src/resolve/resolved-dns-server.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include "sd-messages.h"
   4
   5 #include "alloc-util.h"
   6 #include "resolved-dns-server.h"
   7 #include "resolved-dns-stub.h"
   8 #include "resolved-resolv-conf.h"
   9 #include "siphash24.h"
  10 #include "string-table.h"
  11 #include "string-util.h"
  12
  13 /* The amount of time to wait before retrying with a full feature set */
  14 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC (6 * USEC_PER_HOUR)
  15 #define DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC (5 * USEC_PER_MINUTE)
  16
  17 /* The number of times we will attempt a certain feature set before degrading */
  18 #define DNS_SERVER_FEATURE_RETRY_ATTEMPTS 3
  19
  20 int dns_server_new(
  21                 Manager *m,
  22                 DnsServer **ret,
  23                 DnsServerType type,
  24                 Link *l,
  25                 int family,
  26                 const union in_addr_union *in_addr,
  27                 int ifindex) {
  28
  29         DnsServer *s;
  30
  31         assert(m);
  32         assert((type == DNS_SERVER_LINK) == !!l);
  33         assert(in_addr);
  34
  35         if (!IN_SET(family, AF_INET, AF_INET6))
  36                 return -EAFNOSUPPORT;
  37
  38         if (l) {
  39                 if (l->n_dns_servers >= LINK_DNS_SERVERS_MAX)
  40                         return -E2BIG;
  41         } else {
  42                 if (m->n_dns_servers >= MANAGER_DNS_SERVERS_MAX)
  43                         return -E2BIG;
  44         }
  45
  46         s = new(DnsServer, 1);
  47         if (!s)
  48                 return -ENOMEM;
  49
  50         *s = (DnsServer) {
  51                 .n_ref = 1,
  52                 .manager = m,
  53                 .type = type,
  54                 .family = family,
  55                 .address = *in_addr,
  56                 .ifindex = ifindex,
  57         };
  58
  59         dns_server_reset_features(s);
  60
  61         switch (type) {
  62
  63         case DNS_SERVER_LINK:
  64                 s->link = l;
  65                 LIST_APPEND(servers, l->dns_servers, s);
  66                 l->n_dns_servers++;
  67                 break;
  68
  69         case DNS_SERVER_SYSTEM:
  70                 LIST_APPEND(servers, m->dns_servers, s);
  71                 m->n_dns_servers++;
  72                 break;
  73
  74         case DNS_SERVER_FALLBACK:
  75                 LIST_APPEND(servers, m->fallback_dns_servers, s);
  76                 m->n_dns_servers++;
  77                 break;
  78
  79         default:
  80                 assert_not_reached("Unknown server type");
  81         }
  82
  83         s->linked = true;
  84
  85         /* A new DNS server that isn't fallback is added and the one
  86          * we used so far was a fallback one? Then let's try to pick
  87          * the new one */
  88         if (type != DNS_SERVER_FALLBACK &&
  89             m->current_dns_server &&
  90             m->current_dns_server->type == DNS_SERVER_FALLBACK)
  91                 manager_set_dns_server(m, NULL);
  92
  93         if (ret)
  94                 *ret = s;
  95
  96         return 0;
  97 }
  98
  99 static DnsServer* dns_server_free(DnsServer *s)  {
 100         assert(s);
 101
 102         dns_server_unref_stream(s);
 103
 104 #if ENABLE_DNS_OVER_TLS
 105         dnstls_server_free(s);
 106 #endif
 107
 108         free(s->server_string);
 109         return mfree(s);
 110 }
 111
 112 DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsServer, dns_server, dns_server_free);
 113
 114 void dns_server_unlink(DnsServer *s) {
 115         assert(s);
 116         assert(s->manager);
 117
 118         /* This removes the specified server from the linked list of
 119          * servers, but any server might still stay around if it has
 120          * refs, for example from an ongoing transaction. */
 121
 122         if (!s->linked)
 123                 return;
 124
 125         switch (s->type) {
 126
 127         case DNS_SERVER_LINK:
 128                 assert(s->link);
 129                 assert(s->link->n_dns_servers > 0);
 130                 LIST_REMOVE(servers, s->link->dns_servers, s);
 131                 s->link->n_dns_servers--;
 132                 break;
 133
 134         case DNS_SERVER_SYSTEM:
 135                 assert(s->manager->n_dns_servers > 0);
 136                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 137                 s->manager->n_dns_servers--;
 138                 break;
 139
 140         case DNS_SERVER_FALLBACK:
 141                 assert(s->manager->n_dns_servers > 0);
 142                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 143                 s->manager->n_dns_servers--;
 144                 break;
 145         default:
 146                 assert_not_reached("Unknown server type");
 147         }
 148
 149         s->linked = false;
 150
 151         if (s->link && s->link->current_dns_server == s)
 152                 link_set_dns_server(s->link, NULL);
 153
 154         if (s->manager->current_dns_server == s)
 155                 manager_set_dns_server(s->manager, NULL);
 156
 157         /* No need to keep a default stream around anymore */
 158         dns_server_unref_stream(s);
 159
 160         dns_server_unref(s);
 161 }
 162
 163 void dns_server_move_back_and_unmark(DnsServer *s) {
 164         DnsServer *tail;
 165
 166         assert(s);
 167
 168         if (!s->marked)
 169                 return;
 170
 171         s->marked = false;
 172
 173         if (!s->linked || !s->servers_next)
 174                 return;
 175
 176         /* Move us to the end of the list, so that the order is
 177          * strictly kept, if we are not at the end anyway. */
 178
 179         switch (s->type) {
 180
 181         case DNS_SERVER_LINK:
 182                 assert(s->link);
 183                 LIST_FIND_TAIL(servers, s, tail);
 184                 LIST_REMOVE(servers, s->link->dns_servers, s);
 185                 LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s);
 186                 break;
 187
 188         case DNS_SERVER_SYSTEM:
 189                 LIST_FIND_TAIL(servers, s, tail);
 190                 LIST_REMOVE(servers, s->manager->dns_servers, s);
 191                 LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s);
 192                 break;
 193
 194         case DNS_SERVER_FALLBACK:
 195                 LIST_FIND_TAIL(servers, s, tail);
 196                 LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
 197                 LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s);
 198                 break;
 199
 200         default:
 201                 assert_not_reached("Unknown server type");
 202         }
 203 }
 204
 205 static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) {
 206         assert(s);
 207
 208         if (s->verified_feature_level > level)
 209                 return;
 210
 211         if (s->verified_feature_level != level) {
 212                 log_debug("Verified we get a response at feature level %s from DNS server %s.",
 213                           dns_server_feature_level_to_string(level),
 214                           dns_server_string(s));
 215                 s->verified_feature_level = level;
 216         }
 217
 218         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
 219 }
 220
 221 static void dns_server_reset_counters(DnsServer *s) {
 222         assert(s);
 223
 224         s->n_failed_udp = 0;
 225         s->n_failed_tcp = 0;
 226         s->n_failed_tls = 0;
 227         s->packet_truncated = false;
 228         s->verified_usec = 0;
 229
 230         /* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the
 231          * grace period ends, but not when lowering the possible feature level, as a lower level feature level should
 232          * not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's
 233          * indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that
 234          * either.
 235          *
 236          * This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A),
 237          * but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not
 238          * re-enable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be
 239          * incomplete. */
 240 }
 241
 242 void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, size_t size) {
 243         assert(s);
 244
 245         if (protocol == IPPROTO_UDP) {
 246                 if (s->possible_feature_level == level)
 247                         s->n_failed_udp = 0;
 248         } else if (protocol == IPPROTO_TCP) {
 249                 if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level)) {
 250                         if (s->possible_feature_level == level)
 251                                 s->n_failed_tls = 0;
 252                 } else {
 253                         if (s->possible_feature_level == level)
 254                                 s->n_failed_tcp = 0;
 255
 256                         /* Successful TCP connections are only useful to verify the TCP feature level. */
 257                         level = DNS_SERVER_FEATURE_LEVEL_TCP;
 258                 }
 259         }
 260
 261         /* If the RRSIG data is missing, then we can only validate EDNS0 at max */
 262         if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO)
 263                 level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0;
 264
 265         /* If the OPT RR got lost, then we can only validate UDP at max */
 266         if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 267                 level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1;
 268
 269         /* Even if we successfully receive a reply to a request announcing support for large packets,
 270                 that does not mean we can necessarily receive large packets. */
 271         if (level == DNS_SERVER_FEATURE_LEVEL_LARGE)
 272                 level = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
 273
 274         dns_server_verified(s, level);
 275
 276         /* Remember the size of the largest UDP packet we received from a server,
 277            we know that we can always announce support for packets with at least
 278            this size. */
 279         if (protocol == IPPROTO_UDP && s->received_udp_packet_max < size)
 280                 s->received_udp_packet_max = size;
 281 }
 282
 283 void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level) {
 284         assert(s);
 285         assert(s->manager);
 286
 287         if (s->possible_feature_level == level) {
 288                 if (protocol == IPPROTO_UDP)
 289                         s->n_failed_udp++;
 290                 else if (protocol == IPPROTO_TCP) {
 291                         if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level))
 292                                 s->n_failed_tls++;
 293                         else
 294                                 s->n_failed_tcp++;
 295                 }
 296         }
 297 }
 298
 299 void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) {
 300         assert(s);
 301
 302         /* Invoked whenever we get a packet with TC bit set. */
 303
 304         if (s->possible_feature_level != level)
 305                 return;
 306
 307         s->packet_truncated = true;
 308 }
 309
 310 void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) {
 311         assert(s);
 312
 313         if (level < DNS_SERVER_FEATURE_LEVEL_DO)
 314                 return;
 315
 316         /* If the RRSIG RRs are missing, we have to downgrade what we previously verified */
 317         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO)
 318                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0;
 319
 320         s->packet_rrsig_missing = true;
 321 }
 322
 323 void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) {
 324         assert(s);
 325
 326         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 327                 return;
 328
 329         /* If the OPT RR got lost, we have to downgrade what we previously verified */
 330         if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 331                 s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1;
 332
 333         s->packet_bad_opt = true;
 334 }
 335
 336 void dns_server_packet_rcode_downgrade(DnsServer *s, DnsServerFeatureLevel level) {
 337         assert(s);
 338
 339         /* Invoked whenever we got a FORMERR, SERVFAIL or NOTIMP rcode from a server and downgrading the feature level
 340          * for the transaction made it go away. In this case we immediately downgrade to the feature level that made
 341          * things work. */
 342
 343         if (s->verified_feature_level > level)
 344                 s->verified_feature_level = level;
 345
 346         if (s->possible_feature_level > level) {
 347                 s->possible_feature_level = level;
 348                 dns_server_reset_counters(s);
 349         }
 350
 351         log_debug("Downgrading transaction feature level fixed an RCODE error, downgrading server %s too.", dns_server_string(s));
 352 }
 353
 354 static bool dns_server_grace_period_expired(DnsServer *s) {
 355         usec_t ts;
 356
 357         assert(s);
 358         assert(s->manager);
 359
 360         if (s->verified_usec == 0)
 361                 return false;
 362
 363         assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
 364
 365         if (s->verified_usec + s->features_grace_period_usec > ts)
 366                 return false;
 367
 368         s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
 369
 370         return true;
 371 }
 372
 373 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
 374         DnsServerFeatureLevel best;
 375
 376         assert(s);
 377
 378         /* Determine the best feature level we care about. If DNSSEC mode is off there's no point in using anything
 379          * better than EDNS0, hence don't even try. */
 380         if (dns_server_get_dnssec_mode(s) != DNSSEC_NO)
 381                 best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
 382                         DNS_SERVER_FEATURE_LEVEL_LARGE :
 383                         DNS_SERVER_FEATURE_LEVEL_TLS_DO;
 384         else
 385                 best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
 386                         DNS_SERVER_FEATURE_LEVEL_EDNS0 :
 387                         DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN;
 388
 389         /* Clamp the feature level the highest level we care about. The DNSSEC mode might have changed since the last
 390          * time, hence let's downgrade if we are still at a higher level. */
 391         if (s->possible_feature_level > best)
 392                 s->possible_feature_level = best;
 393
 394         if (s->possible_feature_level < best && dns_server_grace_period_expired(s)) {
 395
 396                 s->possible_feature_level = best;
 397
 398                 dns_server_reset_counters(s);
 399
 400                 s->packet_bad_opt = false;
 401                 s->packet_rrsig_missing = false;
 402
 403                 log_info("Grace period over, resuming full feature set (%s) for DNS server %s.",
 404                          dns_server_feature_level_to_string(s->possible_feature_level),
 405                          dns_server_string(s));
 406
 407                 dns_server_flush_cache(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                 } else if (s->n_failed_tls > 0 &&
 422                            DNS_SERVER_FEATURE_LEVEL_IS_TLS(s->possible_feature_level)) {
 423
 424                         /* We tried to connect using DNS-over-TLS, and it didn't work. Downgrade to plaintext UDP
 425                          * if we don't require DNS-over-TLS */
 426
 427                         log_debug("Server doesn't support DNS-over-TLS, downgrading protocol...");
 428                         s->possible_feature_level--;
 429                 } else if (s->packet_bad_opt &&
 430                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) {
 431
 432                         /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to below
 433                          * EDNS0 levels. After all, some records generate different responses with and without OPT RR
 434                          * in the request. Example:
 435                          * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
 436
 437                         log_debug("Server doesn't support EDNS(0) properly, downgrading feature level...");
 438                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP;
 439
 440                 } else if (s->packet_rrsig_missing &&
 441                            s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) {
 442
 443                         /* RRSIG data was missing on a EDNS0 packet with DO bit set. This means the server doesn't
 444                          * augment responses with DNSSEC RRs. If so, let's better not ask the server for it anymore,
 445                          * after all some servers generate different replies depending if an OPT RR is in the query or
 446                          * not. */
 447
 448                         log_debug("Detected server responses lack RRSIG records, downgrading feature level...");
 449                         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(s->possible_feature_level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0;
 450
 451                 } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 452                            s->possible_feature_level >= (dns_server_get_dnssec_mode(s) == DNSSEC_YES ? DNS_SERVER_FEATURE_LEVEL_LARGE : DNS_SERVER_FEATURE_LEVEL_UDP)) {
 453
 454                         /* We lost too many UDP packets in a row, and are on a feature level of UDP or higher. If the
 455                          * packets are lost, maybe the server cannot parse them, hence downgrading sounds like a good
 456                          * idea. We might downgrade all the way down to TCP this way.
 457                          *
 458                          * If strict DNSSEC mode is used we won't downgrade below DO level however, as packet loss
 459                          * might have many reasons, a broken DNSSEC implementation being only one reason. And if the
 460                          * user is strict on DNSSEC, then let's assume that DNSSEC is not the fault here. */
 461
 462                         log_debug("Lost too many UDP packets, downgrading feature level...");
 463                         s->possible_feature_level--;
 464
 465                 } else if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
 466                            s->packet_truncated &&
 467                            s->possible_feature_level > (dns_server_get_dnssec_mode(s) == DNSSEC_YES ? DNS_SERVER_FEATURE_LEVEL_LARGE : DNS_SERVER_FEATURE_LEVEL_UDP)) {
 468
 469                          /* We got too many TCP connection failures in a row, we had at least one truncated packet, and
 470                           * are on a feature level above UDP. By downgrading things and getting rid of DNSSEC or EDNS0
 471                           * data we hope to make the packet smaller, so that it still works via UDP given that TCP
 472                           * appears not to be a fallback. Note that if we are already at the lowest UDP level, we don't
 473                           * go further down, since that's TCP, and TCP failed too often after all. */
 474
 475                         log_debug("Got too many failed TCP connection failures and truncated UDP packets, downgrading feature level...");
 476                         s->possible_feature_level--;
 477                 }
 478
 479                 if (p != s->possible_feature_level) {
 480
 481                         /* We changed the feature level, reset the counting */
 482                         dns_server_reset_counters(s);
 483
 484                         log_warning("Using degraded feature set (%s) for DNS server %s.",
 485                                     dns_server_feature_level_to_string(s->possible_feature_level),
 486                                     dns_server_string(s));
 487                 }
 488         }
 489
 490         return s->possible_feature_level;
 491 }
 492
 493 int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeatureLevel level) {
 494         size_t packet_size;
 495         bool edns_do;
 496         int r;
 497
 498         assert(server);
 499         assert(packet);
 500         assert(packet->protocol == DNS_PROTOCOL_DNS);
 501
 502         /* Fix the OPT field in the packet to match our current feature level. */
 503
 504         r = dns_packet_truncate_opt(packet);
 505         if (r < 0)
 506                 return r;
 507
 508         if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
 509                 return 0;
 510
 511         edns_do = level >= DNS_SERVER_FEATURE_LEVEL_DO;
 512
 513         if (level >= DNS_SERVER_FEATURE_LEVEL_LARGE)
 514                 packet_size = DNS_PACKET_UNICAST_SIZE_LARGE_MAX;
 515         else
 516                 packet_size = server->received_udp_packet_max;
 517
 518         return dns_packet_append_opt(packet, packet_size, edns_do, 0, NULL);
 519 }
 520
 521 int dns_server_ifindex(const DnsServer *s) {
 522         assert(s);
 523
 524         /* The link ifindex always takes precedence */
 525         if (s->link)
 526                 return s->link->ifindex;
 527
 528         if (s->ifindex > 0)
 529                 return s->ifindex;
 530
 531         return 0;
 532 }
 533
 534 const char *dns_server_string(DnsServer *server) {
 535         assert(server);
 536
 537         if (!server->server_string)
 538                 (void) in_addr_ifindex_to_string(server->family, &server->address, dns_server_ifindex(server), &server->server_string);
 539
 540         return strna(server->server_string);
 541 }
 542
 543 bool dns_server_dnssec_supported(DnsServer *server) {
 544         assert(server);
 545
 546         /* Returns whether the server supports DNSSEC according to what we know about it */
 547
 548         if (server->possible_feature_level < DNS_SERVER_FEATURE_LEVEL_DO)
 549                 return false;
 550
 551         if (server->packet_bad_opt)
 552                 return false;
 553
 554         if (server->packet_rrsig_missing)
 555                 return false;
 556
 557         /* DNSSEC servers need to support TCP properly (see RFC5966), if they don't, we assume DNSSEC is borked too */
 558         if (server->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS)
 559                 return false;
 560
 561         return true;
 562 }
 563
 564 void dns_server_warn_downgrade(DnsServer *server) {
 565         assert(server);
 566
 567         if (server->warned_downgrade)
 568                 return;
 569
 570         log_struct(LOG_NOTICE,
 571                    "MESSAGE_ID=" SD_MESSAGE_DNSSEC_DOWNGRADE_STR,
 572                    LOG_MESSAGE("Server %s does not support DNSSEC, downgrading to non-DNSSEC mode.", dns_server_string(server)),
 573                    "DNS_SERVER=%s", dns_server_string(server),
 574                    "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(server->possible_feature_level));
 575
 576         server->warned_downgrade = true;
 577 }
 578
 579 static void dns_server_hash_func(const DnsServer *s, struct siphash *state) {
 580         assert(s);
 581
 582         siphash24_compress(&s->family, sizeof(s->family), state);
 583         siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state);
 584         siphash24_compress(&s->ifindex, sizeof(s->ifindex), state);
 585 }
 586
 587 static int dns_server_compare_func(const DnsServer *x, const DnsServer *y) {
 588         int r;
 589
 590         r = CMP(x->family, y->family);
 591         if (r != 0)
 592                 return r;
 593
 594         r = memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family));
 595         if (r != 0)
 596                 return r;
 597
 598         r = CMP(x->ifindex, y->ifindex);
 599         if (r != 0)
 600                 return r;
 601
 602         return 0;
 603 }
 604
 605 DEFINE_HASH_OPS(dns_server_hash_ops, DnsServer, dns_server_hash_func, dns_server_compare_func);
 606
 607 void dns_server_unlink_all(DnsServer *first) {
 608         DnsServer *next;
 609
 610         if (!first)
 611                 return;
 612
 613         next = first->servers_next;
 614         dns_server_unlink(first);
 615
 616         dns_server_unlink_all(next);
 617 }
 618
 619 void dns_server_unlink_marked(DnsServer *first) {
 620         DnsServer *next;
 621
 622         if (!first)
 623                 return;
 624
 625         next = first->servers_next;
 626
 627         if (first->marked)
 628                 dns_server_unlink(first);
 629
 630         dns_server_unlink_marked(next);
 631 }
 632
 633 void dns_server_mark_all(DnsServer *first) {
 634         if (!first)
 635                 return;
 636
 637         first->marked = true;
 638         dns_server_mark_all(first->servers_next);
 639 }
 640
 641 DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, int ifindex) {
 642         DnsServer *s;
 643
 644         LIST_FOREACH(servers, s, first)
 645                 if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0 && s->ifindex == ifindex)
 646                         return s;
 647
 648         return NULL;
 649 }
 650
 651 DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) {
 652         assert(m);
 653
 654         switch (t) {
 655
 656         case DNS_SERVER_SYSTEM:
 657                 return m->dns_servers;
 658
 659         case DNS_SERVER_FALLBACK:
 660                 return m->fallback_dns_servers;
 661
 662         default:
 663                 return NULL;
 664         }
 665 }
 666
 667 DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) {
 668         assert(m);
 669
 670         if (m->current_dns_server == s)
 671                 return s;
 672
 673         if (s)
 674                 log_debug("Switching to %s DNS server %s.",
 675                           dns_server_type_to_string(s->type),
 676                           dns_server_string(s));
 677
 678         dns_server_unref(m->current_dns_server);
 679         m->current_dns_server = dns_server_ref(s);
 680
 681         if (m->unicast_scope)
 682                 dns_cache_flush(&m->unicast_scope->cache);
 683
 684         return s;
 685 }
 686
 687 DnsServer *manager_get_dns_server(Manager *m) {
 688         Link *l;
 689         assert(m);
 690
 691         /* Try to read updates resolv.conf */
 692         manager_read_resolv_conf(m);
 693
 694         /* If no DNS server was chosen so far, pick the first one */
 695         if (!m->current_dns_server)
 696                 manager_set_dns_server(m, m->dns_servers);
 697
 698         if (!m->current_dns_server) {
 699                 bool found = false;
 700                 Iterator i;
 701
 702                 /* No DNS servers configured, let's see if there are
 703                  * any on any links. If not, we use the fallback
 704                  * servers */
 705
 706                 HASHMAP_FOREACH(l, m->links, i)
 707                         if (l->dns_servers) {
 708                                 found = true;
 709                                 break;
 710                         }
 711
 712                 if (!found)
 713                         manager_set_dns_server(m, m->fallback_dns_servers);
 714         }
 715
 716         return m->current_dns_server;
 717 }
 718
 719 void manager_next_dns_server(Manager *m) {
 720         assert(m);
 721
 722         /* If there's currently no DNS server set, then the next
 723          * manager_get_dns_server() will find one */
 724         if (!m->current_dns_server)
 725                 return;
 726
 727         /* Change to the next one, but make sure to follow the linked
 728          * list only if the server is still linked. */
 729         if (m->current_dns_server->linked && m->current_dns_server->servers_next) {
 730                 manager_set_dns_server(m, m->current_dns_server->servers_next);
 731                 return;
 732         }
 733
 734         /* If there was no next one, then start from the beginning of
 735          * the list */
 736         if (m->current_dns_server->type == DNS_SERVER_FALLBACK)
 737                 manager_set_dns_server(m, m->fallback_dns_servers);
 738         else
 739                 manager_set_dns_server(m, m->dns_servers);
 740 }
 741
 742 bool dns_server_address_valid(int family, const union in_addr_union *sa) {
 743
 744         /* Refuses the 0 IP addresses as well as 127.0.0.53 (which is our own DNS stub) */
 745
 746         if (in_addr_is_null(family, sa))
 747                 return false;
 748
 749         if (family == AF_INET && sa->in.s_addr == htobe32(INADDR_DNS_STUB))
 750                 return false;
 751
 752         return true;
 753 }
 754
 755 DnssecMode dns_server_get_dnssec_mode(DnsServer *s) {
 756         assert(s);
 757
 758         if (s->link)
 759                 return link_get_dnssec_mode(s->link);
 760
 761         return manager_get_dnssec_mode(s->manager);
 762 }
 763
 764 DnsOverTlsMode dns_server_get_dns_over_tls_mode(DnsServer *s) {
 765         assert(s);
 766
 767         if (s->link)
 768                 return link_get_dns_over_tls_mode(s->link);
 769
 770         return manager_get_dns_over_tls_mode(s->manager);
 771 }
 772
 773 void dns_server_flush_cache(DnsServer *s) {
 774         DnsServer *current;
 775         DnsScope *scope;
 776
 777         assert(s);
 778
 779         /* Flush the cache of the scope this server belongs to */
 780
 781         current = s->link ? s->link->current_dns_server : s->manager->current_dns_server;
 782         if (current != s)
 783                 return;
 784
 785         scope = s->link ? s->link->unicast_scope : s->manager->unicast_scope;
 786         if (!scope)
 787                 return;
 788
 789         dns_cache_flush(&scope->cache);
 790 }
 791
 792 void dns_server_reset_features(DnsServer *s) {
 793         assert(s);
 794
 795         s->verified_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
 796         s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
 797
 798         s->received_udp_packet_max = DNS_PACKET_UNICAST_SIZE_MAX;
 799
 800         s->packet_bad_opt = false;
 801         s->packet_rrsig_missing = false;
 802
 803         s->features_grace_period_usec = DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC;
 804
 805         s->warned_downgrade = false;
 806
 807         dns_server_reset_counters(s);
 808
 809         /* Let's close the default stream, so that we reprobe with the new features */
 810         dns_server_unref_stream(s);
 811 }
 812
 813 void dns_server_reset_features_all(DnsServer *s) {
 814         DnsServer *i;
 815
 816         LIST_FOREACH(servers, i, s)
 817                 dns_server_reset_features(i);
 818 }
 819
 820 void dns_server_dump(DnsServer *s, FILE *f) {
 821         assert(s);
 822
 823         if (!f)
 824                 f = stdout;
 825
 826         fputs("[Server ", f);
 827         fputs(dns_server_string(s), f);
 828         fputs(" type=", f);
 829         fputs(dns_server_type_to_string(s->type), f);
 830
 831         if (s->type == DNS_SERVER_LINK) {
 832                 assert(s->link);
 833
 834                 fputs(" interface=", f);
 835                 fputs(s->link->ifname, f);
 836         }
 837
 838         fputs("]\n", f);
 839
 840         fputs("\tVerified feature level: ", f);
 841         fputs(strna(dns_server_feature_level_to_string(s->verified_feature_level)), f);
 842         fputc('\n', f);
 843
 844         fputs("\tPossible feature level: ", f);
 845         fputs(strna(dns_server_feature_level_to_string(s->possible_feature_level)), f);
 846         fputc('\n', f);
 847
 848         fputs("\tDNSSEC Mode: ", f);
 849         fputs(strna(dnssec_mode_to_string(dns_server_get_dnssec_mode(s))), f);
 850         fputc('\n', f);
 851
 852         fputs("\tCan do DNSSEC: ", f);
 853         fputs(yes_no(dns_server_dnssec_supported(s)), f);
 854         fputc('\n', f);
 855
 856         fprintf(f,
 857                 "\tMaximum UDP packet size received: %zu\n"
 858                 "\tFailed UDP attempts: %u\n"
 859                 "\tFailed TCP attempts: %u\n"
 860                 "\tSeen truncated packet: %s\n"
 861                 "\tSeen OPT RR getting lost: %s\n"
 862                 "\tSeen RRSIG RR missing: %s\n",
 863                 s->received_udp_packet_max,
 864                 s->n_failed_udp,
 865                 s->n_failed_tcp,
 866                 yes_no(s->packet_truncated),
 867                 yes_no(s->packet_bad_opt),
 868                 yes_no(s->packet_rrsig_missing));
 869 }
 870
 871 void dns_server_unref_stream(DnsServer *s) {
 872         DnsStream *ref;
 873
 874         assert(s);
 875
 876         /* Detaches the default stream of this server. Some special care needs to be taken here, as that stream and
 877          * this server reference each other. First, take the stream out of the server. It's destructor will check if it
 878          * is registered with us, hence let's invalidate this separately, so that it is already unregistered. */
 879         ref = TAKE_PTR(s->stream);
 880
 881         /* And then, unref it */
 882         dns_stream_unref(ref);
 883 }
 884
 885 DnsScope *dns_server_scope(DnsServer *s) {
 886         assert(s);
 887         assert((s->type == DNS_SERVER_LINK) == !!s->link);
 888
 889         if (s->link)
 890                 return s->link->unicast_scope;
 891
 892         return s->manager->unicast_scope;
 893 }
 894
 895 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
 896         [DNS_SERVER_SYSTEM] = "system",
 897         [DNS_SERVER_FALLBACK] = "fallback",
 898         [DNS_SERVER_LINK] = "link",
 899 };
 900 DEFINE_STRING_TABLE_LOOKUP(dns_server_type, DnsServerType);
 901
 902 static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = {
 903         [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP",
 904         [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP",
 905         [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0",
 906         [DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN] = "TLS+EDNS0",
 907         [DNS_SERVER_FEATURE_LEVEL_DO] = "UDP+EDNS0+DO",
 908         [DNS_SERVER_FEATURE_LEVEL_LARGE] = "UDP+EDNS0+DO+LARGE",
 909         [DNS_SERVER_FEATURE_LEVEL_TLS_DO] = "TLS+EDNS0+D0",
 910 };
 911 DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);