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Date: Tue, 7 Nov 2017 17:43:49 +0100
From: Kevin Wolf <kwolf@redhat.com>
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References: <cover.1509718618.git.berto@igalia.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/7] qcow2: Don't open
 images with header.refcount_table_clusters == 0
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To: Alberto Garcia <berto@igalia.com>
Cc: Thomas Huth <thuth@redhat.com>, qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>, "R . Nageswara Sastry" <nasastry@in.ibm.com>

Am 03.11.2017 um 15:18 hat Alberto Garcia geschrieben:
> qcow2_do_open() is checking that header.refcount_table_clusters is not
> too large, but it doesn't check that it's greater than zero. Apart
> from the fact that an image like that is obviously corrupted, trying
> to use it crashes QEMU since we end up with a null s->refcount_table
> after qcow2_refcount_init().
> 
> These images can however be repaired, so allow opening them if the
> BDRV_O_CHECK flag is set.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>

> --- a/tests/qemu-iotests/060
> +++ b/tests/qemu-iotests/060
> @@ -270,6 +270,13 @@ poke_file "$TEST_IMG" "$rb_offset"        "\x00\x00\x00\x00\x00\x00\x00\x00"
>  # write will try to allocate a compressed data cluster at offset 0.
>  $QEMU_IO -c "write -c 0k 64k" "$TEST_IMG" | _filter_qemu_io
>  
> +echo
> +echo "=== Testing zero refcount table size ==="
> +echo
> +_make_test_img 64M
> +poke_file "$TEST_IMG" "56"                "\x00\x00\x00\x00"
> +$QEMU_IO -c "write 0 64k" "$TEST_IMG" 2>&1 | _filter_testdir | _filter_imgfmt

In the commit message, you claim that the image can be repaired. Would
it be worth actually testing the repair here?

Kevin