Re: [PATCH] vhost/net: length miscalculation

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2015-01-07 at 10:55 +0200, Michael S. Tsirkin wrote:
> commit 8b38694a2dc8b18374310df50174f1e4376d6824
>     vhost/net: virtio 1.0 byte swap
> had this chunk:
> -       heads[headcount - 1].len += datalen;
> +       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> 
> This adds datalen with the wrong sign, causing guest panics.
> 
> Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
> Reported-by: Alex Williamson <alex.williamson@redhat.com>
> Suggested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> Alex, could you please confirm this fixes the crash for you?

Confirmed, this works.  Thanks,

Alex

>  drivers/vhost/net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 14419a8..d415d69 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -538,7 +538,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
>  		++headcount;
>  		seg += in;
>  	}
> -	heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> +	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
>  	*iovcount = seg;
>  	if (unlikely(log))
>  		*log_num = nlogs;