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gh-144475: Fix use-after-free in functools.partial.__repr__() #145395

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gh-144475: Fix use-after-free in functools.partial.__repr__() #145395

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a445c16
gh-144475: Fix use-after-free in functools.partial.__repr__()
Nicolas0315 Mar 1, 2026
7e73c5d
📜🤖 Added by blurb_it.
Nicolas0315 Mar 1, 2026
6c18a9e
Fix NEWS entry Sphinx references
Nicolas0315 Mar 1, 2026
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5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Library/2026-03-02-02-30-00.gh-issue-144475.CfVOu8Hi.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Fix a heap-buffer-overflow in :func:`functools.partial` ``__repr__`` where a
user-defined :meth:`~object.__repr__` on an argument could mutate the
:class:`~functools.partial` object via ``__setstate__()``, freeing the args
tuple while iteration was still in progress. The fix holds strong references
to the ``args`` tuple, ``kw`` dict, and ``fn`` callable during formatting.
32 changes: 24 additions & 8 deletions Modules/_functoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -705,26 +705,39 @@ partial_repr(PyObject *self)
arglist = Py_GetConstant(Py_CONSTANT_EMPTY_STR);
if (arglist == NULL)
goto done;
/* Pack positional arguments */
/* Pack positional arguments.
* Hold a strong reference to pto->args across the loop, because
* a user-defined __repr__ called via %R could mutate 'pto' (e.g.
* via __setstate__), freeing the original args tuple while we're
* still iterating over it. See gh-144475. */
assert(PyTuple_Check(pto->args));
n = PyTuple_GET_SIZE(pto->args);
PyObject *args = Py_NewRef(pto->args);
n = PyTuple_GET_SIZE(args);
for (i = 0; i < n; i++) {
Py_SETREF(arglist, PyUnicode_FromFormat("%U, %R", arglist,
PyTuple_GET_ITEM(pto->args, i)));
if (arglist == NULL)
PyTuple_GET_ITEM(args, i)));
if (arglist == NULL) {
Py_DECREF(args);
goto done;
}
}
/* Pack keyword arguments */
Py_DECREF(args);
/* Pack keyword arguments.
* Similarly, hold a strong reference to pto->kw. See gh-144475. */
assert (PyDict_Check(pto->kw));
for (i = 0; PyDict_Next(pto->kw, &i, &key, &value);) {
PyObject *kw = Py_NewRef(pto->kw);
for (i = 0; PyDict_Next(kw, &i, &key, &value);) {
/* Prevent key.__str__ from deleting the value. */
Py_INCREF(value);
Py_SETREF(arglist, PyUnicode_FromFormat("%U, %S=%R", arglist,
key, value));
Py_DECREF(value);
if (arglist == NULL)
if (arglist == NULL) {
Py_DECREF(kw);
goto done;
}
}
Py_DECREF(kw);

mod = PyType_GetModuleName(Py_TYPE(pto));
if (mod == NULL) {
Expand All @@ -735,7 +748,10 @@ partial_repr(PyObject *self)
Py_DECREF(mod);
goto error;
}
result = PyUnicode_FromFormat("%S.%S(%R%U)", mod, name, pto->fn, arglist);
/* Hold a strong reference to pto->fn for the same reason as args/kw. */
PyObject *fn = Py_NewRef(pto->fn);
result = PyUnicode_FromFormat("%S.%S(%R%U)", mod, name, fn, arglist);
Py_DECREF(fn);
Py_DECREF(mod);
Py_DECREF(name);
Py_DECREF(arglist);
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