Re: [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get_config()

[Stefano Garzarella]

On Tue, Feb 09, 2021 at 11:24:03AM +0800, Jason Wang wrote:
> On 2021/2/9 上午2:38, Michael S. Tsirkin wrote:
> > On Mon, Feb 08, 2021 at 05:17:41PM +0100, Stefano Garzarella wrote:
> > > It's legal to have 'offset + len' equal to
> > > sizeof(struct virtio_net_config), since 'ndev->config' is a
> > > 'struct virtio_net_config', so we can safely copy its content under
> > > this condition.
> > >
> > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > ---
> > >  drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index dc88559a8d49..10e9b09932eb 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -1820,7 +1820,7 @@ static void mlx5_vdpa_get_config(struct vdpa_device *vdev, unsigned int offset,
> > >  	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> > >  	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> > > -	if (offset + len < sizeof(struct virtio_net_config))
> > > +	if (offset + len <= sizeof(struct virtio_net_config))
> > >  		memcpy(buf, (u8 *)&ndev->config + offset, len);
> > >  }
> > Actually first I am not sure we need these checks at all.
> > vhost_vdpa_config_validate already validates the values, right?
>
>
> I think they're working at different levels. There's no guarantee that 
> vhost-vdpa is the driver for this vdpa device.

Maybe we can do these checks in the vdpa_get_config() helper and we can 
also add a vdpa_set_config() to do the same.

Thanks,
Stefano

> > Second, what will happen when we extend the struct and then
> > run new userspace on an old kernel? Looks like it will just
> > fail right? So what is the plan?
>
>
> In this case, get_config() should match the spec behaviour. That is to 
> say the size of config space depends on the feature negotiated.
>
> Thanks
>
>
> >  I think we should
> > allow a bigger size, and return the copied config size to userspace.
> >
> >
> > > --
> > > 2.29.2