netdev - Re: [PATCH 2/5] hv_sock: Copy packets sent by Hyper-V out of the ring buffer

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Date:   Thu, 21 Apr 2022 15:58:39 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] hv_sock: Copy packets sent by Hyper-V out of the
 ring buffer

On Wed, Apr 20, 2022 at 10:07:17PM +0200, Andrea Parri (Microsoft) wrote:
>Pointers to VMbus packets sent by Hyper-V are used by the hv_sock driver
>within the guest VM.  Hyper-V can send packets with erroneous values or
>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@...il.com>
>---
> 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;
>+

premise, I don't know HyperV channels :-(

Is this change necessary to use hv_pkt_iter_first() instead of 
hv_pkt_iter_first_raw()?

If yes, then please mention that you set this value in the commit 
message, otherwise maybe better to have a separate patch.

Thanks,
Stefano

> 	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
>