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 add_opt,   /* add an OPT RR to this packet? */
 437                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
 438                 bool ad,        /* set the DNSSEC authenticated data bit? */
 439                 bool cd,        /* set the DNSSEC checking disabled bit? */
 440                 uint16_t max_udp_size, /* The maximum UDP datagram size to advertise to clients */
 441                 bool nsid) {    /* whether to add NSID */
 442
 443         int r;
 444
 445         assert(p);
 446
 447         if (add_opt) {
 448                 r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, nsid ? nsid_string() : NULL, rcode, NULL);
 449                 if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */
 450                         tc = true;
 451                 else if (r < 0)
 452                         return r;
 453         } else {
 454                 /* If the client can't to EDNS0, don't do DO either */
 455                 edns0_do = false;
 456
 457                 /* If we don't do EDNS, clamp the rcode to 4 bit */
 458                 if (rcode > 0xF)
 459                         rcode = DNS_RCODE_SERVFAIL;
 460         }
 461
 462         /* Don't set the CD bit unless DO is on, too */
 463         if (!edns0_do)
 464                 cd = false;
 465
 466         /* Note that we allow the AD bit to be set even if client didn't signal DO, as per RFC 6840, section
 467          * 5.7 */
 468
 469         DNS_PACKET_HEADER(p)->id = id;
 470
 471         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 472                                                               1  /* qr */,
 473                                                               0  /* opcode */,
 474                                                               aa /* aa */,
 475                                                               tc /* tc */,
 476                                                               1  /* rd */,
 477                                                               1  /* ra */,
 478                                                               ad /* ad */,
 479                                                               cd /* cd */,
 480                                                               rcode));
 481
 482         return 0;
 483 }
 484
 485 static int dns_stub_send(
 486                 Manager *m,
 487                 DnsStubListenerExtra *l,
 488                 DnsStream *s,
 489                 DnsPacket *p,
 490                 DnsPacket *reply) {
 491
 492         int r;
 493
 494         assert(m);
 495         assert(p);
 496         assert(reply);
 497
 498         if (s)
 499                 r = dns_stream_write_packet(s, reply);
 500         else
 501                 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
 502                  * is because otherwise the kernel will choose it automatically based on the routing table and will
 503                  * thus pick 127.0.0.1 rather than 127.0.0.53. */
 504                 r = manager_send(m,
 505                                  manager_dns_stub_fd_extra(m, l, SOCK_DGRAM),
 506                                  l ? p->ifindex : LOOPBACK_IFINDEX, /* force loopback iface if this is the main listener stub */
 507                                  p->family, &p->sender, p->sender_port, &p->destination,
 508                                  reply);
 509         if (r < 0)
 510                 return log_debug_errno(r, "Failed to send reply packet: %m");
 511
 512         return 0;
 513 }
 514
 515 static int dns_stub_reply_with_edns0_do(DnsQuery *q) {
 516          assert(q);
 517
 518         /* Reply with DNSSEC DO set? Only if client supports it; and we did any DNSSEC verification
 519          * ourselves, or consider the data fully authenticated because we generated it locally, or the client
 520          * set cd */
 521
 522          return DNS_PACKET_DO(q->request_packet) &&
 523                  (q->answer_dnssec_result >= 0 ||        /* we did proper DNSSEC validation … */
 524                   dns_query_fully_authenticated(q) ||    /* … or we considered it authentic otherwise … */
 525                   DNS_PACKET_CD(q->request_packet));     /* … or client set CD */
 526 }
 527
 528 static void dns_stub_suppress_duplicate_section_rrs(DnsQuery *q) {
 529         /* If we follow a CNAME/DNAME chain we might end up populating our sections with redundant RRs
 530          * because we built up the sections from multiple reply packets (one from each CNAME/DNAME chain
 531          * element). E.g. it could be that an RR that was included in the first reply's additional section
 532          * ends up being relevant as main answer in a subsequent reply in the chain. Let's clean this up, and
 533          * remove everything in the "higher priority" sections from the "lower priority" sections.
 534          *
 535          * Note that this removal matches by RR keys instead of the full RRs. This is because RRsets should
 536          * always end up in one section fully or not at all, but never be split among sections.
 537          *
 538          * Specifically: we remove ANSWER section RRs from the AUTHORITATIVE and ADDITIONAL sections, as well
 539          * as AUTHORITATIVE section RRs from the ADDITIONAL section. */
 540
 541         dns_answer_remove_by_answer_keys(&q->reply_authoritative, q->reply_answer);
 542         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_answer);
 543         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_authoritative);
 544 }
 545
 546 static int dns_stub_send_reply(
 547                 DnsQuery *q,
 548                 int rcode) {
 549
 550         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 551         bool truncated, edns0_do;
 552         int r;
 553
 554         assert(q);
 555
 556         edns0_do = dns_stub_reply_with_edns0_do(q); /* let's check if we shall reply with EDNS0 DO? */
 557
 558         r = dns_stub_make_reply_packet(
 559                         &reply,
 560                         DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_packet),
 561                         q->request_packet->question,
 562                         &truncated);
 563         if (r < 0)
 564                 return log_debug_errno(r, "Failed to build reply packet: %m");
 565
 566         dns_stub_suppress_duplicate_section_rrs(q);
 567
 568         r = dns_stub_add_reply_packet_body(
 569                         reply,
 570                         q->reply_answer,
 571                         q->reply_authoritative,
 572                         q->reply_additional,
 573                         edns0_do,
 574                         &truncated);
 575         if (r < 0)
 576                 return log_debug_errno(r, "Failed to append reply packet body: %m");
 577
 578         r = dns_stub_finish_reply_packet(
 579                         reply,
 580                         DNS_PACKET_ID(q->request_packet),
 581                         rcode,
 582                         truncated,
 583                         dns_query_fully_authoritative(q),
 584                         !!q->request_packet->opt,
 585                         edns0_do,
 586                         DNS_PACKET_AD(q->request_packet) && dns_query_fully_authenticated(q),
 587                         DNS_PACKET_CD(q->request_packet),
 588                         q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 589                         dns_packet_has_nsid_request(q->request_packet) > 0 && !q->stub_listener_extra);
 590         if (r < 0)
 591                 return log_debug_errno(r, "Failed to build failure packet: %m");
 592
 593         return dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 594 }
 595
 596 static int dns_stub_send_failure(
 597                 Manager *m,
 598                 DnsStubListenerExtra *l,
 599                 DnsStream *s,
 600                 DnsPacket *p,
 601                 int rcode,
 602                 bool authenticated) {
 603
 604         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 605         bool truncated;
 606         int r;
 607
 608         assert(m);
 609         assert(p);
 610
 611         r = dns_stub_make_reply_packet(
 612                         &reply,
 613                         DNS_PACKET_PAYLOAD_SIZE_MAX(p),
 614                         p->question,
 615                         &truncated);
 616         if (r < 0)
 617                 return log_debug_errno(r, "Failed to make failure packet: %m");
 618
 619         r = dns_stub_finish_reply_packet(
 620                         reply,
 621                         DNS_PACKET_ID(p),
 622                         rcode,
 623                         truncated,
 624                         false,
 625                         !!p->opt,
 626                         DNS_PACKET_DO(p),
 627                         DNS_PACKET_AD(p) && authenticated,
 628                         DNS_PACKET_CD(p),
 629                         l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 630                         dns_packet_has_nsid_request(p) > 0 && !l);
 631         if (r < 0)
 632                 return log_debug_errno(r, "Failed to build failure packet: %m");
 633
 634         return dns_stub_send(m, l, s, p, reply);
 635 }
 636
 637 static int dns_stub_patch_bypass_reply_packet(
 638                 DnsPacket **ret,       /* Where to place the patched packet */
 639                 DnsPacket *original,   /* The packet to patch */
 640                 DnsPacket *request) {  /* The packet the patched packet shall look like a reply to */
 641         _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL;
 642         int r;
 643
 644         assert(ret);
 645         assert(original);
 646         assert(request);
 647
 648         r = dns_packet_dup(&c, original);
 649         if (r < 0)
 650                 return r;
 651
 652         /* Extract the packet, so that we know where the OPT field is */
 653         r = dns_packet_extract(c);
 654         if (r < 0)
 655                 return r;
 656
 657         /* Copy over the original client request ID, so that we can make the upstream query look like our own reply. */
 658         DNS_PACKET_HEADER(c)->id = DNS_PACKET_HEADER(request)->id;
 659
 660         /* Patch in our own maximum datagram size, if EDNS0 was on */
 661         r = dns_packet_patch_max_udp_size(c, ADVERTISE_DATAGRAM_SIZE_MAX);
 662         if (r < 0)
 663                 return r;
 664
 665         /* Lower all TTLs by the time passed since we received the datagram. */
 666         if (timestamp_is_set(original->timestamp)) {
 667                 r = dns_packet_patch_ttls(c, original->timestamp);
 668                 if (r < 0)
 669                         return r;
 670         }
 671
 672         /* Our upstream connection might have supported larger DNS requests than our downstream one, hence
 673          * set the TC bit if our reply is larger than what the client supports, and truncate. */
 674         if (c->size > DNS_PACKET_PAYLOAD_SIZE_MAX(request)) {
 675                 log_debug("Artificially truncating stub response, as advertised size of client is smaller than upstream one.");
 676                 dns_packet_truncate(c, DNS_PACKET_PAYLOAD_SIZE_MAX(request));
 677                 DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC);
 678         }
 679
 680         *ret = TAKE_PTR(c);
 681         return 0;
 682 }
 683
 684 static void dns_stub_query_complete(DnsQuery *q) {
 685         int r;
 686
 687         assert(q);
 688         assert(q->request_packet);
 689
 690         if (q->question_bypass) {
 691                 /* This is a bypass reply. If so, let's propagate the upstream packet, if we have it and it
 692                  * is regular DNS. (We can't do this if the upstream packet is LLMNR or mDNS, since the
 693                  * packets are not 100% compatible.) */
 694
 695                 if (q->answer_full_packet &&
 696                     q->answer_full_packet->protocol == DNS_PROTOCOL_DNS) {
 697                         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 698
 699                         r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet);
 700                         if (r < 0)
 701                                 log_debug_errno(r, "Failed to patch bypass reply packet: %m");
 702                         else
 703                                 (void) dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 704
 705                         dns_query_free(q);
 706                         return;
 707                 }
 708         }
 709
 710         /* Take all data from the current reply, and merge it into the three reply sections we are building
 711          * up. We do this before processing CNAME redirects, so that we gradually build up our sections, and
 712          * and keep adding all RRs in the CNAME chain. */
 713         r = dns_stub_assign_sections(
 714                         q,
 715                         dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
 716                         dns_stub_reply_with_edns0_do(q));
 717         if (r < 0) {
 718                 log_debug_errno(r, "Failed to assign sections: %m");
 719                 dns_query_free(q);
 720                 return;
 721         }
 722
 723         switch (q->state) {
 724
 725         case DNS_TRANSACTION_SUCCESS: {
 726                 bool first = true;
 727
 728                 for (;;) {
 729                         int cname_result;
 730
 731                         cname_result = dns_query_process_cname_one(q);
 732                         if (cname_result == -ELOOP) { /* CNAME loop, let's send what we already have */
 733                                 log_debug_errno(r, "Detected CNAME loop, returning what we already have.");
 734                                 (void) dns_stub_send_reply(q, q->answer_rcode);
 735                                 break;
 736                         }
 737                         if (cname_result < 0) {
 738                                 log_debug_errno(cname_result, "Failed to process CNAME: %m");
 739                                 break;
 740                         }
 741
 742                         if (cname_result == DNS_QUERY_NOMATCH) {
 743                                 /* This answer doesn't contain any RR that would answer our question
 744                                  * positively, i.e. neither directly nor via CNAME. */
 745
 746                                 if (first) /* We never followed a CNAME and the answer doesn't match our
 747                                             * question at all? Then this is final, the empty answer is the
 748                                             * answer. */
 749                                         break;
 750
 751                                 /* Otherwise, we already followed a CNAME once within this packet, and the
 752                                  * packet doesn't answer our question. In that case let's restart the query,
 753                                  * now with the redirected question. We'll */
 754                                 r = dns_query_go(q);
 755                                 if (r < 0)
 756                                         log_debug_errno(r, "Failed to restart query: %m");
 757
 758                                 return;
 759                         }
 760
 761                         r = dns_stub_assign_sections(
 762                                         q,
 763                                         dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
 764                                         dns_stub_reply_with_edns0_do(q));
 765                         if (r < 0) {
 766                                 log_debug_errno(r, "Failed to assign sections: %m");
 767                                 dns_query_free(q);
 768                                 return;
 769                         }
 770
 771                         if (cname_result == DNS_QUERY_MATCH) /* A match? Then we are done, let's return what we got */
 772                                 break;
 773
 774                         /* We followed a CNAME. and collected the RRs that answer the redirected question
 775                          * successfully. Let's not try to do this again. */
 776                         assert(cname_result == DNS_QUERY_CNAME);
 777                         first = false;
 778                 }
 779
 780                 _fallthrough_;
 781         }
 782
 783         case DNS_TRANSACTION_RCODE_FAILURE:
 784                 (void) dns_stub_send_reply(q, q->answer_rcode);
 785                 break;
 786
 787         case DNS_TRANSACTION_NOT_FOUND:
 788                 (void) dns_stub_send_reply(q, DNS_RCODE_NXDOMAIN);
 789                 break;
 790
 791         case DNS_TRANSACTION_TIMEOUT:
 792         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 793                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 794                 break;
 795
 796         case DNS_TRANSACTION_NO_SERVERS:
 797         case DNS_TRANSACTION_INVALID_REPLY:
 798         case DNS_TRANSACTION_ERRNO:
 799         case DNS_TRANSACTION_ABORTED:
 800         case DNS_TRANSACTION_DNSSEC_FAILED:
 801         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 802         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 803         case DNS_TRANSACTION_NETWORK_DOWN:
 804         case DNS_TRANSACTION_NO_SOURCE:
 805         case DNS_TRANSACTION_STUB_LOOP:
 806                 (void) dns_stub_send_reply(q, DNS_RCODE_SERVFAIL);
 807                 break;
 808
 809         case DNS_TRANSACTION_NULL:
 810         case DNS_TRANSACTION_PENDING:
 811         case DNS_TRANSACTION_VALIDATING:
 812         default:
 813                 assert_not_reached("Impossible state");
 814         }
 815
 816         dns_query_free(q);
 817 }
 818
 819 static int dns_stub_stream_complete(DnsStream *s, int error) {
 820         assert(s);
 821
 822         log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");
 823
 824         for (;;) {
 825                 DnsQuery *q;
 826
 827                 q = set_first(s->queries);
 828                 if (!q)
 829                         break;
 830
 831                 dns_query_free(q);
 832         }
 833
 834         /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
 835          * should be kept as long as the client wants to. */
 836         dns_stream_unref(s);
 837         return 0;
 838 }
 839
 840 static void dns_stub_process_query(Manager *m, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) {
 841         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
 842         Hashmap **queries_by_packet;
 843         DnsQuery *existing;
 844         int r;
 845
 846         assert(m);
 847         assert(p);
 848         assert(p->protocol == DNS_PROTOCOL_DNS);
 849
 850         if (!l && /* l == NULL if this is the main stub */
 851             (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 852              in_addr_is_localhost(p->family, &p->destination) <= 0)) {
 853                 log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring.");
 854                 return;
 855         }
 856
 857         if (manager_packet_from_our_transaction(m, p)) {
 858                 log_debug("Got our own packet looped back, ignoring.");
 859                 return;
 860         }
 861
 862         queries_by_packet = l ? &l->queries_by_packet : &m->stub_queries_by_packet;
 863         existing = hashmap_get(*queries_by_packet, p);
 864         if (existing && dns_packet_equal(existing->request_packet, p)) {
 865                 log_debug("Got repeat packet from client, ignoring.");
 866                 return;
 867         }
 868
 869         r = dns_packet_extract(p);
 870         if (r < 0) {
 871                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 872                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_FORMERR, false);
 873                 return;
 874         }
 875
 876         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 877                 log_debug("Got EDNS OPT field with unsupported version number.");
 878                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false);
 879                 return;
 880         }
 881
 882         if (dns_type_is_obsolete(p->question->keys[0]->type)) {
 883                 log_debug("Got message with obsolete key type, refusing.");
 884                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 885                 return;
 886         }
 887
 888         if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
 889                 log_debug("Got request for zone transfer, refusing.");
 890                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 891                 return;
 892         }
 893
 894         if (!DNS_PACKET_RD(p))  {
 895                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 896                 log_debug("Got request with recursion disabled, refusing.");
 897                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 898                 return;
 899         }
 900
 901         r = hashmap_ensure_allocated(queries_by_packet, &stub_packet_hash_ops);
 902         if (r < 0) {
 903                 log_oom();
 904                 return;
 905         }
 906
 907         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
 908                 log_debug("Got request with DNSSEC checking disabled, enabling bypass logic.");
 909
 910                 r = dns_query_new(m, &q, NULL, NULL, p, 0,
 911                                   SD_RESOLVED_PROTOCOLS_ALL|
 912                                   SD_RESOLVED_NO_CNAME|
 913                                   SD_RESOLVED_NO_SEARCH|
 914                                   SD_RESOLVED_NO_VALIDATE|
 915                                   SD_RESOLVED_REQUIRE_PRIMARY|
 916                                   SD_RESOLVED_CLAMP_TTL);
 917         } else
 918                 r = dns_query_new(m, &q, p->question, p->question, NULL, 0,
 919                                   SD_RESOLVED_PROTOCOLS_ALL|
 920                                   SD_RESOLVED_NO_SEARCH|
 921                                   (DNS_PACKET_DO(p) ? SD_RESOLVED_REQUIRE_PRIMARY : 0)|
 922                                   SD_RESOLVED_CLAMP_TTL);
 923         if (r < 0) {
 924                 log_error_errno(r, "Failed to generate query object: %m");
 925                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 926                 return;
 927         }
 928
 929         q->request_packet = dns_packet_ref(p);
 930         q->request_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 931         q->stub_listener_extra = l;
 932         q->complete = dns_stub_query_complete;
 933
 934         if (s) {
 935                 /* Remember which queries belong to this stream, so that we can cancel them when the stream
 936                  * is disconnected early */
 937
 938                 r = set_ensure_put(&s->queries, NULL, q);
 939                 if (r < 0) {
 940                         log_oom();
 941                         return;
 942                 }
 943                 assert(r > 0);
 944         }
 945
 946         /* Add the query to the hash table we use to determine repeat packets now. We don't care about
 947          * failures here, since in the worst case we'll not recognize duplicate incoming requests, which
 948          * isn't particularly bad. */
 949         (void) hashmap_put(*queries_by_packet, q->request_packet, q);
 950
 951         r = dns_query_go(q);
 952         if (r < 0) {
 953                 log_error_errno(r, "Failed to start query: %m");
 954                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 955                 return;
 956         }
 957
 958         log_debug("Processing query...");
 959         TAKE_PTR(q);
 960 }
 961
 962 static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
 963         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 964         int r;
 965
 966         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
 967         if (r <= 0)
 968                 return r;
 969
 970         if (dns_packet_validate_query(p) > 0) {
 971                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
 972
 973                 dns_stub_process_query(m, l, NULL, p);
 974         } else
 975                 log_debug("Invalid DNS stub UDP packet, ignoring.");
 976
 977         return 0;
 978 }
 979
 980 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 981         return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL);
 982 }
 983
 984 static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 985         DnsStubListenerExtra *l = userdata;
 986
 987         assert(l);
 988
 989         return on_dns_stub_packet_internal(s, fd, revents, l->manager, l);
 990 }
 991
 992 static int on_dns_stub_stream_packet(DnsStream *s) {
 993         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 994
 995         assert(s);
 996
 997         p = dns_stream_take_read_packet(s);
 998         assert(p);
 999
1000         if (dns_packet_validate_query(p) > 0) {
1001                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
1002
1003                 dns_stub_process_query(s->manager, s->stub_listener_extra, s, p);
1004         } else
1005                 log_debug("Invalid DNS stub TCP packet, ignoring.");
1006
1007         return 0;
1008 }
1009
1010 static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
1011         DnsStream *stream;
1012         int cfd, r;
1013
1014         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
1015         if (cfd < 0) {
1016                 if (ERRNO_IS_ACCEPT_AGAIN(errno))
1017                         return 0;
1018
1019                 return -errno;
1020         }
1021
1022         r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
1023         if (r < 0) {
1024                 safe_close(cfd);
1025                 return r;
1026         }
1027
1028         stream->stub_listener_extra = l;
1029         stream->on_packet = on_dns_stub_stream_packet;
1030         stream->complete = dns_stub_stream_complete;
1031
1032         /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
1033
1034         return 0;
1035 }
1036
1037 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1038         return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL);
1039 }
1040
1041 static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1042         DnsStubListenerExtra *l = userdata;
1043
1044         assert(l);
1045         return on_dns_stub_stream_internal(s, fd, revents, l->manager, l);
1046 }
1047
1048 static int set_dns_stub_common_socket_options(int fd, int family) {
1049         int r;
1050
1051         assert(fd >= 0);
1052         assert(IN_SET(family, AF_INET, AF_INET6));
1053
1054         r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
1055         if (r < 0)
1056                 return r;
1057
1058         r = socket_set_recvpktinfo(fd, family, true);
1059         if (r < 0)
1060                 return r;
1061
1062         r = socket_set_recvttl(fd, family, true);
1063         if (r < 0)
1064                 return r;
1065
1066         return 0;
1067 }
1068
1069 static int set_dns_stub_common_tcp_socket_options(int fd) {
1070         int r;
1071
1072         assert(fd >= 0);
1073
1074         r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */
1075         if (r < 0)
1076                 log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m");
1077
1078         r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true);
1079         if (r < 0)
1080                 log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m");
1081
1082         return 0;
1083 }
1084
1085 static int manager_dns_stub_fd(Manager *m, int type) {
1086         union sockaddr_union sa = {
1087                 .in.sin_family = AF_INET,
1088                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
1089                 .in.sin_port = htobe16(53),
1090         };
1091         _cleanup_close_ int fd = -1;
1092         int r;
1093
1094         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1095
1096         sd_event_source **event_source = type == SOCK_DGRAM ? &m->dns_stub_udp_event_source : &m->dns_stub_tcp_event_source;
1097         if (*event_source)
1098                 return sd_event_source_get_io_fd(*event_source);
1099
1100         fd = socket(AF_INET, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1101         if (fd < 0)
1102                 return -errno;
1103
1104         r = set_dns_stub_common_socket_options(fd, AF_INET);
1105         if (r < 0)
1106                 return r;
1107
1108         if (type == SOCK_STREAM) {
1109                 r = set_dns_stub_common_tcp_socket_options(fd);
1110                 if (r < 0)
1111                         return r;
1112         }
1113
1114         /* Make sure no traffic from outside the local host can leak to onto this socket */
1115         r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX);
1116         if (r < 0)
1117                 return r;
1118
1119         r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, 1);
1120         if (r < 0)
1121                 return r;
1122
1123         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
1124                 return -errno;
1125
1126         if (type == SOCK_STREAM &&
1127             listen(fd, SOMAXCONN) < 0)
1128                 return -errno;
1129
1130         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1131                             type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream,
1132                             m);
1133         if (r < 0)
1134                 return r;
1135
1136         r = sd_event_source_set_io_fd_own(*event_source, true);
1137         if (r < 0)
1138                 return r;
1139
1140         (void) sd_event_source_set_description(*event_source,
1141                                                type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp");
1142
1143         return TAKE_FD(fd);
1144 }
1145
1146 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) {
1147         _cleanup_free_ char *pretty = NULL;
1148         _cleanup_close_ int fd = -1;
1149         union sockaddr_union sa;
1150         int r;
1151
1152         assert(m);
1153         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1154
1155         if (!l)
1156                 return manager_dns_stub_fd(m, type);
1157
1158         sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source;
1159         if (*event_source)
1160                 return sd_event_source_get_io_fd(*event_source);
1161
1162         if (l->family == AF_INET)
1163                 sa = (union sockaddr_union) {
1164                         .in.sin_family = l->family,
1165                         .in.sin_port = htobe16(dns_stub_listener_extra_port(l)),
1166                         .in.sin_addr = l->address.in,
1167                 };
1168         else
1169                 sa = (union sockaddr_union) {
1170                         .in6.sin6_family = l->family,
1171                         .in6.sin6_port = htobe16(dns_stub_listener_extra_port(l)),
1172                         .in6.sin6_addr = l->address.in6,
1173                 };
1174
1175         fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1176         if (fd < 0) {
1177                 r = -errno;
1178                 goto fail;
1179         }
1180
1181         r = set_dns_stub_common_socket_options(fd, l->family);
1182         if (r < 0)
1183                 goto fail;
1184
1185         if (type == SOCK_STREAM) {
1186                 r = set_dns_stub_common_tcp_socket_options(fd);
1187                 if (r < 0)
1188                         goto fail;
1189         }
1190
1191         /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case
1192          * people may want ttl > 1. */
1193
1194         r = socket_set_freebind(fd, l->family, true);
1195         if (r < 0)
1196                 goto fail;
1197
1198         if (type == SOCK_DGRAM) {
1199                 r = socket_disable_pmtud(fd, l->family);
1200                 if (r < 0)
1201                         log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m");
1202
1203                 r = socket_set_recvfragsize(fd, l->family, true);
1204                 if (r < 0)
1205                         log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m");
1206         }
1207
1208         if (bind(fd, &sa.sa, SOCKADDR_LEN(sa)) < 0) {
1209                 r = -errno;
1210                 goto fail;
1211         }
1212
1213         if (type == SOCK_STREAM &&
1214             listen(fd, SOMAXCONN) < 0) {
1215                 r = -errno;
1216                 goto fail;
1217         }
1218
1219         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1220                             type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra,
1221                             l);
1222         if (r < 0)
1223                 goto fail;
1224
1225         r = sd_event_source_set_io_fd_own(*event_source, true);
1226         if (r < 0)
1227                 goto fail;
1228
1229         (void) sd_event_source_set_description(*event_source,
1230                                                type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra");
1231
1232         if (DEBUG_LOGGING) {
1233                 (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1234                 log_debug("Listening on %s socket %s.",
1235                           type == SOCK_DGRAM ? "UDP" : "TCP",
1236                           strnull(pretty));
1237         }
1238
1239         return TAKE_FD(fd);
1240
1241 fail:
1242         assert(r < 0);
1243         (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1244         return log_warning_errno(r,
1245                                  r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" :
1246                                                     "Failed to listen on %s socket %s: %m",
1247                                  type == SOCK_DGRAM ? "UDP" : "TCP",
1248                                  strnull(pretty));
1249 }
1250
1251 int manager_dns_stub_start(Manager *m) {
1252         const char *t = "UDP";
1253         int r = 0;
1254
1255         assert(m);
1256
1257         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
1258                 log_debug("Not creating stub listener.");
1259         else
1260                 log_debug("Creating stub listener using %s.",
1261                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
1262                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
1263                           "UDP/TCP");
1264
1265         if (FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_UDP))
1266                 r = manager_dns_stub_fd(m, SOCK_DGRAM);
1267
1268         if (r >= 0 &&
1269             FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_TCP)) {
1270                 t = "TCP";
1271                 r = manager_dns_stub_fd(m, SOCK_STREAM);
1272         }
1273
1274         if (IN_SET(r, -EADDRINUSE, -EPERM)) {
1275                 log_warning_errno(r,
1276                                   r == -EADDRINUSE ? "Another process is already listening on %s socket 127.0.0.53:53.\n"
1277                                                      "Turning off local DNS stub support." :
1278                                                      "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
1279                                                      "Turning off local DNS stub support.",
1280                                   t);
1281                 manager_dns_stub_stop(m);
1282         } else if (r < 0)
1283                 return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
1284
1285         if (!ordered_set_isempty(m->dns_extra_stub_listeners)) {
1286                 DnsStubListenerExtra *l;
1287
1288                 log_debug("Creating extra stub listeners.");
1289
1290                 ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) {
1291                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP))
1292                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM);
1293                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP))
1294                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM);
1295                 }
1296         }
1297
1298         return 0;
1299 }
1300
1301 void manager_dns_stub_stop(Manager *m) {
1302         assert(m);
1303
1304         m->dns_stub_udp_event_source = sd_event_source_disable_unref(m->dns_stub_udp_event_source);
1305         m->dns_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_stub_tcp_event_source);
1306 }
1307
1308 static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = {
1309         [DNS_STUB_LISTENER_NO]  = "no",
1310         [DNS_STUB_LISTENER_UDP] = "udp",
1311         [DNS_STUB_LISTENER_TCP] = "tcp",
1312         [DNS_STUB_LISTENER_YES] = "yes",
1313 };
1314 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);