RE: [RFC PATCH 2/6] hv_sock: Copy packets sent by Hyper-V out of the ring buffer

[Michael Kelley (LINUX)]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Wednesday, April 13, 2022 1:48 PM
> 
> Pointers to VMbus packets sent by Hyper-V are used by the hv_sock driver
> within the gues VM.  Hyper-V can send packets with erroneous values or

s/gues/guest/

> modify packet fields after they are processed by the guest.  To defend
> against these scenarios, copy the incoming packet after validating its
> length and offset fields using hv_pkt_iter_{first,next}().  In this way,
> the packet can no longer be modified by the host.
> 
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
>  net/vmw_vsock/hyperv_transport.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index 943352530936e..8c37d07017fc4 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -78,6 +78,9 @@ struct hvs_send_buf {
>  					 ALIGN((payload_len), 8) + \
>  					 VMBUS_PKT_TRAILER_SIZE)
> 
> +/* Upper bound on the size of a VMbus packet for hv_sock */
> +#define HVS_MAX_PKT_SIZE	HVS_PKT_LEN(HVS_MTU_SIZE)
> +
>  union hvs_service_id {
>  	guid_t	srv_id;
> 
> @@ -378,6 +381,8 @@ static void hvs_open_connection(struct vmbus_channel *chan)
>  		rcvbuf = ALIGN(rcvbuf, HV_HYP_PAGE_SIZE);
>  	}
> 
> +	chan->max_pkt_size = HVS_MAX_PKT_SIZE;
> +
>  	ret = vmbus_open(chan, sndbuf, rcvbuf, NULL, 0, hvs_channel_cb,
>  			 conn_from_host ? new : sk);
>  	if (ret != 0) {
> @@ -602,7 +607,7 @@ static ssize_t hvs_stream_dequeue(struct vsock_sock *vsk,
> struct msghdr *msg,
>  		return -EOPNOTSUPP;
> 
>  	if (need_refill) {
> -		hvs->recv_desc = hv_pkt_iter_first_raw(hvs->chan);
> +		hvs->recv_desc = hv_pkt_iter_first(hvs->chan);
>  		if (!hvs->recv_desc)
>  			return -ENOBUFS;
>  		ret = hvs_update_recv_data(hvs);
> @@ -618,7 +623,7 @@ static ssize_t hvs_stream_dequeue(struct vsock_sock *vsk,
> struct msghdr *msg,
> 
>  	hvs->recv_data_len -= to_read;
>  	if (hvs->recv_data_len == 0) {
> -		hvs->recv_desc = hv_pkt_iter_next_raw(hvs->chan, hvs->recv_desc);
> +		hvs->recv_desc = hv_pkt_iter_next(hvs->chan, hvs->recv_desc);
>  		if (hvs->recv_desc) {
>  			ret = hvs_update_recv_data(hvs);
>  			if (ret)
> --
> 2.25.1