[eapol] Send EAPoL-Start packets to trigger EAP authentication

We have no way to force a link-layer restart in iPXE, and therefore no
way to explicitly trigger a restart of EAP authentication.  If an iPXE
script has performed some action that requires such a restart
(e.g. registering a device such that the port VLAN assignment will be
changed), then the only means currently available to effect the
restart is to reboot the whole system.  If iPXE is taking over a
physical link already used by a preceding bootloader, then even a
reboot may not work.

In the EAP model, the supplicant is a pure responder and never
initiates transmissions.  EAPoL extends this to include an EAPoL-Start
packet type that may be sent by the supplicant to (re)trigger EAP.

Add support for sending EAPoL-Start packets at two-second intervals on
links that are open and have reached physical link-up, but for which
EAP has not yet completed.  This allows "ifclose ; ifopen" to be used
to restart the EAP process.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/eapol.h

@@ -30,15 +30,23 @@ struct eapol_header {
 /** EAPoL-encapsulated EAP packets */
 #define EAPOL_TYPE_EAP 0
 
+/** EAPoL start */
+#define EAPOL_TYPE_START 1
+
 /** EAPoL key */
 #define EAPOL_TYPE_KEY 5
 
 /** An EAPoL supplicant */
 struct eapol_supplicant {
 	/** EAP supplicant */
 	struct eap_supplicant eap;
+	/** EAPoL-Start retransmission timer */
+	struct retry_timer timer;
 };
 
+/** Delay between EAPoL-Start packets */
+#define EAPOL_START_INTERVAL ( 2 * TICKS_PER_SEC )
+
 /** An EAPoL handler */
 struct eapol_handler {
 	/** Type */

src/net/eapol.c

@@ -31,6 +31,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/if_arp.h>
 #include <ipxe/netdevice.h>
 #include <ipxe/vlan.h>
+#include <ipxe/retry.h>
 #include <ipxe/eap.h>
 #include <ipxe/eapol.h>
 
@@ -47,6 +48,37 @@ static const uint8_t eapol_mac[ETH_ALEN] = {
 	0x01, 0x80, 0xc2, 0x00, 0x00, 0x03
 };
 
+/**
+ * Update EAPoL supplicant state
+ *
+ * @v supplicant	EAPoL supplicant
+ * @v timeout		Timer ticks until next EAPoL-Start (if applicable)
+ */
+static void eapol_update ( struct eapol_supplicant *supplicant,
+			   unsigned long timeout ) {
+	struct net_device *netdev = supplicant->eap.netdev;
+
+	/* Check device and EAP state */
+	if ( netdev_is_open ( netdev ) && netdev_link_ok ( netdev ) ) {
+		if ( supplicant->eap.done ) {
+
+			/* EAP has completed: stop sending EAPoL-Start */
+			stop_timer ( &supplicant->timer );
+
+		} else if ( ! timer_running ( &supplicant->timer ) ) {
+
+			/* EAP has not yet begun: start sending EAPoL-Start */
+			start_timer_fixed ( &supplicant->timer, timeout );
+		}
+
+	} else {
+
+		/* Not ready: clear completion and stop sending EAPoL-Start */
+		supplicant->eap.done = 0;
+		stop_timer ( &supplicant->timer );
+	}
+}
+
 /**
  * Process EAPoL packet
  *
@@ -154,6 +186,9 @@ static int eapol_eap_rx ( struct eapol_supplicant *supplicant,
 		goto drop;
 	}
 
+	/* Update supplicant state */
+	eapol_update ( supplicant, EAPOL_START_INTERVAL );
+
  drop:
 	free_iob ( iobuf );
 	return rc;
@@ -224,6 +259,25 @@ static int eapol_eap_tx ( struct eap_supplicant *eap, const void *data,
 	return eapol_tx ( supplicant, EAPOL_TYPE_EAP, data, len );
 }
 
+/**
+ * (Re)transmit EAPoL-Start packet
+ *
+ * @v timer		EAPoL-Start timer
+ * @v expired		Failure indicator
+ */
+static void eapol_expired ( struct retry_timer *timer, int fail __unused ) {
+	struct eapol_supplicant *supplicant =
+		container_of ( timer, struct eapol_supplicant, timer );
+	struct net_device *netdev = supplicant->eap.netdev;
+
+	/* Schedule next transmission */
+	start_timer_fixed ( timer, EAPOL_START_INTERVAL );
+
+	/* Transmit EAPoL-Start, ignoring errors */
+	DBGC2 ( netdev, "EAPOL %s transmitting Start\n", netdev->name );
+	eapol_tx ( supplicant, EAPOL_TYPE_START, NULL, 0 );
+}
+
 /**
  * Create EAPoL supplicant
  *
@@ -244,13 +298,32 @@ static int eapol_probe ( struct net_device *netdev, void *priv ) {
 	/* Initialise structure */
 	supplicant->eap.netdev = netdev;
 	supplicant->eap.tx = eapol_eap_tx;
+	timer_init ( &supplicant->timer, eapol_expired, &netdev->refcnt );
 
 	return 0;
 }
 
+/**
+ * Handle EAPoL supplicant state change
+ *
+ * @v netdev		Network device
+ * @v priv		Private data
+ */
+static void eapol_notify ( struct net_device *netdev __unused, void *priv ) {
+	struct eapol_supplicant *supplicant = priv;
+
+	/* Ignore non-EAPoL devices */
+	if ( ! supplicant->eap.netdev )
+		return;
+
+	/* Update supplicant state */
+	eapol_update ( supplicant, 0 );
+}
+
 /** EAPoL driver */
 struct net_driver eapol_driver __net_driver = {
 	.name = "EAPoL",
 	.priv_len = sizeof ( struct eapol_supplicant ),
 	.probe = eapol_probe,
+	.notify = eapol_notify,
 };