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

[Jason Wang]

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.


> 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