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Re: [Qemu-devel] [PATCH for-2.8 v1 1/1] block/vmdk: Fix the endian probl

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH for-2.8 v1 1/1] block/vmdk: Fix the endian problem of buf_len
Date: Fri, 25 Nov 2016 11:21:21 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

[ Cc: Fam, qemu-stable ]

Am 25.11.2016 um 11:06 hat QingFeng Hao geschrieben:
> The problem was triggered by qemu-iotests case 055. It failed when it
> was comparing the compressed vmdk image with original test.img.
> The cause is that buf_len in vmdk_write_extent wasn't converted to
> little-endian before it was stored to disk. But later vmdk_read_extent
> read it and converted it from little-endian to cpu endian.
> If the cpu is big-endian like s390, the problem will happen and
> the data length read by vmdk_read_extent will become invalid!
> The fix is to add the conversion in vmdk_write_extent.
> Signed-off-by: QingFeng Hao <address@hidden>
> Signed-off-by: Jing Liu <address@hidden>

Sounds like something that should still be fixed for 2.8 and in the
stable branches.

> diff --git a/block/vmdk.c b/block/vmdk.c
> index a11c27a..bf6667f 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -1355,7 +1355,7 @@ static int vmdk_write_extent(VmdkExtent *extent, 
> int64_t cluster_offset,
>          }
>          data->lba = offset >> BDRV_SECTOR_BITS;
> -        data->size = buf_len;
> +        data->size = cpu_to_le32(buf_len);

At least data->lba needs to be fixed, too, both here and in
vmdk_read_extent(). Host endianness in an image file is always wrong.

Maybe we should audit the whole driver for endianness problems.


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