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gh-123083: Fix a potential use-after-free in STORE_ATTR_WITH_HINT #123092

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Merged
merged 4 commits into from
Aug 22, 2024
Merged

gh-123083: Fix a potential use-after-free in STORE_ATTR_WITH_HINT #123092

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c732019
gh-123083: Fix STORE_ATTR_WITH_HINT has potential use-after-free
corona10 Aug 17, 2024
59ea4f2
Address code review
corona10 Aug 20, 2024
4237506
Address code review
corona10 Aug 20, 2024
2603cb4
Merge remote-tracking branch 'upstream/main' into gh-123083
corona10 Aug 21, 2024
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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):
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I am not sure that this is the proper place.

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``.
2 changes: 2 additions & 0 deletions Objects/dictobject.c
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Expand Up @@ -1703,6 +1703,8 @@ insert_split_value(PyInterpreterState *interp, PyDictObject *mp, PyObject *key,
uint64_t new_version = _PyDict_NotifyEvent(interp, PyDict_EVENT_MODIFIED, mp, key, value);
STORE_SPLIT_VALUE(mp, ix, Py_NewRef(value));
mp->ma_version_tag = new_version;
// 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);
}
ASSERT_CONSISTENT(mp);
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13 changes: 7 additions & 6 deletions Python/bytecodes.c
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Expand Up @@ -2233,18 +2233,19 @@ dummy_func(
DEOPT_IF(!DK_IS_UNICODE(dict->ma_keys));
PyDictUnicodeEntry *ep = DK_UNICODE_ENTRIES(dict->ma_keys) + hint;
DEOPT_IF(ep->me_key != name);
/* Ensure dict is GC tracked if it needs to be */
if (!_PyObject_GC_IS_TRACKED(dict) && _PyObject_GC_MAY_BE_TRACKED(PyStackRef_AsPyObjectBorrow(value))) {
_PyObject_GC_TRACK(dict);
}
old_value = ep->me_value;
PyDict_WatchEvent event = old_value == NULL ? PyDict_EVENT_ADDED : PyDict_EVENT_MODIFIED;
new_version = _PyDict_NotifyEvent(tstate->interp, event, dict, name, PyStackRef_AsPyObjectBorrow(value));
ep->me_value = PyStackRef_AsPyObjectSteal(value);
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_XDECREF(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(PyStackRef_AsPyObjectBorrow(value))) {
_PyObject_GC_TRACK(dict);
}
/* PEP 509 */
dict->ma_version_tag = new_version;
PyStackRef_CLOSE(owner);
}

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13 changes: 7 additions & 6 deletions Python/executor_cases.c.h
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13 changes: 7 additions & 6 deletions Python/generated_cases.c.h
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