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

[Hao QingFeng <haoqf@linux.vnet.ibm.com>]

在 2016-11-25 18:21, Kevin Wolf 写道:
> [ 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 <haoqf@linux.vnet.ibm.com>
>> Signed-off-by: Jing Liu <liujbjl@linux.vnet.ibm.com>
> Sounds like something that should still be fixed for 2.8 and in the
> stable branches.
I didn't find the stable branch on upstream, the latest is 2.6 maybe 
it's a private one? :-)
>
>> 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.
Good detection!
>
> Maybe we should audit the whole driver for endianness problems.
Good sight! maybe we can encapsulate a suite of endianness functions
for the structures to avoid missing some elements of them like lba?
Also will be better for reuse. When I am checking the endianness calls
in vmdk_create_extent, I am just afraid of missing one. :-)
Thanks!
>
> Kevin
>

-- 
QingFeng Hao(Robin)