Pablo Galindo Salgado <[email protected]> added the comment:
I think the real problem is in vectorcall. tp_clear will make sure all internal
pointers are either NULL or valid (by using Py_CLEAR, which also protects
against re-entrancy) and it the responsibility of the object or its users to
check that the fields that are needed are valid. From the docs on tp_clear:
> The Py_CLEAR() macro should be used, because clearing references is delicate:
> the reference to the contained object must not be decremented until after the
> pointer to the contained object is set to NULL. This is because decrementing
> the reference count may cause the contained object to become trash,
> triggering a chain of reclamation activity that may include invoking
> arbitrary Python code (due to finalizers, or weakref callbacks, associated
> with the contained object). If it’s possible for such code to reference self
> again, it’s important that the pointer to the contained object be NULL at
> that time, so that self knows the contained object can no longer be used.
Notice the "so that self knows the contained object can no longer be used". I
think _PyFunction_Vectorcall is missing the check "to see of the contained
object can or cannot be used". Here the contained object being everything that
has being cleaned before:
Py_CLEAR(op->func_code);
Py_CLEAR(op->func_globals);
Py_CLEAR(op->func_module);
Py_CLEAR(op->func_name);
Py_CLEAR(op->func_defaults);
Py_CLEAR(op->func_kwdefaults);
Py_CLEAR(op->func_doc);
Py_CLEAR(op->func_dict);
Py_CLEAR(op->func_closure); <----- Everything before this
Py_CLEAR(op->func_annotations);
Py_CLEAR(op->func_qualname);
I think it will be enough to make a check for func_code being NULL in
_PyFunction_Vectorcall or before.
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<https://bugs.python.org/issue38006>
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