net_util: Tolerate some unsupported command classes

Windows NetKVM driver (>= 0.1.271) issues unsupported command classes
even when they are not even advertised.

According to the Virtio 1.2 specification:

RX, VLAN, and ANNOUNCE control paths are only meaningful when their
corresponding features are negotiated in sections 5.1.3.1, 5.1.6.5.1.2,
5.1.6.5.2.2, and 5.1.6.5.4.1.

RX and VLAN are explicitly described as best-effort in sections
5.1.6.5.1 and 5.1.6.5.3.

Instead of returning an error to the guest, return success to the guest.

Fixes: cloud-hypervisor#7925
Signed-off-by: Wei Liu <liuwe@microsoft.com>

Author: liuw

net_util/src/ctrl_queue.rs

@@ -2,12 +2,16 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use log::{error, info, warn};
+use log::{debug, error, info, warn};
 use thiserror::Error;
 use virtio_bindings::virtio_net::{
-    VIRTIO_NET_CTRL_GUEST_OFFLOADS, VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, VIRTIO_NET_CTRL_MQ,
-    VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN,
-    VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET, VIRTIO_NET_ERR, VIRTIO_NET_OK,
+    VIRTIO_NET_CTRL_ANNOUNCE, VIRTIO_NET_CTRL_ANNOUNCE_ACK, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
+    VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, VIRTIO_NET_CTRL_MQ, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX,
+    VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET, VIRTIO_NET_CTRL_RX,
+    VIRTIO_NET_CTRL_RX_ALLMULTI, VIRTIO_NET_CTRL_RX_ALLUNI, VIRTIO_NET_CTRL_RX_NOBCAST,
+    VIRTIO_NET_CTRL_RX_NOMULTI, VIRTIO_NET_CTRL_RX_NOUNI, VIRTIO_NET_CTRL_RX_PROMISC,
+    VIRTIO_NET_CTRL_VLAN, VIRTIO_NET_CTRL_VLAN_ADD, VIRTIO_NET_CTRL_VLAN_DEL, VIRTIO_NET_ERR,
+    VIRTIO_NET_OK,
 };
 use virtio_queue::{Queue, QueueT};
 use vm_memory::{ByteValued, Bytes, GuestMemoryError};
@@ -53,6 +57,26 @@ pub struct ControlHeader {
 // SAFETY: ControlHeader only contains a series of integers
 unsafe impl ByteValued for ControlHeader {}
 
+fn is_tolerated_ctrl_command(ctrl_hdr: ControlHeader) -> bool {
+    match u32::from(ctrl_hdr.class) {
+        VIRTIO_NET_CTRL_RX => matches!(
+            u32::from(ctrl_hdr.cmd),
+            VIRTIO_NET_CTRL_RX_PROMISC
+                | VIRTIO_NET_CTRL_RX_ALLMULTI
+                | VIRTIO_NET_CTRL_RX_ALLUNI
+                | VIRTIO_NET_CTRL_RX_NOMULTI
+                | VIRTIO_NET_CTRL_RX_NOUNI
+                | VIRTIO_NET_CTRL_RX_NOBCAST
+        ),
+        VIRTIO_NET_CTRL_VLAN => matches!(
+            u32::from(ctrl_hdr.cmd),
+            VIRTIO_NET_CTRL_VLAN_ADD | VIRTIO_NET_CTRL_VLAN_DEL
+        ),
+        VIRTIO_NET_CTRL_ANNOUNCE => u32::from(ctrl_hdr.cmd) == VIRTIO_NET_CTRL_ANNOUNCE_ACK,
+        _ => false,
+    }
+}
+
 pub struct CtrlQueue {
     pub taps: Vec<Tap>,
 }
@@ -128,6 +152,10 @@ impl CtrlQueue {
                         false
                     }
                 }
+                _ if is_tolerated_ctrl_command(ctrl_hdr) => {
+                    debug!("Ignoring unsupported but tolerated control command {ctrl_hdr:?}");
+                    true
+                }
                 _ => {
                     warn!("Unsupported command {ctrl_hdr:?}");
                     false