj.__dict__ = {}
for _ in range(10):
obj.attr = EvilAttr(obj.__dict__)

def test_str_nonstr(self):
# cpython uses a different lookup function if the dict only contains
# `str` keys. Make sure the unoptimized path is used when a non-`str`
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2024-08-17-17-26-25.gh-issue-123083.9xWLJ-.rst
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@@ -0,0 +1 @@
Fix a potential use-after-free in ``STORE_ATTR_WITH_HINT``.
9 changes: 5 additions & 4 deletions Python/bytecodes.c
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Expand Up @@ -1999,14 +1999,15 @@ dummy_func(
new_version = _PyDict_NotifyEvent(tstate->interp, PyDict_EVENT_MODIFIED, dict, name, value);
ep->me_value = value;
}
Py_DECREF(old_value);
STAT_INC(STORE_ATTR, hit);
/* Ensure dict is GC tracked if it needs to be */
if (!_PyObject_GC_IS_TRACKED(dict) && _PyObject_GC_MAY_BE_TRACKED(value)) {
_PyObject_GC_TRACK(dict);
}
/* PEP 509 */
dict->ma_version_tag = new_version;
dict->ma_version_tag = new_version; // PEP 509
// old_value should be DECREFed after GC track checking is done, if not, it could raise a segmentation fault,
// when dict only holds the strong reference to value in ep->me_value.
Py_DECREF(old_value);
STAT_INC(STORE_ATTR, hit);
Py_DECREF(owner);
}

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