src/resolve/resolved-dns-server.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2014 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <sd-messages.h>
  21
  22 #include "alloc-util.h"
  23 #include "resolved-dns-server.h"
  24 #include "resolved-resolv-conf.h"
  25 #include "siphash24.h"
  26 #include "string-table.h"
  27 #include "string-util.h"
  28
  29 /* After how much time to repeat classic DNS requests */
  30 #define DNS_TIMEOUT_MIN_USEC (500 * USEC_PER_MSEC)
  31 #define DNS_TIMEOUT_MAX_USEC (5 * USEC_PER_SEC)
  32
  33 /* The amount of time to wait before retrying with a full feature set */
  34 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC (6 * USEC_PER_HOUR)
  35 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC (5 * USEC_PER_MINUTE)
  36
  37 /* The number of times we will attempt a certain feature set before degrading */
  38 #define DNS_SERVER_FEATURE_RETRY_ATTEMPTS 3
  39
  40 int dns_server_new(
  41                 Manager *m,
  42                 DnsServer **ret,
  43                 DnsServerType type,
  44                 Link *l,
  45                 int family,
  46                 const union in_addr_union *in_addr) {
  47
  48         DnsServer *s;
  49
  50         assert(m);
  51         assert((type == DNS_SERVER_LINK) == !!l);
  52         assert(in_addr);
  53
  54         if (!IN_SET(family, AF_INET, AF_INET6))
  55                 return -EAFNOSUPPORT;
  56
  57         if (l) {
  58                 if (l->n_dns_servers >= LINK_DNS_SERVERS_MAX)
  59                         return -E2BIG;
  60         } else {
  61                 if (m->n_dns_servers >= MANAGER_DNS_SERVERS_MAX)
  62                         return -E2BIG;
  63         }
  64
  65         s = new0(DnsServer, 1);
  66         if (!s)
  67                 return -ENOMEM;
  68
  69         s->n_ref = 1;
  70         s->manager = m;
  71         s->verified_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
  72         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
  73         s->features_grace_period_usec = DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC;
  74         s->received_udp_packet_max = DNS_PACKET_UNICAST_SIZE_MAX;
  75         s->type = type;
  76         s->family = family;
  77         s->address = *in_addr;
  78         s->resend_timeout = DNS_TIMEOUT_MIN_USEC;
  79
  80         switch (type) {
  81
  82         case DNS_SERVER_LINK:
  83                 s->link = l;
  84                 LIST_APPEND(servers, l->dns_servers, s);
  85                 l->n_dns_servers++;
  86                 break;
  87
  88         case DNS_SERVER_SYSTEM:
  89                 LIST_APPEND(servers, m->dns_servers, s);
  90                 m->n_dns_servers++;
  91                 break;
  92
  93         case DNS_SERVER_FALLBACK:
  94                 LIST_APPEND(servers, m->fallback_dns_servers, s);
  95                 m->n_dns_servers++;
  96                 break;
  97
  98         default:
  99                 assert_not_reached("Unknown server type");
 100         }
 101
 102         s->linked = true;
 103
 104         /* A new DNS server that isn't fallback is added and the one
 105          * we used so far was a fallback one? Then let's try to pick
 106          * the new one */
 107         if (type != DNS_SERVER_FALLBACK &&
 108             m->current_dns_server &&
 109             m->current_dns_server->type == DNS_SERVER_FALLBACK)
 110                 manager_set_dns_server(m, NULL);
 111
 112         if (ret)
 113                 *ret = s;
 114
 115         return 0;
 116 }
 117
 118 DnsServer* dns_server_ref(DnsServer *s)  {
 119         if (!s)
 120                 return NULL;
 121
 122         assert(s->n_ref > 0);
 123         s->n_ref++;
 124
 125         return s;
 126 }
 127
 128 DnsServer* dns_server_unref(DnsServer *s)  {
 129         if (!s)
 130                 return NULL;
 131
 132         assert(s->n_ref > 0);
 133         s->n_ref--;
 134
 135         if (s->n_ref > 0)
 136                 return NULL;
 137
 138         free(s->server_string);
 139         free(s);
 140         return NULL;
 141 }
 142
 143 void dns_server_unlink(DnsServer *s) {
 144         assert(s);
 145         assert(s->manager);
 146
 147         /* This removes the specified server from the linked list of
 148          * servers, but any server might still stay around if it has
 149          * refs, for example from an ongoing transaction. */
 150
 151         if (!s->linked)
 152                 return;
 153
 154         switch (s->type) {
 155
 156         case DNS_SERVER_LINK:
 157                 assert(s->link);
 158                 assert(s->link->n_dns_servers > 0);
 159                 LIST_REMOVE(servers, s->link->dns_servers, s);
 160                 break;
 161
 162         case DNS_SERVER_SYSTEM:
 163                 assert(s->manager->n_dns_servers > 0);
 164                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 165                 s->manager->n_dns_servers--;
 166                 break;
 167
 168         case DNS_SERVER_FALLBACK:
 169                 assert(s->manager->n_dns_servers > 0);
 170                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 171                 s->manager->n_dns_servers--;
 172                 break;
 173         }
 174
 175         s->linked = false;
 176
 177         if (s->link && s->link->current_dns_server == s)
 178                 link_set_dns_server(s->link, NULL);
 179
 180         if (s->manager->current_dns_server == s)
 181                 manager_set_dns_server(s->manager, NULL);
 182
 183         dns_server_unref(s);
 184 }
 185
 186 void dns_server_move_back_and_unmark(DnsServer *s) {
 187         DnsServer *tail;
 188
 189         assert(s);
 190
 191         if (!s->marked)
 192                 return;
 193
 194         s->marked = false;
 195
 196         if (!s->linked || !s->servers_next)
 197                 return;
 198
 199         /* Move us to the end of the list, so that the order is
 200          * strictly kept, if we are not at the end anyway. */
 201
 202         switch (s->type) {
 203
 204         case DNS_SERVER_LINK:
 205                 assert(s->link);
 206                 LIST_FIND_TAIL(servers, s, tail);
 207                 LIST_REMOVE(servers, s->link->dns_servers, s);
 208                 LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s);
 209                 break;
 210
 211         case DNS_SERVER_SYSTEM:
 212                 LIST_FIND_TAIL(servers, s, tail);
 213                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 214                 LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s);
 215                 break;
 216
 217         case DNS_SERVER_FALLBACK:
 218                 LIST_FIND_TAIL(servers, s, tail);
 219                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 220                 LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s);
 221                 break;
 222
 223         default:
 224                 assert_not_reached("Unknown server type");
 225         }
 226 }
 227
 228 static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) {
 229         assert(s);
 230
 231         if (s->verified_feature_level > level)
 232                 return;
 233
 234         if (s->verified_feature_level != level) {
 235                 log_debug("Verified we get a response at feature level %s from DNS server %s.",
 236                           dns_server_feature_level_to_string(level),
 237                           dns_server_string(s));
 238                 s->verified_feature_level = level;
 239         }
 240
 241         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
 242 }
 243
 244 void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size) {
 245         assert(s);
 246
 247         if (protocol == IPPROTO_UDP) {
 248                 if (s->possible_feature_level == level)
 249                         s->n_failed_udp = 0;
 250
 251                 /* If the RRSIG data is missing, then we can only validate EDNS0 at max */
 252                 if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO)
 253                         level = DNS_SERVER_FEATURE_LEVEL_DO - 1;
 254
 255                 /* If the OPT RR got lost, then we can only validate UDP at max */
 256                 if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 257                         level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1;
 258
 259                 /* Even if we successfully receive a reply to a request announcing support for large packets,
 260                    that does not mean we can necessarily receive large packets. */
 261                 if (level == DNS_SERVER_FEATURE_LEVEL_LARGE)
 262                         level = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
 263
 264         } else if (protocol == IPPROTO_TCP) {
 265
 266                 if (s->possible_feature_level == level)
 267                         s->n_failed_tcp = 0;
 268
 269                 /* Successful TCP connections are only useful to verify the TCP feature level. */
 270                 level = DNS_SERVER_FEATURE_LEVEL_TCP;
 271         }
 272
 273         dns_server_verified(s, level);
 274
 275         /* Remember the size of the largest UDP packet we received from a server,
 276            we know that we can always announce support for packets with at least
 277            this size. */
 278         if (protocol == IPPROTO_UDP && s->received_udp_packet_max < size)
 279                 s->received_udp_packet_max = size;
 280
 281         if (s->max_rtt < rtt) {
 282                 s->max_rtt = rtt;
 283                 s->resend_timeout = CLAMP(s->max_rtt * 2, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC);
 284         }
 285 }
 286
 287 void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec) {
 288         assert(s);
 289         assert(s->manager);
 290
 291         if (s->possible_feature_level == level) {
 292                 if (protocol == IPPROTO_UDP)
 293                         s->n_failed_udp++;
 294                 else if (protocol == IPPROTO_TCP)
 295                         s->n_failed_tcp++;
 296         }
 297
 298         if (s->resend_timeout > usec)
 299                 return;
 300
 301         s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC);
 302 }
 303
 304 void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level) {
 305         assert(s);
 306
 307         /* Invoked whenever we get a FORMERR, SERVFAIL or NOTIMP rcode from a server. */
 308
 309         if (s->possible_feature_level != level)
 310                 return;
 311
 312         s->packet_failed = true;
 313 }
 314
 315 void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) {
 316         assert(s);
 317
 318         /* Invoked whenever we get a packet with TC bit set. */
 319
 320         if (s->possible_feature_level != level)
 321                 return;
 322
 323         s->packet_truncated = true;
 324 }
 325
 326 void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) {
 327         assert(s);
 328
 329         if (level < DNS_SERVER_FEATURE_LEVEL_DO)
 330                 return;
 331
 332         /* If the RRSIG RRs are missing, we have to downgrade what we previously verified */
 333         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO)
 334                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_DO-1;
 335
 336         s->packet_rrsig_missing = true;
 337 }
 338
 339 void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) {
 340         assert(s);
 341
 342         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 343                 return;
 344
 345         /* If the OPT RR got lost, we have to downgrade what we previously verified */
 346         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 347                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1;
 348
 349         s->packet_bad_opt = true;
 350 }
 351
 352 static bool dns_server_grace_period_expired(DnsServer *s) {
 353         usec_t ts;
 354
 355         assert(s);
 356         assert(s->manager);
 357
 358         if (s->verified_usec == 0)
 359                 return false;
 360
 361         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
 362
 363         if (s->verified_usec + s->features_grace_period_usec > ts)
 364                 return false;
 365
 366         s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
 367
 368         return true;
 369 }
 370
 371 static void dns_server_reset_counters(DnsServer *s) {
 372         assert(s);
 373
 374         s->n_failed_udp = 0;
 375         s->n_failed_tcp = 0;
 376         s->packet_failed = false;
 377         s->packet_truncated = false;
 378         s->verified_usec = 0;
 379
 380         /* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the
 381          * grace period ends, but not when lowering the possible feature level, as a lower level feature level should
 382          * not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's
 383          * indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that
 384          * either.
 385          *
 386          * This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A),
 387          * but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not
 388          * reenable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be
 389          * incomplete. */
 390 }
 391
 392 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
 393         assert(s);
 394
 395         if (s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_BEST &&
 396             dns_server_grace_period_expired(s)) {
 397
 398                 s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
 399
 400                 dns_server_reset_counters(s);
 401
 402                 s->packet_bad_opt = false;
 403                 s->packet_rrsig_missing = false;
 404
 405                 log_info("Grace period over, resuming full feature set (%s) for DNS server %s.",
 406                          dns_server_feature_level_to_string(s->possible_feature_level),
 407                          dns_server_string(s));
 408
 409         } else if (s->possible_feature_level <= s->verified_feature_level)
 410                 s->possible_feature_level = s->verified_feature_level;
 411         else {
 412                 DnsServerFeatureLevel p = s->possible_feature_level;
 413
 414                 if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 415                     s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TCP) {
 416
 417                         /* We are at the TCP (lowest) level, and we tried a couple of TCP connections, and it didn't
 418                          * work. Upgrade back to UDP again. */
 419                         log_debug("Reached maximum number of failed TCP connection attempts, trying UDP again...");
 420                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 421
 422                 } else if (s->packet_bad_opt &&
 423                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) {
 424
 425                         /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to below
 426                          * EDNS0 levels. After all, some records generate different responses with and without OPT RR
 427                          * in the request. Example:
 428                          * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
 429
 430                         log_debug("Server doesn't support EDNS(0) properly, downgrading feature level...");
 431                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 432
 433                 } else if (s->packet_rrsig_missing &&
 434                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) {
 435
 436                         /* RRSIG data was missing on a EDNS0 packet with DO bit set. This means the server doesn't
 437                          * augment responses with DNSSEC RRs. If so, let's better not ask the server for it anymore,
 438                          * after all some servers generate different replies depending if an OPT RR is in the query or
 439                          * not. */
 440
 441                         log_debug("Detected server responses lack RRSIG records, downgrading feature level...");
 442                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0;
 443
 444                 } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 445                             s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_UDP) {
 446
 447                         /* We lost too many UDP packets in a row, and are on a feature level of UDP or higher. If the
 448                          * packets are lost, maybe the server cannot parse them, hence downgrading sounds like a good
 449                          * idea. We might downgrade all the way down to TCP this way. */
 450
 451                         log_debug("Lost too many UDP packets, downgrading feature level...");
 452                         s->possible_feature_level--;
 453
 454                 } else if (s->packet_failed &&
 455                            s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP) {
 456
 457                         /* We got a failure packet, and are at a feature level above UDP. Note that in this case we
 458                          * downgrade no further than UDP, under the assumption that a failure packet indicates an
 459                          * incompatible packet contents, but not a problem with the transport. */
 460
 461                         log_debug("Got server failure, downgrading feature level...");
 462                         s->possible_feature_level--;
 463
 464                 } else if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 465                            s->packet_truncated &&
 466                            s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP) {
 467
 468                          /* We got too many TCP connection failures in a row, we had at least one truncated packet, and
 469                           * are on a feature level above UDP. By downgrading things and getting rid of DNSSEC or EDNS0
 470                           * data we hope to make the packet smaller, so that it still works via UDP given that TCP
 471                           * appears not to be a fallback. Note that if we are already at the lowest UDP level, we don't
 472                           * go further down, since that's TCP, and TCP failed too often after all. */
 473
 474                         log_debug("Got too many failed TCP connection failures and truncated UDP packets, downgrading feature level...");
 475                         s->possible_feature_level--;
 476                 }
 477
 478                 if (p != s->possible_feature_level) {
 479
 480                         /* We changed the feature level, reset the counting */
 481                         dns_server_reset_counters(s);
 482
 483                         log_warning("Using degraded feature set (%s) for DNS server %s.",
 484                                     dns_server_feature_level_to_string(s->possible_feature_level),
 485                                     dns_server_string(s));
 486                 }
 487         }
 488
 489         return s->possible_feature_level;
 490 }
 491
 492 int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeatureLevel level) {
 493         size_t packet_size;
 494         bool edns_do;
 495         int r;
 496
 497         assert(server);
 498         assert(packet);
 499         assert(packet->protocol == DNS_PROTOCOL_DNS);
 500
 501         /* Fix the OPT field in the packet to match our current feature level. */
 502
 503         r = dns_packet_truncate_opt(packet);
 504         if (r < 0)
 505                 return r;
 506
 507         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 508                 return 0;
 509
 510         edns_do = level >= DNS_SERVER_FEATURE_LEVEL_DO;
 511
 512         if (level >= DNS_SERVER_FEATURE_LEVEL_LARGE)
 513                 packet_size = DNS_PACKET_UNICAST_SIZE_LARGE_MAX;
 514         else
 515                 packet_size = server->received_udp_packet_max;
 516
 517         return dns_packet_append_opt(packet, packet_size, edns_do, NULL);
 518 }
 519
 520 const char *dns_server_string(DnsServer *server) {
 521         assert(server);
 522
 523         if (!server->server_string)
 524                 (void) in_addr_to_string(server->family, &server->address, &server->server_string);
 525
 526         return strna(server->server_string);
 527 }
 528
 529 bool dns_server_dnssec_supported(DnsServer *server) {
 530         assert(server);
 531
 532         /* Returns whether the server supports DNSSEC according to what we know about it */
 533
 534         if (server->possible_feature_level < DNS_SERVER_FEATURE_LEVEL_DO)
 535                 return false;
 536
 537         if (server->packet_bad_opt)
 538                 return false;
 539
 540         if (server->packet_rrsig_missing)
 541                 return false;
 542
 543         /* DNSSEC servers need to support TCP properly (see RFC5966), if they don't, we assume DNSSEC is borked too */
 544         if (server->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS)
 545                 return false;
 546
 547         return true;
 548 }
 549
 550 void dns_server_warn_downgrade(DnsServer *server) {
 551         assert(server);
 552
 553         if (server->warned_downgrade)
 554                 return;
 555
 556         log_struct(LOG_NOTICE,
 557                    LOG_MESSAGE_ID(SD_MESSAGE_DNSSEC_DOWNGRADE),
 558                    LOG_MESSAGE("Server %s does not support DNSSEC, downgrading to non-DNSSEC mode.", dns_server_string(server)),
 559                    "DNS_SERVER=%s", dns_server_string(server),
 560                    "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(server->possible_feature_level),
 561                    NULL);
 562
 563         server->warned_downgrade = true;
 564 }
 565
 566 static void dns_server_hash_func(const void *p, struct siphash *state) {
 567         const DnsServer *s = p;
 568
 569         assert(s);
 570
 571         siphash24_compress(&s->family, sizeof(s->family), state);
 572         siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state);
 573 }
 574
 575 static int dns_server_compare_func(const void *a, const void *b) {
 576         const DnsServer *x = a, *y = b;
 577
 578         if (x->family < y->family)
 579                 return -1;
 580         if (x->family > y->family)
 581                 return 1;
 582
 583         return memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family));
 584 }
 585
 586 const struct hash_ops dns_server_hash_ops = {
 587         .hash = dns_server_hash_func,
 588         .compare = dns_server_compare_func
 589 };
 590
 591 void dns_server_unlink_all(DnsServer *first) {
 592         DnsServer *next;
 593
 594         if (!first)
 595                 return;
 596
 597         next = first->servers_next;
 598         dns_server_unlink(first);
 599
 600         dns_server_unlink_all(next);
 601 }
 602
 603 void dns_server_unlink_marked(DnsServer *first) {
 604         DnsServer *next;
 605
 606         if (!first)
 607                 return;
 608
 609         next = first->servers_next;
 610
 611         if (first->marked)
 612                 dns_server_unlink(first);
 613
 614         dns_server_unlink_marked(next);
 615 }
 616
 617 void dns_server_mark_all(DnsServer *first) {
 618         if (!first)
 619                 return;
 620
 621         first->marked = true;
 622         dns_server_mark_all(first->servers_next);
 623 }
 624
 625 DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr) {
 626         DnsServer *s;
 627
 628         LIST_FOREACH(servers, s, first)
 629                 if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0)
 630                         return s;
 631
 632         return NULL;
 633 }
 634
 635 DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) {
 636         assert(m);
 637
 638         switch (t) {
 639
 640         case DNS_SERVER_SYSTEM:
 641                 return m->dns_servers;
 642
 643         case DNS_SERVER_FALLBACK:
 644                 return m->fallback_dns_servers;
 645
 646         default:
 647                 return NULL;
 648         }
 649 }
 650
 651 DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) {
 652         assert(m);
 653
 654         if (m->current_dns_server == s)
 655                 return s;
 656
 657         if (s)
 658                 log_info("Switching to %s DNS server %s.",
 659                          dns_server_type_to_string(s->type),
 660                          dns_server_string(s));
 661
 662         dns_server_unref(m->current_dns_server);
 663         m->current_dns_server = dns_server_ref(s);
 664
 665         if (m->unicast_scope)
 666                 dns_cache_flush(&m->unicast_scope->cache);
 667
 668         return s;
 669 }
 670
 671 DnsServer *manager_get_dns_server(Manager *m) {
 672         Link *l;
 673         assert(m);
 674
 675         /* Try to read updates resolv.conf */
 676         manager_read_resolv_conf(m);
 677
 678         /* If no DNS server was chosen so far, pick the first one */
 679         if (!m->current_dns_server)
 680                 manager_set_dns_server(m, m->dns_servers);
 681
 682         if (!m->current_dns_server) {
 683                 bool found = false;
 684                 Iterator i;
 685
 686                 /* No DNS servers configured, let's see if there are
 687                  * any on any links. If not, we use the fallback
 688                  * servers */
 689
 690                 HASHMAP_FOREACH(l, m->links, i)
 691                         if (l->dns_servers) {
 692                                 found = true;
 693                                 break;
 694                         }
 695
 696                 if (!found)
 697                         manager_set_dns_server(m, m->fallback_dns_servers);
 698         }
 699
 700         return m->current_dns_server;
 701 }
 702
 703 void manager_next_dns_server(Manager *m) {
 704         assert(m);
 705
 706         /* If there's currently no DNS server set, then the next
 707          * manager_get_dns_server() will find one */
 708         if (!m->current_dns_server)
 709                 return;
 710
 711         /* Change to the next one, but make sure to follow the linked
 712          * list only if the server is still linked. */
 713         if (m->current_dns_server->linked && m->current_dns_server->servers_next) {
 714                 manager_set_dns_server(m, m->current_dns_server->servers_next);
 715                 return;
 716         }
 717
 718         /* If there was no next one, then start from the beginning of
 719          * the list */
 720         if (m->current_dns_server->type == DNS_SERVER_FALLBACK)
 721                 manager_set_dns_server(m, m->fallback_dns_servers);
 722         else
 723                 manager_set_dns_server(m, m->dns_servers);
 724 }
 725
 726 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
 727         [DNS_SERVER_SYSTEM] = "system",
 728         [DNS_SERVER_FALLBACK] = "fallback",
 729         [DNS_SERVER_LINK] = "link",
 730 };
 731 DEFINE_STRING_TABLE_LOOKUP(dns_server_type, DnsServerType);
 732
 733 static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = {
 734         [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP",
 735         [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP",
 736         [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0",
 737         [DNS_SERVER_FEATURE_LEVEL_DO] = "UDP+EDNS0+DO",
 738         [DNS_SERVER_FEATURE_LEVEL_LARGE] = "UDP+EDNS0+DO+LARGE",
 739 };
 740 DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);