[Qemu-devel] [PATCH] qcow2: Correct snapshots size for overlap check

[Qemu-devel] [PATCH] qcow2: Correct snapshots size for overlap check

[Max Reitz]

Using s->snapshots_size instead of snapshots_size for the metadata
overlap check in qcow2_write_snapshots leads to the detection of an
overlap with the main qcow2 image header when deleting the last
snapshot, since s->snapshots_size has not yet been updated and is
therefore non-zero. However, the offset returned by qcow2_alloc_clusters
will be zero since snapshots_size is zero. Therefore, an overlap is
detected albeit no such will occur.

This patch fixes this by replacing s->snapshots_size by snapshots_size
when calling qcow2_pre_write_overlap_check.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-snapshot.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 7d14420..5e8a779 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -192,7 +192,7 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
     /* The snapshot list position has not yet been updated, so these clusters
      * must indeed be completely free */
     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_DEFAULT, offset,
-                                        s->snapshots_size);
+                                        snapshots_size);
     if (ret < 0) {
         return ret;
     }
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] qcow2: Correct snapshots size for overlap check

[Stefan Hajnoczi]

On Thu, Sep 19, 2013 at 12:29:15PM +0200, Max Reitz wrote:
> Using s->snapshots_size instead of snapshots_size for the metadata
> overlap check in qcow2_write_snapshots leads to the detection of an
> overlap with the main qcow2 image header when deleting the last
> snapshot, since s->snapshots_size has not yet been updated and is
> therefore non-zero. However, the offset returned by qcow2_alloc_clusters
> will be zero since snapshots_size is zero. Therefore, an overlap is
> detected albeit no such will occur.
> 
> This patch fixes this by replacing s->snapshots_size by snapshots_size
> when calling qcow2_pre_write_overlap_check.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-snapshot.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan