Re: [Qemu-devel] [Qemu-block] [PATCH 2/2] qcow2: Fix qcow2_get_cluster_offset()

[Eric Blake <eblake@redhat.com>]

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On 06/20/2016 08:26 AM, Max Reitz wrote:
> Recently, qcow2_get_cluster_offset() has been changed to work with bytes
> instead of sectors. This invalidated some assertions and introduced a
> possible integer multiplication overflow.
> 
> This could be reproduced using e.g.
> 
> $ qemu-img create -f qcow2 -o cluster_size=1M blub.qcow2 8G
> Formatting 'foo.qcow2', fmt=qcow2 size=8589934592 encryption=off
> cluster_size=1048576 lazy_refcounts=off refcount_bits=16
> $ qemu-io -c map blub.qcow2
> qemu-io: qemu/block/qcow2-cluster.c:504: qcow2_get_cluster_offset:
> Assertion `bytes_needed <= INT_MAX' failed.
> [1]    20775 abort (core dumped)  qemu-io -c map foo.qcow2
> 
> This patch removes the now wrong assertion, adding comments and more
> assertions to prove its correctness (and fixing the overflow which would
> become apparent with the original assertion removed).
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-cluster.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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