udhcp6: read_interface should save link-local ipv6 address

Patch is based on work by tiggerswelt.net. They say:
"Using this patch it was no problem to acquire an IPv6-Address via DHCPv6
using ISC DHCPD6 on server-side."

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/udhcp/d6_common.h

@@ -91,10 +91,14 @@ struct client6_data_t {
 	struct d6_option *ia_na;
 	char **env_ptr;
 	unsigned env_idx;
+	/* link-local IPv6 address */
+	struct in6_addr ll_ip6;
 };
 
 #define client6_data (*(struct client6_data_t*)(&bb_common_bufsiz1[COMMON_BUFSIZE - sizeof(struct client6_data_t)]))
 
+int FAST_FUNC d6_read_interface(const char *interface, int *ifindex, struct in6_addr *nip6, uint8_t *mac);
+
 int FAST_FUNC d6_listen_socket(int port, const char *inf);
 
 int FAST_FUNC d6_recv_kernel_packet(

networking/udhcp/d6_dhcpc.c

@@ -311,7 +311,7 @@ static int d6_mcast_from_client_config_ifindex(struct d6_packet *packet, uint8_t
 
 	return d6_send_raw_packet(
 		packet, (end - (uint8_t*) packet),
-		/*src*/ NULL, CLIENT_PORT6,
+		/*src*/ &client6_data.ll_ip6, CLIENT_PORT6,
 		/*dst*/ (struct in6_addr*)FF02__1_2, SERVER_PORT6, MAC_BCAST_ADDR,
 		client_config.ifindex
 	);
@@ -1003,9 +1003,9 @@ int udhcpc6_main(int argc UNUSED_PARAM, char **argv)
 		udhcp_str2optset(optstr, &client_config.options);
 	}
 
-	if (udhcp_read_interface(client_config.interface,
+	if (d6_read_interface(client_config.interface,
 			&client_config.ifindex,
-			NULL,
+			&client6_data.ll_ip6,
 			client_config.client_mac)
 	) {
 		return 1;
@@ -1106,13 +1106,14 @@ int udhcpc6_main(int argc UNUSED_PARAM, char **argv)
 			 * or if the status of the bridge changed).
 			 * Refresh ifindex and client_mac:
 			 */
-			if (udhcp_read_interface(client_config.interface,
+			if (d6_read_interface(client_config.interface,
 					&client_config.ifindex,
-					NULL,
+					&client6_data.ll_ip6,
 					client_config.client_mac)
 			) {
 				goto ret0; /* iface is gone? */
 			}
+
 			memcpy(clientid_mac_ptr, client_config.client_mac, 6);
 
 			/* We will restart the wait in any case */

networking/udhcp/d6_socket.c

@@ -7,6 +7,67 @@
 #include "common.h"
 #include "d6_common.h"
 #include <net/if.h>
+#include <ifaddrs.h>
+#include <netpacket/packet.h>
+
+int FAST_FUNC d6_read_interface(const char *interface, int *ifindex, struct in6_addr *nip6, uint8_t *mac)
+{
+	int retval = 3;
+	struct ifaddrs *ifap, *ifa;
+
+	getifaddrs(&ifap);
+
+	for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
+		struct sockaddr_in6 *sip6;
+
+		if (!ifa->ifa_addr || (strcmp(ifa->ifa_name, interface) != 0))
+			continue;
+
+		sip6 = (struct sockaddr_in6*)(ifa->ifa_addr);
+
+		if (ifa->ifa_addr->sa_family == AF_PACKET) {
+			struct sockaddr_ll *sll = (struct sockaddr_ll*)(ifa->ifa_addr);
+			memcpy(mac, sll->sll_addr, 6);
+			log1("MAC %02x:%02x:%02x:%02x:%02x:%02x", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
+			log1("adapter index %d", sll->sll_ifindex);
+			*ifindex = sll->sll_ifindex;
+			retval &= (0xf - (1<<0));
+		}
+#if 0
+		if (ifa->ifa_addr->sa_family == AF_INET) {
+			*nip = ((struct sockaddr_in *)ifa->ifa_addr)->sin_addr.s_addr;
+			log1("IP %s", inet_ntoa(((struct sockaddr_in *)ifa->ifa_addr)->sin_addr));
+		}
+#endif
+		if (ifa->ifa_addr->sa_family == AF_INET6
+		 && IN6_IS_ADDR_LINKLOCAL(&sip6->sin6_addr)
+		) {
+			*nip6 = sip6->sin6_addr; /* struct copy */
+			log1(
+				"IPv6 %02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x",
+				nip6->s6_addr[0], nip6->s6_addr[1],
+				nip6->s6_addr[2], nip6->s6_addr[3],
+				nip6->s6_addr[4], nip6->s6_addr[5],
+				nip6->s6_addr[6], nip6->s6_addr[7],
+				nip6->s6_addr[8], nip6->s6_addr[9],
+				nip6->s6_addr[10], nip6->s6_addr[11],
+				nip6->s6_addr[12], nip6->s6_addr[13],
+				nip6->s6_addr[14], nip6->s6_addr[15]
+			);
+			retval &= (0xf - (1<<1));
+		}
+	}
+
+	freeifaddrs(ifap);
+	if (retval == 0)
+		return retval;
+
+	if (retval & (1<<0))
+		bb_error_msg("can't get %s", "MAC");
+	if (retval & (1<<1))
+		bb_error_msg("can't get %s", "link-local IPv6 address");
+	return -1;
+}
 
 int FAST_FUNC d6_listen_socket(int port, const char *inf)
 {