[Libguestfs] [libnbd PATCH v2 2/8] python: Plug uninit leak in nbd.Buffer.to_bytearray

[Eric Blake]

On Mon, Jun 06, 2022 at 09:08:27PM -0500, Eric Blake wrote:
> 
> The solution employed here is to mark when a buffer has been
> initialized, in nbd.Buffer.from_bytearray() and
> h.aio_pread[_structured], as well as force-initialize an uninitialized
> buffer before b.to_bytearray() or h.aio_pwrite.  Furthermore, we can
> make b.is_zero() pretend an uninitialized buffer is all zeroes (since
> the user can no longer easily get at any other contents).
> 

> @@ -288,7 +295,7 @@ nbd_internal_py_aio_buffer_is_zero (PyObject *self, PyObject *args)
>      return NULL;
>    }
> 
> -  if (is_zero (buf->data + offset, size))
> +  if (!buf->initialized || is_zero (buf->data + offset, size))
>      Py_RETURN_TRUE;
>    else
>      Py_RETURN_FALSE;

I just noticed this function has an odd order of execution - if size
is 0, it returns true even if offset is out-of-bounds.  It would also
be more Pythonic if we changed offset/size to instead be more like
Python range start/stop parameters (particularly since future patches
can then compute memoryview(buffer)[start:end] as the bytes to check
for being zero), but that's an API change.  I'll have to think about
that one more...

But that doesn't change the content of this patch.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org