_imp.get_frozen_object possible incorrect use of PyBUF_READ

@serhiy-storchaka

Bug report

It is documented that PyBUF_READ should be used with memoryview objects. But, it is used in PyObject_GetBuffer:

cpython/Python/import.c

Line 3547 in 5ecfd75

if (PyObject_GetBuffer(dataobj, &buf, PyBUF_READ) != 0) {

Other similar places that access .buf and .len just use PyBUF_SIMPLE, which I think we should use here as well.

I will send a PR.

Originally found by @serhiy-storchaka in #114669 (comment)

Linked PRs

pythongh-114685: Fix incorrect use of `PyBUF_READ` in `import.c`

Other question, why it was not caught in tests? Does PyObject_GetBuffer() ignore unknown flags or this code was never executed?

PyObject_GetBuffer() expects a numeric flag, but it uses bitflag model with example logic:

    if (!REQ_FORMAT(flags)) {
        /* NULL indicates that the buffer's data type has been cast to 'B'.
           view->itemsize is the _previous_ itemsize. If shape is present,
           the equality product(shape) * itemsize = len still holds at this
           point. The equality calcsize(format) = itemsize does _not_ hold
           from here on! */
        view->format = NULL;
    }
    if (REQ_C_CONTIGUOUS(flags) && !MV_C_CONTIGUOUS(baseflags)) {
        PyErr_SetString(PyExc_BufferError,
            "memoryview: underlying buffer is not C-contiguous");
        return -1;
    }
    if (REQ_F_CONTIGUOUS(flags) && !MV_F_CONTIGUOUS(baseflags)) {
        PyErr_SetString(PyExc_BufferError,
            "memoryview: underlying buffer is not Fortran contiguous");
        return -1;
    }
    if (REQ_ANY_CONTIGUOUS(flags) && !MV_ANY_CONTIGUOUS(baseflags)) {
        PyErr_SetString(PyExc_BufferError,
            "memoryview: underlying buffer is not contiguous");
        return -1;
    }

PyBYF_READ is equal to 256, so it just contains all the features. PyBUF_SIMPLE is just 0, so no extras.

gh-114685: Fix incorrect use of PyBUF_READ in import.c (GH-114686)

pythongh-114685: Fix incorrect use of PyBUF_READ in import.c (pythonG…

[3.11] gh-114685: Fix incorrect use of PyBUF_READ in import.c (GH-114686

[3.12] gh-114685: Fix incorrect use of PyBUF_READ in import.c (GH-114686

pythongh-114685: Check flags in PyObject_GetBuffer()

gh-114685: Check flags in PyObject_GetBuffer() (GH-114707)

Unfortunately the value of PyBUF_READ intersects with PyBUF_INDIRECT, PyBUF_FULL and PyBUF_FULL_RO, so we cannot just ban this bit. But fortunately other values has other bits set, so this error is still distinguishable.

What about PyBuffer_FillInfo(Py_buffer *view, PyObject *obj, void *buf, Py_ssize_t len, int readonly, int flags)? Do we need to check flags there as well?

Maybe. We do not have examples of the misuse in this case, and it is much less used, but a similar error is possible here too.

I will send an example PR, so we can decide 👍

pythongh-114685: `PyBuffer_FillInfo` now raises on `PyBUF_{READ,WRITE}`

gh-114685: PyBuffer_FillInfo() now raises on PyBUF_{READ,WRITE} (GH-1…

pythongh-114685: Fix incorrect use of PyBUF_READ in import.c (pythonG…

pythongh-114685: Check flags in PyObject_GetBuffer() (pythonGH-114707)

pythongh-114685: PyBuffer_FillInfo() now raises on PyBUF_{READ,WRITE} (…

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`_imp.get_frozen_object` possible incorrect use of `PyBUF_READ` #114685

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_imp.get_frozen_object possible incorrect use of PyBUF_READ #114685

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serhiy-storchaka commented on Jan 28, 2024

sobolevn commented on Jan 29, 2024

serhiy-storchaka commented on Jan 31, 2024

sobolevn commented on Jan 31, 2024

serhiy-storchaka commented on Jan 31, 2024

sobolevn commented on Jan 31, 2024

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`_imp.get_frozen_object` possible incorrect use of `PyBUF_READ` #114685