Send source link-layer address option in router advertisements.

With this, hosts immediately learn the layer 2 (i.e. ethernet mac)
address of their default router and don't need to do another round
trip.

It also turns out that apple devices (macOS & iOS) install the default
route as what they call "interface scoped" if a DNS option is present
and the source link-layer address option is absent. This effectively
makes the default route unusable.

Problem with fruit devices tracked down & diff by Ryan Vogt (rvogt.ca
AT gmail), thanks!

OK sthen, bket

6 files changed, 64 insertions, 7 deletions

diff --git a/usr.sbin/rad/frontend.c b/usr.sbin/rad/frontend.c
index 6748e43732d..ca8719a4a1b 100644
--- a/usr.sbin/rad/frontend.c
+++ b/usr.sbin/rad/frontend.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: frontend.c,v 1.45 2024/04/23 22:11:59 florian Exp $	*/
+/*	$OpenBSD: frontend.c,v 1.46 2024/05/17 06:50:14 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -56,6 +56,7 @@
 #include <sys/uio.h>
 
 #include <net/if.h>
+#include <net/if_dl.h>
 #include <net/if_types.h>
 #include <net/route.h>
 
@@ -120,6 +121,12 @@ struct nd_opt_pref64 {
 	u_int8_t	nd_opt_pref64[12];
 };
 
+struct nd_opt_source_link_addr {
+	u_int8_t		nd_opt_source_link_addr_type;
+	u_int8_t		nd_opt_source_link_addr_len;
+	struct ether_addr	nd_opt_source_link_addr_hw_addr;
+};
+
 TAILQ_HEAD(, ra_iface)	ra_interfaces;
 
 __dead void		 frontend_shutdown(void);
@@ -1099,6 +1106,7 @@ void
 build_packet(struct ra_iface *ra_iface)
 {
 	struct nd_router_advert		*ra;
+	struct nd_opt_source_link_addr	*ndopt_source_link_addr;
 	struct nd_opt_mtu		*ndopt_mtu;
 	struct nd_opt_prefix_info	*ndopt_pi;
 	struct ra_iface_conf		*ra_iface_conf;
@@ -1110,6 +1118,8 @@ build_packet(struct ra_iface *ra_iface)
 	struct ra_rdnss_conf		*ra_rdnss;
 	struct ra_dnssl_conf		*ra_dnssl;
 	struct ra_pref64_conf		*pref64;
+	struct ifaddrs			*ifap, *ifa;
+	struct sockaddr_dl		*sdl;
 	size_t				 len, label_len;
 	uint8_t				*p, buf[RA_MAX_SIZE];
 	char				*label_start, *label_end;
@@ -1119,6 +1129,8 @@ build_packet(struct ra_iface *ra_iface)
 	ra_options_conf = &ra_iface_conf->ra_options;
 
 	len = sizeof(*ra);
+	if (ra_iface_conf->ra_options.source_link_addr)
+		len += sizeof(*ndopt_source_link_addr);
 	if (ra_options_conf->mtu > 0)
 		len += sizeof(*ndopt_mtu);
 	len += sizeof(*ndopt_pi) * ra_iface->prefix_count;
@@ -1170,6 +1182,37 @@ build_packet(struct ra_iface *ra_iface)
 	ra->nd_ra_retransmit = htonl(ra_options_conf->retrans_timer);
 	p += sizeof(*ra);
 
+	if (ra_iface_conf->ra_options.source_link_addr) {
+		ndopt_source_link_addr = (struct nd_opt_source_link_addr *)p;
+		ndopt_source_link_addr->nd_opt_source_link_addr_type =
+		    ND_OPT_SOURCE_LINKADDR;
+		ndopt_source_link_addr->nd_opt_source_link_addr_len = 1;
+		if (getifaddrs(&ifap) != 0) {
+			ifap = NULL;
+			log_warn("getifaddrs");
+		}
+		for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
+			if (ifa->ifa_addr == NULL ||
+			    ifa->ifa_addr->sa_family != AF_LINK)
+				continue;
+			if (strcmp(ra_iface->name, ifa->ifa_name) != 0)
+				continue;
+			sdl = (struct sockaddr_dl *)ifa->ifa_addr;
+			if (sdl->sdl_type != IFT_ETHER ||
+			    sdl->sdl_alen != ETHER_ADDR_LEN)
+				continue;
+			memcpy(&ndopt_source_link_addr->
+			    nd_opt_source_link_addr_hw_addr,
+			    LLADDR(sdl), ETHER_ADDR_LEN);
+			break;
+		}
+		if (ifap != NULL) {
+			freeifaddrs(ifap);
+			p += sizeof(*ndopt_source_link_addr);
+		} else
+			len -= sizeof(*ndopt_source_link_addr);
+	}
+
 	if (ra_options_conf->mtu > 0) {
 		ndopt_mtu = (struct nd_opt_mtu *)p;
 		ndopt_mtu->nd_opt_mtu_type = ND_OPT_MTU;
diff --git a/usr.sbin/rad/parse.y b/usr.sbin/rad/parse.y
index 66cc0c0ab64..bf6b6e6b86d 100644
--- a/usr.sbin/rad/parse.y
+++ b/usr.sbin/rad/parse.y
@@ -1,4 +1,4 @@
-/*	$OpenBSD: parse.y,v 1.22 2024/04/23 22:11:59 florian Exp $	*/
+/*	$OpenBSD: parse.y,v 1.23 2024/05/17 06:50:14 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -122,6 +122,7 @@ typedef struct {
 %token	CONFIGURATION OTHER LIFETIME REACHABLE TIME RETRANS TIMER
 %token	AUTO PREFIX VALID PREFERENCE PREFERRED LIFETIME ONLINK AUTONOMOUS
 %token	ADDRESS_CONFIGURATION DNS NAMESERVER SEARCH MTU NAT64 HIGH MEDIUM LOW
+%token	SOURCE LINK_LAYER
 
 %token	<v.string>	STRING
 %token	<v.number>	NUMBER
@@ -226,6 +227,9 @@ ra_opt_block	: DEFAULT ROUTER yesno {
 		| RETRANS TIMER NUMBER {
 			ra_options->retrans_timer = $3;
 		}
+		| SOURCE LINK_LAYER ADDRESS yesno {
+			ra_options->source_link_addr = $4;
+		}
 		| MTU NUMBER {
 			ra_options->mtu = $2;
 		}
@@ -523,6 +527,7 @@ lookup(char *s)
 		{"interface",		RA_IFACE},
 		{"lifetime",		LIFETIME},
 		{"limit",		LIMIT},
+		{"link-layer",		LINK_LAYER},
 		{"low",			LOW},
 		{"managed",		MANAGED},
 		{"medium",		MEDIUM},
@@ -539,6 +544,7 @@ lookup(char *s)
 		{"retrans",		RETRANS},
 		{"router",		ROUTER},
 		{"search",		SEARCH},
+		{"source",		SOURCE},
 		{"time",		TIME},
 		{"timer",		TIMER},
 		{"valid",		VALID},
diff --git a/usr.sbin/rad/printconf.c b/usr.sbin/rad/printconf.c
index 184a5df2dc1..b49a7748ae7 100644
--- a/usr.sbin/rad/printconf.c
+++ b/usr.sbin/rad/printconf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: printconf.c,v 1.8 2024/04/23 22:11:59 florian Exp $	*/
+/*	$OpenBSD: printconf.c,v 1.9 2024/05/17 06:50:14 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -78,6 +78,8 @@ print_ra_options(const char *indent, const struct ra_options_conf *ra_options)
 	printf("%srouter lifetime %d\n", indent, ra_options->router_lifetime);
 	printf("%sreachable time %u\n", indent, ra_options->reachable_time);
 	printf("%sretrans timer %u\n", indent, ra_options->retrans_timer);
+	printf("%ssource link-layer address %s\n", indent,
+	    yesno(ra_options->source_link_addr));
 	if (ra_options->mtu > 0)
 		printf("%smtu %u\n", indent, ra_options->mtu);
 
diff --git a/usr.sbin/rad/rad.c b/usr.sbin/rad/rad.c
index b283e58fbf1..a0c317265b0 100644
--- a/usr.sbin/rad/rad.c
+++ b/usr.sbin/rad/rad.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rad.c,v 1.29 2023/04/19 12:58:16 jsg Exp $	*/
+/*	$OpenBSD: rad.c,v 1.30 2024/05/17 06:50:14 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -757,6 +757,7 @@ config_new_empty(void)
 	xconf->ra_options.router_lifetime = ADV_DEFAULT_LIFETIME;
 	xconf->ra_options.reachable_time = 0;
 	xconf->ra_options.retrans_timer = 0;
+	xconf->ra_options.source_link_addr = 1;
 	xconf->ra_options.mtu = 0;
 	xconf->ra_options.rdns_lifetime = DEFAULT_RDNS_LIFETIME;
 	SIMPLEQ_INIT(&xconf->ra_options.ra_rdnss_list);
diff --git a/usr.sbin/rad/rad.conf.5 b/usr.sbin/rad/rad.conf.5
index f82ccfd216e..87c2b328662 100644
--- a/usr.sbin/rad/rad.conf.5
+++ b/usr.sbin/rad/rad.conf.5
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: rad.conf.5,v 1.23 2024/04/23 22:17:49 florian Exp $
+.\"	$OpenBSD: rad.conf.5,v 1.24 2024/05/17 06:50:14 florian Exp $
 .\"
 .\" Copyright (c) 2018 Florian Obser <florian@openbsd.org>
 .\" Copyright (c) 2005 Esben Norby <norby@openbsd.org>
@@ -18,7 +18,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: April 23 2024 $
+.Dd $Mdocdate: May 17 2024 $
 .Dt RAD.CONF 5
 .Os
 .Sh NAME
@@ -127,6 +127,10 @@ The default is medium.
 .\" XXX
 .\" .It Ic retrans timer Ar number
 .\" XXX
+.It Ic source link-layer address Pq Ic yes Ns | Ns Ic no
+Add a source link-layer address option to router advertisement messages, to
+communicate the link-layer address of the sending interface.
+The default is yes.
 .El
 .Sh INTERFACES
 A list of interfaces or interface groups to send advertisements on:
diff --git a/usr.sbin/rad/rad.h b/usr.sbin/rad/rad.h
index 787e78c7c4a..442ff00fcce 100644
--- a/usr.sbin/rad/rad.h
+++ b/usr.sbin/rad/rad.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rad.h,v 1.26 2024/04/23 22:11:59 florian Exp $	*/
+/*	$OpenBSD: rad.h,v 1.27 2024/05/17 06:50:14 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -97,6 +97,7 @@ struct ra_options_conf {
 	int		router_lifetime;	/* default router lifetime */
 	uint32_t	reachable_time;
 	uint32_t	retrans_timer;
+	int		source_link_addr;	/* source link-layer address */
 	uint32_t	mtu;
 	uint32_t	rdns_lifetime;
 	SIMPLEQ_HEAD(, ra_rdnss_conf)		 ra_rdnss_list;