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gh-151403: Fix use-after-free when an argv item's __fspath__ mutates args #151404

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gpshead merged 2 commits into from
Jun 13, 2026
+10 −1
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gh-151403: Fix use-after-free when an argv item's __fspath__ mutates args #151404

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gh-151403: Fix use-after-free when an argv item's __fspath__ mutates …
tonghuaroot Jun 12, 2026
b4aff15
gh-151403: Use os.PathLike.__fspath__ reference in NEWS to fix docs b…
tonghuaroot Jun 13, 2026
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-12-22-46-31.gh-issue-151403.DalZWh.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fixed a crash in :class:`subprocess.Popen` (and ``_posixsubprocess.fork_exec``)
when an ``argv`` item's :meth:`~os.PathLike.__fspath__` concurrently mutates the
``args`` sequence being converted.
8 changes: 7 additions & 1 deletion Modules/_posixsubprocess.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1090,8 +1090,14 @@ subprocess_fork_exec_impl(PyObject *module, PyObject *process_args,
goto cleanup;
}
borrowed_arg = PySequence_Fast_GET_ITEM(fast_args, arg_num);
if (PyUnicode_FSConverter(borrowed_arg, &converted_arg) == 0)
/* borrowed_arg is only borrowed; its __fspath__() may run Python
that drops fast_args' last reference to it. */
Py_INCREF(borrowed_arg);
if (PyUnicode_FSConverter(borrowed_arg, &converted_arg) == 0) {
Py_DECREF(borrowed_arg);
goto cleanup;
}
Py_DECREF(borrowed_arg);
PyTuple_SET_ITEM(converted_args, arg_num, converted_arg);
}

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