macsec: MACsec SCI assignment for ES = 0

JIRA: https://issues.redhat.com/browse/RHEL-115574

commit d9816ec
Author: Carlos Fernandez <carlos.fernandez@technica-engineering.de>
Date:   Mon Jun 9 09:26:26 2025 +0200

    macsec: MACsec SCI assignment for ES = 0

    According to 802.1AE standard, when ES and SC flags in TCI are zero,
    used SCI should be the current active SC_RX. Current code uses the
    header MAC address. Without this patch, when ES flag is 0 (using a
    bridge or switch), header MAC will not fit the SCI and MACSec frames
    will be discarted.

    In order to test this issue, MACsec link should be stablished between
    two interfaces, setting SC and ES flags to zero and a port identifier
    different than one. For example, using ip macsec tools:

    ip link add link $ETH0 macsec0 type macsec port 11 send_sci off
    end_station off
    ip macsec add macsec0 tx sa 0 pn 2 on key 01 $ETH1_KEY
    ip macsec add macsec0 rx port 11 address $ETH1_MAC
    ip macsec add macsec0 rx port 11 address $ETH1_MAC sa 0 pn 2 on key 02
    ip link set dev macsec0 up

    ip link add link $ETH1 macsec1 type macsec port 11 send_sci off
    end_station off
    ip macsec add macsec1 tx sa 0 pn 2 on key 01 $ETH0_KEY
    ip macsec add macsec1 rx port 11 address $ETH0_MAC
    ip macsec add macsec1 rx port 11 address $ETH0_MAC sa 0 pn 2 on key 02
    ip link set dev macsec1 up

    Fixes: c09440f ("macsec: introduce IEEE 802.1AE driver")
    Co-developed-by: Andreu Montiel <Andreu.Montiel@technica-engineering.de>
    Signed-off-by: Andreu Montiel <Andreu.Montiel@technica-engineering.de>
    Signed-off-by: Carlos Fernandez <carlos.fernandez@technica-engineering.de>
    Reviewed-by: Subbaraya Sundeep <sbhatta@marvell.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

drivers/net/macsec.c

@@ -246,15 +246,39 @@ static sci_t make_sci(const u8 *addr, __be16 port)
 	return sci;
 }
 
-static sci_t macsec_frame_sci(struct macsec_eth_header *hdr, bool sci_present)
+static sci_t macsec_active_sci(struct macsec_secy *secy)
 {
-	sci_t sci;
+	struct macsec_rx_sc *rx_sc = rcu_dereference_bh(secy->rx_sc);
+
+	/* Case single RX SC */
+	if (rx_sc && !rcu_dereference_bh(rx_sc->next))
+		return (rx_sc->active) ? rx_sc->sci : 0;
+	/* Case no RX SC or multiple */
+	else
+		return 0;
+}
+
+static sci_t macsec_frame_sci(struct macsec_eth_header *hdr, bool sci_present,
+			      struct macsec_rxh_data *rxd)
+{
+	struct macsec_dev *macsec;
+	sci_t sci = 0;
 
-	if (sci_present)
+	/* SC = 1 */
+	if (sci_present) {
 		memcpy(&sci, hdr->secure_channel_id,
 		       sizeof(hdr->secure_channel_id));
-	else
+	/* SC = 0; ES = 0 */
+	} else if ((!(hdr->tci_an & (MACSEC_TCI_ES | MACSEC_TCI_SC))) &&
+		   (list_is_singular(&rxd->secys))) {
+		/* Only one SECY should exist on this scenario */
+		macsec = list_first_or_null_rcu(&rxd->secys, struct macsec_dev,
+						secys);
+		if (macsec)
+			return macsec_active_sci(&macsec->secy);
+	} else {
 		sci = make_sci(hdr->eth.h_source, MACSEC_PORT_ES);
+	}
 
 	return sci;
 }
@@ -1108,7 +1132,7 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 	struct macsec_rxh_data *rxd;
 	struct macsec_dev *macsec;
 	unsigned int len;
-	sci_t sci;
+	sci_t sci = 0;
 	u32 hdr_pn;
 	bool cbit;
 	struct pcpu_rx_sc_stats *rxsc_stats;
@@ -1155,11 +1179,14 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 
 	macsec_skb_cb(skb)->has_sci = !!(hdr->tci_an & MACSEC_TCI_SC);
 	macsec_skb_cb(skb)->assoc_num = hdr->tci_an & MACSEC_AN_MASK;
-	sci = macsec_frame_sci(hdr, macsec_skb_cb(skb)->has_sci);
 
 	rcu_read_lock();
 	rxd = macsec_data_rcu(skb->dev);
 
+	sci = macsec_frame_sci(hdr, macsec_skb_cb(skb)->has_sci, rxd);
+	if (!sci)
+		goto drop_nosc;
+
 	list_for_each_entry_rcu(macsec, &rxd->secys, secys) {
 		struct macsec_rx_sc *sc = find_rx_sc(&macsec->secy, sci);
 
@@ -1282,6 +1309,7 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 	macsec_rxsa_put(rx_sa);
 drop_nosa:
 	macsec_rxsc_put(rx_sc);
+drop_nosc:
 	rcu_read_unlock();
 drop_direct:
 	kfree_skb(skb);