Le Thursday 23 Jan 2014 à 11:04:06 (+0800), Hu Tao a écrit :
> When cluster size is big enough it can lead offset overflow
Maybe "it can lead to an offset overflow in"
> in qcow2_alloc_clusters_at(). This patch fixes it.
>
> The allocation each time is stopped at L2 table boundary
"The allocation is stopped each time at"
> (see handle_alloc()), so the possible maximum bytes could be
>
> 2^(cluster_bits - 3 + cluster_bits)
So if understand cluster_bits - 3 is used to compute the number of entry by L2
and the additional cluster_bits is to take into account each clusters referenced
by the L2 entries.
It makes sense.
>
> so int is safe for cluster_bits<=17, unsafe otherwise.
>
> Reviewed-by: Max Reitz <mre...@redhat.com>
> Signed-off-by: Hu Tao <hu...@cn.fujitsu.com>
> ---
> block/qcow2-refcount.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index c974abe..8712d8b 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -676,7 +676,13 @@ 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;
> +
> + assert(nb_clusters >= 0);
> + if (nb_clusters == 0) {
> + return 0;
> + }
^
Adding a a line on the commit message about this assertion and chunk of code
would be helpful.
Best regards
Benoît
>
> /* Check how many clusters there are free */
> cluster_index = offset >> s->cluster_bits;
> --
> 1.8.5.2.229.g4448466
>
>
