macsec: Detect if Rx skb is macsec-related for offloading devices that update md_dst

Can now correctly identify where the packets should be delivered by using
md_dst or its absence on devices that provide it.

This detection is not possible without device drivers that update md_dst. A
fallback pattern should be used for supporting such device drivers. This
fallback mode causes multicast messages to be cloned to both the non-macsec
and macsec ports, independent of whether the multicast message received was
encrypted over MACsec or not. Other non-macsec traffic may also fail to be
handled correctly for devices in promiscuous mode.

Link: https://lore.kernel.org/netdev/ZULRxX9eIbFiVi7v@hog/
Cc: Sabrina Dubroca <sd@queasysnail.net>
Cc: stable@vger.kernel.org
Fixes: 860ead89 ("net/macsec: Add MACsec skb_metadata_dst Rx Data path support")
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Benjamin Poirier <bpoirier@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/20240423181319.115860-4-rrameshbabu@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/macsec.c

@@ -999,10 +999,12 @@ static enum rx_handler_result handle_not_macsec(struct sk_buff *skb)
 	struct metadata_dst *md_dst;
 	struct macsec_rxh_data *rxd;
 	struct macsec_dev *macsec;
+	bool is_macsec_md_dst;
 
 	rcu_read_lock();
 	rxd = macsec_data_rcu(skb->dev);
 	md_dst = skb_metadata_dst(skb);
+	is_macsec_md_dst = md_dst && md_dst->type == METADATA_MACSEC;
 
 	list_for_each_entry_rcu(macsec, &rxd->secys, secys) {
 		struct sk_buff *nskb;
@@ -1013,14 +1015,42 @@ static enum rx_handler_result handle_not_macsec(struct sk_buff *skb)
 		 * the SecTAG, so we have to deduce which port to deliver to.
 		 */
 		if (macsec_is_offloaded(macsec) && netif_running(ndev)) {
-			struct macsec_rx_sc *rx_sc = NULL;
+			const struct macsec_ops *ops;
+
+			ops = macsec_get_ops(macsec, NULL);
+
+			if (ops->rx_uses_md_dst && !is_macsec_md_dst)
+				continue;
 
-			if (md_dst && md_dst->type == METADATA_MACSEC)
-				rx_sc = find_rx_sc(&macsec->secy, md_dst->u.macsec_info.sci);
+			if (is_macsec_md_dst) {
+				struct macsec_rx_sc *rx_sc;
 
-			if (md_dst && md_dst->type == METADATA_MACSEC && !rx_sc)
+				/* All drivers that implement MACsec offload
+				 * support using skb metadata destinations must
+				 * indicate that they do so.
+				 */
+				DEBUG_NET_WARN_ON_ONCE(!ops->rx_uses_md_dst);
+				rx_sc = find_rx_sc(&macsec->secy,
+						   md_dst->u.macsec_info.sci);
+				if (!rx_sc)
 					continue;
+				/* device indicated macsec offload occurred */
+				skb->dev = ndev;
+				skb->pkt_type = PACKET_HOST;
+				eth_skb_pkt_type(skb, ndev);
+				ret = RX_HANDLER_ANOTHER;
+				goto out;
+			}
 
+			/* This datapath is insecure because it is unable to
+			 * enforce isolation of broadcast/multicast traffic and
+			 * unicast traffic with promiscuous mode on the macsec
+			 * netdev. Since the core stack has no mechanism to
+			 * check that the hardware did indeed receive MACsec
+			 * traffic, it is possible that the response handling
+			 * done by the MACsec port was to a plaintext packet.
+			 * This violates the MACsec protocol standard.
+			 */
 			if (ether_addr_equal_64bits(hdr->h_dest,
 						    ndev->dev_addr)) {
 				/* exact match, divert skb to this port */
@@ -1036,14 +1066,10 @@ static enum rx_handler_result handle_not_macsec(struct sk_buff *skb)
 					break;
 
 				nskb->dev = ndev;
-				if (ether_addr_equal_64bits(hdr->h_dest,
-							    ndev->broadcast))
-					nskb->pkt_type = PACKET_BROADCAST;
-				else
-					nskb->pkt_type = PACKET_MULTICAST;
+				eth_skb_pkt_type(nskb, ndev);
 
 				__netif_rx(nskb);
-			} else if (rx_sc || ndev->flags & IFF_PROMISC) {
+			} else if (ndev->flags & IFF_PROMISC) {
 				skb->dev = ndev;
 				skb->pkt_type = PACKET_HOST;
 				ret = RX_HANDLER_ANOTHER;