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

From: Hao QingFeng
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 18:48:28 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.5.0

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 <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.
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 
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. :-)


QingFeng Hao(Robin)

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