src/dhcpv6.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  * Copyright (C) 2018 Hans Dedecker <dedeckeh@gmail.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License v2 as published by
   7  * the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  *
  15  */
  16
  17 #include <errno.h>
  18 #include <unistd.h>
  19 #include <stddef.h>
  20 #include <resolv.h>
  21 #include <sys/timerfd.h>
  22 #include <arpa/inet.h>
  23
  24 #include <libubox/utils.h>
  25
  26 #include "odhcpd.h"
  27 #include "dhcpv6.h"
  28
  29
  30 static void relay_client_request(struct sockaddr_in6 *source,
  31                 const void *data, size_t len, struct interface *iface);
  32 static void relay_server_response(uint8_t *data, size_t len);
  33
  34 static void handle_dhcpv6(void *addr, void *data, size_t len,
  35                 struct interface *iface, void *dest);
  36 static void handle_client_request(void *addr, void *data, size_t len,
  37                 struct interface *iface, void *dest_addr);
  38
  39
  40 /* Create socket and register events */
  41 int dhcpv6_init(void)
  42 {
  43         return dhcpv6_ia_init();
  44 }
  45
  46 int dhcpv6_setup_interface(struct interface *iface, bool enable)
  47 {
  48         int ret = 0;
  49
  50         if (iface->dhcpv6_event.uloop.fd > 0) {
  51                 uloop_fd_delete(&iface->dhcpv6_event.uloop);
  52                 close(iface->dhcpv6_event.uloop.fd);
  53                 iface->dhcpv6_event.uloop.fd = -1;
  54         }
  55
  56         /* Configure multicast settings */
  57         if (enable && iface->dhcpv6) {
  58                 struct sockaddr_in6 bind_addr = {AF_INET6, htons(DHCPV6_SERVER_PORT),
  59                                         0, IN6ADDR_ANY_INIT, 0};
  60                 struct ipv6_mreq mreq;
  61                 int val = 1;
  62
  63                 iface->dhcpv6_event.uloop.fd = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  64                 if (iface->dhcpv6_event.uloop.fd < 0) {
  65                         syslog(LOG_ERR, "socket(AF_INET6): %m");
  66                         ret = -1;
  67                         goto out;
  68                 }
  69
  70                 /* Basic IPv6 configuration */
  71                 if (setsockopt(iface->dhcpv6_event.uloop.fd, SOL_SOCKET, SO_BINDTODEVICE,
  72                                         iface->ifname, strlen(iface->ifname)) < 0) {
  73                         syslog(LOG_ERR, "setsockopt(SO_BINDTODEVICE): %m");
  74                         ret = -1;
  75                         goto out;
  76                 }
  77
  78                 if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_V6ONLY,
  79                                         &val, sizeof(val)) < 0) {
  80                         syslog(LOG_ERR, "setsockopt(IPV6_V6ONLY): %m");
  81                         ret = -1;
  82                         goto out;
  83                 }
  84
  85                 if (setsockopt(iface->dhcpv6_event.uloop.fd, SOL_SOCKET, SO_REUSEADDR,
  86                                         &val, sizeof(val)) < 0) {
  87                         syslog(LOG_ERR, "setsockopt(SO_REUSEADDR): %m");
  88                         ret = -1;
  89                         goto out;
  90                 }
  91
  92                 if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_RECVPKTINFO,
  93                                         &val, sizeof(val)) < 0) {
  94                         syslog(LOG_ERR, "setsockopt(IPV6_RECVPKTINFO): %m");
  95                         ret = -1;
  96                         goto out;
  97                 }
  98
  99                 val = DHCPV6_HOP_COUNT_LIMIT;
 100                 if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS,
 101                                         &val, sizeof(val)) < 0) {
 102                         syslog(LOG_ERR, "setsockopt(IPV6_MULTICAST_HOPS): %m");
 103                         ret = -1;
 104                         goto out;
 105                 }
 106
 107                 val = 0;
 108                 if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP,
 109                                         &val, sizeof(val)) < 0) {
 110                         syslog(LOG_ERR, "setsockopt(IPV6_MULTICAST_LOOP): %m");
 111                         ret = -1;
 112                         goto out;
 113                 }
 114
 115                 if (bind(iface->dhcpv6_event.uloop.fd, (struct sockaddr*)&bind_addr,
 116                                         sizeof(bind_addr)) < 0) {
 117                         syslog(LOG_ERR, "bind(): %m");
 118                         ret = -1;
 119                         goto out;
 120                 }
 121
 122                 memset(&mreq, 0, sizeof(mreq));
 123                 inet_pton(AF_INET6, ALL_DHCPV6_RELAYS, &mreq.ipv6mr_multiaddr);
 124                 mreq.ipv6mr_interface = iface->ifindex;
 125
 126                 if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP,
 127                                         &mreq, sizeof(mreq)) < 0) {
 128                         syslog(LOG_ERR, "setsockopt(IPV6_ADD_MEMBERSHIP): %m");
 129                         ret = -1;
 130                         goto out;
 131                 }
 132
 133                 if (iface->dhcpv6 == MODE_SERVER) {
 134                         memset(&mreq, 0, sizeof(mreq));
 135                         inet_pton(AF_INET6, ALL_DHCPV6_SERVERS, &mreq.ipv6mr_multiaddr);
 136                         mreq.ipv6mr_interface = iface->ifindex;
 137
 138                         if (setsockopt(iface->dhcpv6_event.uloop.fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP,
 139                                                 &mreq, sizeof(mreq)) < 0) {
 140                                 syslog(LOG_ERR, "setsockopt(IPV6_ADD_MEMBERSHIP): %m");
 141                                 ret = -1;
 142                                 goto out;
 143                         }
 144                 }
 145
 146                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
 147                 odhcpd_register(&iface->dhcpv6_event);
 148         }
 149
 150         ret = dhcpv6_setup_ia_interface(iface, enable);
 151
 152 out:
 153         if (ret < 0 && iface->dhcpv6_event.uloop.fd > 0) {
 154                 close(iface->dhcpv6_event.uloop.fd);
 155                 iface->dhcpv6_event.uloop.fd = -1;
 156         }
 157
 158         return ret;
 159 }
 160
 161 enum {
 162         IOV_NESTED = 0,
 163         IOV_DEST,
 164         IOV_MAXRT,
 165 #define IOV_STAT IOV_MAXRT
 166         IOV_DNS,
 167         IOV_DNS_ADDR,
 168         IOV_SEARCH,
 169         IOV_SEARCH_DOMAIN,
 170         IOV_PDBUF,
 171 #define IOV_REFRESH IOV_PDBUF
 172         IOV_CERID,
 173         IOV_DHCPV6_RAW,
 174         IOV_RELAY_MSG,
 175         IOV_TOTAL
 176 };
 177
 178 static void handle_nested_message(uint8_t *data, size_t len,
 179                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL])
 180 {
 181         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 182         if (iov[IOV_NESTED].iov_base == NULL) {
 183                 iov[IOV_NESTED].iov_base = data;
 184                 iov[IOV_NESTED].iov_len = len;
 185         }
 186
 187         if (len < sizeof(struct dhcpv6_client_header))
 188                 return;
 189
 190         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 191                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 192                 struct dhcpv6_client_header *hdr = (void*)data;
 193                 *opts = (uint8_t*)&hdr[1];
 194                 *end = data + len;
 195                 return;
 196         }
 197
 198         uint16_t otype, olen;
 199         uint8_t *odata;
 200         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 201                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 202                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 203                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 204                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 205                         handle_nested_message(odata, olen, opts, end, iov);
 206                         return;
 207                 }
 208         }
 209 }
 210
 211
 212 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 213 {
 214         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 215         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 216                 return;
 217
 218         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 219
 220         uint16_t otype, olen;
 221         uint8_t *odata;
 222         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 223                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 224                         olen += pdiff;
 225                         odata[-2] = (olen >> 8) & 0xff;
 226                         odata[-1] = olen & 0xff;
 227                         update_nested_message(odata, olen - pdiff, pdiff);
 228                         return;
 229                 }
 230         }
 231 }
 232
 233 /* Simple DHCPv6-server for information requests */
 234 static void handle_client_request(void *addr, void *data, size_t len,
 235                 struct interface *iface, void *dest_addr)
 236 {
 237         struct dhcpv6_client_header *hdr = data;
 238
 239         if (len < sizeof(*hdr))
 240                 return;
 241
 242         syslog(LOG_NOTICE, "Got DHCPv6 request on %s", iface->name);
 243
 244         /* Construct reply message */
 245         struct __attribute__((packed)) {
 246                 uint8_t msg_type;
 247                 uint8_t tr_id[3];
 248                 uint16_t serverid_type;
 249                 uint16_t serverid_length;
 250                 uint16_t duid_type;
 251                 uint16_t hardware_type;
 252                 uint8_t mac[6];
 253                 uint16_t clientid_type;
 254                 uint16_t clientid_length;
 255                 uint8_t clientid_buf[130];
 256         } dest = {
 257                 .msg_type = DHCPV6_MSG_REPLY,
 258                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 259                 .serverid_length = htons(10),
 260                 .duid_type = htons(3),
 261                 .hardware_type = htons(1),
 262                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 263                 .clientid_buf = {0}
 264         };
 265         odhcpd_get_mac(iface, dest.mac);
 266
 267         struct __attribute__((packed)) {
 268                 uint16_t type;
 269                 uint16_t len;
 270                 uint32_t value;
 271         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 272                         htonl(60)};
 273
 274         struct __attribute__((packed)) {
 275                 uint16_t type;
 276                 uint16_t len;
 277                 uint16_t value;
 278         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 279                         htons(DHCPV6_STATUS_USEMULTICAST)};
 280
 281         struct __attribute__((packed)) {
 282                 uint16_t type;
 283                 uint16_t len;
 284                 uint32_t value;
 285         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 286                         htonl(600)};
 287
 288         struct in6_addr dns_addr, *dns_addr_ptr = iface->dns;
 289         size_t dns_cnt = iface->dns_cnt;
 290
 291         if ((dns_cnt == 0) &&
 292                 !odhcpd_get_interface_dns_addr(iface, &dns_addr)) {
 293                 dns_addr_ptr = &dns_addr;
 294                 dns_cnt = 1;
 295         }
 296
 297         struct {
 298                 uint16_t type;
 299                 uint16_t len;
 300         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr_ptr))};
 301
 302
 303
 304         /* DNS Search options */
 305         uint8_t search_buf[256], *search_domain = iface->search;
 306         size_t search_len = iface->search_len;
 307
 308         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 309                 int len = dn_comp(_res.dnsrch[0], search_buf,
 310                                 sizeof(search_buf), NULL, NULL);
 311                 if (len > 0) {
 312                         search_domain = search_buf;
 313                         search_len = len;
 314                 }
 315         }
 316
 317         struct {
 318                 uint16_t type;
 319                 uint16_t len;
 320         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 321
 322
 323         struct dhcpv6_cer_id cerid = {
 324 #ifdef EXT_CER_ID
 325                 .type = htons(EXT_CER_ID),
 326 #endif
 327                 .len = htons(36),
 328                 .addr = iface->dhcpv6_pd_cer,
 329         };
 330
 331
 332         uint8_t pdbuf[512];
 333         struct iovec iov[IOV_TOTAL] = {
 334                 [IOV_NESTED] = {NULL, 0},
 335                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 336                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 337                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 338                 [IOV_DNS_ADDR] = {dns_addr_ptr, dns_cnt * sizeof(*dns_addr_ptr)},
 339                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 340                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 341                 [IOV_PDBUF] = {pdbuf, 0},
 342                 [IOV_CERID] = {&cerid, 0},
 343                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 344                 [IOV_RELAY_MSG] = {NULL, 0}
 345         };
 346
 347         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 348         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 349                 handle_nested_message(data, len, &opts, &opts_end, iov);
 350
 351         memcpy(dest.tr_id, hdr->transaction_id, sizeof(dest.tr_id));
 352
 353         if (hdr->msg_type == DHCPV6_MSG_ADVERTISE || hdr->msg_type == DHCPV6_MSG_REPLY ||
 354             hdr->msg_type == DHCPV6_MSG_RELAY_REPL)
 355                 return;
 356
 357         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 358                 (hdr->msg_type == DHCPV6_MSG_SOLICIT || hdr->msg_type == DHCPV6_MSG_CONFIRM ||
 359                  hdr->msg_type == DHCPV6_MSG_REBIND || hdr->msg_type == DHCPV6_MSG_INFORMATION_REQUEST))
 360                 return;
 361
 362         if (hdr->msg_type == DHCPV6_MSG_SOLICIT) {
 363                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 364         } else if (hdr->msg_type == DHCPV6_MSG_INFORMATION_REQUEST) {
 365                 iov[IOV_REFRESH].iov_base = &refresh;
 366                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 367
 368                 /* Return inf max rt option in reply to information request */
 369                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 370         }
 371
 372         /* Go through options and find what we need */
 373         uint16_t otype, olen;
 374         uint8_t *odata;
 375         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 376                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 377                         dest.clientid_length = htons(olen);
 378                         memcpy(dest.clientid_buf, odata, olen);
 379                         iov[IOV_DEST].iov_len += 4 + olen;
 380                 } else if (otype == DHCPV6_OPT_SERVERID) {
 381                         if (olen != ntohs(dest.serverid_length) ||
 382                                         memcmp(odata, &dest.duid_type, olen))
 383                                 return; /* Not for us */
 384                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 385                         uint8_t *c = odata, *cend = &odata[olen];
 386                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 387                                 size_t elen = strlen(iface->filter_class);
 388                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 389                                         return; /* Ignore from homenet */
 390                         }
 391                 } else if (otype == DHCPV6_OPT_IA_PD) {
 392 #ifdef EXT_CER_ID
 393                         iov[IOV_CERID].iov_len = sizeof(cerid);
 394
 395                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 396                                 struct odhcpd_ipaddr *addrs;
 397                                 ssize_t len = netlink_get_interface_addrs(0, true, &addrs);
 398
 399                                 for (ssize_t i = 0; i < len; ++i)
 400                                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)
 401                                                         || memcmp(&addrs[i].addr, &cerid.addr, sizeof(cerid.addr)) < 0)
 402                                                 cerid.addr = addrs[i].addr.in6;
 403
 404                                 free(addrs);
 405                         }
 406 #endif
 407                 }
 408         }
 409
 410         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 411             (hdr->msg_type == DHCPV6_MSG_REQUEST || hdr->msg_type == DHCPV6_MSG_RENEW ||
 412              hdr->msg_type == DHCPV6_MSG_RELEASE || hdr->msg_type == DHCPV6_MSG_DECLINE)) {
 413                 iov[IOV_STAT].iov_base = &stat;
 414                 iov[IOV_STAT].iov_len = sizeof(stat);
 415
 416                 for (ssize_t i = IOV_STAT + 1; i < IOV_TOTAL; ++i)
 417                         iov[i].iov_len = 0;
 418
 419                 odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 420                 return;
 421         }
 422
 423         if (hdr->msg_type != DHCPV6_MSG_INFORMATION_REQUEST) {
 424                 ssize_t ialen = dhcpv6_handle_ia(pdbuf, sizeof(pdbuf), iface, addr, data, opts_end);
 425
 426                 iov[IOV_PDBUF].iov_len = ialen;
 427                 if (ialen < 0 ||
 428                     (ialen == 0 && (hdr->msg_type == DHCPV6_MSG_REBIND || hdr->msg_type == DHCPV6_MSG_CONFIRM)))
 429                         return;
 430         }
 431
 432         if (iov[IOV_NESTED].iov_len > 0) /* Update length */
 433                 update_nested_message(data, len, iov[IOV_DEST].iov_len + iov[IOV_MAXRT].iov_len +
 434                                 iov[IOV_DNS].iov_len + iov[IOV_DNS_ADDR].iov_len +
 435                                 iov[IOV_SEARCH].iov_len + iov[IOV_SEARCH_DOMAIN].iov_len +
 436                                 iov[IOV_PDBUF].iov_len + iov[IOV_CERID].iov_len +
 437                                 iov[IOV_DHCPV6_RAW].iov_len - (4 + opts_end - opts));
 438
 439         odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 440 }
 441
 442
 443 /* Central DHCPv6-relay handler */
 444 static void handle_dhcpv6(void *addr, void *data, size_t len,
 445                 struct interface *iface, void *dest_addr)
 446 {
 447         if (iface->dhcpv6 == MODE_SERVER) {
 448                 handle_client_request(addr, data, len, iface, dest_addr);
 449         } else if (iface->dhcpv6 == MODE_RELAY) {
 450                 if (iface->master)
 451                         relay_server_response(data, len);
 452                 else
 453                         relay_client_request(addr, data, len, iface);
 454         }
 455 }
 456
 457
 458 /* Relay server response (regular relay server handling) */
 459 static void relay_server_response(uint8_t *data, size_t len)
 460 {
 461         /* Information we need to gather */
 462         uint8_t *payload_data = NULL;
 463         size_t payload_len = 0;
 464         int32_t ifaceidx = 0;
 465         struct sockaddr_in6 target = {AF_INET6, htons(DHCPV6_CLIENT_PORT),
 466                 0, IN6ADDR_ANY_INIT, 0};
 467
 468         syslog(LOG_NOTICE, "Got a DHCPv6-reply");
 469
 470         int otype, olen;
 471         uint8_t *odata, *end = data + len;
 472
 473         /* Relay DHCPv6 reply from server to client */
 474         struct dhcpv6_relay_header *h = (void*)data;
 475         if (len < sizeof(*h) || h->msg_type != DHCPV6_MSG_RELAY_REPL)
 476                 return;
 477
 478         memcpy(&target.sin6_addr, &h->peer_address,
 479                         sizeof(struct in6_addr));
 480
 481         /* Go through options and find what we need */
 482         dhcpv6_for_each_option(h->options, end, otype, olen, odata) {
 483                 if (otype == DHCPV6_OPT_INTERFACE_ID
 484                                 && olen == sizeof(ifaceidx)) {
 485                         memcpy(&ifaceidx, odata, sizeof(ifaceidx));
 486                 } else if (otype == DHCPV6_OPT_RELAY_MSG) {
 487                         payload_data = odata;
 488                         payload_len = olen;
 489                 }
 490         }
 491
 492         /* Invalid interface-id or basic payload */
 493         struct interface *iface = odhcpd_get_interface_by_index(ifaceidx);
 494         if (!iface || iface->master || !payload_data || payload_len < 4)
 495                 return;
 496
 497         bool is_authenticated = false;
 498         struct in6_addr *dns_ptr = NULL;
 499         size_t dns_count = 0;
 500
 501         /* If the payload is relay-reply we have to send to the server port */
 502         if (payload_data[0] == DHCPV6_MSG_RELAY_REPL) {
 503                 target.sin6_port = htons(DHCPV6_SERVER_PORT);
 504         } else { /* Go through the payload data */
 505                 struct dhcpv6_client_header *h = (void*)payload_data;
 506                 end = payload_data + payload_len;
 507
 508                 dhcpv6_for_each_option(&h[1], end, otype, olen, odata) {
 509                         if (otype == DHCPV6_OPT_DNS_SERVERS && olen >= 16) {
 510                                 dns_ptr = (struct in6_addr*)odata;
 511                                 dns_count = olen / 16;
 512                         } else if (otype == DHCPV6_OPT_AUTH) {
 513                                 is_authenticated = true;
 514                         }
 515                 }
 516         }
 517
 518         /* Rewrite DNS servers if requested */
 519         if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 520                 if (is_authenticated)
 521                         return; /* Impossible to rewrite */
 522
 523                 const struct in6_addr *rewrite = iface->dns;
 524                 struct in6_addr addr;
 525                 size_t rewrite_cnt = iface->dns_cnt;
 526
 527                 if (rewrite_cnt == 0) {
 528                         if (odhcpd_get_interface_dns_addr(iface, &addr))
 529                                 return; // Unable to get interface address
 530
 531                         rewrite = &addr;
 532                         rewrite_cnt = 1;
 533                 }
 534
 535                 /* Copy over any other addresses */
 536                 for (size_t i = 0; i < dns_count; ++i) {
 537                         size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 538                         memcpy(&dns_ptr[i], &rewrite[j], sizeof(*rewrite));
 539                 }
 540         }
 541
 542         struct iovec iov = {payload_data, payload_len};
 543         odhcpd_send(iface->dhcpv6_event.uloop.fd, &target, &iov, 1, iface);
 544 }
 545
 546 static struct odhcpd_ipaddr *relay_link_address(struct interface *iface)
 547 {
 548         struct odhcpd_ipaddr *addr = NULL;
 549         time_t now = odhcpd_time();
 550
 551         for (size_t i = 0; i < iface->addr6_len; i++) {
 552                 if (iface->addr6[i].valid <= (uint32_t)now)
 553                         continue;
 554
 555                 if (iface->addr6[i].preferred > (uint32_t)now) {
 556                         addr = &iface->addr6[i];
 557                         break;
 558                 }
 559
 560                 if (!addr || (iface->addr6[i].valid > addr->valid))
 561                         addr = &iface->addr6[i];
 562         }
 563
 564         return addr;
 565 }
 566
 567 /* Relay client request (regular DHCPv6-relay) */
 568 static void relay_client_request(struct sockaddr_in6 *source,
 569                 const void *data, size_t len, struct interface *iface)
 570 {
 571         struct interface *master = odhcpd_get_master_interface();
 572         const struct dhcpv6_relay_header *h = data;
 573         struct sockaddr_in6 s;
 574
 575         if (!master || master->dhcpv6 != MODE_RELAY ||
 576                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 577                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 578                         h->msg_type == DHCPV6_MSG_REPLY ||
 579                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 580                 return; /* Invalid message types for client */
 581
 582         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 583
 584         /* Construct our forwarding envelope */
 585         struct dhcpv6_relay_forward_envelope hdr = {
 586                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 587                 .hop_count = 0,
 588                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 589                 .interface_id_len = htons(sizeof(uint32_t)),
 590                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 591                 .relay_message_len = htons(len),
 592         };
 593
 594         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { /* handle relay-forward */
 595                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 596                         return; // Invalid hop count
 597                 else
 598                         hdr.hop_count = h->hop_count + 1;
 599         }
 600
 601         /* use memcpy here as the destination fields are unaligned */
 602         uint32_t ifindex = iface->ifindex;
 603         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 604         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 605
 606         /* Detect public IP of slave interface to use as link-address */
 607         struct odhcpd_ipaddr *ip = relay_link_address(iface);
 608         if (!ip) {
 609                 /* No suitable address! Is the slave not configured yet?
 610                  * Detect public IP of master interface and use it instead
 611                  * This is WRONG and probably violates the RFC. However
 612                  * otherwise we have a hen and egg problem because the
 613                  * slave-interface cannot be auto-configured. */
 614                 ip = relay_link_address(master);
 615                 if (!ip)
 616                         return; /* Could not obtain a suitable address */
 617         }
 618
 619         memcpy(&hdr.link_address, &ip->addr.in6, sizeof(hdr.link_address));
 620
 621         memset(&s, 0, sizeof(s));
 622         s.sin6_family = AF_INET6;
 623         s.sin6_port = htons(DHCPV6_SERVER_PORT);
 624         inet_pton(AF_INET6, ALL_DHCPV6_SERVERS, &s.sin6_addr);
 625
 626         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 627         odhcpd_send(master->dhcpv6_event.uloop.fd, &s, iov, 2, master);
 628 }