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Date: Sun, 26 Apr 2009 15:24:44 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH] qcow2 corruption: Fix alloc_cluster_link_l2
Message-ID: <20090426132444.GA22238@lst.de>
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To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, dlaor@redhat.com, gleb@redhat.com

On Wed, Apr 15, 2009 at 11:52:31AM +0200, Kevin Wolf wrote:
> This patch fixes a qcow2 corruption bug introduced in SVN Rev 5861. L2 tables
> are big endian, so entries must be converted before being passed to functions.
> 
> This bug is easy to trigger. The following script will create and destroy a
> qcow2 image (the header is gone after three loop iterations):
> 
>     #!/bin/bash
>     qemu-img create -f qcow2 test.qcow 1M
>     for i in $(seq 1 10); do
>     qemu-system-x86_64 -hda test.qcow -monitor stdio > /dev/null 2>&1 <<EOF
>     savevm test-$i
>     quit
>     EOF
>     done
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block-qcow2.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/block-qcow2.c b/block-qcow2.c
> index da8fb42..985214f 100644
> --- a/block-qcow2.c
> +++ b/block-qcow2.c
> @@ -1007,7 +1007,7 @@ static int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset,
>          goto err;
>  
>      for (i = 0; i < j; i++)
> -        free_any_clusters(bs, old_cluster[i], 1);
> +        free_any_clusters(bs, be64_to_cpu(old_cluster[i]), 1);

Maybe it's time to make use of sparse's endianess annotations in qcow2
to prevent further problems like this one?