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-dns-stub.h"
  25 #include "resolved-resolv-conf.h"
  26 #include "siphash24.h"
  27 #include "string-table.h"
  28 #include "string-util.h"
  29
  30 /* After how much time to repeat classic DNS requests */
  31 #define DNS_TIMEOUT_MIN_USEC (500 * USEC_PER_MSEC)
  32 #define DNS_TIMEOUT_MAX_USEC (5 * USEC_PER_SEC)
  33
  34 /* The amount of time to wait before retrying with a full feature set */
  35 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC (6 * USEC_PER_HOUR)
  36 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC (5 * USEC_PER_MINUTE)
  37
  38 /* The number of times we will attempt a certain feature set before degrading */
  39 #define DNS_SERVER_FEATURE_RETRY_ATTEMPTS 3
  40
  41 int dns_server_new(
  42                 Manager *m,
  43                 DnsServer **ret,
  44                 DnsServerType type,
  45                 Link *l,
  46                 int family,
  47                 const union in_addr_union *in_addr,
  48                 int ifindex) {
  49
  50         DnsServer *s;
  51
  52         assert(m);
  53         assert((type == DNS_SERVER_LINK) == !!l);
  54         assert(in_addr);
  55
  56         if (!IN_SET(family, AF_INET, AF_INET6))
  57                 return -EAFNOSUPPORT;
  58
  59         if (l) {
  60                 if (l->n_dns_servers >= LINK_DNS_SERVERS_MAX)
  61                         return -E2BIG;
  62         } else {
  63                 if (m->n_dns_servers >= MANAGER_DNS_SERVERS_MAX)
  64                         return -E2BIG;
  65         }
  66
  67         s = new0(DnsServer, 1);
  68         if (!s)
  69                 return -ENOMEM;
  70
  71         s->n_ref = 1;
  72         s->manager = m;
  73         s->verified_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
  74         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
  75         s->features_grace_period_usec = DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC;
  76         s->received_udp_packet_max = DNS_PACKET_UNICAST_SIZE_MAX;
  77         s->type = type;
  78         s->family = family;
  79         s->address = *in_addr;
  80         s->ifindex = ifindex;
  81         s->resend_timeout = DNS_TIMEOUT_MIN_USEC;
  82
  83         switch (type) {
  84
  85         case DNS_SERVER_LINK:
  86                 s->link = l;
  87                 LIST_APPEND(servers, l->dns_servers, s);
  88                 l->n_dns_servers++;
  89                 break;
  90
  91         case DNS_SERVER_SYSTEM:
  92                 LIST_APPEND(servers, m->dns_servers, s);
  93                 m->n_dns_servers++;
  94                 break;
  95
  96         case DNS_SERVER_FALLBACK:
  97                 LIST_APPEND(servers, m->fallback_dns_servers, s);
  98                 m->n_dns_servers++;
  99                 break;
 100
 101         default:
 102                 assert_not_reached("Unknown server type");
 103         }
 104
 105         s->linked = true;
 106
 107         /* A new DNS server that isn't fallback is added and the one
 108          * we used so far was a fallback one? Then let's try to pick
 109          * the new one */
 110         if (type != DNS_SERVER_FALLBACK &&
 111             m->current_dns_server &&
 112             m->current_dns_server->type == DNS_SERVER_FALLBACK)
 113                 manager_set_dns_server(m, NULL);
 114
 115         if (ret)
 116                 *ret = s;
 117
 118         return 0;
 119 }
 120
 121 DnsServer* dns_server_ref(DnsServer *s)  {
 122         if (!s)
 123                 return NULL;
 124
 125         assert(s->n_ref > 0);
 126         s->n_ref++;
 127
 128         return s;
 129 }
 130
 131 DnsServer* dns_server_unref(DnsServer *s)  {
 132         if (!s)
 133                 return NULL;
 134
 135         assert(s->n_ref > 0);
 136         s->n_ref--;
 137
 138         if (s->n_ref > 0)
 139                 return NULL;
 140
 141         free(s->server_string);
 142         free(s);
 143         return NULL;
 144 }
 145
 146 void dns_server_unlink(DnsServer *s) {
 147         assert(s);
 148         assert(s->manager);
 149
 150         /* This removes the specified server from the linked list of
 151          * servers, but any server might still stay around if it has
 152          * refs, for example from an ongoing transaction. */
 153
 154         if (!s->linked)
 155                 return;
 156
 157         switch (s->type) {
 158
 159         case DNS_SERVER_LINK:
 160                 assert(s->link);
 161                 assert(s->link->n_dns_servers > 0);
 162                 LIST_REMOVE(servers, s->link->dns_servers, s);
 163                 s->link->n_dns_servers--;
 164                 break;
 165
 166         case DNS_SERVER_SYSTEM:
 167                 assert(s->manager->n_dns_servers > 0);
 168                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 169                 s->manager->n_dns_servers--;
 170                 break;
 171
 172         case DNS_SERVER_FALLBACK:
 173                 assert(s->manager->n_dns_servers > 0);
 174                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 175                 s->manager->n_dns_servers--;
 176                 break;
 177         }
 178
 179         s->linked = false;
 180
 181         if (s->link && s->link->current_dns_server == s)
 182                 link_set_dns_server(s->link, NULL);
 183
 184         if (s->manager->current_dns_server == s)
 185                 manager_set_dns_server(s->manager, NULL);
 186
 187         dns_server_unref(s);
 188 }
 189
 190 void dns_server_move_back_and_unmark(DnsServer *s) {
 191         DnsServer *tail;
 192
 193         assert(s);
 194
 195         if (!s->marked)
 196                 return;
 197
 198         s->marked = false;
 199
 200         if (!s->linked || !s->servers_next)
 201                 return;
 202
 203         /* Move us to the end of the list, so that the order is
 204          * strictly kept, if we are not at the end anyway. */
 205
 206         switch (s->type) {
 207
 208         case DNS_SERVER_LINK:
 209                 assert(s->link);
 210                 LIST_FIND_TAIL(servers, s, tail);
 211                 LIST_REMOVE(servers, s->link->dns_servers, s);
 212                 LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s);
 213                 break;
 214
 215         case DNS_SERVER_SYSTEM:
 216                 LIST_FIND_TAIL(servers, s, tail);
 217                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 218                 LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s);
 219                 break;
 220
 221         case DNS_SERVER_FALLBACK:
 222                 LIST_FIND_TAIL(servers, s, tail);
 223                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 224                 LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s);
 225                 break;
 226
 227         default:
 228                 assert_not_reached("Unknown server type");
 229         }
 230 }
 231
 232 static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) {
 233         assert(s);
 234
 235         if (s->verified_feature_level > level)
 236                 return;
 237
 238         if (s->verified_feature_level != level) {
 239                 log_debug("Verified we get a response at feature level %s from DNS server %s.",
 240                           dns_server_feature_level_to_string(level),
 241                           dns_server_string(s));
 242                 s->verified_feature_level = level;
 243         }
 244
 245         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
 246 }
 247
 248 void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size) {
 249         assert(s);
 250
 251         if (protocol == IPPROTO_UDP) {
 252                 if (s->possible_feature_level == level)
 253                         s->n_failed_udp = 0;
 254
 255                 /* If the RRSIG data is missing, then we can only validate EDNS0 at max */
 256                 if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO)
 257                         level = DNS_SERVER_FEATURE_LEVEL_DO - 1;
 258
 259                 /* If the OPT RR got lost, then we can only validate UDP at max */
 260                 if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 261                         level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1;
 262
 263                 /* Even if we successfully receive a reply to a request announcing support for large packets,
 264                    that does not mean we can necessarily receive large packets. */
 265                 if (level == DNS_SERVER_FEATURE_LEVEL_LARGE)
 266                         level = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
 267
 268         } else if (protocol == IPPROTO_TCP) {
 269
 270                 if (s->possible_feature_level == level)
 271                         s->n_failed_tcp = 0;
 272
 273                 /* Successful TCP connections are only useful to verify the TCP feature level. */
 274                 level = DNS_SERVER_FEATURE_LEVEL_TCP;
 275         }
 276
 277         dns_server_verified(s, level);
 278
 279         /* Remember the size of the largest UDP packet we received from a server,
 280            we know that we can always announce support for packets with at least
 281            this size. */
 282         if (protocol == IPPROTO_UDP && s->received_udp_packet_max < size)
 283                 s->received_udp_packet_max = size;
 284
 285         if (s->max_rtt < rtt) {
 286                 s->max_rtt = rtt;
 287                 s->resend_timeout = CLAMP(s->max_rtt * 2, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC);
 288         }
 289 }
 290
 291 void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec) {
 292         assert(s);
 293         assert(s->manager);
 294
 295         if (s->possible_feature_level == level) {
 296                 if (protocol == IPPROTO_UDP)
 297                         s->n_failed_udp++;
 298                 else if (protocol == IPPROTO_TCP)
 299                         s->n_failed_tcp++;
 300         }
 301
 302         if (s->resend_timeout > usec)
 303                 return;
 304
 305         s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC);
 306 }
 307
 308 void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level) {
 309         assert(s);
 310
 311         /* Invoked whenever we get a FORMERR, SERVFAIL or NOTIMP rcode from a server. */
 312
 313         if (s->possible_feature_level != level)
 314                 return;
 315
 316         s->packet_failed = true;
 317 }
 318
 319 void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) {
 320         assert(s);
 321
 322         /* Invoked whenever we get a packet with TC bit set. */
 323
 324         if (s->possible_feature_level != level)
 325                 return;
 326
 327         s->packet_truncated = true;
 328 }
 329
 330 void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) {
 331         assert(s);
 332
 333         if (level < DNS_SERVER_FEATURE_LEVEL_DO)
 334                 return;
 335
 336         /* If the RRSIG RRs are missing, we have to downgrade what we previously verified */
 337         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO)
 338                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_DO-1;
 339
 340         s->packet_rrsig_missing = true;
 341 }
 342
 343 void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) {
 344         assert(s);
 345
 346         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 347                 return;
 348
 349         /* If the OPT RR got lost, we have to downgrade what we previously verified */
 350         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 351                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1;
 352
 353         s->packet_bad_opt = true;
 354 }
 355
 356 static bool dns_server_grace_period_expired(DnsServer *s) {
 357         usec_t ts;
 358
 359         assert(s);
 360         assert(s->manager);
 361
 362         if (s->verified_usec == 0)
 363                 return false;
 364
 365         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
 366
 367         if (s->verified_usec + s->features_grace_period_usec > ts)
 368                 return false;
 369
 370         s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
 371
 372         return true;
 373 }
 374
 375 static void dns_server_reset_counters(DnsServer *s) {
 376         assert(s);
 377
 378         s->n_failed_udp = 0;
 379         s->n_failed_tcp = 0;
 380         s->packet_failed = false;
 381         s->packet_truncated = false;
 382         s->verified_usec = 0;
 383
 384         /* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the
 385          * grace period ends, but not when lowering the possible feature level, as a lower level feature level should
 386          * not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's
 387          * indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that
 388          * either.
 389          *
 390          * This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A),
 391          * but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not
 392          * reenable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be
 393          * incomplete. */
 394 }
 395
 396 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
 397         assert(s);
 398
 399         if (s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_BEST &&
 400             dns_server_grace_period_expired(s)) {
 401
 402                 s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
 403
 404                 dns_server_reset_counters(s);
 405
 406                 s->packet_bad_opt = false;
 407                 s->packet_rrsig_missing = false;
 408
 409                 log_info("Grace period over, resuming full feature set (%s) for DNS server %s.",
 410                          dns_server_feature_level_to_string(s->possible_feature_level),
 411                          dns_server_string(s));
 412
 413         } else if (s->possible_feature_level <= s->verified_feature_level)
 414                 s->possible_feature_level = s->verified_feature_level;
 415         else {
 416                 DnsServerFeatureLevel p = s->possible_feature_level;
 417
 418                 if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 419                     s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TCP) {
 420
 421                         /* We are at the TCP (lowest) level, and we tried a couple of TCP connections, and it didn't
 422                          * work. Upgrade back to UDP again. */
 423                         log_debug("Reached maximum number of failed TCP connection attempts, trying UDP again...");
 424                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 425
 426                 } else if (s->packet_bad_opt &&
 427                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) {
 428
 429                         /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to below
 430                          * EDNS0 levels. After all, some records generate different responses with and without OPT RR
 431                          * in the request. Example:
 432                          * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
 433
 434                         log_debug("Server doesn't support EDNS(0) properly, downgrading feature level...");
 435                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 436
 437                 } else if (s->packet_rrsig_missing &&
 438                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) {
 439
 440                         /* RRSIG data was missing on a EDNS0 packet with DO bit set. This means the server doesn't
 441                          * augment responses with DNSSEC RRs. If so, let's better not ask the server for it anymore,
 442                          * after all some servers generate different replies depending if an OPT RR is in the query or
 443                          * not. */
 444
 445                         log_debug("Detected server responses lack RRSIG records, downgrading feature level...");
 446                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0;
 447
 448                 } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 449                             s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_UDP) {
 450
 451                         /* We lost too many UDP packets in a row, and are on a feature level of UDP or higher. If the
 452                          * packets are lost, maybe the server cannot parse them, hence downgrading sounds like a good
 453                          * idea. We might downgrade all the way down to TCP this way. */
 454
 455                         log_debug("Lost too many UDP packets, downgrading feature level...");
 456                         s->possible_feature_level--;
 457
 458                 } else if (s->packet_failed &&
 459                            s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP) {
 460
 461                         /* We got a failure packet, and are at a feature level above UDP. Note that in this case we
 462                          * downgrade no further than UDP, under the assumption that a failure packet indicates an
 463                          * incompatible packet contents, but not a problem with the transport. */
 464
 465                         log_debug("Got server failure, downgrading feature level...");
 466                         s->possible_feature_level--;
 467
 468                 } else if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 469                            s->packet_truncated &&
 470                            s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP) {
 471
 472                          /* We got too many TCP connection failures in a row, we had at least one truncated packet, and
 473                           * are on a feature level above UDP. By downgrading things and getting rid of DNSSEC or EDNS0
 474                           * data we hope to make the packet smaller, so that it still works via UDP given that TCP
 475                           * appears not to be a fallback. Note that if we are already at the lowest UDP level, we don't
 476                           * go further down, since that's TCP, and TCP failed too often after all. */
 477
 478                         log_debug("Got too many failed TCP connection failures and truncated UDP packets, downgrading feature level...");
 479                         s->possible_feature_level--;
 480                 }
 481
 482                 if (p != s->possible_feature_level) {
 483
 484                         /* We changed the feature level, reset the counting */
 485                         dns_server_reset_counters(s);
 486
 487                         log_warning("Using degraded feature set (%s) for DNS server %s.",
 488                                     dns_server_feature_level_to_string(s->possible_feature_level),
 489                                     dns_server_string(s));
 490                 }
 491         }
 492
 493         return s->possible_feature_level;
 494 }
 495
 496 int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeatureLevel level) {
 497         size_t packet_size;
 498         bool edns_do;
 499         int r;
 500
 501         assert(server);
 502         assert(packet);
 503         assert(packet->protocol == DNS_PROTOCOL_DNS);
 504
 505         /* Fix the OPT field in the packet to match our current feature level. */
 506
 507         r = dns_packet_truncate_opt(packet);
 508         if (r < 0)
 509                 return r;
 510
 511         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 512                 return 0;
 513
 514         edns_do = level >= DNS_SERVER_FEATURE_LEVEL_DO;
 515
 516         if (level >= DNS_SERVER_FEATURE_LEVEL_LARGE)
 517                 packet_size = DNS_PACKET_UNICAST_SIZE_LARGE_MAX;
 518         else
 519                 packet_size = server->received_udp_packet_max;
 520
 521         return dns_packet_append_opt(packet, packet_size, edns_do, 0, NULL);
 522 }
 523
 524 int dns_server_ifindex(const DnsServer *s) {
 525         assert(s);
 526
 527         /* The link ifindex always takes precedence */
 528         if (s->link)
 529                 return s->link->ifindex;
 530
 531         if (s->ifindex > 0)
 532                 return s->ifindex;
 533
 534         return 0;
 535 }
 536
 537 const char *dns_server_string(DnsServer *server) {
 538         assert(server);
 539
 540         if (!server->server_string)
 541                 (void) in_addr_ifindex_to_string(server->family, &server->address, dns_server_ifindex(server), &server->server_string);
 542
 543         return strna(server->server_string);
 544 }
 545
 546 bool dns_server_dnssec_supported(DnsServer *server) {
 547         assert(server);
 548
 549         /* Returns whether the server supports DNSSEC according to what we know about it */
 550
 551         if (server->possible_feature_level < DNS_SERVER_FEATURE_LEVEL_DO)
 552                 return false;
 553
 554         if (server->packet_bad_opt)
 555                 return false;
 556
 557         if (server->packet_rrsig_missing)
 558                 return false;
 559
 560         /* DNSSEC servers need to support TCP properly (see RFC5966), if they don't, we assume DNSSEC is borked too */
 561         if (server->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS)
 562                 return false;
 563
 564         return true;
 565 }
 566
 567 void dns_server_warn_downgrade(DnsServer *server) {
 568         assert(server);
 569
 570         if (server->warned_downgrade)
 571                 return;
 572
 573         log_struct(LOG_NOTICE,
 574                    LOG_MESSAGE_ID(SD_MESSAGE_DNSSEC_DOWNGRADE),
 575                    LOG_MESSAGE("Server %s does not support DNSSEC, downgrading to non-DNSSEC mode.", dns_server_string(server)),
 576                    "DNS_SERVER=%s", dns_server_string(server),
 577                    "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(server->possible_feature_level),
 578                    NULL);
 579
 580         server->warned_downgrade = true;
 581 }
 582
 583 static void dns_server_hash_func(const void *p, struct siphash *state) {
 584         const DnsServer *s = p;
 585
 586         assert(s);
 587
 588         siphash24_compress(&s->family, sizeof(s->family), state);
 589         siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state);
 590         siphash24_compress(&s->ifindex, sizeof(s->ifindex), state);
 591 }
 592
 593 static int dns_server_compare_func(const void *a, const void *b) {
 594         const DnsServer *x = a, *y = b;
 595         int r;
 596
 597         if (x->family < y->family)
 598                 return -1;
 599         if (x->family > y->family)
 600                 return 1;
 601
 602         r = memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family));
 603         if (r != 0)
 604                 return r;
 605
 606         if (x->ifindex < y->ifindex)
 607                 return -1;
 608         if (x->ifindex > y->ifindex)
 609                 return 1;
 610
 611         return 0;
 612 }
 613
 614 const struct hash_ops dns_server_hash_ops = {
 615         .hash = dns_server_hash_func,
 616         .compare = dns_server_compare_func
 617 };
 618
 619 void dns_server_unlink_all(DnsServer *first) {
 620         DnsServer *next;
 621
 622         if (!first)
 623                 return;
 624
 625         next = first->servers_next;
 626         dns_server_unlink(first);
 627
 628         dns_server_unlink_all(next);
 629 }
 630
 631 void dns_server_unlink_marked(DnsServer *first) {
 632         DnsServer *next;
 633
 634         if (!first)
 635                 return;
 636
 637         next = first->servers_next;
 638
 639         if (first->marked)
 640                 dns_server_unlink(first);
 641
 642         dns_server_unlink_marked(next);
 643 }
 644
 645 void dns_server_mark_all(DnsServer *first) {
 646         if (!first)
 647                 return;
 648
 649         first->marked = true;
 650         dns_server_mark_all(first->servers_next);
 651 }
 652
 653 DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, int ifindex) {
 654         DnsServer *s;
 655
 656         LIST_FOREACH(servers, s, first)
 657                 if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0 && s->ifindex == ifindex)
 658                         return s;
 659
 660         return NULL;
 661 }
 662
 663 DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) {
 664         assert(m);
 665
 666         switch (t) {
 667
 668         case DNS_SERVER_SYSTEM:
 669                 return m->dns_servers;
 670
 671         case DNS_SERVER_FALLBACK:
 672                 return m->fallback_dns_servers;
 673
 674         default:
 675                 return NULL;
 676         }
 677 }
 678
 679 DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) {
 680         assert(m);
 681
 682         if (m->current_dns_server == s)
 683                 return s;
 684
 685         if (s)
 686                 log_info("Switching to %s DNS server %s.",
 687                          dns_server_type_to_string(s->type),
 688                          dns_server_string(s));
 689
 690         dns_server_unref(m->current_dns_server);
 691         m->current_dns_server = dns_server_ref(s);
 692
 693         if (m->unicast_scope)
 694                 dns_cache_flush(&m->unicast_scope->cache);
 695
 696         return s;
 697 }
 698
 699 DnsServer *manager_get_dns_server(Manager *m) {
 700         Link *l;
 701         assert(m);
 702
 703         /* Try to read updates resolv.conf */
 704         manager_read_resolv_conf(m);
 705
 706         /* If no DNS server was chosen so far, pick the first one */
 707         if (!m->current_dns_server)
 708                 manager_set_dns_server(m, m->dns_servers);
 709
 710         if (!m->current_dns_server) {
 711                 bool found = false;
 712                 Iterator i;
 713
 714                 /* No DNS servers configured, let's see if there are
 715                  * any on any links. If not, we use the fallback
 716                  * servers */
 717
 718                 HASHMAP_FOREACH(l, m->links, i)
 719                         if (l->dns_servers) {
 720                                 found = true;
 721                                 break;
 722                         }
 723
 724                 if (!found)
 725                         manager_set_dns_server(m, m->fallback_dns_servers);
 726         }
 727
 728         return m->current_dns_server;
 729 }
 730
 731 void manager_next_dns_server(Manager *m) {
 732         assert(m);
 733
 734         /* If there's currently no DNS server set, then the next
 735          * manager_get_dns_server() will find one */
 736         if (!m->current_dns_server)
 737                 return;
 738
 739         /* Change to the next one, but make sure to follow the linked
 740          * list only if the server is still linked. */
 741         if (m->current_dns_server->linked && m->current_dns_server->servers_next) {
 742                 manager_set_dns_server(m, m->current_dns_server->servers_next);
 743                 return;
 744         }
 745
 746         /* If there was no next one, then start from the beginning of
 747          * the list */
 748         if (m->current_dns_server->type == DNS_SERVER_FALLBACK)
 749                 manager_set_dns_server(m, m->fallback_dns_servers);
 750         else
 751                 manager_set_dns_server(m, m->dns_servers);
 752 }
 753
 754 bool dns_server_address_valid(int family, const union in_addr_union *sa) {
 755
 756         /* Refuses the 0 IP addresses as well as 127.0.0.53 (which is our own DNS stub) */
 757
 758         if (in_addr_is_null(family, sa))
 759                 return false;
 760
 761         if (family == AF_INET && sa->in.s_addr == htobe32(INADDR_DNS_STUB))
 762                 return false;
 763
 764         return true;
 765 }
 766
 767 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
 768         [DNS_SERVER_SYSTEM] = "system",
 769         [DNS_SERVER_FALLBACK] = "fallback",
 770         [DNS_SERVER_LINK] = "link",
 771 };
 772 DEFINE_STRING_TABLE_LOOKUP(dns_server_type, DnsServerType);
 773
 774 static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = {
 775         [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP",
 776         [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP",
 777         [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0",
 778         [DNS_SERVER_FEATURE_LEVEL_DO] = "UDP+EDNS0+DO",
 779         [DNS_SERVER_FEATURE_LEVEL_LARGE] = "UDP+EDNS0+DO+LARGE",
 780 };
 781 DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);