Re: [Qemu-devel] [PATCH v3 4/4] qcow2: Avoid memory over-allocation on compressed images

[Eric Blake <eblake@redhat.com>]

On 02/22/2018 10:23 AM, Alberto Garcia wrote:
> On Thu 22 Feb 2018 04:59:22 PM CET, Eric Blake wrote:
>>           sector_offset = coffset & 511;
>>           csize = nb_csectors * 512 - sector_offset;
>             [...]
>> +        assert(csize < 2 * s->cluster_size);
> 
> I think it should be <=
> 
> If sector_offset is 0 and nb_csector is the maximum allowed value then
> csize is exactly 2 * s->cluster_size bytes.

Sigh, yes you're right.  I was thinking that "qemu sets csize to a 
maximum of s->cluster_size, but only when sector_offset is not 0" - but 
as long as we're dealing with externally-produced images, sector_offset 
can be 0 at the same time as providing all 1s to the field.  So I did 
indeed have an off-by-one.

Perhaps the maintainer can fix it up, instead of me spinning a v4?

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