Re: [Xen-devel] [PATCH] blktap2: Invalid logic detecting unaligned buffers in vhd_write_block

[Ross Philipson <ross.philipson@xxxxxxxxx>]

On 03/25/2016 12:11 PM, Wei Liu wrote:
> On Thu, Mar 17, 2016 at 06:10:59PM -0400, Ross Philipson wrote:
>> It seems the logic is meant to detect sector unaligned buffers for block
>> writes. The NOTing of the logic instead masks off any unaligned bits and
>> also would cause the function to always fail. It seems the function is not
>> used in any of the tools so that is probably why the problem is not seen.
>> In the vhd_read_block function it is correct.
>>
>> Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxxxx>
> 
> This seems to fall under tools umbrella. I've look at blktap2 code,
> the reasoning is convincing to me so:
> 
>   Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> But I've never used blktap2 and we don't normally test it so I would
> also wait a bit longer to see if anybody objects to this change.
> 
> OOI if no code was using this, how did you discover this problem?

We have an old fork of blktap2 from way back when. I was working to extract our
changes and turn them into patches so we could rebase on upstream blktap2.
Someone long ago found that - I have no idea how but it was a valid fix so I
upstreamed it.

There are a number of other ones that were found that are still in upstream
blktap2 - I plan to send them too.

> 
> Wei.
> 
>> ---
>> diff --git a/tools/blktap2/vhd/lib/libvhd.c b/tools/blktap2/vhd/lib/libvhd.c
>> index 1fd5b4e..4ebe012 100644
>> --- a/tools/blktap2/vhd/lib/libvhd.c
>> +++ b/tools/blktap2/vhd/lib/libvhd.c
>> @@ -2188,7 +2188,7 @@ vhd_write_block(vhd_context_t *ctx, uint32_t block, 
>> char *data)
>>         if (block >= ctx->bat.entries)
>>                 return -ERANGE;
>>
>> -       if ((unsigned long)data & ~(VHD_SECTOR_SIZE -1))
>> +       if ((unsigned long)data & (VHD_SECTOR_SIZE -1))
>>                 return -EINVAL;
>>
>>         blk  = ctx->bat.bat[block];
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxx
>> http://lists.xen.org/xen-devel


-- 
Ross Philipson

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