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 (750 * 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         return mfree(s);
 143 }
 144
 145 void dns_server_unlink(DnsServer *s) {
 146         assert(s);
 147         assert(s->manager);
 148
 149         /* This removes the specified server from the linked list of
 150          * servers, but any server might still stay around if it has
 151          * refs, for example from an ongoing transaction. */
 152
 153         if (!s->linked)
 154                 return;
 155
 156         switch (s->type) {
 157
 158         case DNS_SERVER_LINK:
 159                 assert(s->link);
 160                 assert(s->link->n_dns_servers > 0);
 161                 LIST_REMOVE(servers, s->link->dns_servers, s);
 162                 s->link->n_dns_servers--;
 163                 break;
 164
 165         case DNS_SERVER_SYSTEM:
 166                 assert(s->manager->n_dns_servers > 0);
 167                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 168                 s->manager->n_dns_servers--;
 169                 break;
 170
 171         case DNS_SERVER_FALLBACK:
 172                 assert(s->manager->n_dns_servers > 0);
 173                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 174                 s->manager->n_dns_servers--;
 175                 break;
 176         }
 177
 178         s->linked = false;
 179
 180         if (s->link && s->link->current_dns_server == s)
 181                 link_set_dns_server(s->link, NULL);
 182
 183         if (s->manager->current_dns_server == s)
 184                 manager_set_dns_server(s->manager, NULL);
 185
 186         dns_server_unref(s);
 187 }
 188
 189 void dns_server_move_back_and_unmark(DnsServer *s) {
 190         DnsServer *tail;
 191
 192         assert(s);
 193
 194         if (!s->marked)
 195                 return;
 196
 197         s->marked = false;
 198
 199         if (!s->linked || !s->servers_next)
 200                 return;
 201
 202         /* Move us to the end of the list, so that the order is
 203          * strictly kept, if we are not at the end anyway. */
 204
 205         switch (s->type) {
 206
 207         case DNS_SERVER_LINK:
 208                 assert(s->link);
 209                 LIST_FIND_TAIL(servers, s, tail);
 210                 LIST_REMOVE(servers, s->link->dns_servers, s);
 211                 LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s);
 212                 break;
 213
 214         case DNS_SERVER_SYSTEM:
 215                 LIST_FIND_TAIL(servers, s, tail);
 216                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 217                 LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s);
 218                 break;
 219
 220         case DNS_SERVER_FALLBACK:
 221                 LIST_FIND_TAIL(servers, s, tail);
 222                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 223                 LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s);
 224                 break;
 225
 226         default:
 227                 assert_not_reached("Unknown server type");
 228         }
 229 }
 230
 231 static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) {
 232         assert(s);
 233
 234         if (s->verified_feature_level > level)
 235                 return;
 236
 237         if (s->verified_feature_level != level) {
 238                 log_debug("Verified we get a response at feature level %s from DNS server %s.",
 239                           dns_server_feature_level_to_string(level),
 240                           dns_server_string(s));
 241                 s->verified_feature_level = level;
 242         }
 243
 244         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
 245 }
 246
 247 static void dns_server_reset_counters(DnsServer *s) {
 248         assert(s);
 249
 250         s->n_failed_udp = 0;
 251         s->n_failed_tcp = 0;
 252         s->packet_truncated = false;
 253         s->verified_usec = 0;
 254
 255         /* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the
 256          * grace period ends, but not when lowering the possible feature level, as a lower level feature level should
 257          * not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's
 258          * indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that
 259          * either.
 260          *
 261          * This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A),
 262          * but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not
 263          * reenable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be
 264          * incomplete. */
 265 }
 266
 267 void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size) {
 268         assert(s);
 269
 270         if (protocol == IPPROTO_UDP) {
 271                 if (s->possible_feature_level == level)
 272                         s->n_failed_udp = 0;
 273
 274                 /* If the RRSIG data is missing, then we can only validate EDNS0 at max */
 275                 if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO)
 276                         level = DNS_SERVER_FEATURE_LEVEL_DO - 1;
 277
 278                 /* If the OPT RR got lost, then we can only validate UDP at max */
 279                 if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 280                         level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1;
 281
 282                 /* Even if we successfully receive a reply to a request announcing support for large packets,
 283                    that does not mean we can necessarily receive large packets. */
 284                 if (level == DNS_SERVER_FEATURE_LEVEL_LARGE)
 285                         level = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
 286
 287         } else if (protocol == IPPROTO_TCP) {
 288
 289                 if (s->possible_feature_level == level)
 290                         s->n_failed_tcp = 0;
 291
 292                 /* Successful TCP connections are only useful to verify the TCP feature level. */
 293                 level = DNS_SERVER_FEATURE_LEVEL_TCP;
 294         }
 295
 296         dns_server_verified(s, level);
 297
 298         /* Remember the size of the largest UDP packet we received from a server,
 299            we know that we can always announce support for packets with at least
 300            this size. */
 301         if (protocol == IPPROTO_UDP && s->received_udp_packet_max < size)
 302                 s->received_udp_packet_max = size;
 303
 304         if (s->max_rtt < rtt) {
 305                 s->max_rtt = rtt;
 306                 s->resend_timeout = CLAMP(s->max_rtt * 2, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC);
 307         }
 308 }
 309
 310 void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec) {
 311         assert(s);
 312         assert(s->manager);
 313
 314         if (s->possible_feature_level == level) {
 315                 if (protocol == IPPROTO_UDP)
 316                         s->n_failed_udp++;
 317                 else if (protocol == IPPROTO_TCP)
 318                         s->n_failed_tcp++;
 319         }
 320
 321         if (s->resend_timeout > usec)
 322                 return;
 323
 324         s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC);
 325 }
 326
 327 void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) {
 328         assert(s);
 329
 330         /* Invoked whenever we get a packet with TC bit set. */
 331
 332         if (s->possible_feature_level != level)
 333                 return;
 334
 335         s->packet_truncated = true;
 336 }
 337
 338 void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) {
 339         assert(s);
 340
 341         if (level < DNS_SERVER_FEATURE_LEVEL_DO)
 342                 return;
 343
 344         /* If the RRSIG RRs are missing, we have to downgrade what we previously verified */
 345         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO)
 346                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_DO-1;
 347
 348         s->packet_rrsig_missing = true;
 349 }
 350
 351 void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) {
 352         assert(s);
 353
 354         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 355                 return;
 356
 357         /* If the OPT RR got lost, we have to downgrade what we previously verified */
 358         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 359                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1;
 360
 361         s->packet_bad_opt = true;
 362 }
 363
 364 void dns_server_packet_rcode_downgrade(DnsServer *s, DnsServerFeatureLevel level) {
 365         assert(s);
 366
 367         /* Invoked whenever we got a FORMERR, SERVFAIL or NOTIMP rcode from a server and downgrading the feature level
 368          * for the transaction made it go away. In this case we immediately downgrade to the feature level that made
 369          * things work. */
 370
 371         if (s->verified_feature_level > level)
 372                 s->verified_feature_level = level;
 373
 374         if (s->possible_feature_level > level) {
 375                 s->possible_feature_level = level;
 376                 dns_server_reset_counters(s);
 377         }
 378
 379         log_debug("Downgrading transaction feature level fixed an RCODE error, downgrading server %s too.", dns_server_string(s));
 380 }
 381
 382 static bool dns_server_grace_period_expired(DnsServer *s) {
 383         usec_t ts;
 384
 385         assert(s);
 386         assert(s->manager);
 387
 388         if (s->verified_usec == 0)
 389                 return false;
 390
 391         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
 392
 393         if (s->verified_usec + s->features_grace_period_usec > ts)
 394                 return false;
 395
 396         s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
 397
 398         return true;
 399 }
 400
 401 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
 402         DnsServerFeatureLevel best;
 403
 404         assert(s);
 405
 406         /* Determine the best feature level we care about. If DNSSEC mode is off there's no point in using anything
 407          * better than EDNS0, hence don't even try. */
 408         best = dns_server_get_dnssec_mode(s) == DNSSEC_NO ?
 409                 DNS_SERVER_FEATURE_LEVEL_EDNS0 :
 410                 DNS_SERVER_FEATURE_LEVEL_BEST;
 411
 412         /* Clamp the feature level the highest level we care about. The DNSSEC mode might have changed since the last
 413          * time, hence let's downgrade if we are still at a higher level. */
 414         if (s->possible_feature_level > best)
 415                 s->possible_feature_level = best;
 416
 417         if (s->possible_feature_level < best && dns_server_grace_period_expired(s)) {
 418
 419                 s->possible_feature_level = best;
 420
 421                 dns_server_reset_counters(s);
 422
 423                 s->packet_bad_opt = false;
 424                 s->packet_rrsig_missing = false;
 425
 426                 log_info("Grace period over, resuming full feature set (%s) for DNS server %s.",
 427                          dns_server_feature_level_to_string(s->possible_feature_level),
 428                          dns_server_string(s));
 429
 430                 dns_server_flush_cache(s);
 431
 432         } else if (s->possible_feature_level <= s->verified_feature_level)
 433                 s->possible_feature_level = s->verified_feature_level;
 434         else {
 435                 DnsServerFeatureLevel p = s->possible_feature_level;
 436
 437                 if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 438                     s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TCP) {
 439
 440                         /* We are at the TCP (lowest) level, and we tried a couple of TCP connections, and it didn't
 441                          * work. Upgrade back to UDP again. */
 442                         log_debug("Reached maximum number of failed TCP connection attempts, trying UDP again...");
 443                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 444
 445                 } else if (s->packet_bad_opt &&
 446                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) {
 447
 448                         /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to below
 449                          * EDNS0 levels. After all, some records generate different responses with and without OPT RR
 450                          * in the request. Example:
 451                          * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
 452
 453                         log_debug("Server doesn't support EDNS(0) properly, downgrading feature level...");
 454                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 455
 456                 } else if (s->packet_rrsig_missing &&
 457                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) {
 458
 459                         /* RRSIG data was missing on a EDNS0 packet with DO bit set. This means the server doesn't
 460                          * augment responses with DNSSEC RRs. If so, let's better not ask the server for it anymore,
 461                          * after all some servers generate different replies depending if an OPT RR is in the query or
 462                          * not. */
 463
 464                         log_debug("Detected server responses lack RRSIG records, downgrading feature level...");
 465                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0;
 466
 467                 } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 468                            s->possible_feature_level >= (dns_server_get_dnssec_mode(s) == DNSSEC_YES ? DNS_SERVER_FEATURE_LEVEL_LARGE : DNS_SERVER_FEATURE_LEVEL_UDP)) {
 469
 470                         /* We lost too many UDP packets in a row, and are on a feature level of UDP or higher. If the
 471                          * packets are lost, maybe the server cannot parse them, hence downgrading sounds like a good
 472                          * idea. We might downgrade all the way down to TCP this way.
 473                          *
 474                          * If strict DNSSEC mode is used we won't downgrade below DO level however, as packet loss
 475                          * might have many reasons, a broken DNSSEC implementation being only one reason. And if the
 476                          * user is strict on DNSSEC, then let's assume that DNSSEC is not the fault here. */
 477
 478                         log_debug("Lost too many UDP packets, downgrading feature level...");
 479                         s->possible_feature_level--;
 480
 481                 } else if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 482                            s->packet_truncated &&
 483                            s->possible_feature_level > (dns_server_get_dnssec_mode(s) == DNSSEC_YES ? DNS_SERVER_FEATURE_LEVEL_LARGE : DNS_SERVER_FEATURE_LEVEL_UDP)) {
 484
 485                          /* We got too many TCP connection failures in a row, we had at least one truncated packet, and
 486                           * are on a feature level above UDP. By downgrading things and getting rid of DNSSEC or EDNS0
 487                           * data we hope to make the packet smaller, so that it still works via UDP given that TCP
 488                           * appears not to be a fallback. Note that if we are already at the lowest UDP level, we don't
 489                           * go further down, since that's TCP, and TCP failed too often after all. */
 490
 491                         log_debug("Got too many failed TCP connection failures and truncated UDP packets, downgrading feature level...");
 492                         s->possible_feature_level--;
 493                 }
 494
 495                 if (p != s->possible_feature_level) {
 496
 497                         /* We changed the feature level, reset the counting */
 498                         dns_server_reset_counters(s);
 499
 500                         log_warning("Using degraded feature set (%s) for DNS server %s.",
 501                                     dns_server_feature_level_to_string(s->possible_feature_level),
 502                                     dns_server_string(s));
 503                 }
 504         }
 505
 506         return s->possible_feature_level;
 507 }
 508
 509 int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeatureLevel level) {
 510         size_t packet_size;
 511         bool edns_do;
 512         int r;
 513
 514         assert(server);
 515         assert(packet);
 516         assert(packet->protocol == DNS_PROTOCOL_DNS);
 517
 518         /* Fix the OPT field in the packet to match our current feature level. */
 519
 520         r = dns_packet_truncate_opt(packet);
 521         if (r < 0)
 522                 return r;
 523
 524         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 525                 return 0;
 526
 527         edns_do = level >= DNS_SERVER_FEATURE_LEVEL_DO;
 528
 529         if (level >= DNS_SERVER_FEATURE_LEVEL_LARGE)
 530                 packet_size = DNS_PACKET_UNICAST_SIZE_LARGE_MAX;
 531         else
 532                 packet_size = server->received_udp_packet_max;
 533
 534         return dns_packet_append_opt(packet, packet_size, edns_do, 0, NULL);
 535 }
 536
 537 int dns_server_ifindex(const DnsServer *s) {
 538         assert(s);
 539
 540         /* The link ifindex always takes precedence */
 541         if (s->link)
 542                 return s->link->ifindex;
 543
 544         if (s->ifindex > 0)
 545                 return s->ifindex;
 546
 547         return 0;
 548 }
 549
 550 const char *dns_server_string(DnsServer *server) {
 551         assert(server);
 552
 553         if (!server->server_string)
 554                 (void) in_addr_ifindex_to_string(server->family, &server->address, dns_server_ifindex(server), &server->server_string);
 555
 556         return strna(server->server_string);
 557 }
 558
 559 bool dns_server_dnssec_supported(DnsServer *server) {
 560         assert(server);
 561
 562         /* Returns whether the server supports DNSSEC according to what we know about it */
 563
 564         if (server->possible_feature_level < DNS_SERVER_FEATURE_LEVEL_DO)
 565                 return false;
 566
 567         if (server->packet_bad_opt)
 568                 return false;
 569
 570         if (server->packet_rrsig_missing)
 571                 return false;
 572
 573         /* DNSSEC servers need to support TCP properly (see RFC5966), if they don't, we assume DNSSEC is borked too */
 574         if (server->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS)
 575                 return false;
 576
 577         return true;
 578 }
 579
 580 void dns_server_warn_downgrade(DnsServer *server) {
 581         assert(server);
 582
 583         if (server->warned_downgrade)
 584                 return;
 585
 586         log_struct(LOG_NOTICE,
 587                    "MESSAGE_ID=" SD_MESSAGE_DNSSEC_DOWNGRADE_STR,
 588                    LOG_MESSAGE("Server %s does not support DNSSEC, downgrading to non-DNSSEC mode.", dns_server_string(server)),
 589                    "DNS_SERVER=%s", dns_server_string(server),
 590                    "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(server->possible_feature_level),
 591                    NULL);
 592
 593         server->warned_downgrade = true;
 594 }
 595
 596 bool dns_server_limited_domains(DnsServer *server) {
 597         DnsSearchDomain *domain;
 598         bool domain_restricted = false;
 599
 600         /* Check if the server has route-only domains without ~., i. e. whether
 601          * it should only be used for particular domains */
 602         if (!server->link)
 603                 return false;
 604
 605         LIST_FOREACH(domains, domain, server->link->search_domains)
 606                 if (domain->route_only) {
 607                         domain_restricted = true;
 608                         /* ~. means "any domain", thus it is a global server */
 609                         if (dns_name_is_root(DNS_SEARCH_DOMAIN_NAME(domain)))
 610                                 return false;
 611                 }
 612
 613         return domain_restricted;
 614 }
 615
 616 static void dns_server_hash_func(const void *p, struct siphash *state) {
 617         const DnsServer *s = p;
 618
 619         assert(s);
 620
 621         siphash24_compress(&s->family, sizeof(s->family), state);
 622         siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state);
 623         siphash24_compress(&s->ifindex, sizeof(s->ifindex), state);
 624 }
 625
 626 static int dns_server_compare_func(const void *a, const void *b) {
 627         const DnsServer *x = a, *y = b;
 628         int r;
 629
 630         if (x->family < y->family)
 631                 return -1;
 632         if (x->family > y->family)
 633                 return 1;
 634
 635         r = memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family));
 636         if (r != 0)
 637                 return r;
 638
 639         if (x->ifindex < y->ifindex)
 640                 return -1;
 641         if (x->ifindex > y->ifindex)
 642                 return 1;
 643
 644         return 0;
 645 }
 646
 647 const struct hash_ops dns_server_hash_ops = {
 648         .hash = dns_server_hash_func,
 649         .compare = dns_server_compare_func
 650 };
 651
 652 void dns_server_unlink_all(DnsServer *first) {
 653         DnsServer *next;
 654
 655         if (!first)
 656                 return;
 657
 658         next = first->servers_next;
 659         dns_server_unlink(first);
 660
 661         dns_server_unlink_all(next);
 662 }
 663
 664 void dns_server_unlink_marked(DnsServer *first) {
 665         DnsServer *next;
 666
 667         if (!first)
 668                 return;
 669
 670         next = first->servers_next;
 671
 672         if (first->marked)
 673                 dns_server_unlink(first);
 674
 675         dns_server_unlink_marked(next);
 676 }
 677
 678 void dns_server_mark_all(DnsServer *first) {
 679         if (!first)
 680                 return;
 681
 682         first->marked = true;
 683         dns_server_mark_all(first->servers_next);
 684 }
 685
 686 DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, int ifindex) {
 687         DnsServer *s;
 688
 689         LIST_FOREACH(servers, s, first)
 690                 if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0 && s->ifindex == ifindex)
 691                         return s;
 692
 693         return NULL;
 694 }
 695
 696 DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) {
 697         assert(m);
 698
 699         switch (t) {
 700
 701         case DNS_SERVER_SYSTEM:
 702                 return m->dns_servers;
 703
 704         case DNS_SERVER_FALLBACK:
 705                 return m->fallback_dns_servers;
 706
 707         default:
 708                 return NULL;
 709         }
 710 }
 711
 712 DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) {
 713         assert(m);
 714
 715         if (m->current_dns_server == s)
 716                 return s;
 717
 718         if (s)
 719                 log_info("Switching to %s DNS server %s.",
 720                          dns_server_type_to_string(s->type),
 721                          dns_server_string(s));
 722
 723         dns_server_unref(m->current_dns_server);
 724         m->current_dns_server = dns_server_ref(s);
 725
 726         if (m->unicast_scope)
 727                 dns_cache_flush(&m->unicast_scope->cache);
 728
 729         return s;
 730 }
 731
 732 DnsServer *manager_get_dns_server(Manager *m) {
 733         Link *l;
 734         assert(m);
 735
 736         /* Try to read updates resolv.conf */
 737         manager_read_resolv_conf(m);
 738
 739         /* If no DNS server was chosen so far, pick the first one */
 740         if (!m->current_dns_server)
 741                 manager_set_dns_server(m, m->dns_servers);
 742
 743         if (!m->current_dns_server) {
 744                 bool found = false;
 745                 Iterator i;
 746
 747                 /* No DNS servers configured, let's see if there are
 748                  * any on any links. If not, we use the fallback
 749                  * servers */
 750
 751                 HASHMAP_FOREACH(l, m->links, i)
 752                         if (l->dns_servers) {
 753                                 found = true;
 754                                 break;
 755                         }
 756
 757                 if (!found)
 758                         manager_set_dns_server(m, m->fallback_dns_servers);
 759         }
 760
 761         return m->current_dns_server;
 762 }
 763
 764 void manager_next_dns_server(Manager *m) {
 765         assert(m);
 766
 767         /* If there's currently no DNS server set, then the next
 768          * manager_get_dns_server() will find one */
 769         if (!m->current_dns_server)
 770                 return;
 771
 772         /* Change to the next one, but make sure to follow the linked
 773          * list only if the server is still linked. */
 774         if (m->current_dns_server->linked && m->current_dns_server->servers_next) {
 775                 manager_set_dns_server(m, m->current_dns_server->servers_next);
 776                 return;
 777         }
 778
 779         /* If there was no next one, then start from the beginning of
 780          * the list */
 781         if (m->current_dns_server->type == DNS_SERVER_FALLBACK)
 782                 manager_set_dns_server(m, m->fallback_dns_servers);
 783         else
 784                 manager_set_dns_server(m, m->dns_servers);
 785 }
 786
 787 bool dns_server_address_valid(int family, const union in_addr_union *sa) {
 788
 789         /* Refuses the 0 IP addresses as well as 127.0.0.53 (which is our own DNS stub) */
 790
 791         if (in_addr_is_null(family, sa))
 792                 return false;
 793
 794         if (family == AF_INET && sa->in.s_addr == htobe32(INADDR_DNS_STUB))
 795                 return false;
 796
 797         return true;
 798 }
 799
 800 DnssecMode dns_server_get_dnssec_mode(DnsServer *s) {
 801         assert(s);
 802
 803         if (s->link)
 804                 return link_get_dnssec_mode(s->link);
 805
 806         return manager_get_dnssec_mode(s->manager);
 807 }
 808
 809 void dns_server_flush_cache(DnsServer *s) {
 810         DnsServer *current;
 811         DnsScope *scope;
 812
 813         assert(s);
 814
 815         /* Flush the cache of the scope this server belongs to */
 816
 817         current = s->link ? s->link->current_dns_server : s->manager->current_dns_server;
 818         if (current != s)
 819                 return;
 820
 821         scope = s->link ? s->link->unicast_scope : s->manager->unicast_scope;
 822         if (!scope)
 823                 return;
 824
 825         dns_cache_flush(&scope->cache);
 826 }
 827
 828 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
 829         [DNS_SERVER_SYSTEM] = "system",
 830         [DNS_SERVER_FALLBACK] = "fallback",
 831         [DNS_SERVER_LINK] = "link",
 832 };
 833 DEFINE_STRING_TABLE_LOOKUP(dns_server_type, DnsServerType);
 834
 835 static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = {
 836         [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP",
 837         [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP",
 838         [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0",
 839         [DNS_SERVER_FEATURE_LEVEL_DO] = "UDP+EDNS0+DO",
 840         [DNS_SERVER_FEATURE_LEVEL_LARGE] = "UDP+EDNS0+DO+LARGE",
 841 };
 842 DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);