[libvirt] [PATCH 12/30] storagefile: Fix backing format \0 check

[Cole Robinson]

On 10/11/19 9:04 AM, Michal Privoznik wrote:
> On 10/7/19 11:49 PM, Cole Robinson wrote:
>>> From qemu.git docs/interop/qcow2.txt
>>
>>    == String header extensions ==
>>
>>    Some header extensions (such as the backing file format name and
>>    the external data file name) are just a single string. In this case,
>>    the header extension length is the string length and the string is
>>    not '\0' terminated. (The header extension padding can make it look
>>    like a string is '\0' terminated, but neither is padding always
>>    necessary nor is there a guarantee that zero bytes are used
>>    for padding.)
>>
>> So we shouldn't be checking for a \0 byte at the end of the backing
>> format section. I think in practice there always is a \0 but we
>> shouldn't depend on that.
>>
>> Signed-off-by: Cole Robinson <crobinso at redhat.com>
>> ---
>>   src/util/virstoragefile.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
>> index 8cd576a463..5a4e4b24ae 100644
>> --- a/src/util/virstoragefile.c
>> +++ b/src/util/virstoragefile.c
>> @@ -506,13 +506,18 @@ qcow2GetExtensions(const char *buf,
>>           case QCOW2_HDR_EXTENSION_END:
>>               goto done;
>> -        case QCOW2_HDR_EXTENSION_BACKING_FORMAT:
>> -            if (buf[offset+len] != '\0')
>> -                break;
>> -            *backingFormat = 
>> virStorageFileFormatTypeFromString(buf+offset);
>> +        case QCOW2_HDR_EXTENSION_BACKING_FORMAT: {
>> +            VIR_AUTOFREE(char *) tmp = NULL;
>> +            if (VIR_ALLOC_N(tmp, len + 1) < 0)
>> +                return -1;
>> +            memcpy(tmp, buf + offset, len);
>> +            tmp[len] = '\0';
>> +
>> +            *backingFormat = virStorageFileFormatTypeFromString(tmp);
>>               if (*backingFormat <= VIR_STORAGE_FILE_NONE)
>>                   return -1;
>>           }
>> +        }
> 
> Pre-existing, but there's missing 'break;' here. Since you're touching 
> these lines, might be worth putting it here.
> 

Thanks, will fix before pushing

- Cole