[Qemu-devel] [PATCH] qcow2: Fix access after end of array

[Qemu-devel] [PATCH] qcow2: Fix access after end of array

[Kevin Wolf]

If a write requests crosses a L2 table boundary and all clusters until the
end of the L2 table are usable for the request, we must not look at the next
L2 entry because we already have arrived at the end of the array.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2-cluster.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 3501a94..b13b693 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -750,12 +750,15 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
     while (i < nb_clusters) {
         i += count_contiguous_clusters(nb_clusters - i, s->cluster_size,
                 &l2_table[l2_index], i, 0);
-
-        if(be64_to_cpu(l2_table[l2_index + i]))
+        if ((i >= nb_clusters) || be64_to_cpu(l2_table[l2_index + i])) {
             break;
+        }
 
         i += count_contiguous_free_clusters(nb_clusters - i,
                 &l2_table[l2_index + i]);
+        if (i >= nb_clusters) {
+            break;
+        }
 
         cluster_offset = be64_to_cpu(l2_table[l2_index + i]);
 
@@ -763,6 +766,7 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
                 (cluster_offset & QCOW_OFLAG_COMPRESSED))
             break;
     }
+    assert(i <= nb_clusters);
     nb_clusters = i;
 
     /*
-- 
1.6.6

Re: [Qemu-devel] [PATCH] qcow2: Fix access after end of array

[Anthony Liguori]

On 02/16/2010 08:54 AM, Kevin Wolf wrote:
> If a write requests crosses a L2 table boundary and all clusters until the
> end of the L2 table are usable for the request, we must not look at the next
> L2 entry because we already have arrived at the end of the array.
>
> Signed-off-by: Kevin Wolf<kwolf@redhat.com>
>    

Applied.  Thanks.

Regards,

Anthony Liguori
> ---
>   block/qcow2-cluster.c |    8 ++++++--
>   1 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 3501a94..b13b693 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -750,12 +750,15 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
>       while (i<  nb_clusters) {
>           i += count_contiguous_clusters(nb_clusters - i, s->cluster_size,
>                   &l2_table[l2_index], i, 0);
> -
> -        if(be64_to_cpu(l2_table[l2_index + i]))
> +        if ((i>= nb_clusters) || be64_to_cpu(l2_table[l2_index + i])) {
>               break;
> +        }
>
>           i += count_contiguous_free_clusters(nb_clusters - i,
>                   &l2_table[l2_index + i]);
> +        if (i>= nb_clusters) {
> +            break;
> +        }
>
>           cluster_offset = be64_to_cpu(l2_table[l2_index + i]);
>
> @@ -763,6 +766,7 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
>                   (cluster_offset&  QCOW_OFLAG_COMPRESSED))
>               break;
>       }
> +    assert(i<= nb_clusters);
>       nb_clusters = i;
>
>       /*
>