https://github.com/python/cpython/commit/02288bf0225bea892eaab0d3e13c271761849e22
commit: 02288bf0225bea892eaab0d3e13c271761849e22
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2026-03-02T12:25:13-05:00
summary:
gh-130555: Fix use-after-free in dict.clear() with embedded values (gh-145268)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-02-26-12-00-00.gh-issue-130555.TMSOIu.rst
M Lib/test/test_dict.py
M Objects/dictobject.c
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 8a4e19c95a36ef..f28155fe50148d 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1680,6 +1680,69 @@ def test_hash_collision_remove_add(self):
self.assertEqual(len(d), len(items), d)
self.assertEqual(d, dict(items))
+ def test_clear_reentrant_embedded(self):
+ # gh-130555: dict.clear() must be safe when values are embedded
+ # in an object and a destructor mutates the dict.
+ class MyObj: pass
+ class ClearOnDelete:
+ def __del__(self):
+ nonlocal x
+ del x
+
+ x = MyObj()
+ x.a = ClearOnDelete()
+
+ d = x.__dict__
+ d.clear()
+
+ def test_clear_reentrant_cycle(self):
+ # gh-130555: dict.clear() must be safe for embedded dicts when the
+ # object is part of a reference cycle and the last reference to the
+ # dict is via the cycle.
+ class MyObj: pass
+ obj = MyObj()
+ obj.f = obj
+ obj.attr = "attr"
+
+ d = obj.__dict__
+ del obj
+
+ d.clear()
+
+ def test_clear_reentrant_force_combined(self):
+ # gh-130555: dict.clear() must be safe when a destructor forces the
+ # dict from embedded/split to combined (setting ma_values to NULL).
+ class MyObj: pass
+ class ForceConvert:
+ def __del__(self):
+ d[1] = "trigger"
+
+ x = MyObj()
+ x.a = ForceConvert()
+ x.b = "other"
+
+ d = x.__dict__
+ d.clear()
+
+ def test_clear_reentrant_delete(self):
+ # gh-130555: dict.clear() must be safe when a destructor deletes
+ # a key from the same embedded dict.
+ class MyObj: pass
+ class DelKey:
+ def __del__(self):
+ try:
+ del d['b']
+ except KeyError:
+ pass
+
+ x = MyObj()
+ x.a = DelKey()
+ x.b = "value_b"
+ x.c = "value_c"
+
+ d = x.__dict__
+ d.clear()
+
class CAPITest(unittest.TestCase):
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-02-26-12-00-00.gh-issue-130555.TMSOIu.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-02-26-12-00-00.gh-issue-130555.TMSOIu.rst
new file mode 100644
index 00000000000000..5a2106480fb843
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-02-26-12-00-00.gh-issue-130555.TMSOIu.rst
@@ -0,0 +1,3 @@
+Fix use-after-free in :meth:`dict.clear` when the dictionary values are
+embedded in an object and a destructor causes re-entrant mutation of the
+dictionary.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 35ca9933bfa8ae..bcd3c862fd59b2 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -2969,6 +2969,21 @@ _PyDict_DelItemIf(PyObject *op, PyObject *key,
return res;
}
+static void
+clear_embedded_values(PyDictValues *values, Py_ssize_t nentries)
+{
+ PyObject *refs[SHARED_KEYS_MAX_SIZE];
+ assert(nentries <= SHARED_KEYS_MAX_SIZE);
+ for (Py_ssize_t i = 0; i < nentries; i++) {
+ refs[i] = values->values[i];
+ values->values[i] = NULL;
+ }
+ values->size = 0;
+ for (Py_ssize_t i = 0; i < nentries; i++) {
+ Py_XDECREF(refs[i]);
+ }
+}
+
static void
clear_lock_held(PyObject *op)
{
@@ -2997,20 +3012,18 @@ clear_lock_held(PyObject *op)
assert(oldkeys->dk_refcnt == 1);
dictkeys_decref(oldkeys, IS_DICT_SHARED(mp));
}
+ else if (oldvalues->embedded) {
+ clear_embedded_values(oldvalues, oldkeys->dk_nentries);
+ }
else {
+ set_values(mp, NULL);
+ set_keys(mp, Py_EMPTY_KEYS);
n = oldkeys->dk_nentries;
for (i = 0; i < n; i++) {
Py_CLEAR(oldvalues->values[i]);
}
- if (oldvalues->embedded) {
- oldvalues->size = 0;
- }
- else {
- set_values(mp, NULL);
- set_keys(mp, Py_EMPTY_KEYS);
- free_values(oldvalues, IS_DICT_SHARED(mp));
- dictkeys_decref(oldkeys, false);
- }
+ free_values(oldvalues, IS_DICT_SHARED(mp));
+ dictkeys_decref(oldkeys, false);
}
ASSERT_CONSISTENT(mp);
}
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