Re: [PATCH for 5.10] vdpa_sim: fix param validation in vdpasim_get_config()

[Greg KH]

On Thu, Feb 11, 2021 at 05:25:19PM +0100, Stefano Garzarella wrote:
> Commit 65b709586e222fa6ffd4166ac7fdb5d5dad113ee upstream.

No, this really is not that commit, so please do not say it is.

> Before this patch, if 'offset + len' was equal to
> sizeof(struct virtio_net_config), the entire buffer wasn't filled,
> returning incorrect values to the caller.
> 
> Since 'vdpasim->config' type is 'struct virtio_net_config', we can
> safely copy its content under this condition.
> 
> Commit 65b709586e22 ("vdpa_sim: add get_config callback in
> vdpasim_dev_attr") unintentionally solved it upstream while
> refactoring vdpa_sim.c to support multiple devices. But we don't want
> to backport it to stable branches as it contains many changes.
> 
> Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 6a90fdb9cbfc..8ca178d7b02f 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -572,7 +572,7 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
>  {
>  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>  
> -	if (offset + len < sizeof(struct virtio_net_config))
> +	if (offset + len <= sizeof(struct virtio_net_config))
>  		memcpy(buf, (u8 *)&vdpasim->config + offset, len);
>  }

I'll be glad to take a one-off patch, but why can't we take the real
upstream patch?  That is always the better long-term solution, right?

thanks,

greg k-h