https://github.com/python/cpython/commit/4dd9d94619be5c2795ec849f1edb810c0c048f79 commit: 4dd9d94619be5c2795ec849f1edb810c0c048f79 branch: 3.13 author: Miss Islington (bot) <[email protected]> committer: serhiy-storchaka <[email protected]> date: 2025-12-25T13:41:24+02:00 summary:
[3.13] gh-143004: Fix possible use-after-free in collections.Counter.update() (GH-143044) (GH-143167) This happened when the Counter was mutated when incrementing the value for an existing key. (cherry picked from commit 86d904588e8c84c7fccb8faf84b343f03461970d) Co-authored-by: kaushal trivedi <[email protected]> files: A Misc/NEWS.d/next/Library/2025-12-22-00-00-00.gh-issue-143004.uaf-counter.rst M Lib/test/test_collections.py M Modules/_collectionsmodule.c diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py index 843f4ffcd25aa4..4b9b47cd740a57 100644 --- a/Lib/test/test_collections.py +++ b/Lib/test/test_collections.py @@ -2119,6 +2119,19 @@ def test_basics(self): self.assertEqual(c.setdefault('e', 5), 5) self.assertEqual(c['e'], 5) + def test_update_reentrant_add_clears_counter(self): + c = Counter() + key = object() + + class Evil(int): + def __add__(self, other): + c.clear() + return NotImplemented + + c[key] = Evil() + c.update([key]) + self.assertEqual(c[key], 1) + def test_init(self): self.assertEqual(list(Counter(self=42).items()), [('self', 42)]) self.assertEqual(list(Counter(iterable=42).items()), [('iterable', 42)]) diff --git a/Misc/NEWS.d/next/Library/2025-12-22-00-00-00.gh-issue-143004.uaf-counter.rst b/Misc/NEWS.d/next/Library/2025-12-22-00-00-00.gh-issue-143004.uaf-counter.rst new file mode 100644 index 00000000000000..278066e9b706bf --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-12-22-00-00-00.gh-issue-143004.uaf-counter.rst @@ -0,0 +1,2 @@ +Fix a potential use-after-free in :meth:`collections.Counter.update` when user code +mutates the Counter during an update. diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c index b356c917c1d5ef..f5fc0d02a16607 100644 --- a/Modules/_collectionsmodule.c +++ b/Modules/_collectionsmodule.c @@ -2549,7 +2549,12 @@ _collections__count_elements_impl(PyObject *module, PyObject *mapping, if (_PyDict_SetItem_KnownHash(mapping, key, one, hash) < 0) goto done; } else { + /* oldval is a borrowed reference. Keep it alive across + PyNumber_Add(), which can execute arbitrary user code and + mutate (or even clear) the underlying dict. */ + Py_INCREF(oldval); newval = PyNumber_Add(oldval, one); + Py_DECREF(oldval); if (newval == NULL) goto done; if (_PyDict_SetItem_KnownHash(mapping, key, newval, hash) < 0) _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
