First stab at IPv6-only preferred from RFC8925.

This lets dhcpleased(8) request "IPv6-only preferred". If the
server replies with this option dhcpleased stops and does not request
a lease and deconfigures IPv4 on the interface.

For now this is pretty much useless unless one dynamically configures
pf(4) to act as a CLAT. gelatod(8) from ports can help with this.

However, this helps me while hacking on a kernel based stateless CLAT
by moving dhcpleased out of the way while having an IPv6-mostly
network configured to compare behaviour with macOS.

Input jmc
OK phessler
Input & OK sthen

6 files changed, 94 insertions, 10 deletions

diff --git a/sbin/dhcpleased/dhcpleased.conf.5 b/sbin/dhcpleased/dhcpleased.conf.5
index 4d3eb86fbad..27798d74d34 100644
--- a/sbin/dhcpleased/dhcpleased.conf.5
+++ b/sbin/dhcpleased/dhcpleased.conf.5
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: dhcpleased.conf.5,v 1.12 2023/03/02 17:09:52 jmc Exp $
+.\"	$OpenBSD: dhcpleased.conf.5,v 1.13 2023/11/25 12:00:39 florian Exp $
 .\"
 .\" Copyright (c) 2018, 2021 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: March 2 2023 $
+.Dd $Mdocdate: November 25 2023 $
 .Dt DHCPLEASED.CONF 5
 .Os
 .Sh NAME
@@ -68,6 +68,9 @@ Ignore leases from
 .Ar server-ip .
 This option can be listed multiple times.
 The default is to not ignore servers.
+.It Ic prefer ipv6
+Send the IPv6-Only preferred option to the server.
+If the server responds with the option, no lease is configured.
 .It Ic send client id Ar client-id
 Send the DHCP client identifier option with a value of
 .Ar client-id .
diff --git a/sbin/dhcpleased/dhcpleased.h b/sbin/dhcpleased/dhcpleased.h
index c5d7e204651..80fe9dcf5fe 100644
--- a/sbin/dhcpleased/dhcpleased.h
+++ b/sbin/dhcpleased/dhcpleased.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: dhcpleased.h,v 1.14 2022/03/21 04:35:41 dlg Exp $	*/
+/*	$OpenBSD: dhcpleased.h,v 1.15 2023/11/25 12:00:39 florian Exp $	*/
 
 /*
  * Copyright (c) 2017, 2021 Florian Obser <florian@openbsd.org>
@@ -132,6 +132,7 @@
 #define	DHO_NDS_SERVERS			85
 #define	DHO_NDS_TREE_NAME		86
 #define	DHO_NDS_CONTEXT			87
+#define	DHO_IPV6_ONLY_PREFERRED		108
 #define	DHO_DOMAIN_SEARCH		119
 #define	DHO_CLASSLESS_STATIC_ROUTES	121
 #define	DHO_TFTP_CONFIG_FILE		144
@@ -258,6 +259,7 @@ struct iface_conf {
 	int				 ignore;
 	struct in_addr			 ignore_servers[MAX_SERVERS];
 	int				 ignore_servers_len;
+	int				 prefer_ipv6;
 };
 
 struct dhcpleased_conf {
diff --git a/sbin/dhcpleased/engine.c b/sbin/dhcpleased/engine.c
index b2e34ef6dbc..d435850af1d 100644
--- a/sbin/dhcpleased/engine.c
+++ b/sbin/dhcpleased/engine.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: engine.c,v 1.39 2023/11/03 15:02:06 tb Exp $	*/
+/*	$OpenBSD: engine.c,v 1.40 2023/11/25 12:00:39 florian Exp $	*/
 
 /*
  * Copyright (c) 2017, 2021 Florian Obser <florian@openbsd.org>
@@ -70,6 +70,7 @@ enum if_state {
 	IF_REBINDING,
 	/* IF_INIT_REBOOT, */
 	IF_REBOOTING,
+	IF_IPV6_ONLY,
 };
 
 const char* if_state_name[] = {
@@ -82,6 +83,7 @@ const char* if_state_name[] = {
 	"Rebinding",
 	/* "Init-Reboot", */
 	"Rebooting",
+	"IPv6 only",
 };
 
 struct dhcpleased_iface {
@@ -113,6 +115,7 @@ struct dhcpleased_iface {
 	uint32_t			 lease_time;
 	uint32_t			 renewal_time;
 	uint32_t			 rebinding_time;
+	uint32_t			 ipv6_only_time;
 };
 
 LIST_HEAD(, dhcpleased_iface) dhcpleased_interfaces;
@@ -339,6 +342,7 @@ engine_dispatch_frontend(int fd, short event, void *bula)
 				case IF_REBINDING:
 				case IF_REBOOTING:
 				case IF_BOUND:
+				case IF_IPV6_ONLY:
 					state_transition(iface, IF_REBOOTING);
 					break;
 				}
@@ -727,6 +731,7 @@ parse_dhcp(struct dhcpleased_iface *iface, struct imsg_dhcp *dhcp)
 	size_t			 rem, i;
 	uint32_t		 sum, usum, lease_time = 0, renewal_time = 0;
 	uint32_t		 rebinding_time = 0;
+	uint32_t		 ipv6_only_time = 0;
 	uint8_t			*p, dho = DHO_PAD, dho_len, slen;
 	uint8_t			 dhcp_message_type = 0;
 	int			 routes_len = 0, routers = 0, csr = 0;
@@ -1173,6 +1178,18 @@ parse_dhcp(struct dhcpleased_iface *iface, struct imsg_dhcp *dhcp)
 			}
 			break;
 		}
+		case DHO_IPV6_ONLY_PREFERRED:
+			if (dho_len != sizeof(ipv6_only_time))
+				goto wrong_length;
+			memcpy(&ipv6_only_time, p, sizeof(ipv6_only_time));
+			ipv6_only_time = ntohl(ipv6_only_time);
+			if (log_getverbose() > 1) {
+				log_debug("DHO_IPV6_ONLY_PREFERRED %us",
+				    ipv6_only_time);
+			}
+			p += dho_len;
+			rem -= dho_len;
+			break;
 		default:
 			if (log_getverbose() > 1)
 				log_debug("DHO_%u, len: %u", dho, dho_len);
@@ -1207,6 +1224,14 @@ parse_dhcp(struct dhcpleased_iface *iface, struct imsg_dhcp *dhcp)
 			    "offered IP address", __func__);
 			return;
 		}
+#ifndef SMALL
+		if (iface_conf != NULL && iface_conf->prefer_ipv6 &&
+		    ipv6_only_time > 0) {
+			iface->ipv6_only_time = ipv6_only_time;
+			state_transition(iface, IF_IPV6_ONLY);
+			break;
+		}
+#endif
 		iface->server_identifier = server_identifier;
 		iface->dhcp_server = server_identifier;
 		iface->requested_ip = dhcp_hdr->yiaddr;
@@ -1307,6 +1332,14 @@ parse_dhcp(struct dhcpleased_iface *iface, struct imsg_dhcp *dhcp)
 		strlcpy(iface->domainname, domainname,
 		    sizeof(iface->domainname));
 		strlcpy(iface->hostname, hostname, sizeof(iface->hostname));
+#ifndef SMALL
+		if (iface_conf != NULL && iface_conf->prefer_ipv6 &&
+		    ipv6_only_time > 0) {
+			iface->ipv6_only_time = ipv6_only_time;
+			state_transition(iface, IF_IPV6_ONLY);
+			break;
+		}
+#endif
 		state_transition(iface, IF_BOUND);
 		break;
 	case DHCPNAK:
@@ -1386,6 +1419,7 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 			send_deconfigure_interface(iface);
 			/* fall through */
 		case IF_DOWN:
+		case IF_IPV6_ONLY:
 			iface->timo.tv_sec = START_EXP_BACKOFF;
 			break;
 		case IF_BOUND:
@@ -1434,6 +1468,25 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 			iface->timo.tv_sec /= 2;
 		request_dhcp_request(iface);
 		break;
+	case IF_IPV6_ONLY:
+		switch (old_state) {
+		case IF_REQUESTING:
+		case IF_RENEWING:
+		case IF_REBINDING:
+		case IF_REBOOTING:
+			/* going IPv6 only: delete legacy IP */
+			send_rdns_withdraw(iface);
+			send_deconfigure_interface(iface);
+			/* fall through */
+		case IF_INIT:
+		case IF_DOWN:
+		case IF_IPV6_ONLY:
+			iface->timo.tv_sec = iface->ipv6_only_time;
+			break;
+		case IF_BOUND:
+			fatal("invalid transition Bound -> IPv6 only");
+			break;
+		}
 	}
 
 	if_name = if_indextoname(iface->if_index, ifnamebuf);
@@ -1499,6 +1552,9 @@ iface_timeout(int fd, short events, void *arg)
 		else
 			state_transition(iface, IF_REBINDING);
 		break;
+	case IF_IPV6_ONLY:
+		state_transition(iface, IF_REQUESTING);
+		break;
 	}
 }
 
@@ -1584,6 +1640,9 @@ request_dhcp_request(struct dhcpleased_iface *iface)
 		imsg.requested_ip.s_addr = INADDR_ANY;		/* MUST NOT */
 		imsg.ciaddr = iface->requested_ip;		/* IP address */
 		break;
+	case IF_IPV6_ONLY:
+		fatalx("invalid state IF_IPV6_ONLY in %s", __func__);
+		break;
 	}
 
 	engine_imsg_compose_frontend(IMSG_SEND_REQUEST, 0, &imsg, sizeof(imsg));
diff --git a/sbin/dhcpleased/frontend.c b/sbin/dhcpleased/frontend.c
index e94a3591c6a..3640f3bdbbc 100644
--- a/sbin/dhcpleased/frontend.c
+++ b/sbin/dhcpleased/frontend.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: frontend.c,v 1.30 2022/07/14 15:23:09 florian Exp $	*/
+/*	$OpenBSD: frontend.c,v 1.31 2023/11/25 12:00:39 florian Exp $	*/
 
 /*
  * Copyright (c) 2017, 2021 Florian Obser <florian@openbsd.org>
@@ -924,6 +924,11 @@ build_packet(uint8_t message_type, char *if_name, uint32_t xid,
 		8, DHO_SUBNET_MASK, DHO_ROUTERS, DHO_DOMAIN_NAME_SERVERS,
 		DHO_HOST_NAME, DHO_DOMAIN_NAME, DHO_BROADCAST_ADDRESS,
 		DHO_DOMAIN_SEARCH, DHO_CLASSLESS_STATIC_ROUTES};
+	static uint8_t	 dhcp_req_list_v6[] = {DHO_DHCP_PARAMETER_REQUEST_LIST,
+		9, DHO_SUBNET_MASK, DHO_ROUTERS, DHO_DOMAIN_NAME_SERVERS,
+		DHO_HOST_NAME, DHO_DOMAIN_NAME, DHO_BROADCAST_ADDRESS,
+		DHO_DOMAIN_SEARCH, DHO_CLASSLESS_STATIC_ROUTES,
+		DHO_IPV6_ONLY_PREFERRED};
 	static uint8_t	 dhcp_requested_address[] = {DHO_DHCP_REQUESTED_ADDRESS,
 		4, 0, 0, 0, 0};
 	static uint8_t	 dhcp_server_identifier[] = {DHO_DHCP_SERVER_IDENTIFIER,
@@ -997,15 +1002,23 @@ build_packet(uint8_t message_type, char *if_name, uint32_t xid,
 			memcpy(p, iface_conf->vc_id, iface_conf->vc_id_len);
 			p += iface_conf->vc_id_len;
 		}
+		if (iface_conf->prefer_ipv6) {
+			memcpy(p, dhcp_req_list_v6, sizeof(dhcp_req_list_v6));
+			p += sizeof(dhcp_req_list_v6);
+
+		} else {
+			memcpy(p, dhcp_req_list, sizeof(dhcp_req_list));
+			p += sizeof(dhcp_req_list);
+		}
 	} else
 #endif /* SMALL */
 	{
 		memcpy(dhcp_client_id + 3, hw_address, sizeof(*hw_address));
 		memcpy(p, dhcp_client_id, sizeof(dhcp_client_id));
 		p += sizeof(dhcp_client_id);
+		memcpy(p, dhcp_req_list, sizeof(dhcp_req_list));
+		p += sizeof(dhcp_req_list);
 	}
-	memcpy(p, dhcp_req_list, sizeof(dhcp_req_list));
-	p += sizeof(dhcp_req_list);
 
 	if (requested_ip->s_addr != INADDR_ANY) {
 		memcpy(dhcp_requested_address + 2, requested_ip,
diff --git a/sbin/dhcpleased/parse.y b/sbin/dhcpleased/parse.y
index e3a68953aea..eeae4289e39 100644
--- a/sbin/dhcpleased/parse.y
+++ b/sbin/dhcpleased/parse.y
@@ -1,4 +1,4 @@
-/*	$OpenBSD: parse.y,v 1.7 2022/03/21 04:35:41 dlg Exp $	*/
+/*	$OpenBSD: parse.y,v 1.8 2023/11/25 12:00:39 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -109,7 +109,7 @@ typedef struct {
 %}
 
 %token	DHCP_IFACE ERROR SEND VENDOR CLASS ID CLIENT IGNORE DNS ROUTES HOST NAME
-%token	NO
+%token	NO PREFER IPV6
 
 %token	<v.string>	STRING
 %token	<v.number>	NUMBER
@@ -324,6 +324,9 @@ ifaceoptsl	: SEND VENDOR CLASS ID STRING {
 			}
 			free($2);
 		}
+		| PREFER IPV6 {
+			iface_conf->prefer_ipv6 = 1;
+		}
 		;
 %%
 
@@ -366,8 +369,10 @@ lookup(char *s)
 		{"id",			ID},
 		{"ignore",		IGNORE},
 		{"interface",		DHCP_IFACE},
+		{"ipv6",		IPV6},
 		{"name",		NAME},
 		{"no",			NO},
+		{"prefer",		PREFER},
 		{"routes",		ROUTES},
 		{"send",		SEND},
 		{"vendor",		VENDOR},
diff --git a/sbin/dhcpleased/printconf.c b/sbin/dhcpleased/printconf.c
index 076fe2ec0ad..0ef3970366c 100644
--- a/sbin/dhcpleased/printconf.c
+++ b/sbin/dhcpleased/printconf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: printconf.c,v 1.4 2022/01/04 06:20:37 florian Exp $	*/
+/*	$OpenBSD: printconf.c,v 1.5 2023/11/25 12:00:39 florian Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -126,6 +126,8 @@ print_config(struct dhcpleased_conf *conf)
 			printf("\tignore %s\n", hbuf);
 
 		}
+		if (iface->prefer_ipv6)
+			printf("\t prefer ipv6\n");
 		printf("}\n");
 	}
 }