Re: [Qemu-devel] [PATCH v1 2/3] qcow2: fix offset overflow

[Hu Tao]

On Mon, Dec 30, 2013 at 01:29:08PM +0800, Hu Tao wrote:
> When cluster size is big enough it can lead offset overflow
> in qcow2_alloc_clusters_at(). This patch fixes it.

ping. and be more descriptive:

The allocation each time is stopped at L2 table boundary(see handle_alloc()),
so the possible maximum bytes could be

  2^(cluster_bits - 3 + cluster_bits)

so int is safe for cluster_bits<=17, unsafe otherwise.


> 
> Signed-off-by: Hu Tao <address@hidden>
> ---
>  block/qcow2-refcount.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index c974abe..b3ebb7f 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -676,7 +676,12 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, 
> uint64_t offset,
>      BDRVQcowState *s = bs->opaque;
>      uint64_t cluster_index;
>      uint64_t old_free_cluster_index;
> -    int i, refcount, ret;
> +    uint64_t i;
> +    int refcount, ret;
> +
> +    if (nb_clusters <= 0) {
> +        return 0;
> +    }
>  
>      /* Check how many clusters there are free */
>      cluster_index = offset >> s->cluster_bits;
> -- 
> 1.7.11.7
>