src/resolve/resolved-dns-stub.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <net/if_arp.h>
   4 #include <netinet/tcp.h>
   5
   6 #include "errno-util.h"
   7 #include "fd-util.h"
   8 #include "missing_network.h"
   9 #include "missing_socket.h"
  10 #include "resolved-dns-stub.h"
  11 #include "socket-netlink.h"
  12 #include "socket-util.h"
  13 #include "stdio-util.h"
  14 #include "string-table.h"
  15
  16 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
  17  * IP and UDP header sizes */
  18 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
  19
  20 /* On the extra stubs, use a more conservative choice */
  21 #define ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX DNS_PACKET_UNICAST_SIZE_LARGE_MAX
  22
  23 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type);
  24
  25 static void dns_stub_listener_extra_hash_func(const DnsStubListenerExtra *a, struct siphash *state) {
  26         assert(a);
  27
  28         siphash24_compress(&a->mode, sizeof(a->mode), state);
  29         siphash24_compress(&a->family, sizeof(a->family), state);
  30         siphash24_compress(&a->address, FAMILY_ADDRESS_SIZE(a->family), state);
  31         siphash24_compress(&a->port, sizeof(a->port), state);
  32 }
  33
  34 static int dns_stub_listener_extra_compare_func(const DnsStubListenerExtra *a, const DnsStubListenerExtra *b) {
  35         int r;
  36
  37         assert(a);
  38         assert(b);
  39
  40         r = CMP(a->mode, b->mode);
  41         if (r != 0)
  42                 return r;
  43
  44         r = CMP(a->family, b->family);
  45         if (r != 0)
  46                 return r;
  47
  48         r = memcmp(&a->address, &b->address, FAMILY_ADDRESS_SIZE(a->family));
  49         if (r != 0)
  50                 return r;
  51
  52         return CMP(a->port, b->port);
  53 }
  54
  55 DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR(
  56                 dns_stub_listener_extra_hash_ops,
  57                 DnsStubListenerExtra,
  58                 dns_stub_listener_extra_hash_func,
  59                 dns_stub_listener_extra_compare_func,
  60                 dns_stub_listener_extra_free);
  61
  62 int dns_stub_listener_extra_new(
  63                 Manager *m,
  64                 DnsStubListenerExtra **ret) {
  65
  66         DnsStubListenerExtra *l;
  67
  68         l = new(DnsStubListenerExtra, 1);
  69         if (!l)
  70                 return -ENOMEM;
  71
  72         *l = (DnsStubListenerExtra) {
  73                 .manager = m,
  74         };
  75
  76         *ret = TAKE_PTR(l);
  77         return 0;
  78 }
  79
  80 DnsStubListenerExtra *dns_stub_listener_extra_free(DnsStubListenerExtra *p) {
  81         if (!p)
  82                 return NULL;
  83
  84         p->udp_event_source = sd_event_source_disable_unref(p->udp_event_source);
  85         p->tcp_event_source = sd_event_source_disable_unref(p->tcp_event_source);
  86
  87         hashmap_free(p->queries_by_packet);
  88
  89         return mfree(p);
  90 }
  91
  92 static void stub_packet_hash_func(const DnsPacket *p, struct siphash *state) {
  93         assert(p);
  94
  95         siphash24_compress(&p->protocol, sizeof(p->protocol), state);
  96         siphash24_compress(&p->family, sizeof(p->family), state);
  97         siphash24_compress(&p->sender, sizeof(p->sender), state);
  98         siphash24_compress(&p->ipproto, sizeof(p->ipproto), state);
  99         siphash24_compress(&p->sender_port, sizeof(p->sender_port), state);
 100         siphash24_compress(DNS_PACKET_HEADER(p), sizeof(DnsPacketHeader), state);
 101
 102         /* We don't bother hashing the full packet here, just the header */
 103 }
 104
 105 static int stub_packet_compare_func(const DnsPacket *x, const DnsPacket *y) {
 106         int r;
 107
 108         r = CMP(x->protocol, y->protocol);
 109         if (r != 0)
 110                 return r;
 111
 112         r = CMP(x->family, y->family);
 113         if (r != 0)
 114                 return r;
 115
 116         r = memcmp(&x->sender, &y->sender, sizeof(x->sender));
 117         if (r != 0)
 118                 return r;
 119
 120         r = CMP(x->ipproto, y->ipproto);
 121         if (r != 0)
 122                 return r;
 123
 124         r = CMP(x->sender_port, y->sender_port);
 125         if (r != 0)
 126                 return r;
 127
 128         return memcmp(DNS_PACKET_HEADER(x), DNS_PACKET_HEADER(y), sizeof(DnsPacketHeader));
 129 }
 130
 131 DEFINE_HASH_OPS(stub_packet_hash_ops, DnsPacket, stub_packet_hash_func, stub_packet_compare_func);
 132
 133 static int reply_add_with_rrsig(
 134                 DnsAnswer **reply,
 135                 DnsResourceRecord *rr,
 136                 int ifindex,
 137                 DnsAnswerFlags flags,
 138                 DnsResourceRecord *rrsig,
 139                 bool with_rrsig) {
 140         int r;
 141
 142         assert(reply);
 143         assert(rr);
 144
 145         r = dns_answer_add_extend(reply, rr, ifindex, flags, rrsig);
 146         if (r < 0)
 147                 return r;
 148
 149         if (with_rrsig && rrsig) {
 150                 r = dns_answer_add_extend(reply, rrsig, ifindex, flags, NULL);
 151                 if (r < 0)
 152                         return r;
 153         }
 154
 155         return 0;
 156 }
 157
 158 static int dns_stub_collect_answer_by_question(
 159                 DnsAnswer **reply,
 160                 DnsAnswer *answer,
 161                 DnsQuestion *question,
 162                 bool with_rrsig) { /* Add RRSIG RR matching each RR */
 163
 164         DnsAnswerItem *item;
 165         int r;
 166
 167         assert(reply);
 168
 169         /* Copies all RRs from 'answer' into 'reply', if they match 'question'. */
 170
 171         DNS_ANSWER_FOREACH_ITEM(item, answer) {
 172
 173                 /* We have a question, let's see if this RR matches it */
 174                 r = dns_question_matches_rr(question, item->rr, NULL);
 175                 if (r < 0)
 176                         return r;
 177                 if (!r) {
 178                         /* Maybe there's a CNAME/DNAME in here? If so, that's an answer too */
 179                         r = dns_question_matches_cname_or_dname(question, item->rr, NULL);
 180                         if (r < 0)
 181                                 return r;
 182                         if (!r)
 183                                 continue;
 184                 }
 185
 186                 /* Mask the section info, we want the primary answers to always go without section
 187                  * info, so that it is added to the answer section when we synthesize a reply. */
 188
 189                 r = reply_add_with_rrsig(
 190                                 reply,
 191                                 item->rr,
 192                                 item->ifindex,
 193                                 item->flags & ~DNS_ANSWER_MASK_SECTIONS,
 194                                 item->rrsig,
 195                                 with_rrsig);
 196                 if (r < 0)
 197                         return r;
 198         }
 199
 200         return 0;
 201 }
 202
 203 static int dns_stub_collect_answer_by_section(
 204                 DnsAnswer **reply,
 205                 DnsAnswer *answer,
 206                 DnsAnswerFlags section,
 207                 DnsAnswer *exclude1,
 208                 DnsAnswer *exclude2,
 209                 bool with_dnssec) { /* Include DNSSEC RRs. RRSIG, NSEC, … */
 210
 211         DnsAnswerItem *item;
 212         int r;
 213
 214         assert(reply);
 215
 216         /* Copies all RRs from 'answer' into 'reply', if they originate from the specified section. Also,
 217          * avoid any RRs listed in 'exclude'. */
 218
 219         DNS_ANSWER_FOREACH_ITEM(item, answer) {
 220
 221                 if (dns_answer_contains(exclude1, item->rr) ||
 222                     dns_answer_contains(exclude2, item->rr))
 223                         continue;
 224
 225                 if (!with_dnssec &&
 226                     dns_type_is_dnssec(item->rr->key->type))
 227                         continue;
 228
 229                 if (((item->flags ^ section) & DNS_ANSWER_MASK_SECTIONS) != 0)
 230                         continue;
 231
 232                 r = reply_add_with_rrsig(
 233                                 reply,
 234                                 item->rr,
 235                                 item->ifindex,
 236                                 item->flags,
 237                                 item->rrsig,
 238                                 with_dnssec);
 239                 if (r < 0)
 240                         return r;
 241         }
 242
 243         return 0;
 244 }
 245
 246 static int dns_stub_assign_sections(
 247                 DnsQuery *q,
 248                 DnsQuestion *question,
 249                 bool edns0_do) {
 250
 251         int r;
 252
 253         assert(q);
 254         assert(question);
 255
 256         /* Let's assign the 'answer' RRs we collected to their respective sections in the reply datagram. We
 257          * try to reproduce a section assignment similar to what the upstream DNS server responded to us. We
 258          * use the DNS_ANSWER_SECTION_xyz flags to match things up, which is where the original upstream's
 259          * packet section assignment is stored in the DnsAnswer object. Not all RRs in the 'answer' objects
 260          * come with section information though (for example, because they were synthesized locally, and not
 261          * from a DNS packet). To deal with that we extend the assignment logic a bit: anything from the
 262          * 'answer' object that directly matches the original question is always put in the ANSWER section,
 263          * regardless if it carries section info, or what that section info says. Then, anything from the
 264          * 'answer' objects that is from the ANSWER or AUTHORITY sections, and wasn't already added to the
 265          * ANSWER section is placed in the AUTHORITY section. Everything else from either object is added to
 266          * the ADDITIONAL section. */
 267
 268         /* Include all RRs that directly answer the question in the answer section */
 269         r = dns_stub_collect_answer_by_question(
 270                         &q->reply_answer,
 271                         q->answer,
 272                         question,
 273                         edns0_do);
 274         if (r < 0)
 275                 return r;
 276
 277         /* Include all RRs that originate from the authority sections, and aren't already listed in the
 278          * answer section, in the authority section */
 279         r = dns_stub_collect_answer_by_section(
 280                         &q->reply_authoritative,
 281                         q->answer,
 282                         DNS_ANSWER_SECTION_AUTHORITY,
 283                         q->reply_answer, NULL,
 284                         edns0_do);
 285         if (r < 0)
 286                 return r;
 287
 288         /* Include all RRs that originate from the answer or additional sections in the additional section
 289          * (except if already listed in the other two sections). Also add all RRs with no section marking. */
 290         r = dns_stub_collect_answer_by_section(
 291                         &q->reply_additional,
 292                         q->answer,
 293                         DNS_ANSWER_SECTION_ANSWER,
 294                         q->reply_answer, q->reply_authoritative,
 295                         edns0_do);
 296         if (r < 0)
 297                 return r;
 298         r = dns_stub_collect_answer_by_section(
 299                         &q->reply_additional,
 300                         q->answer,
 301                         DNS_ANSWER_SECTION_ADDITIONAL,
 302                         q->reply_answer, q->reply_authoritative,
 303                         edns0_do);
 304         if (r < 0)
 305                 return r;
 306         r = dns_stub_collect_answer_by_section(
 307                         &q->reply_additional,
 308                         q->answer,
 309                         0,
 310                         q->reply_answer, q->reply_authoritative,
 311                         edns0_do);
 312         if (r < 0)
 313                 return r;
 314
 315         return 0;
 316 }
 317
 318 static int dns_stub_make_reply_packet(
 319                 DnsPacket **ret,
 320                 size_t max_size,
 321                 DnsQuestion *q,
 322                 bool *ret_truncated) {
 323
 324         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 325         bool tc = false;
 326         int r;
 327
 328         assert(ret);
 329
 330         r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0, max_size);
 331         if (r < 0)
 332                 return r;
 333
 334         r = dns_packet_append_question(p, q);
 335         if (r == -EMSGSIZE)
 336                 tc = true;
 337         else if (r < 0)
 338                 return r;
 339
 340         if (ret_truncated)
 341                 *ret_truncated = tc;
 342         else if (tc)
 343                 return -EMSGSIZE;
 344
 345         DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
 346
 347         *ret = TAKE_PTR(p);
 348         return 0;
 349 }
 350
 351 static int dns_stub_add_reply_packet_body(
 352                 DnsPacket *p,
 353                 DnsAnswer *answer,
 354                 DnsAnswer *authoritative,
 355                 DnsAnswer *additional,
 356                 bool edns0_do, /* Client expects DNSSEC RRs? */
 357                 bool *truncated) {
 358
 359         unsigned n_answer = 0, n_authoritative = 0, n_additional = 0;
 360         bool tc = false;
 361         int r;
 362
 363         assert(p);
 364
 365         /* Add the three sections to the packet. If the answer section doesn't fit we'll signal that as
 366          * truncation. If the authoritative section doesn't fit and we are in DNSSEC mode, also signal
 367          * truncation. In all other cases where things don't fit don't signal truncation, as for those cases
 368          * the dropped RRs should not be essential. */
 369
 370         r = dns_packet_append_answer(p, answer, &n_answer);
 371         if (r == -EMSGSIZE)
 372                 tc = true;
 373         else if (r < 0)
 374                 return r;
 375         else {
 376                 r = dns_packet_append_answer(p, authoritative, &n_authoritative);
 377                 if (r == -EMSGSIZE) {
 378                         if (edns0_do)
 379                                 tc = true;
 380                 } else if (r < 0)
 381                         return r;
 382                 else {
 383                         r = dns_packet_append_answer(p, additional, &n_additional);
 384                         if (r < 0 && r != -EMSGSIZE)
 385                                 return r;
 386                 }
 387         }
 388
 389         if (tc) {
 390                 if (!truncated)
 391                         return -EMSGSIZE;
 392
 393                 *truncated = true;
 394         }
 395
 396         DNS_PACKET_HEADER(p)->ancount = htobe16(n_answer);
 397         DNS_PACKET_HEADER(p)->nscount = htobe16(n_authoritative);
 398         DNS_PACKET_HEADER(p)->arcount = htobe16(n_additional);
 399         return 0;
 400 }
 401
 402 static const char *nsid_string(void) {
 403         static char buffer[SD_ID128_STRING_MAX + STRLEN(".resolved.systemd.io")] = "";
 404         sd_id128_t id;
 405         int r;
 406
 407         /* Let's generate a string that we can use as RFC5001 NSID identifier. The string shall identify us
 408          * as systemd-resolved, and return a different string for each resolved instance without leaking host
 409          * identity. Hence let's use a fixed suffix that identifies resolved, and a prefix generated from the
 410          * machine ID but from which the machine ID cannot be determined.
 411          *
 412          * Clients can use this to determine whether an answer is originating locally or is proxied from
 413          * upstream. */
 414
 415         if (!isempty(buffer))
 416                 return buffer;
 417
 418         r = sd_id128_get_machine_app_specific(
 419                         SD_ID128_MAKE(ed,d3,12,5d,16,b9,41,f9,a1,49,5f,ab,15,62,ab,27),
 420                         &id);
 421         if (r < 0) {
 422                 log_debug_errno(r, "Failed to determine machine ID, ignoring: %m");
 423                 return NULL;
 424         }
 425
 426         xsprintf(buffer, SD_ID128_FORMAT_STR ".resolved.systemd.io", SD_ID128_FORMAT_VAL(id));
 427         return buffer;
 428 }
 429
 430 static int dns_stub_finish_reply_packet(
 431                 DnsPacket *p,
 432                 uint16_t id,
 433                 int rcode,
 434                 bool tc,        /* set the Truncated bit? */
 435                 bool aa,        /* set the Authoritative Answer bit? */
 436                 bool rd,        /* set the Recursion Desired bit? */
 437                 bool add_opt,   /* add an OPT RR to this packet? */
 438                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
 439                 bool ad,        /* set the DNSSEC authenticated data bit? */
 440                 bool cd,        /* set the DNSSEC checking disabled bit? */
 441                 uint16_t max_udp_size, /* The maximum UDP datagram size to advertise to clients */
 442                 bool nsid) {    /* whether to add NSID */
 443
 444         int r;
 445
 446         assert(p);
 447
 448         if (add_opt) {
 449                 r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, nsid ? nsid_string() : NULL, rcode, NULL);
 450                 if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */
 451                         tc = true;
 452                 else if (r < 0)
 453                         return r;
 454         } else {
 455                 /* If the client can't to EDNS0, don't do DO either */
 456                 edns0_do = false;
 457
 458                 /* If we don't do EDNS, clamp the rcode to 4 bit */
 459                 if (rcode > 0xF)
 460                         rcode = DNS_RCODE_SERVFAIL;
 461         }
 462
 463         /* Don't set the CD bit unless DO is on, too */
 464         if (!edns0_do)
 465                 cd = false;
 466
 467         /* Note that we allow the AD bit to be set even if client didn't signal DO, as per RFC 6840, section
 468          * 5.7 */
 469
 470         DNS_PACKET_HEADER(p)->id = id;
 471
 472         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 473                                                               1  /* qr */,
 474                                                               0  /* opcode */,
 475                                                               aa /* aa */,
 476                                                               tc /* tc */,
 477                                                               rd /* rd */,
 478                                                               1  /* ra */,
 479                                                               ad /* ad */,
 480                                                               cd /* cd */,
 481                                                               rcode));
 482
 483         return 0;
 484 }
 485
 486 static int dns_stub_send(
 487                 Manager *m,
 488                 DnsStubListenerExtra *l,
 489                 DnsStream *s,
 490                 DnsPacket *p,
 491                 DnsPacket *reply) {
 492
 493         int r;
 494
 495         assert(m);
 496         assert(p);
 497         assert(reply);
 498
 499         if (s)
 500                 r = dns_stream_write_packet(s, reply);
 501         else
 502                 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
 503                  * is because otherwise the kernel will choose it automatically based on the routing table and will
 504                  * thus pick 127.0.0.1 rather than 127.0.0.53. */
 505                 r = manager_send(m,
 506                                  manager_dns_stub_fd_extra(m, l, SOCK_DGRAM),
 507                                  l ? p->ifindex : LOOPBACK_IFINDEX, /* force loopback iface if this is the main listener stub */
 508                                  p->family, &p->sender, p->sender_port, &p->destination,
 509                                  reply);
 510         if (r < 0)
 511                 return log_debug_errno(r, "Failed to send reply packet: %m");
 512
 513         return 0;
 514 }
 515
 516 static int dns_stub_reply_with_edns0_do(DnsQuery *q) {
 517          assert(q);
 518
 519         /* Reply with DNSSEC DO set? Only if client supports it; and we did any DNSSEC verification
 520          * ourselves, or consider the data fully authenticated because we generated it locally, or the client
 521          * set cd */
 522
 523          return DNS_PACKET_DO(q->request_packet) &&
 524                  (q->answer_dnssec_result >= 0 ||        /* we did proper DNSSEC validation … */
 525                   dns_query_fully_authenticated(q) ||    /* … or we considered it authentic otherwise … */
 526                   DNS_PACKET_CD(q->request_packet));     /* … or client set CD */
 527 }
 528
 529 static void dns_stub_suppress_duplicate_section_rrs(DnsQuery *q) {
 530         /* If we follow a CNAME/DNAME chain we might end up populating our sections with redundant RRs
 531          * because we built up the sections from multiple reply packets (one from each CNAME/DNAME chain
 532          * element). E.g. it could be that an RR that was included in the first reply's additional section
 533          * ends up being relevant as main answer in a subsequent reply in the chain. Let's clean this up, and
 534          * remove everything in the "higher priority" sections from the "lower priority" sections.
 535          *
 536          * Note that this removal matches by RR keys instead of the full RRs. This is because RRsets should
 537          * always end up in one section fully or not at all, but never be split among sections.
 538          *
 539          * Specifically: we remove ANSWER section RRs from the AUTHORITATIVE and ADDITIONAL sections, as well
 540          * as AUTHORITATIVE section RRs from the ADDITIONAL section. */
 541
 542         dns_answer_remove_by_answer_keys(&q->reply_authoritative, q->reply_answer);
 543         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_answer);
 544         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_authoritative);
 545 }
 546
 547 static int dns_stub_send_reply(
 548                 DnsQuery *q,
 549                 int rcode) {
 550
 551         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 552         bool truncated, edns0_do;
 553         int r;
 554
 555         assert(q);
 556
 557         edns0_do = dns_stub_reply_with_edns0_do(q); /* let's check if we shall reply with EDNS0 DO? */
 558
 559         r = dns_stub_make_reply_packet(
 560                         &reply,
 561                         DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_packet),
 562                         q->request_packet->question,
 563                         &truncated);
 564         if (r < 0)
 565                 return log_debug_errno(r, "Failed to build reply packet: %m");
 566
 567         dns_stub_suppress_duplicate_section_rrs(q);
 568
 569         r = dns_stub_add_reply_packet_body(
 570                         reply,
 571                         q->reply_answer,
 572                         q->reply_authoritative,
 573                         q->reply_additional,
 574                         edns0_do,
 575                         &truncated);
 576         if (r < 0)
 577                 return log_debug_errno(r, "Failed to append reply packet body: %m");
 578
 579         r = dns_stub_finish_reply_packet(
 580                         reply,
 581                         DNS_PACKET_ID(q->request_packet),
 582                         rcode,
 583                         truncated,
 584                         dns_query_fully_authoritative(q),
 585                         DNS_PACKET_RD(q->request_packet),
 586                         !!q->request_packet->opt,
 587                         edns0_do,
 588                         DNS_PACKET_AD(q->request_packet) && dns_query_fully_authenticated(q),
 589                         DNS_PACKET_CD(q->request_packet),
 590                         q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 591                         dns_packet_has_nsid_request(q->request_packet) > 0 && !q->stub_listener_extra);
 592         if (r < 0)
 593                 return log_debug_errno(r, "Failed to build failure packet: %m");
 594
 595         return dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 596 }
 597
 598 static int dns_stub_send_failure(
 599                 Manager *m,
 600                 DnsStubListenerExtra *l,
 601                 DnsStream *s,
 602                 DnsPacket *p,
 603                 int rcode,
 604                 bool authenticated) {
 605
 606         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 607         bool truncated;
 608         int r;
 609
 610         assert(m);
 611         assert(p);
 612
 613         r = dns_stub_make_reply_packet(
 614                         &reply,
 615                         DNS_PACKET_PAYLOAD_SIZE_MAX(p),
 616                         p->question,
 617                         &truncated);
 618         if (r < 0)
 619                 return log_debug_errno(r, "Failed to make failure packet: %m");
 620
 621         r = dns_stub_finish_reply_packet(
 622                         reply,
 623                         DNS_PACKET_ID(p),
 624                         rcode,
 625                         truncated,
 626                         false,
 627                         DNS_PACKET_RD(p),
 628                         !!p->opt,
 629                         DNS_PACKET_DO(p),
 630                         DNS_PACKET_AD(p) && authenticated,
 631                         DNS_PACKET_CD(p),
 632                         l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 633                         dns_packet_has_nsid_request(p) > 0 && !l);
 634         if (r < 0)
 635                 return log_debug_errno(r, "Failed to build failure packet: %m");
 636
 637         return dns_stub_send(m, l, s, p, reply);
 638 }
 639
 640 static int dns_stub_patch_bypass_reply_packet(
 641                 DnsPacket **ret,       /* Where to place the patched packet */
 642                 DnsPacket *original,   /* The packet to patch */
 643                 DnsPacket *request) {  /* The packet the patched packet shall look like a reply to */
 644         _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL;
 645         int r;
 646
 647         assert(ret);
 648         assert(original);
 649         assert(request);
 650
 651         r = dns_packet_dup(&c, original);
 652         if (r < 0)
 653                 return r;
 654
 655         /* Extract the packet, so that we know where the OPT field is */
 656         r = dns_packet_extract(c);
 657         if (r < 0)
 658                 return r;
 659
 660         /* Copy over the original client request ID, so that we can make the upstream query look like our own reply. */
 661         DNS_PACKET_HEADER(c)->id = DNS_PACKET_HEADER(request)->id;
 662
 663         /* Patch in our own maximum datagram size, if EDNS0 was on */
 664         r = dns_packet_patch_max_udp_size(c, ADVERTISE_DATAGRAM_SIZE_MAX);
 665         if (r < 0)
 666                 return r;
 667
 668         /* Lower all TTLs by the time passed since we received the datagram. */
 669         if (timestamp_is_set(original->timestamp)) {
 670                 r = dns_packet_patch_ttls(c, original->timestamp);
 671                 if (r < 0)
 672                         return r;
 673         }
 674
 675         /* Our upstream connection might have supported larger DNS requests than our downstream one, hence
 676          * set the TC bit if our reply is larger than what the client supports, and truncate. */
 677         if (c->size > DNS_PACKET_PAYLOAD_SIZE_MAX(request)) {
 678                 log_debug("Artificially truncating stub response, as advertised size of client is smaller than upstream one.");
 679                 dns_packet_truncate(c, DNS_PACKET_PAYLOAD_SIZE_MAX(request));
 680                 DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC);
 681         }
 682
 683         *ret = TAKE_PTR(c);
 684         return 0;
 685 }
 686
 687 static void dns_stub_query_complete(DnsQuery *q) {
 688         int r;
 689
 690         assert(q);
 691         assert(q->request_packet);
 692
 693         if (q->question_bypass) {
 694                 /* This is a bypass reply. If so, let's propagate the upstream packet, if we have it and it
 695                  * is regular DNS. (We can't do this if the upstream packet is LLMNR or mDNS, since the
 696                  * packets are not 100% compatible.) */
 697
 698                 if (q->answer_full_packet &&
 699                     q->answer_full_packet->protocol == DNS_PROTOCOL_DNS) {
 700                         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 701
 702                         r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet);
 703                         if (r < 0)
 704                                 log_debug_errno(r, "Failed to patch bypass reply packet: %m");
 705                         else
 706                                 (void) dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 707
 708                         dns_query_free(q);
 709                         return;
 710                 }
 711         }
 712
 713         /* Take all data from the current reply, and merge it into the three reply sections we are building
 714          * up. We do this before processing CNAME redirects, so that we gradually build up our sections, and
 715          * and keep adding all RRs in the CNAME chain. */
 716         r = dns_stub_assign_sections(
 717                         q,
 718                         dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
 719                         dns_stub_reply_with_edns0_do(q));
 720         if (r < 0) {
 721                 log_debug_errno(r, "Failed to assign sections: %m");
 722                 dns_query_free(q);
 723                 return;
 724         }
 725
 726         switch (q->state) {
 727
 728         case DNS_TRANSACTION_SUCCESS: {
 729                 bool first = true;
 730
 731                 for (;;) {
 732                         int cname_result;
 733
 734                         cname_result = dns_query_process_cname_one(q);
 735                         if (cname_result == -ELOOP) { /* CNAME loop, let's send what we already have */
 736                                 log_debug_errno(r, "Detected CNAME loop, returning what we already have.");
 737                                 (void) dns_stub_send_reply(q, q->answer_rcode);
 738                                 break;
 739                         }
 740                         if (cname_result < 0) {
 741                                 log_debug_errno(cname_result, "Failed to process CNAME: %m");
 742                                 break;
 743                         }
 744
 745                         if (cname_result == DNS_QUERY_NOMATCH) {
 746                                 /* This answer doesn't contain any RR that would answer our question
 747                                  * positively, i.e. neither directly nor via CNAME. */
 748
 749                                 if (first) /* We never followed a CNAME and the answer doesn't match our
 750                                             * question at all? Then this is final, the empty answer is the
 751                                             * answer. */
 752                                         break;
 753
 754                                 /* Otherwise, we already followed a CNAME once within this packet, and the
 755                                  * packet doesn't answer our question. In that case let's restart the query,
 756                                  * now with the redirected question. We'll */
 757                                 r = dns_query_go(q);
 758                                 if (r < 0)
 759                                         log_debug_errno(r, "Failed to restart query: %m");
 760
 761                                 return;
 762                         }
 763
 764                         r = dns_stub_assign_sections(
 765                                         q,
 766                                         dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
 767                                         dns_stub_reply_with_edns0_do(q));
 768                         if (r < 0) {
 769                                 log_debug_errno(r, "Failed to assign sections: %m");
 770                                 dns_query_free(q);
 771                                 return;
 772                         }
 773
 774                         if (cname_result == DNS_QUERY_MATCH) /* A match? Then we are done, let's return what we got */
 775                                 break;
 776
 777                         /* We followed a CNAME. and collected the RRs that answer the redirected question
 778                          * successfully. Let's not try to do this again. */
 779                         assert(cname_result == DNS_QUERY_CNAME);
 780                         first = false;
 781                 }
 782
 783                 _fallthrough_;
 784         }
 785
 786         case DNS_TRANSACTION_RCODE_FAILURE:
 787                 (void) dns_stub_send_reply(q, q->answer_rcode);
 788                 break;
 789
 790         case DNS_TRANSACTION_NOT_FOUND:
 791                 (void) dns_stub_send_reply(q, DNS_RCODE_NXDOMAIN);
 792                 break;
 793
 794         case DNS_TRANSACTION_TIMEOUT:
 795         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 796                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 797                 break;
 798
 799         case DNS_TRANSACTION_NO_SERVERS:
 800         case DNS_TRANSACTION_INVALID_REPLY:
 801         case DNS_TRANSACTION_ERRNO:
 802         case DNS_TRANSACTION_ABORTED:
 803         case DNS_TRANSACTION_DNSSEC_FAILED:
 804         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 805         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 806         case DNS_TRANSACTION_NETWORK_DOWN:
 807         case DNS_TRANSACTION_NO_SOURCE:
 808         case DNS_TRANSACTION_STUB_LOOP:
 809                 (void) dns_stub_send_reply(q, DNS_RCODE_SERVFAIL);
 810                 break;
 811
 812         case DNS_TRANSACTION_NULL:
 813         case DNS_TRANSACTION_PENDING:
 814         case DNS_TRANSACTION_VALIDATING:
 815         default:
 816                 assert_not_reached("Impossible state");
 817         }
 818
 819         dns_query_free(q);
 820 }
 821
 822 static int dns_stub_stream_complete(DnsStream *s, int error) {
 823         assert(s);
 824
 825         log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");
 826
 827         for (;;) {
 828                 DnsQuery *q;
 829
 830                 q = set_first(s->queries);
 831                 if (!q)
 832                         break;
 833
 834                 dns_query_free(q);
 835         }
 836
 837         /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
 838          * should be kept as long as the client wants to. */
 839         dns_stream_unref(s);
 840         return 0;
 841 }
 842
 843 static void dns_stub_process_query(Manager *m, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) {
 844         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
 845         Hashmap **queries_by_packet;
 846         DnsQuery *existing;
 847         int r;
 848
 849         assert(m);
 850         assert(p);
 851         assert(p->protocol == DNS_PROTOCOL_DNS);
 852
 853         if (!l && /* l == NULL if this is the main stub */
 854             (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 855              in_addr_is_localhost(p->family, &p->destination) <= 0)) {
 856                 log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring.");
 857                 return;
 858         }
 859
 860         if (manager_packet_from_our_transaction(m, p)) {
 861                 log_debug("Got our own packet looped back, ignoring.");
 862                 return;
 863         }
 864
 865         queries_by_packet = l ? &l->queries_by_packet : &m->stub_queries_by_packet;
 866         existing = hashmap_get(*queries_by_packet, p);
 867         if (existing && dns_packet_equal(existing->request_packet, p)) {
 868                 log_debug("Got repeat packet from client, ignoring.");
 869                 return;
 870         }
 871
 872         r = dns_packet_extract(p);
 873         if (r < 0) {
 874                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 875                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_FORMERR, false);
 876                 return;
 877         }
 878
 879         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 880                 log_debug("Got EDNS OPT field with unsupported version number.");
 881                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false);
 882                 return;
 883         }
 884
 885         if (dns_type_is_obsolete(dns_question_first_key(p->question)->type)) {
 886                 log_debug("Got message with obsolete key type, refusing.");
 887                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 888                 return;
 889         }
 890
 891         if (dns_type_is_zone_transer(dns_question_first_key(p->question)->type)) {
 892                 log_debug("Got request for zone transfer, refusing.");
 893                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 894                 return;
 895         }
 896
 897         if (!DNS_PACKET_RD(p))  {
 898                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 899                 log_debug("Got request with recursion disabled, refusing.");
 900                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 901                 return;
 902         }
 903
 904         r = hashmap_ensure_allocated(queries_by_packet, &stub_packet_hash_ops);
 905         if (r < 0) {
 906                 log_oom();
 907                 return;
 908         }
 909
 910         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
 911                 log_debug("Got request with DNSSEC checking disabled, enabling bypass logic.");
 912
 913                 r = dns_query_new(m, &q, NULL, NULL, p, 0,
 914                                   SD_RESOLVED_PROTOCOLS_ALL|
 915                                   SD_RESOLVED_NO_CNAME|
 916                                   SD_RESOLVED_NO_SEARCH|
 917                                   SD_RESOLVED_NO_VALIDATE|
 918                                   SD_RESOLVED_REQUIRE_PRIMARY|
 919                                   SD_RESOLVED_CLAMP_TTL);
 920         } else
 921                 r = dns_query_new(m, &q, p->question, p->question, NULL, 0,
 922                                   SD_RESOLVED_PROTOCOLS_ALL|
 923                                   SD_RESOLVED_NO_SEARCH|
 924                                   (DNS_PACKET_DO(p) ? SD_RESOLVED_REQUIRE_PRIMARY : 0)|
 925                                   SD_RESOLVED_CLAMP_TTL);
 926         if (r < 0) {
 927                 log_error_errno(r, "Failed to generate query object: %m");
 928                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 929                 return;
 930         }
 931
 932         q->request_packet = dns_packet_ref(p);
 933         q->request_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 934         q->stub_listener_extra = l;
 935         q->complete = dns_stub_query_complete;
 936
 937         if (s) {
 938                 /* Remember which queries belong to this stream, so that we can cancel them when the stream
 939                  * is disconnected early */
 940
 941                 r = set_ensure_put(&s->queries, NULL, q);
 942                 if (r < 0) {
 943                         log_oom();
 944                         return;
 945                 }
 946                 assert(r > 0);
 947         }
 948
 949         /* Add the query to the hash table we use to determine repeat packets now. We don't care about
 950          * failures here, since in the worst case we'll not recognize duplicate incoming requests, which
 951          * isn't particularly bad. */
 952         (void) hashmap_put(*queries_by_packet, q->request_packet, q);
 953
 954         r = dns_query_go(q);
 955         if (r < 0) {
 956                 log_error_errno(r, "Failed to start query: %m");
 957                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 958                 return;
 959         }
 960
 961         log_debug("Processing query...");
 962         TAKE_PTR(q);
 963 }
 964
 965 static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
 966         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 967         int r;
 968
 969         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
 970         if (r <= 0)
 971                 return r;
 972
 973         if (dns_packet_validate_query(p) > 0) {
 974                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
 975
 976                 dns_stub_process_query(m, l, NULL, p);
 977         } else
 978                 log_debug("Invalid DNS stub UDP packet, ignoring.");
 979
 980         return 0;
 981 }
 982
 983 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 984         return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL);
 985 }
 986
 987 static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 988         DnsStubListenerExtra *l = userdata;
 989
 990         assert(l);
 991
 992         return on_dns_stub_packet_internal(s, fd, revents, l->manager, l);
 993 }
 994
 995 static int on_dns_stub_stream_packet(DnsStream *s) {
 996         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 997
 998         assert(s);
 999
1000         p = dns_stream_take_read_packet(s);
1001         assert(p);
1002
1003         if (dns_packet_validate_query(p) > 0) {
1004                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
1005
1006                 dns_stub_process_query(s->manager, s->stub_listener_extra, s, p);
1007         } else
1008                 log_debug("Invalid DNS stub TCP packet, ignoring.");
1009
1010         return 0;
1011 }
1012
1013 static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
1014         DnsStream *stream;
1015         int cfd, r;
1016
1017         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
1018         if (cfd < 0) {
1019                 if (ERRNO_IS_ACCEPT_AGAIN(errno))
1020                         return 0;
1021
1022                 return -errno;
1023         }
1024
1025         r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
1026         if (r < 0) {
1027                 safe_close(cfd);
1028                 return r;
1029         }
1030
1031         stream->stub_listener_extra = l;
1032         stream->on_packet = on_dns_stub_stream_packet;
1033         stream->complete = dns_stub_stream_complete;
1034
1035         /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
1036
1037         return 0;
1038 }
1039
1040 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1041         return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL);
1042 }
1043
1044 static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1045         DnsStubListenerExtra *l = userdata;
1046
1047         assert(l);
1048         return on_dns_stub_stream_internal(s, fd, revents, l->manager, l);
1049 }
1050
1051 static int set_dns_stub_common_socket_options(int fd, int family) {
1052         int r;
1053
1054         assert(fd >= 0);
1055         assert(IN_SET(family, AF_INET, AF_INET6));
1056
1057         r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
1058         if (r < 0)
1059                 return r;
1060
1061         r = socket_set_recvpktinfo(fd, family, true);
1062         if (r < 0)
1063                 return r;
1064
1065         r = socket_set_recvttl(fd, family, true);
1066         if (r < 0)
1067                 return r;
1068
1069         return 0;
1070 }
1071
1072 static int set_dns_stub_common_tcp_socket_options(int fd) {
1073         int r;
1074
1075         assert(fd >= 0);
1076
1077         r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */
1078         if (r < 0)
1079                 log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m");
1080
1081         r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true);
1082         if (r < 0)
1083                 log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m");
1084
1085         return 0;
1086 }
1087
1088 static int manager_dns_stub_fd(Manager *m, int type) {
1089         union sockaddr_union sa = {
1090                 .in.sin_family = AF_INET,
1091                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
1092                 .in.sin_port = htobe16(53),
1093         };
1094         _cleanup_close_ int fd = -1;
1095         int r;
1096
1097         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1098
1099         sd_event_source **event_source = type == SOCK_DGRAM ? &m->dns_stub_udp_event_source : &m->dns_stub_tcp_event_source;
1100         if (*event_source)
1101                 return sd_event_source_get_io_fd(*event_source);
1102
1103         fd = socket(AF_INET, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1104         if (fd < 0)
1105                 return -errno;
1106
1107         r = set_dns_stub_common_socket_options(fd, AF_INET);
1108         if (r < 0)
1109                 return r;
1110
1111         if (type == SOCK_STREAM) {
1112                 r = set_dns_stub_common_tcp_socket_options(fd);
1113                 if (r < 0)
1114                         return r;
1115         }
1116
1117         /* Make sure no traffic from outside the local host can leak to onto this socket */
1118         r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX);
1119         if (r < 0)
1120                 return r;
1121
1122         r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, 1);
1123         if (r < 0)
1124                 return r;
1125
1126         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
1127                 return -errno;
1128
1129         if (type == SOCK_STREAM &&
1130             listen(fd, SOMAXCONN) < 0)
1131                 return -errno;
1132
1133         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1134                             type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream,
1135                             m);
1136         if (r < 0)
1137                 return r;
1138
1139         r = sd_event_source_set_io_fd_own(*event_source, true);
1140         if (r < 0)
1141                 return r;
1142
1143         (void) sd_event_source_set_description(*event_source,
1144                                                type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp");
1145
1146         return TAKE_FD(fd);
1147 }
1148
1149 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) {
1150         _cleanup_free_ char *pretty = NULL;
1151         _cleanup_close_ int fd = -1;
1152         union sockaddr_union sa;
1153         int r;
1154
1155         assert(m);
1156         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1157
1158         if (!l)
1159                 return manager_dns_stub_fd(m, type);
1160
1161         sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source;
1162         if (*event_source)
1163                 return sd_event_source_get_io_fd(*event_source);
1164
1165         if (l->family == AF_INET)
1166                 sa = (union sockaddr_union) {
1167                         .in.sin_family = l->family,
1168                         .in.sin_port = htobe16(dns_stub_listener_extra_port(l)),
1169                         .in.sin_addr = l->address.in,
1170                 };
1171         else
1172                 sa = (union sockaddr_union) {
1173                         .in6.sin6_family = l->family,
1174                         .in6.sin6_port = htobe16(dns_stub_listener_extra_port(l)),
1175                         .in6.sin6_addr = l->address.in6,
1176                 };
1177
1178         fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1179         if (fd < 0) {
1180                 r = -errno;
1181                 goto fail;
1182         }
1183
1184         r = set_dns_stub_common_socket_options(fd, l->family);
1185         if (r < 0)
1186                 goto fail;
1187
1188         if (type == SOCK_STREAM) {
1189                 r = set_dns_stub_common_tcp_socket_options(fd);
1190                 if (r < 0)
1191                         goto fail;
1192         }
1193
1194         /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case
1195          * people may want ttl > 1. */
1196
1197         r = socket_set_freebind(fd, l->family, true);
1198         if (r < 0)
1199                 goto fail;
1200
1201         if (type == SOCK_DGRAM) {
1202                 r = socket_disable_pmtud(fd, l->family);
1203                 if (r < 0)
1204                         log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m");
1205
1206                 r = socket_set_recvfragsize(fd, l->family, true);
1207                 if (r < 0)
1208                         log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m");
1209         }
1210
1211         if (bind(fd, &sa.sa, SOCKADDR_LEN(sa)) < 0) {
1212                 r = -errno;
1213                 goto fail;
1214         }
1215
1216         if (type == SOCK_STREAM &&
1217             listen(fd, SOMAXCONN) < 0) {
1218                 r = -errno;
1219                 goto fail;
1220         }
1221
1222         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1223                             type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra,
1224                             l);
1225         if (r < 0)
1226                 goto fail;
1227
1228         r = sd_event_source_set_io_fd_own(*event_source, true);
1229         if (r < 0)
1230                 goto fail;
1231
1232         (void) sd_event_source_set_description(*event_source,
1233                                                type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra");
1234
1235         if (DEBUG_LOGGING) {
1236                 (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1237                 log_debug("Listening on %s socket %s.",
1238                           type == SOCK_DGRAM ? "UDP" : "TCP",
1239                           strnull(pretty));
1240         }
1241
1242         return TAKE_FD(fd);
1243
1244 fail:
1245         assert(r < 0);
1246         (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1247         return log_warning_errno(r,
1248                                  r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" :
1249                                                     "Failed to listen on %s socket %s: %m",
1250                                  type == SOCK_DGRAM ? "UDP" : "TCP",
1251                                  strnull(pretty));
1252 }
1253
1254 int manager_dns_stub_start(Manager *m) {
1255         const char *t = "UDP";
1256         int r = 0;
1257
1258         assert(m);
1259
1260         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
1261                 log_debug("Not creating stub listener.");
1262         else
1263                 log_debug("Creating stub listener using %s.",
1264                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
1265                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
1266                           "UDP/TCP");
1267
1268         if (FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_UDP))
1269                 r = manager_dns_stub_fd(m, SOCK_DGRAM);
1270
1271         if (r >= 0 &&
1272             FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_TCP)) {
1273                 t = "TCP";
1274                 r = manager_dns_stub_fd(m, SOCK_STREAM);
1275         }
1276
1277         if (IN_SET(r, -EADDRINUSE, -EPERM)) {
1278                 log_warning_errno(r,
1279                                   r == -EADDRINUSE ? "Another process is already listening on %s socket 127.0.0.53:53.\n"
1280                                                      "Turning off local DNS stub support." :
1281                                                      "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
1282                                                      "Turning off local DNS stub support.",
1283                                   t);
1284                 manager_dns_stub_stop(m);
1285         } else if (r < 0)
1286                 return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
1287
1288         if (!ordered_set_isempty(m->dns_extra_stub_listeners)) {
1289                 DnsStubListenerExtra *l;
1290
1291                 log_debug("Creating extra stub listeners.");
1292
1293                 ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) {
1294                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP))
1295                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM);
1296                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP))
1297                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM);
1298                 }
1299         }
1300
1301         return 0;
1302 }
1303
1304 void manager_dns_stub_stop(Manager *m) {
1305         assert(m);
1306
1307         m->dns_stub_udp_event_source = sd_event_source_disable_unref(m->dns_stub_udp_event_source);
1308         m->dns_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_stub_tcp_event_source);
1309 }
1310
1311 static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = {
1312         [DNS_STUB_LISTENER_NO]  = "no",
1313         [DNS_STUB_LISTENER_UDP] = "udp",
1314         [DNS_STUB_LISTENER_TCP] = "tcp",
1315         [DNS_STUB_LISTENER_YES] = "yes",
1316 };
1317 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);