Re: [Qemu-devel] [Qemu-block] [PATCH for-2.8 v2] hbitmap: Fix shifts of constants by granularity

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Nov 15, 2016 at 11:47:32PM +0100, Max Reitz wrote:
> An hbitmap's granularity may be anything from 0 to 63, so when shifting
> constants by its value, they should not be plain ints.
> 
> Even having changed the types, hbitmap_serialization_granularity() still
> tries to shift 64 to the right by the granularity. This operation is
> undefined if the granularity is greater than 57. Adding an assertion is
> fine for now, because serializing is done only in tests so far, but this
> means that only bitmaps with a granularity below 58 can be serialized
> and we should thus add a hbitmap_is_serializable() function later.
> 
> One of the two places touched in this patch uses
> QEMU_ALIGN_UP(x, 1 << y). We can use ROUND_UP() there, since the second
> parameter is obviously a power of two.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
> v2:
> - Fix the same issue in hbitmap_truncate() [Stefan]
> - Use ROUND_UP() instead of QEMU_ALIGN_UP() there (because we can)
> - Add an assertion to hbitmap_serialization_granularity() guaranteeing
>   that the shift doesn't overflow; we can guarantee this so far because
>   the only place where serialization functions are used in is the
>   hbitmap test
>   (I'll send a follow-up patch to allow users to check whether a certain
>   bitmap can be (de-)serialized)
> ---
>  util/hbitmap.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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