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gh-150157: fix: critical section for PyDict_Next in _pickle.c #150158

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gh-150157: fix: critical section for PyDict_Next in _pickle.c #150158

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5d4d511
fix: pickle whichmodule has a UAF on free-threading
KowalskiThomas May 20, 2026
1fd7911
review: address comment on code order
KowalskiThomas May 21, 2026
adea962
misc: add news entry
KowalskiThomas May 21, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-05-21-20-47-45.gh-issue-150157.ZvmO-bQZ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a heap use-after-free in :mod:`pickle`\'s ``whichmodule`` on
free-threaded builds. Patch by Thomas Kowalski.
20 changes: 16 additions & 4 deletions Modules/_pickle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2055,22 +2055,34 @@ whichmodule(PickleState *st, PyObject *global, PyObject *global_name, PyObject *
return NULL;
}
if (PyDict_CheckExact(modules)) {
PyObject *found_name = NULL;
int error = 0;
i = 0;
Py_BEGIN_CRITICAL_SECTION(modules);
while (PyDict_Next(modules, &i, &module_name, &module)) {
Py_INCREF(module_name);
Py_INCREF(module);
if (_checkmodule(module_name, module, global, dotted_path) == 0) {
Py_DECREF(module);
Py_DECREF(modules);
return module_name;
found_name = module_name;
break;
}
Py_DECREF(module);
Py_DECREF(module_name);
if (PyErr_Occurred()) {
Py_DECREF(modules);
return NULL;
error = 1;
break;
}
}
Py_END_CRITICAL_SECTION();
if (error) {
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@vstinner vstinner May 21, 2026

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nitpick: i would prefer checking for errors before checking if (found_name != NULL).

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@KowalskiThomas KowalskiThomas May 21, 2026

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Thanks for taking a look! Updated it.

Py_DECREF(modules);
return NULL;
}
if (found_name != NULL) {
Py_DECREF(modules);
return found_name;
}
}
else {
PyObject *iterator = PyObject_GetIter(modules);
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