Re: [PATCH v2] qcow2-bitmap: Fix uint64_t left-shift overflow

[Vladimir Sementsov-Ogievskiy]

28.10.2019 9:33, Tuguoyi wrote:
> In check_constraints_on_bitmap(), the sanity check on the
> granularity will cause uint64_t integer left-shift overflow
> when cluster_size is 2M and the granularity is BIGGER than
> 32K. As a result, for a qcow2 disk with cluster_size set to
> 2M, we could not even create a dirty bitmap with default
> granularity. This patch fix the issue by dividing @len by
> granularity instead.
> 
> Signed-off-by: Guoyi Tu <address@hidden>

The buggy code was introduced in 5f72826e7fc6216 (by me, sorry :(,
so it's an old bug, appeared in 2.10. Still, I add stable to CC,
as fix is very simple.

Fixes: 5f72826e7fc62167cf3a
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

> ---
>   block/qcow2-bitmap.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
> index 98294a7..71ac822 100644
> --- a/block/qcow2-bitmap.c
> +++ b/block/qcow2-bitmap.c
> @@ -172,8 +172,8 @@ static int check_constraints_on_bitmap(BlockDriverState 
> *bs,
>       }
>   
>       if ((len > (uint64_t)BME_MAX_PHYS_SIZE << granularity_bits) ||
> -        (len > (uint64_t)BME_MAX_TABLE_SIZE * s->cluster_size <<
> -               granularity_bits))
> +        (DIV_ROUND_UP(len, granularity) > (uint64_t)BME_MAX_TABLE_SIZE *
> +                s->cluster_size))
>       {
>           error_setg(errp, "Too much space will be occupied by the bitmap. "
>                      "Use larger granularity");
> 


-- 
Best regards,
Vladimir