dhcpv6: add config for strict RFC7550

Some ISPs don't comply with RFC7550 and need workarounds to get proper
IPv6 connectivity.

Link: #152
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

Author: Noltari

src/config.c

@@ -318,6 +318,11 @@ bool config_set_auth_token(const char* token)
 	return config_dhcp.auth_token != NULL;
 }
 
+void config_set_client_opt_cfg(struct odhcp6c_opt_cfg *opt_cfg)
+{
+	config_dhcp.strict_rfc7550 = opt_cfg->strict_rfc7550 != 0;
+}
+
 static int config_parse_opt_u8(const char *src, uint8_t **dst)
 {
 	int len = strlen(src);

src/config.h

@@ -100,6 +100,7 @@ struct config_dhcp {
 	uint16_t rand_factor;
 	enum odhcp6c_auth_protocol auth_protocol;
 	char* auth_token;
+	bool strict_rfc7550;
 };
 
 struct config_dhcp *config_dhcp_get(void);
@@ -126,6 +127,7 @@ bool config_set_irt_min(unsigned int value);
 bool config_set_rand_factor(unsigned int value);
 bool config_set_auth_protocol(const char* protocol);
 bool config_set_auth_token(const char* token);
+void config_set_client_opt_cfg(struct odhcp6c_opt_cfg *opt_cfg);
 
 int config_add_opt(const uint16_t code, const uint8_t *data, const uint16_t len);
 int config_parse_opt_data(const char *data, uint8_t **dst, const unsigned int type, const bool array);

src/dhcpv6.c

@@ -985,13 +985,15 @@ static void dhcpv6_send(enum dhcpv6_msg req_msg_type, uint8_t trid[3], uint32_t
 
 		switch (req_msg_type) {
 		case DHCPV6_MSG_REQUEST:
-			/* Some broken ISPs won't behave properly if IA_NA is
-			 * sent on Requests when they have provided an empty
-			 * IA_NA on Advertise.
-			 * Therefore we don't comply with RFC7550 and omit
-			 * IA_NA as a workaround.
-			 */
-			iov[IOV_HDR_IA_NA].iov_len = 0;
+			if (!config_dhcp->strict_rfc7550) {
+				/* Some broken ISPs won't behave properly if IA_NA is
+				 * sent on Requests when they have provided an empty
+				 * IA_NA on Advertise.
+				 * Therefore we don't comply with RFC7550 and omit
+				 * IA_NA as a workaround.
+				 */
+				iov[IOV_HDR_IA_NA].iov_len = 0;
+			}
 			break;
 		case DHCPV6_MSG_SOLICIT:
 			break;
@@ -2134,6 +2136,7 @@ int dhcpv6_promote_server_cand(void)
 	struct dhcpv6_server_cand *cand = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);
 	uint16_t hdr[2];
 	int ret = DHCPV6_STATELESS;
+	bool override_ia = false;
 
 	// Clear lingering candidate state info
 	odhcp6c_clear_state(STATE_SERVER_ID);
@@ -2143,25 +2146,47 @@ int dhcpv6_promote_server_cand(void)
 	if (!cand_len)
 		return -1;
 
-	if (!cand->ia_pd_len && cand->has_noaddravail) {
-		bool override = false;
+	if (config_dhcp->strict_rfc7550) {
+		if (!cand->ia_pd_len && cand->has_noaddravail) {
+			/* Some ISPs provide neither IA_NA nor IA_PD, so we
+			 * should fallback to SLAAC.
+			 */
+
+			if (na_mode == IA_MODE_TRY) {
+				na_mode = IA_MODE_NONE;
+				override_ia = true;
+			}
 
-		if (na_mode == IA_MODE_TRY) {
+			if (pd_mode == IA_MODE_TRY) {
+				pd_mode = IA_MODE_NONE;
+				override_ia = true;
+			}
+		}
+	} else {
+		if (cand->has_noaddravail && na_mode == IA_MODE_TRY) {
+			/* Some broken ISPs require a new Solicit message
+			 * without IA_NA if they haven't provided an address
+			 * on the Advertise message.
+			 */
 			na_mode = IA_MODE_NONE;
-			override = true;
+			override_ia = true;
 		}
 
-		if (pd_mode == IA_MODE_TRY) {
+		if (!cand->ia_pd_len && pd_mode == IA_MODE_TRY) {
+			/* Some broken ISPs require a new Solicit message
+			 * without IA_PD if they haven't provided a prefix
+			 * on the Advertise message.
+			 */
 			pd_mode = IA_MODE_NONE;
-			override = true;
+			override_ia = true;
 		}
+	}
 
-		if (override) {
-			dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = cand->sol_max_rt;
-			dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = cand->inf_max_rt;
+	if (override_ia) {
+		dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = cand->sol_max_rt;
+		dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = cand->inf_max_rt;
 
-			return -1;
-		}
+		return -1;
 	}
 
 	hdr[0] = htons(DHCPV6_OPT_SERVERID);

src/odhcp6c.c

@@ -17,6 +17,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <getopt.h>
 #include <limits.h>
 #include <linux/if_addr.h>
 #include <net/if.h>
@@ -201,6 +202,15 @@ static struct odhcp6c_opt opts[] = {
 	{ .code = 0, .flags = 0, .str = NULL },
 };
 
+static struct odhcp6c_opt_cfg opt_cfg = {
+	.strict_rfc7550 = 0,
+};
+
+static struct option opt_long[] = {
+	{ "strict-rfc7550", no_argument, &opt_cfg.strict_rfc7550, 1 },
+	{ NULL, 0, NULL, 0 },
+};
+
 int main(_o_unused int argc, char* const argv[])
 {
 	static struct in6_addr ifid = IN6ADDR_ANY_INIT;
@@ -209,6 +219,7 @@ int main(_o_unused int argc, char* const argv[])
 	const char *script = "/lib/netifd/dhcpv6.script";
 	ssize_t l;
 	uint8_t buf[134], *o_data;
+	int optidx;
 	char *optpos;
 	uint16_t opttype;
 	struct odhcp6c_opt *opt;
@@ -228,8 +239,11 @@ int main(_o_unused int argc, char* const argv[])
 
 	atexit(odhcp6c_cleanup);
 
-	while ((c = getopt(argc, argv, "SDN:V:P:FB:c:i:r:Ru:Ux:s:EkK:t:C:m:Lhedp:favl:")) != -1) {
+	while ((c = getopt_long(argc, argv, "SDN:V:P:FB:c:i:r:Ru:Ux:s:EkK:t:C:m:Lhedp:favl:", opt_long, &optidx)) != -1) {
 		switch (c) {
+		case 0:
+			break;
+
 		case 'S':
 			config_set_allow_slaac_only(false);
 			break;
@@ -477,6 +491,8 @@ int main(_o_unused int argc, char* const argv[])
 		}
 	}
 
+	config_set_client_opt_cfg(&opt_cfg);
+
 	openlog("odhcp6c", logopt, LOG_DAEMON);
 	setlogmask(LOG_UPTO(config_dhcp->log_level));
 
@@ -858,6 +874,7 @@ static int usage(void)
 	"	-m <seconds>	Minimum time between accepting RA updates (3)\n"
 	"	-L		Ignore default lifetime for RDNSS records\n"
 	"	-U		Ignore Server Unicast option\n"
+	"       --strict-rfc7550 Enforce RFC7550 compliance\n"
 	"\nInvocation options:\n"
 	"	-p <pidfile>	Set pidfile (/var/run/odhcp6c.pid)\n"
 	"	-d		Daemonize\n"

src/odhcp6c.h

@@ -552,6 +552,10 @@ struct odhcp6c_opt {
 	const char *str;
 };
 
+struct odhcp6c_opt_cfg {
+	int strict_rfc7550;
+};
+
 uint32_t hash_ifname(const char *s);
 int init_dhcpv6(const char *ifname);
 int dhcpv6_get_ia_mode(void);