Re: [Qemu-devel] [PATCH] qemu-img: Add --backing-chain option to info command

[Kevin Wolf]

Am 12.10.2012 16:24, schrieb Eric Blake:
> On 10/12/2012 08:09 AM, Stefan Hajnoczi wrote:
>> The qemu-img info --backing-chain option enumerates the backing file
>> chain.  For example, for base.qcow2 <- snap1.qcow2 <- snap2.qcow2 the
>> output becomes:
>>
> 
>> +    do {
>> +        bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS | BDRV_O_NO_BACKING,
>> +                           false);
>> +        if (!bs) {
>> +            goto err;
>> +        }
> 
>> +    } while (filename);
> 
> Eww - infinite loop if presented with malicious data where someone has
> used 'qemu-img rebase -u' to create a cycle.  I think you need a
> followup patch that hashes which files have been opened to date, and
> abort the loop once a cycle is detected.

That would already cause problems in bdrv_open(), so I'd consider it a
separate bug. We should fail gracefully when trying to open such an
image. Once it's open, other code can trust that the chain makes sense.

Kevin