PyMemoryView_FromBuffer discards owner reference from Py_buffer

Bug report

Bug description:

https://github.com/python/cpython/blob/0274d8304e5eec23de100d827eb4da06ab7fd8aa/Objects/memoryobject.c#L769-L788

This means that if you use PyMemoryView_FromBuffer with a buffer that requires an owner to be kept alive, you get a UAF hazard here.

This is not mentioned in the documentation: https://docs.python.org/3/c-api/memoryview.html#c.PyMemoryView_FromBuffer

An extremely cursory didn't find any vulnerable callers within CPython itself, however this was discovered in the process of implementing https://github.com/PyO3/pyo3/pull/5937 where it definitely would have been an issue.

It seems like there's two possible choices here:

• Change this to keep owner around -- potentially breaks existing callers?
• Document this, and introduce a new API with clearer semantics here.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Comienza con Objects/memoryobject.c, en la implementación enlazada de PyMemoryView_FromBuffer, y lee la documentación de la C-API de PyMemoryView_FromBuffer. Revisa el pull request #5937 de PyO3 para entender el requisito de la duración del owner y, después, compara las implicaciones de compatibilidad de conservar el owner frente a introducir una nueva API. Se considera terminado cuando la semántica de ownership está decidida, documentada y cubierta por las pruebas de CPython adecuadas.