Re: [Qemu-devel] [PATCH 2/3] virtio: Strictly check queue_size when adding virtqueue

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/15/2011 05:53 PM, Amos Kong wrote:
> On Wed, Jun 15, 2011 at 11:36:02PM +0300, Michael S. Tsirkin wrote:
>> On Wed, Jun 15, 2011 at 10:25:33PM +0800, Amos Kong wrote:
>>> Qemu should abort when 'queue_size' is less than or equals to zero.
>>>
>>> Signed-off-by: Amos Kong<akong@redhat.com>
>>
>> BTW, these patches apply upstream so should be sent to qemu-devel.
>>
>>> ---
>>>   hw/virtio.c |    3 ++-
>>>   1 files changed, 2 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/hw/virtio.c b/hw/virtio.c
>>> index a3d0eee..855fe54 100644
>>> --- a/hw/virtio.c
>>> +++ b/hw/virtio.c
>>> @@ -612,7 +612,8 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
>>>               break;
>>>       }
>>>
>>> -    if (i == VIRTIO_PCI_QUEUE_MAX || queue_size>  VIRTQUEUE_MAX_SIZE)
>>> +    if (i == VIRTIO_PCI_QUEUE_MAX || queue_size>  VIRTQUEUE_MAX_SIZE ||
>>> +        queue_size<= 0)
>>>           abort();
>>>
>>>       vdev->vq[i].vring.num = queue_size;
>>
>> These checks are just a debugging aid - there's no way
>> for the guest or user to trigger this.
>> I guess it does no harm, but what are we guarding against?
>> Why would anyone pass in a negative value?
>
> It seems all exist usage of this function are all right, guest/user could not trigger this right now.
> So we don't need to fix this kind of problem?

If it's not valid for queue_size to be negative, then the type ought to 
be unsigned.

Regards,

Anthony Liguori

>