src/dhcpv6.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License v2 as published by
   6  * the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  *
  14  */
  15
  16 #include <errno.h>
  17 #include <unistd.h>
  18 #include <stddef.h>
  19 #include <resolv.h>
  20 #include <sys/timerfd.h>
  21 #include <arpa/inet.h>
  22
  23 #include "odhcpd.h"
  24 #include "dhcpv6.h"
  25
  26
  27 static void relay_client_request(struct sockaddr_in6 *source,
  28                 const void *data, size_t len, struct interface *iface);
  29 static void relay_server_response(uint8_t *data, size_t len);
  30
  31 static void handle_dhcpv6(void *addr, void *data, size_t len,
  32                 struct interface *iface, void *dest);
  33 static void handle_client_request(void *addr, void *data, size_t len,
  34                 struct interface *iface, void *dest_addr);
  35
  36
  37 // Create socket and register events
  38 int dhcpv6_init(void)
  39 {
  40         dhcpv6_ia_init();
  41         return 0;
  42 }
  43
  44 int dhcpv6_setup_interface(struct interface *iface, bool enable)
  45 {
  46         if (iface->dhcpv6_event.uloop.fd > 0) {
  47                 uloop_fd_delete(&iface->dhcpv6_event.uloop);
  48                 close(iface->dhcpv6_event.uloop.fd);
  49                 iface->dhcpv6_event.uloop.fd = -1;
  50         }
  51
  52         // Configure multicast settings
  53         if (enable && iface->dhcpv6) {
  54                 int sock = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  55                 if (sock < 0) {
  56                         syslog(LOG_ERR, "Failed to create DHCPv6 server socket: %m");
  57                         return -1;
  58                 }
  59
  60                 // Basic IPv6 configuration
  61                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, iface->ifname, strlen(iface->ifname));
  62
  63                 int val = 1;
  64                 setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
  65                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  66                 setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val));
  67
  68                 val = DHCPV6_HOP_COUNT_LIMIT;
  69                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  70
  71                 val = 0;
  72                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &val, sizeof(val));
  73
  74                 struct sockaddr_in6 bind_addr = {AF_INET6, htons(DHCPV6_SERVER_PORT),
  75                                         0, IN6ADDR_ANY_INIT, 0};
  76
  77                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  78                         syslog(LOG_ERR, "Failed to open DHCPv6 server socket: %m");
  79                         return -1;
  80                 }
  81
  82                 struct ipv6_mreq relay = {ALL_DHCPV6_RELAYS, iface->ifindex};
  83                 struct ipv6_mreq server = {ALL_DHCPV6_SERVERS, iface->ifindex};
  84                 setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &relay, sizeof(relay));
  85
  86                 if (iface->dhcpv6 == MODE_SERVER)
  87                         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &server, sizeof(server));
  88
  89                 iface->dhcpv6_event.uloop.fd = sock;
  90                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
  91                 odhcpd_register(&iface->dhcpv6_event);
  92         }
  93
  94         return dhcpv6_setup_ia_interface(iface, enable);
  95 }
  96
  97 enum {
  98         IOV_NESTED = 0,
  99         IOV_DEST,
 100         IOV_MAXRT,
 101 #define IOV_STAT IOV_MAXRT
 102         IOV_DNS,
 103         IOV_DNS_ADDR,
 104         IOV_SEARCH,
 105         IOV_SEARCH_DOMAIN,
 106         IOV_PDBUF,
 107 #define IOV_REFRESH IOV_PDBUF
 108         IOV_CERID,
 109         IOV_DHCPV6_RAW,
 110         IOV_RELAY_MSG,
 111         IOV_TOTAL
 112 };
 113
 114 static void handle_nested_message(uint8_t *data, size_t len,
 115                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL - 1])
 116 {
 117         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 118         if (iov[IOV_NESTED].iov_base == NULL) {
 119                 iov[IOV_NESTED].iov_base = data;
 120                 iov[IOV_NESTED].iov_len = len;
 121         }
 122
 123         if (len < sizeof(struct dhcpv6_client_header))
 124                 return;
 125
 126         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 127                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 128                 struct dhcpv6_client_header *hdr = (void*)data;
 129                 *opts = (uint8_t*)&hdr[1];
 130                 *end = data + len;
 131                 return;
 132         }
 133
 134         uint16_t otype, olen;
 135         uint8_t *odata;
 136         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 137                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 138                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 139                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 140                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 141                         handle_nested_message(odata, olen, opts, end, iov);
 142                         return;
 143                 }
 144         }
 145 }
 146
 147
 148 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 149 {
 150         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 151         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 152                 return;
 153
 154         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 155
 156         uint16_t otype, olen;
 157         uint8_t *odata;
 158         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 159                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 160                         olen += pdiff;
 161                         odata[-2] = (olen >> 8) & 0xff;
 162                         odata[-1] = olen & 0xff;
 163                         update_nested_message(odata, olen - pdiff, pdiff);
 164                         return;
 165                 }
 166         }
 167 }
 168
 169 // Simple DHCPv6-server for information requests
 170 static void handle_client_request(void *addr, void *data, size_t len,
 171                 struct interface *iface, void *dest_addr)
 172 {
 173         struct dhcpv6_client_header *hdr = data;
 174
 175         if (len < sizeof(*hdr))
 176                 return;
 177
 178         syslog(LOG_NOTICE, "Got DHCPv6 request");
 179
 180         // Construct reply message
 181         struct __attribute__((packed)) {
 182                 uint8_t msg_type;
 183                 uint8_t tr_id[3];
 184                 uint16_t serverid_type;
 185                 uint16_t serverid_length;
 186                 uint16_t duid_type;
 187                 uint16_t hardware_type;
 188                 uint8_t mac[6];
 189                 uint16_t clientid_type;
 190                 uint16_t clientid_length;
 191                 uint8_t clientid_buf[130];
 192         } dest = {
 193                 .msg_type = DHCPV6_MSG_REPLY,
 194                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 195                 .serverid_length = htons(10),
 196                 .duid_type = htons(3),
 197                 .hardware_type = htons(1),
 198                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 199                 .clientid_buf = {0}
 200         };
 201         odhcpd_get_mac(iface, dest.mac);
 202
 203         struct __attribute__((packed)) {
 204                 uint16_t type;
 205                 uint16_t len;
 206                 uint32_t value;
 207         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 208                         htonl(60)};
 209
 210         struct __attribute__((packed)) {
 211                 uint16_t type;
 212                 uint16_t len;
 213                 uint16_t value;
 214         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 215                         htons(DHCPV6_STATUS_USEMULTICAST)};
 216
 217         struct __attribute__((packed)) {
 218                 uint16_t type;
 219                 uint16_t len;
 220                 uint32_t value;
 221         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 222                         htonl(600)};
 223
 224         struct in6_addr dns_addr, *dns_addr_ptr = iface->dns;
 225         size_t dns_cnt = iface->dns_cnt;
 226
 227         if ((dns_cnt == 0) &&
 228                 !odhcpd_get_interface_dns_addr(iface, &dns_addr)) {
 229                 dns_addr_ptr = &dns_addr;
 230                 dns_cnt = 1;
 231         }
 232
 233         struct {
 234                 uint16_t type;
 235                 uint16_t len;
 236         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr_ptr))};
 237
 238
 239
 240         // DNS Search options
 241         uint8_t search_buf[256], *search_domain = iface->search;
 242         size_t search_len = iface->search_len;
 243
 244         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 245                 int len = dn_comp(_res.dnsrch[0], search_buf,
 246                                 sizeof(search_buf), NULL, NULL);
 247                 if (len > 0) {
 248                         search_domain = search_buf;
 249                         search_len = len;
 250                 }
 251         }
 252
 253         struct {
 254                 uint16_t type;
 255                 uint16_t len;
 256         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 257
 258
 259         struct dhcpv6_cer_id cerid = {
 260 #ifdef EXT_CER_ID
 261                 .type = htons(EXT_CER_ID),
 262 #endif
 263                 .len = htons(36),
 264                 .addr = iface->dhcpv6_pd_cer,
 265         };
 266
 267
 268         uint8_t pdbuf[512];
 269         struct iovec iov[IOV_TOTAL] = {
 270                 [IOV_NESTED] = {NULL, 0},
 271                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 272                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 273                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 274                 [IOV_DNS_ADDR] = {dns_addr_ptr, dns_cnt * sizeof(*dns_addr_ptr)},
 275                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 276                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 277                 [IOV_PDBUF] = {pdbuf, 0},
 278                 [IOV_CERID] = {&cerid, 0},
 279                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 280                 [IOV_RELAY_MSG] = {NULL, 0}
 281         };
 282
 283         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 284         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 285                 handle_nested_message(data, len, &opts, &opts_end, iov);
 286
 287         memcpy(dest.tr_id, &opts[-3], sizeof(dest.tr_id));
 288
 289         if (opts[-4] == DHCPV6_MSG_ADVERTISE || opts[-4] == DHCPV6_MSG_REPLY || opts[-4] == DHCPV6_MSG_RELAY_REPL)
 290                 return;
 291
 292         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 293                 (opts[-4] == DHCPV6_MSG_SOLICIT || opts[-4] == DHCPV6_MSG_CONFIRM ||
 294                  opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST))
 295                 return;
 296
 297         if (opts[-4] == DHCPV6_MSG_SOLICIT) {
 298                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 299         } else if (opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST) {
 300                 iov[IOV_REFRESH].iov_base = &refresh;
 301                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 302
 303                 // Return inf max rt option in reply to information request
 304                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 305         }
 306
 307         // Go through options and find what we need
 308         uint16_t otype, olen;
 309         uint8_t *odata;
 310         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 311                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 312                         dest.clientid_length = htons(olen);
 313                         memcpy(dest.clientid_buf, odata, olen);
 314                         iov[IOV_DEST].iov_len += 4 + olen;
 315                 } else if (otype == DHCPV6_OPT_SERVERID) {
 316                         if (olen != ntohs(dest.serverid_length) ||
 317                                         memcmp(odata, &dest.duid_type, olen))
 318                                 return; // Not for us
 319                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 320                         uint8_t *c = odata, *cend = &odata[olen];
 321                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 322                                 size_t elen = strlen(iface->filter_class);
 323                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 324                                         return; // Ignore from homenet
 325                         }
 326                 } else if (otype == DHCPV6_OPT_IA_PD) {
 327 #ifdef EXT_CER_ID
 328                         iov[IOV_CERID].iov_len = sizeof(cerid);
 329
 330                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 331                                 struct odhcpd_ipaddr *addrs;
 332                                 ssize_t len = netlink_get_interface_addrs(0, true, &addrs);
 333
 334                                 for (ssize_t i = 0; i < len; ++i)
 335                                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)
 336                                                         || memcmp(&addrs[i].addr, &cerid.addr, sizeof(cerid.addr)) < 0)
 337                                                 cerid.addr = addrs[i].addr.in6;
 338
 339                                 free(addrs);
 340                         }
 341 #endif
 342                 }
 343         }
 344
 345         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 346                 (opts[-4] == DHCPV6_MSG_REQUEST || opts[-4] == DHCPV6_MSG_RENEW ||
 347                  opts[-4] == DHCPV6_MSG_RELEASE || opts[-4] == DHCPV6_MSG_DECLINE)) {
 348                 iov[IOV_STAT].iov_base = &stat;
 349                 iov[IOV_STAT].iov_len = sizeof(stat);
 350
 351                 for (ssize_t i = IOV_STAT + 1; i < IOV_TOTAL; ++i)
 352                         iov[i].iov_len = 0;
 353
 354                 odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 355                 return;
 356         }
 357
 358         if (opts[-4] != DHCPV6_MSG_INFORMATION_REQUEST) {
 359                 ssize_t ialen = dhcpv6_handle_ia(pdbuf, sizeof(pdbuf), iface, addr, &opts[-4], opts_end);
 360                 iov[IOV_PDBUF].iov_len = ialen;
 361                 if (ialen < 0 || (ialen == 0 && (opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_CONFIRM)))
 362                         return;
 363         }
 364
 365         if (iov[IOV_NESTED].iov_len > 0) // Update length
 366                 update_nested_message(data, len, iov[IOV_DEST].iov_len + iov[IOV_MAXRT].iov_len +
 367                                 iov[IOV_DNS].iov_len + iov[IOV_DNS_ADDR].iov_len +
 368                                 iov[IOV_SEARCH].iov_len + iov[IOV_SEARCH_DOMAIN].iov_len +
 369                                 iov[IOV_PDBUF].iov_len + iov[IOV_CERID].iov_len +
 370                                 iov[IOV_DHCPV6_RAW].iov_len - (4 + opts_end - opts));
 371
 372         odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 373 }
 374
 375
 376 // Central DHCPv6-relay handler
 377 static void handle_dhcpv6(void *addr, void *data, size_t len,
 378                 struct interface *iface, void *dest_addr)
 379 {
 380         if (iface->dhcpv6 == MODE_SERVER) {
 381                 handle_client_request(addr, data, len, iface, dest_addr);
 382         } else if (iface->dhcpv6 == MODE_RELAY) {
 383                 if (iface->master)
 384                         relay_server_response(data, len);
 385                 else
 386                         relay_client_request(addr, data, len, iface);
 387         }
 388 }
 389
 390
 391 // Relay server response (regular relay server handling)
 392 static void relay_server_response(uint8_t *data, size_t len)
 393 {
 394         // Information we need to gather
 395         uint8_t *payload_data = NULL;
 396         size_t payload_len = 0;
 397         int32_t ifaceidx = 0;
 398         struct sockaddr_in6 target = {AF_INET6, htons(DHCPV6_CLIENT_PORT),
 399                 0, IN6ADDR_ANY_INIT, 0};
 400
 401         syslog(LOG_NOTICE, "Got a DHCPv6-reply");
 402
 403         int otype, olen;
 404         uint8_t *odata, *end = data + len;
 405
 406         // Relay DHCPv6 reply from server to client
 407         struct dhcpv6_relay_header *h = (void*)data;
 408         if (len < sizeof(*h) || h->msg_type != DHCPV6_MSG_RELAY_REPL)
 409                 return;
 410
 411         memcpy(&target.sin6_addr, &h->peer_address,
 412                         sizeof(struct in6_addr));
 413
 414         // Go through options and find what we need
 415         dhcpv6_for_each_option(h->options, end, otype, olen, odata) {
 416                 if (otype == DHCPV6_OPT_INTERFACE_ID
 417                                 && olen == sizeof(ifaceidx)) {
 418                         memcpy(&ifaceidx, odata, sizeof(ifaceidx));
 419                 } else if (otype == DHCPV6_OPT_RELAY_MSG) {
 420                         payload_data = odata;
 421                         payload_len = olen;
 422                 }
 423         }
 424
 425         // Invalid interface-id or basic payload
 426         struct interface *iface = odhcpd_get_interface_by_index(ifaceidx);
 427         if (!iface || iface->master || !payload_data || payload_len < 4)
 428                 return;
 429
 430         bool is_authenticated = false;
 431         struct in6_addr *dns_ptr = NULL;
 432         size_t dns_count = 0;
 433
 434         // If the payload is relay-reply we have to send to the server port
 435         if (payload_data[0] == DHCPV6_MSG_RELAY_REPL) {
 436                 target.sin6_port = htons(DHCPV6_SERVER_PORT);
 437         } else { // Go through the payload data
 438                 struct dhcpv6_client_header *h = (void*)payload_data;
 439                 end = payload_data + payload_len;
 440
 441                 dhcpv6_for_each_option(&h[1], end, otype, olen, odata) {
 442                         if (otype == DHCPV6_OPT_DNS_SERVERS && olen >= 16) {
 443                                 dns_ptr = (struct in6_addr*)odata;
 444                                 dns_count = olen / 16;
 445                         } else if (otype == DHCPV6_OPT_AUTH) {
 446                                 is_authenticated = true;
 447                         }
 448                 }
 449         }
 450
 451         // Rewrite DNS servers if requested
 452         if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 453                 if (is_authenticated)
 454                         return; // Impossible to rewrite
 455
 456                 const struct in6_addr *rewrite = iface->dns;
 457                 struct in6_addr addr;
 458                 size_t rewrite_cnt = iface->dns_cnt;
 459
 460                 if (rewrite_cnt == 0) {
 461                         if (odhcpd_get_interface_dns_addr(iface, &addr))
 462                                 return; // Unable to get interface address
 463
 464                         rewrite = &addr;
 465                         rewrite_cnt = 1;
 466                 }
 467
 468                 // Copy over any other addresses
 469                 for (size_t i = 0; i < dns_count; ++i) {
 470                         size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 471                         memcpy(&dns_ptr[i], &rewrite[j], sizeof(*rewrite));
 472                 }
 473         }
 474
 475         struct iovec iov = {payload_data, payload_len};
 476         odhcpd_send(iface->dhcpv6_event.uloop.fd, &target, &iov, 1, iface);
 477 }
 478
 479 static struct odhcpd_ipaddr *relay_link_address(struct interface *iface)
 480 {
 481         struct odhcpd_ipaddr *addr = NULL;
 482         time_t now = odhcpd_time();
 483
 484         for (size_t i = 0; i < iface->addr6_len; i++) {
 485                 if (iface->addr6[i].valid <= (uint32_t)now)
 486                         continue;
 487
 488                 if (iface->addr6[i].preferred > (uint32_t)now) {
 489                         addr = &iface->addr6[i];
 490                         break;
 491                 }
 492
 493                 if (!addr || (iface->addr6[i].valid > addr->valid))
 494                         addr = &iface->addr6[i];
 495         }
 496
 497         return addr;
 498 }
 499
 500 // Relay client request (regular DHCPv6-relay)
 501 static void relay_client_request(struct sockaddr_in6 *source,
 502                 const void *data, size_t len, struct interface *iface)
 503 {
 504         struct interface *master = odhcpd_get_master_interface();
 505         const struct dhcpv6_relay_header *h = data;
 506         if (!master || master->dhcpv6 != MODE_RELAY ||
 507                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 508                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 509                         h->msg_type == DHCPV6_MSG_REPLY ||
 510                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 511                 return; // Invalid message types for client
 512
 513         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 514
 515         // Construct our forwarding envelope
 516         struct dhcpv6_relay_forward_envelope hdr = {
 517                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 518                 .hop_count = 0,
 519                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 520                 .interface_id_len = htons(sizeof(uint32_t)),
 521                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 522                 .relay_message_len = htons(len),
 523         };
 524
 525         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { // handle relay-forward
 526                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 527                         return; // Invalid hop count
 528                 else
 529                         hdr.hop_count = h->hop_count + 1;
 530         }
 531
 532         // use memcpy here as the destination fields are unaligned
 533         uint32_t ifindex = iface->ifindex;
 534         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 535         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 536
 537         // Detect public IP of slave interface to use as link-address
 538         struct odhcpd_ipaddr *ip = relay_link_address(iface);
 539         if (!ip) {
 540                 // No suitable address! Is the slave not configured yet?
 541                 // Detect public IP of master interface and use it instead
 542                 // This is WRONG and probably violates the RFC. However
 543                 // otherwise we have a hen and egg problem because the
 544                 // slave-interface cannot be auto-configured.
 545                 ip = relay_link_address(master);
 546                 if (!ip)
 547                         return; // Could not obtain a suitable address
 548         }
 549
 550         memcpy(&hdr.link_address, &ip->addr.in6, sizeof(hdr.link_address));
 551
 552         struct sockaddr_in6 dhcpv6_servers = {AF_INET6,
 553                         htons(DHCPV6_SERVER_PORT), 0, ALL_DHCPV6_SERVERS, 0};
 554         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 555         odhcpd_send(master->dhcpv6_event.uloop.fd, &dhcpv6_servers, iov, 2, master);
 556 }