Subject: Re: [PATCH] vhost/vsock: accept only packets with the right dst_cid

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 10 Dec 2019 09:05:58 -0500

On Fri, Dec 06, 2019 at 03:39:12PM +0100, Stefano Garzarella wrote:
> When we receive a new packet from the guest, we check if the
> src_cid is correct, but we forgot to check the dst_cid.
> 
> The host should accept only packets where dst_cid is
> equal to the host CID.
> 
> Signed-off-by: Stefano Garzarella <[email-masked]>

what's the implication of processing incorrect dst cid?
I think mostly it's malformed guests, right?
Everyone else just passes the known host cid ...

> ---
>  drivers/vhost/vsock.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 50de0642dea6..c2d7d57e98cf 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -480,7 +480,9 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
>  		virtio_transport_deliver_tap_pkt(pkt);
>  
>  		/* Only accept correctly addressed packets */
> -		if (le64_to_cpu(pkt->hdr.src_cid) == vsock->guest_cid)
> +		if (le64_to_cpu(pkt->hdr.src_cid) == vsock->guest_cid &&
> +		    le64_to_cpu(pkt->hdr.dst_cid) ==
> +		    vhost_transport_get_local_cid())
>  			virtio_transport_recv_pkt(&vhost_transport, pkt);
>  		else
>  			virtio_transport_free_pkt(pkt);
> -- 
> 2.23.0