Re: [PATCH for-4.2 0/2] qcow2: Fix QCOW2_COMPRESSED_SECTOR_MASK

[Max Reitz <mreitz@redhat.com>]

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On 28.10.19 17:18, Max Reitz wrote:
> This fixes a bug reported on
> https://bugs.launchpad.net/qemu/+bug/1850000.  The problem is that
> QCOW2_COMPRESSED_SECTOR_MASK is a 32-bit mask when it really needs to be
> a 64-bit mask.
> 
> The launchpad report mentions only problems with qemu-img check on large
> compressed images, but I think it might extend further than that:
> - I suppose qcow2_free_any_clusters() would free every compressed offset
>   modulo 4G, which isn’t good
> - qcow2_update_snapshot_refcount() will probably update compressed
>   cluster’s refcounts (in snapshots) modulo 4G, which also isn’t good
> - And then we have check_refcount_l2() which updates the wrong clusters
>   for qemu-img check (as demonstrated in the bug report)
> 
> - (qcow2_co_preadv_compressed() is safe because it uses the inverted
>   mask, which of course is again just 32 bit)
> 
> 
> But I haven’t tested those other cases.
> 
> 
> Max Reitz (2):
>   qcow2: Fix QCOW2_COMPRESSED_SECTOR_MASK
>   iotests: Add test for 4G+ compressed qcow2 write
> 
>  block/qcow2.h              |  2 +-
>  tests/qemu-iotests/272     | 79 ++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/272.out | 10 +++++
>  tests/qemu-iotests/group   |  1 +
>  4 files changed, 91 insertions(+), 1 deletion(-)
>  create mode 100755 tests/qemu-iotests/272
>  create mode 100644 tests/qemu-iotests/272.out

Thanks for the review, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max


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