Re: Re: [PATCH v3] virtio-blk: Add validation for block size in config space

[Yongji Xie]

On Tue, Jun 22, 2021 at 6:11 PM Stefan Hajnoczi <stefanha@xxxxxxxxxx> wrote:
>
> On Thu, Jun 17, 2021 at 01:10:04PM +0800, Xie Yongji wrote:
> > This ensures that we will not use an invalid block size
> > in config space (might come from an untrusted device).
> >
> > Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
> > ---
> >  drivers/block/virtio_blk.c | 29 +++++++++++++++++++++++------
> >  1 file changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index b9fa3ef5b57c..bbdae989f1ea 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -696,6 +696,28 @@ static const struct blk_mq_ops virtio_mq_ops = {
> >  static unsigned int virtblk_queue_depth;
> >  module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);
> >
> > +static int virtblk_validate(struct virtio_device *vdev)
> > +{
> > +     u32 blk_size;
> > +
> > +     if (!vdev->config->get) {
> > +             dev_err(&vdev->dev, "%s failure: config access disabled\n",
> > +                     __func__);
> > +             return -EINVAL;
> > +     }
> > +
> > +     if (!virtio_has_feature(vdev, VIRTIO_BLK_F_BLK_SIZE))
> > +             return 0;
> > +
> > +     blk_size = virtio_cread32(vdev,
> > +                     offsetof(struct virtio_blk_config, blk_size));
> > +
> > +     if (blk_size < SECTOR_SIZE || blk_size > PAGE_SIZE)
> > +             __virtio_clear_bit(vdev, VIRTIO_BLK_F_BLK_SIZE);
> > +
> > +     return 0;
> > +}
>
> I saw Michael asked for .validate() in v2. I would prefer to keep
> everything in virtblk_probe() instead of adding .validate() because:
>
> - There is a race condition that an untrusted device can exploit since
>   virtblk_probe() fetches the value again.
>

Good point! I agree that it's better to add the validation in virtblk_probe().

Thanks,
Yongji