8000 [3.13] GH-132417: ctypes: Fix potential `Py_DECREF(NULL)` when handling functions returning `PyObject *` (GH-132418) by miss-islington · Pull Request #132425 · python/cpython · GitHub
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[3.13] GH-132417: ctypes: Fix potential Py_DECREF(NULL) when handling functions returning PyObject * (GH-132418) #132425

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Merged
merged 1 commit into from
Apr 12, 2025
Merged

[3.13] GH-132417: ctypes: Fix potential Py_DECREF(NULL) when handling functions returning PyObject * (GH-132418) #132425

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15 changes: 15 additions & 0 deletions Lib/test/test_ctypes/test_refcounts.py
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Original file line number Diff line number Diff line change
Expand Up @@ -124,5 +124,20 @@ def test_finalize(self):
script_helper.assert_python_ok("-c", script)


class PyObjectRestypeTest(unittest.TestCase):
def test_restype_py_object_with_null_return(self):
# Test that a function which returns a NULL PyObject *
# without setting an exception does not crash.
PyErr_Occurred = ctypes.pythonapi.PyErr_Occurred
PyErr_Occurred.argtypes = []
PyErr_Occurred.restype = ctypes.py_object

# At this point, there's no exception set, so PyErr_Occurred
# returns NULL. Given the restype is py_object, the
# ctypes machinery will raise a custom error.
with self.assertRaisesRegex(ValueError, "PyObject is NULL"):
PyErr_Occurred()


if __name__ == '__main__':
unittest.main()
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-04-11-21-48-49.gh-issue-132417.uILGdS.rst
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@@ -0,0 +1,3 @@
Fix a ``NULL`` pointer dereference when a C function called using
:mod:`ctypes` with ``restype`` :class:`~ctypes.py_object` returns
``NULL``.
7 changes: 4 additions & 3 deletions Modules/_ctypes/callproc.c
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< 5B31 td id="diff-4e23b3237d0aa08bf4c434d75fab19200a80837bd147051fefccd98b7f2480faR1022" data-line-number="1022" class="blob-num blob-num-context js-linkable-line-number js-blob-rnum">
Original file line number Diff line number Diff line change
Expand Up @@ -1016,11 +1016,12 @@ static PyObject *GetResult(ctypes_state *st,
if (info->getfunc && !_ctypes_simple_instance(st, restype)) {
retval = info->getfunc(result, info->size);
/* If restype is py_object (detected by comparing getfunc with
O_get), we have to call Py_DECREF because O_get has already
called Py_INCREF.
O_get), we have to call Py_XDECREF because O_get has already
called Py_INCREF, unless the result was NULL, in which case
an error is set (by the called function, or by O_get).
*/
if (info->getfunc == _ctypes_get_fielddesc("O")->getfunc) {
Py_DECREF(retval);
Py_XDECREF(retval);
}
}
else {
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