Re: [Qemu-devel] [PATCH v2] vmdk: return ERROR when cluster sector is larger than vmdk limitation

[Eric Blake <eblake@redhat.com>]

On 03/22/2018 02:41 AM, Fam Zheng wrote:
> On Thu, 03/22 14:24, yuchenlin@synology.com wrote:
>> From: yuchenlin <yuchenlin@synology.com>
>>
>> VMDK has a hard limitation of extent size, which is due to the size of grain
>> table entry is 32 bits. It means it can only point to a grain located at
>> offset = 2^32. To avoid writing the user data beyond limitation and record a useless offset
>> in grain table. We should return ERROR here.
>>
>> Signed-off-by: yuchenlin <yuchenlin@synology.com>
>> ---

>> +++ b/block/vmdk.c
>> @@ -47,6 +47,8 @@
>>   #define VMDK4_FLAG_MARKER (1 << 17)
>>   #define VMDK4_GD_AT_END 0xffffffffffffffffULL
>>   
>> +#define VMDK_EXTENT_MAX_SECTORS (4294967296)
>> +

Hmm, with sectors instead of bytes, you don't want to use Phillipe's '2 
* T_BYTE' macro after all; but it would still look better spelled as 
'(1ULL << 32)' or '(4ULL * 1024 * 1024 * 1024)'.  Most importantly, 
since the value does NOT fit in a 32-bit unsigned integer, I think you 
NEED to use the ULL suffix to make your intent clear.

>>   #define VMDK_GTE_ZEROED 0x1
>>   
>>   /* VMDK internal error codes */
>> @@ -1250,6 +1252,10 @@ static int get_cluster_offset(BlockDriverState *bs,
>>               return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;
>>           }
>>   
>> +        if (extent->next_cluster_sector >= VMDK_EXTENT_MAX_SECTORS) {
>> +            return VMDK_ERROR;
>> +        }
>> +
>>           cluster_sector = extent->next_cluster_sector;
>>           extent->next_cluster_sector += extent->cluster_sectors;
>>   
>> -- 
>> 2.16.2
>>
> 
> Cc'ing Kevin and Max who merge block/ patches.

Also, CC'ing qemu-block, as all block-related patches should go through 
there.

> 
> Reviewed-by: Fam Zheng <famz@redhat.com>
> 
> 
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org