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         _cleanup_(dns_resource_key_unrefp) DnsResourceKey *redirected_key = NULL;
 165         unsigned n_cname_redirects = 0;
 166         DnsAnswerItem *item;
 167         int r;
 168
 169         assert(reply);
 170
 171         /* Copies all RRs from 'answer' into 'reply', if they match 'question'. There might be direct and
 172          * indirect matches (i.e. via CNAME/DNAME). If they have an indirect one, remember where we need to
 173          * go, and restart the loop */
 174
 175         for (;;) {
 176                 _cleanup_(dns_resource_key_unrefp) DnsResourceKey *next_redirected_key = NULL;
 177
 178                 DNS_ANSWER_FOREACH_ITEM(item, answer) {
 179                         DnsResourceKey *k = NULL;
 180
 181                         if (redirected_key) {
 182                                 /* There was a redirect in this packet, let's collect all matching RRs for the redirect */
 183                                 r = dns_resource_key_match_rr(redirected_key, item->rr, NULL);
 184                                 if (r < 0)
 185                                         return r;
 186
 187                                 k = redirected_key;
 188                         } else if (question) {
 189                                 /* We have a question, let's see if this RR matches it */
 190                                 r = dns_question_matches_rr(question, item->rr, NULL);
 191                                 if (r < 0)
 192                                         return r;
 193
 194                                 k = question->keys[0];
 195                         } else
 196                                 r = 1; /* No question, everything matches */
 197
 198                         if (r == 0) {
 199                                 _cleanup_free_ char *target = NULL;
 200
 201                                 /* OK, so the RR doesn't directly match. Let's see if the RR is a matching
 202                                  * CNAME or DNAME */
 203
 204                                 assert(k);
 205
 206                                 r = dns_resource_record_get_cname_target(k, item->rr, &target);
 207                                 if (r == -EUNATCH)
 208                                         continue; /* Not a CNAME/DNAME or doesn't match */
 209                                 if (r < 0)
 210                                         return r;
 211
 212                                 /* Oh, wow, this is a redirect. Let's remember where this points, and store
 213                                  * it in 'next_redirected_key'. Once we finished iterating through the rest
 214                                  * of the RR's we'll start again, with the redirected RR key. */
 215
 216                                 n_cname_redirects++;
 217                                 if (n_cname_redirects > CNAME_REDIRECT_MAX) /* don't loop forever */
 218                                         return -ELOOP;
 219
 220                                 dns_resource_key_unref(next_redirected_key);
 221
 222                                 /* There can only be one CNAME per name, hence no point in storing more than one here */
 223                                 next_redirected_key = dns_resource_key_new(k->class, k->type, target);
 224                                 if (!next_redirected_key)
 225                                         return -ENOMEM;
 226                         }
 227
 228                         /* Mask the section info, we want the primary answers to always go without section info, so
 229                          * that it is added to the answer section when we synthesize a reply. */
 230
 231                         r = reply_add_with_rrsig(
 232                                         reply,
 233                                         item->rr,
 234                                         item->ifindex,
 235                                         item->flags & ~DNS_ANSWER_MASK_SECTIONS,
 236                                         item->rrsig,
 237                                         with_rrsig);
 238                         if (r < 0)
 239                                 return r;
 240                 }
 241
 242                 if (!next_redirected_key)
 243                         break;
 244
 245                 dns_resource_key_unref(redirected_key);
 246                 redirected_key = TAKE_PTR(next_redirected_key);
 247         }
 248
 249         return 0;
 250 }
 251
 252 static int dns_stub_collect_answer_by_section(
 253                 DnsAnswer **reply,
 254                 DnsAnswer *answer,
 255                 DnsAnswerFlags section,
 256                 DnsAnswer *exclude1,
 257                 DnsAnswer *exclude2,
 258                 bool with_dnssec) { /* Include DNSSEC RRs. RRSIG, NSEC, … */
 259
 260         DnsAnswerItem *item;
 261         int r;
 262
 263         assert(reply);
 264
 265         /* Copies all RRs from 'answer' into 'reply', if they originate from the specified section. Also,
 266          * avoid any RRs listed in 'exclude'. */
 267
 268         DNS_ANSWER_FOREACH_ITEM(item, answer) {
 269
 270                 if (dns_answer_contains(exclude1, item->rr) ||
 271                     dns_answer_contains(exclude2, item->rr))
 272                         continue;
 273
 274                 if (!with_dnssec &&
 275                     dns_type_is_dnssec(item->rr->key->type))
 276                         continue;
 277
 278                 if (((item->flags ^ section) & (DNS_ANSWER_SECTION_ANSWER|DNS_ANSWER_SECTION_AUTHORITY|DNS_ANSWER_SECTION_ADDITIONAL)) != 0)
 279                         continue;
 280
 281                 r = reply_add_with_rrsig(
 282                                 reply,
 283                                 item->rr,
 284                                 item->ifindex,
 285                                 item->flags,
 286                                 item->rrsig,
 287                                 with_dnssec);
 288                 if (r < 0)
 289                         return r;
 290         }
 291
 292         return 0;
 293 }
 294
 295 static int dns_stub_assign_sections(
 296                 DnsQuery *q,
 297                 DnsQuestion *question,
 298                 bool edns0_do) {
 299
 300         int r;
 301
 302         assert(q);
 303         assert(question);
 304
 305         /* Let's assign the 'answer' RRs we collected to their respective sections in the reply datagram. We
 306          * try to reproduce a section assignment similar to what the upstream DNS server responded to us. We
 307          * use the DNS_ANSWER_SECTION_xyz flags to match things up, which is where the original upstream's
 308          * packet section assignment is stored in the DnsAnswer object. Not all RRs in the 'answer' objects
 309          * come with section information though (for example, because they were synthesized locally, and not
 310          * from a DNS packet). To deal with that we extend the assignment logic a bit: anything from the
 311          * 'answer' object that directly matches the original question is always put in the ANSWER section,
 312          * regardless if it carries section info, or what that section info says. Then, anything from the
 313          * 'answer' objects that is from the ANSWER or AUTHORITY sections, and wasn't already added to the
 314          * ANSWER section is placed in the AUTHORITY section. Everything else from either object is added to
 315          * the ADDITIONAL section. */
 316
 317         /* Include all RRs that directly answer the question in the answer section */
 318         r = dns_stub_collect_answer_by_question(
 319                         &q->reply_answer,
 320                         q->answer,
 321                         question,
 322                         edns0_do);
 323         if (r < 0)
 324                 return r;
 325
 326         /* Include all RRs that originate from the answer or authority sections, and aren't listed in the
 327          * answer section, in the authority section */
 328         r = dns_stub_collect_answer_by_section(
 329                         &q->reply_authoritative,
 330                         q->answer,
 331                         DNS_ANSWER_SECTION_ANSWER,
 332                         q->reply_answer, NULL,
 333                         edns0_do);
 334         if (r < 0)
 335                 return r;
 336         r = dns_stub_collect_answer_by_section(
 337                         &q->reply_authoritative,
 338                         q->answer,
 339                         DNS_ANSWER_SECTION_AUTHORITY,
 340                         q->reply_answer, NULL,
 341                         edns0_do);
 342         if (r < 0)
 343                 return r;
 344
 345         /* Include all RRs that originate from the additional sections in the additional section (except if
 346          * already listed in the other two sections). Also add all RRs with no section marking. */
 347         r = dns_stub_collect_answer_by_section(
 348                         &q->reply_additional,
 349                         q->answer,
 350                         DNS_ANSWER_SECTION_ADDITIONAL,
 351                         q->reply_answer, q->reply_authoritative,
 352                         edns0_do);
 353         if (r < 0)
 354                 return r;
 355         r = dns_stub_collect_answer_by_section(
 356                         &q->reply_additional,
 357                         q->answer,
 358                         0,
 359                         q->reply_answer, q->reply_authoritative,
 360                         edns0_do);
 361         if (r < 0)
 362                 return r;
 363
 364         return 0;
 365 }
 366
 367 static int dns_stub_make_reply_packet(
 368                 DnsPacket **ret,
 369                 size_t max_size,
 370                 DnsQuestion *q,
 371                 bool *ret_truncated) {
 372
 373         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 374         bool tc = false;
 375         int r;
 376
 377         assert(ret);
 378
 379         r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0, max_size);
 380         if (r < 0)
 381                 return r;
 382
 383         r = dns_packet_append_question(p, q);
 384         if (r == -EMSGSIZE)
 385                 tc = true;
 386         else if (r < 0)
 387                 return r;
 388
 389         if (ret_truncated)
 390                 *ret_truncated = tc;
 391         else if (tc)
 392                 return -EMSGSIZE;
 393
 394         DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
 395
 396         *ret = TAKE_PTR(p);
 397         return 0;
 398 }
 399
 400 static int dns_stub_add_reply_packet_body(
 401                 DnsPacket *p,
 402                 DnsAnswer *answer,
 403                 DnsAnswer *authoritative,
 404                 DnsAnswer *additional,
 405                 bool edns0_do, /* Client expects DNSSEC RRs? */
 406                 bool *truncated) {
 407
 408         unsigned n_answer = 0, n_authoritative = 0, n_additional = 0;
 409         bool tc = false;
 410         int r;
 411
 412         assert(p);
 413
 414         /* Add the three sections to the packet. If the answer section doesn't fit we'll signal that as
 415          * truncation. If the authoritative section doesn't fit and we are in DNSSEC mode, also signal
 416          * truncation. In all other cases where things don't fit don't signal truncation, as for those cases
 417          * the dropped RRs should not be essential. */
 418
 419         r = dns_packet_append_answer(p, answer, &n_answer);
 420         if (r == -EMSGSIZE)
 421                 tc = true;
 422         else if (r < 0)
 423                 return r;
 424         else {
 425                 r = dns_packet_append_answer(p, authoritative, &n_authoritative);
 426                 if (r == -EMSGSIZE) {
 427                         if (edns0_do)
 428                                 tc = true;
 429                 } else if (r < 0)
 430                         return r;
 431                 else {
 432                         r = dns_packet_append_answer(p, additional, &n_additional);
 433                         if (r < 0 && r != -EMSGSIZE)
 434                                 return r;
 435                 }
 436         }
 437
 438         if (tc) {
 439                 if (!truncated)
 440                         return -EMSGSIZE;
 441
 442                 *truncated = true;
 443         }
 444
 445         DNS_PACKET_HEADER(p)->ancount = htobe16(n_answer);
 446         DNS_PACKET_HEADER(p)->nscount = htobe16(n_authoritative);
 447         DNS_PACKET_HEADER(p)->arcount = htobe16(n_additional);
 448         return 0;
 449 }
 450
 451 static const char *nsid_string(void) {
 452         static char buffer[SD_ID128_STRING_MAX + STRLEN(".resolved.systemd.io")] = "";
 453         sd_id128_t id;
 454         int r;
 455
 456         /* Let's generate a string that we can use as RFC5001 NSID identifier. The string shall identify us
 457          * as systemd-resolved, and return a different string for each resolved instance without leaking host
 458          * identity. Hence let's use a fixed suffix that identifies resolved, and a prefix generated from the
 459          * machine ID but from which the machine ID cannot be determined.
 460          *
 461          * Clients can use this to determine whether an answer is originating locally or is proxied from
 462          * upstream. */
 463
 464         if (!isempty(buffer))
 465                 return buffer;
 466
 467         r = sd_id128_get_machine_app_specific(
 468                         SD_ID128_MAKE(ed,d3,12,5d,16,b9,41,f9,a1,49,5f,ab,15,62,ab,27),
 469                         &id);
 470         if (r < 0) {
 471                 log_debug_errno(r, "Failed to determine machine ID, ignoring: %m");
 472                 return NULL;
 473         }
 474
 475         xsprintf(buffer, SD_ID128_FORMAT_STR ".resolved.systemd.io", SD_ID128_FORMAT_VAL(id));
 476         return buffer;
 477 }
 478
 479 static int dns_stub_finish_reply_packet(
 480                 DnsPacket *p,
 481                 uint16_t id,
 482                 int rcode,
 483                 bool tc,        /* set the Truncated bit? */
 484                 bool aa,        /* set the Authoritative Answer bit? */
 485                 bool add_opt,   /* add an OPT RR to this packet? */
 486                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
 487                 bool ad,        /* set the DNSSEC authenticated data bit? */
 488                 bool cd,        /* set the DNSSEC checking disabled bit? */
 489                 uint16_t max_udp_size, /* The maximum UDP datagram size to advertise to clients */
 490                 bool nsid) {    /* whether to add NSID */
 491
 492         int r;
 493
 494         assert(p);
 495
 496         if (add_opt) {
 497                 r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, nsid ? nsid_string() : NULL, rcode, NULL);
 498                 if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */
 499                         tc = true;
 500                 else if (r < 0)
 501                         return r;
 502         } else {
 503                 /* If the client can't to EDNS0, don't do DO either */
 504                 edns0_do = false;
 505
 506                 /* If we don't do EDNS, clamp the rcode to 4 bit */
 507                 if (rcode > 0xF)
 508                         rcode = DNS_RCODE_SERVFAIL;
 509         }
 510
 511         /* Don't set the CD bit unless DO is on, too */
 512         if (!edns0_do)
 513                 cd = false;
 514
 515         /* Note that we allow the AD bit to be set even if client didn't signal DO, as per RFC 6840, section
 516          * 5.7 */
 517
 518         DNS_PACKET_HEADER(p)->id = id;
 519
 520         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 521                                                               1  /* qr */,
 522                                                               0  /* opcode */,
 523                                                               aa /* aa */,
 524                                                               tc /* tc */,
 525                                                               1  /* rd */,
 526                                                               1  /* ra */,
 527                                                               ad /* ad */,
 528                                                               cd /* cd */,
 529                                                               rcode));
 530
 531         return 0;
 532 }
 533
 534 static int dns_stub_send(
 535                 Manager *m,
 536                 DnsStubListenerExtra *l,
 537                 DnsStream *s,
 538                 DnsPacket *p,
 539                 DnsPacket *reply) {
 540
 541         int r;
 542
 543         assert(m);
 544         assert(p);
 545         assert(reply);
 546
 547         if (s)
 548                 r = dns_stream_write_packet(s, reply);
 549         else
 550                 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
 551                  * is because otherwise the kernel will choose it automatically based on the routing table and will
 552                  * thus pick 127.0.0.1 rather than 127.0.0.53. */
 553                 r = manager_send(m,
 554                                  manager_dns_stub_fd_extra(m, l, SOCK_DGRAM),
 555                                  l ? p->ifindex : LOOPBACK_IFINDEX, /* force loopback iface if this is the main listener stub */
 556                                  p->family, &p->sender, p->sender_port, &p->destination,
 557                                  reply);
 558         if (r < 0)
 559                 return log_debug_errno(r, "Failed to send reply packet: %m");
 560
 561         return 0;
 562 }
 563
 564 static int dns_stub_reply_with_edns0_do(DnsQuery *q) {
 565          assert(q);
 566
 567         /* Reply with DNSSEC DO set? Only if client supports it; and we did any DNSSEC verification
 568          * ourselves, or consider the data fully authenticated because we generated it locally, or the client
 569          * set cd */
 570
 571          return DNS_PACKET_DO(q->request_packet) &&
 572                  (q->answer_dnssec_result >= 0 ||        /* we did proper DNSSEC validation … */
 573                   dns_query_fully_authenticated(q) ||    /* … or we considered it authentic otherwise … */
 574                   DNS_PACKET_CD(q->request_packet));     /* … or client set CD */
 575 }
 576
 577 static void dns_stub_suppress_duplicate_section_rrs(DnsQuery *q) {
 578         /* If we follow a CNAME/DNAME chain we might end up populating our sections with redundant RRs
 579          * because we built up the sections from multiple reply packets (one from each CNAME/DNAME chain
 580          * element). E.g. it could be that an RR that was included in the first reply's additional section
 581          * ends up being relevant as main answer in a subsequent reply in the chain. Let's clean this up, and
 582          * remove everything in the "higher priority" sections from the "lower priority" sections.
 583          *
 584          * Note that this removal matches by RR keys instead of the full RRs. This is because RRsets should
 585          * always end up in one section fully or not at all, but never be split among sections.
 586          *
 587          * Specifically: we remove ANSWER section RRs from the AUTHORITATIVE and ADDITIONAL sections, as well
 588          * as AUTHORITATIVE section RRs from the ADDITIONAL section. */
 589
 590         dns_answer_remove_by_answer_keys(&q->reply_authoritative, q->reply_answer);
 591         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_answer);
 592         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_authoritative);
 593 }
 594
 595 static int dns_stub_send_reply(
 596                 DnsQuery *q,
 597                 int rcode) {
 598
 599         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 600         bool truncated, edns0_do;
 601         int r;
 602
 603         assert(q);
 604
 605         edns0_do = dns_stub_reply_with_edns0_do(q); /* let's check if we shall reply with EDNS0 DO? */
 606
 607         r = dns_stub_make_reply_packet(
 608                         &reply,
 609                         DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_packet),
 610                         q->request_packet->question,
 611                         &truncated);
 612         if (r < 0)
 613                 return log_debug_errno(r, "Failed to build reply packet: %m");
 614
 615         dns_stub_suppress_duplicate_section_rrs(q);
 616
 617         r = dns_stub_add_reply_packet_body(
 618                         reply,
 619                         q->reply_answer,
 620                         q->reply_authoritative,
 621                         q->reply_additional,
 622                         edns0_do,
 623                         &truncated);
 624         if (r < 0)
 625                 return log_debug_errno(r, "Failed to append reply packet body: %m");
 626
 627         r = dns_stub_finish_reply_packet(
 628                         reply,
 629                         DNS_PACKET_ID(q->request_packet),
 630                         rcode,
 631                         truncated,
 632                         dns_query_fully_synthetic(q),
 633                         !!q->request_packet->opt,
 634                         edns0_do,
 635                         DNS_PACKET_AD(q->request_packet) && dns_query_fully_authenticated(q),
 636                         DNS_PACKET_CD(q->request_packet),
 637                         q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 638                         dns_packet_has_nsid_request(q->request_packet) > 0 && !q->stub_listener_extra);
 639         if (r < 0)
 640                 return log_debug_errno(r, "Failed to build failure packet: %m");
 641
 642         return dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 643 }
 644
 645 static int dns_stub_send_failure(
 646                 Manager *m,
 647                 DnsStubListenerExtra *l,
 648                 DnsStream *s,
 649                 DnsPacket *p,
 650                 int rcode,
 651                 bool authenticated) {
 652
 653         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 654         bool truncated;
 655         int r;
 656
 657         assert(m);
 658         assert(p);
 659
 660         r = dns_stub_make_reply_packet(
 661                         &reply,
 662                         DNS_PACKET_PAYLOAD_SIZE_MAX(p),
 663                         p->question,
 664                         &truncated);
 665         if (r < 0)
 666                 return log_debug_errno(r, "Failed to make failure packet: %m");
 667
 668         r = dns_stub_finish_reply_packet(
 669                         reply,
 670                         DNS_PACKET_ID(p),
 671                         rcode,
 672                         truncated,
 673                         false,
 674                         !!p->opt,
 675                         DNS_PACKET_DO(p),
 676                         DNS_PACKET_AD(p) && authenticated,
 677                         DNS_PACKET_CD(p),
 678                         l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 679                         dns_packet_has_nsid_request(p) > 0 && !l);
 680         if (r < 0)
 681                 return log_debug_errno(r, "Failed to build failure packet: %m");
 682
 683         return dns_stub_send(m, l, s, p, reply);
 684 }
 685
 686 static int dns_stub_patch_bypass_reply_packet(
 687                 DnsPacket **ret,       /* Where to place the patched packet */
 688                 DnsPacket *original,   /* The packet to patch */
 689                 DnsPacket *request) {  /* The packet the patched packet shall look like a reply to */
 690         _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL;
 691         int r;
 692
 693         assert(ret);
 694         assert(original);
 695         assert(request);
 696
 697         r = dns_packet_dup(&c, original);
 698         if (r < 0)
 699                 return r;
 700
 701         /* Extract the packet, so that we know where the OPT field is */
 702         r = dns_packet_extract(c);
 703         if (r < 0)
 704                 return r;
 705
 706         /* Copy over the original client request ID, so that we can make the upstream query look like our own reply. */
 707         DNS_PACKET_HEADER(c)->id = DNS_PACKET_HEADER(request)->id;
 708
 709         /* Patch in our own maximum datagram size, if EDNS0 was on */
 710         r = dns_packet_patch_max_udp_size(c, ADVERTISE_DATAGRAM_SIZE_MAX);
 711         if (r < 0)
 712                 return r;
 713
 714         /* Lower all TTLs by the time passed since we received the datagram. */
 715         if (timestamp_is_set(original->timestamp)) {
 716                 r = dns_packet_patch_ttls(c, original->timestamp);
 717                 if (r < 0)
 718                         return r;
 719         }
 720
 721         /* Our upstream connection might have supported larger DNS requests than our downstream one, hence
 722          * set the TC bit if our reply is larger than what the client supports, and truncate. */
 723         if (c->size > DNS_PACKET_PAYLOAD_SIZE_MAX(request)) {
 724                 log_debug("Artificially truncating stub response, as advertised size of client is smaller than upstream one.");
 725                 dns_packet_truncate(c, DNS_PACKET_PAYLOAD_SIZE_MAX(request));
 726                 DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC);
 727         }
 728
 729         *ret = TAKE_PTR(c);
 730         return 0;
 731 }
 732
 733 static void dns_stub_query_complete(DnsQuery *q) {
 734         int r;
 735
 736         assert(q);
 737         assert(q->request_packet);
 738
 739         if (q->question_bypass) {
 740                 /* This is a bypass reply. If so, let's propagate the upstream packet, if we have it and it
 741                  * is regular DNS. (We can't do this if the upstream packet is LLMNR or mDNS, since the
 742                  * packets are not 100% compatible.) */
 743
 744                 if (q->answer_full_packet &&
 745                     q->answer_full_packet->protocol == DNS_PROTOCOL_DNS) {
 746                         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 747
 748                         r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet);
 749                         if (r < 0)
 750                                 log_debug_errno(r, "Failed to patch bypass reply packet: %m");
 751                         else
 752                                 (void) dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 753
 754                         dns_query_free(q);
 755                         return;
 756                 }
 757         }
 758
 759         /* Take all data from the current reply, and merge it into the three reply sections we are building
 760          * up. We do this before processing CNAME redirects, so that we gradually build up our sections, and
 761          * and keep adding all RRs in the CNAME chain. */
 762         r = dns_stub_assign_sections(
 763                         q,
 764                         q->request_packet->question,
 765                         dns_stub_reply_with_edns0_do(q));
 766         if (r < 0) {
 767                 log_debug_errno(r, "Failed to assign sections: %m");
 768                 dns_query_free(q);
 769                 return;
 770         }
 771
 772         switch (q->state) {
 773
 774         case DNS_TRANSACTION_SUCCESS:
 775                 r = dns_query_process_cname(q);
 776                 if (r == -ELOOP) { /* CNAME loop, let's send what we already have */
 777                         log_debug_errno(r, "Detected CNAME loop, returning what we already have.");
 778                         (void) dns_stub_send_reply(q, q->answer_rcode);
 779                         break;
 780                 }
 781                 if (r < 0) {
 782                         log_debug_errno(r, "Failed to process CNAME: %m");
 783                         break;
 784                 }
 785                 if (r == DNS_QUERY_RESTARTED)
 786                         return;
 787
 788                 _fallthrough_;
 789
 790         case DNS_TRANSACTION_RCODE_FAILURE:
 791                 (void) dns_stub_send_reply(q, q->answer_rcode);
 792                 break;
 793
 794         case DNS_TRANSACTION_NOT_FOUND:
 795                 (void) dns_stub_send_reply(q, DNS_RCODE_NXDOMAIN);
 796                 break;
 797
 798         case DNS_TRANSACTION_TIMEOUT:
 799         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 800                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 801                 break;
 802
 803         case DNS_TRANSACTION_NO_SERVERS:
 804         case DNS_TRANSACTION_INVALID_REPLY:
 805         case DNS_TRANSACTION_ERRNO:
 806         case DNS_TRANSACTION_ABORTED:
 807         case DNS_TRANSACTION_DNSSEC_FAILED:
 808         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 809         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 810         case DNS_TRANSACTION_NETWORK_DOWN:
 811         case DNS_TRANSACTION_NO_SOURCE:
 812         case DNS_TRANSACTION_STUB_LOOP:
 813                 (void) dns_stub_send_reply(q, DNS_RCODE_SERVFAIL);
 814                 break;
 815
 816         case DNS_TRANSACTION_NULL:
 817         case DNS_TRANSACTION_PENDING:
 818         case DNS_TRANSACTION_VALIDATING:
 819         default:
 820                 assert_not_reached("Impossible state");
 821         }
 822
 823         dns_query_free(q);
 824 }
 825
 826 static int dns_stub_stream_complete(DnsStream *s, int error) {
 827         assert(s);
 828
 829         log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");
 830
 831         for (;;) {
 832                 DnsQuery *q;
 833
 834                 q = set_first(s->queries);
 835                 if (!q)
 836                         break;
 837
 838                 dns_query_free(q);
 839         }
 840
 841         /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
 842          * should be kept as long as the client wants to. */
 843         dns_stream_unref(s);
 844         return 0;
 845 }
 846
 847 static void dns_stub_process_query(Manager *m, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) {
 848         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
 849         Hashmap **queries_by_packet;
 850         DnsQuery *existing;
 851         int r;
 852
 853         assert(m);
 854         assert(p);
 855         assert(p->protocol == DNS_PROTOCOL_DNS);
 856
 857         if (!l && /* l == NULL if this is the main stub */
 858             (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 859              in_addr_is_localhost(p->family, &p->destination) <= 0)) {
 860                 log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring.");
 861                 return;
 862         }
 863
 864         if (manager_packet_from_our_transaction(m, p)) {
 865                 log_debug("Got our own packet looped back, ignoring.");
 866                 return;
 867         }
 868
 869         queries_by_packet = l ? &l->queries_by_packet : &m->stub_queries_by_packet;
 870         existing = hashmap_get(*queries_by_packet, p);
 871         if (existing && dns_packet_equal(existing->request_packet, p)) {
 872                 log_debug("Got repeat packet from client, ignoring.");
 873                 return;
 874         }
 875
 876         r = dns_packet_extract(p);
 877         if (r < 0) {
 878                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 879                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_FORMERR, false);
 880                 return;
 881         }
 882
 883         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 884                 log_debug("Got EDNS OPT field with unsupported version number.");
 885                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false);
 886                 return;
 887         }
 888
 889         if (dns_type_is_obsolete(p->question->keys[0]->type)) {
 890                 log_debug("Got message with obsolete key type, refusing.");
 891                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 892                 return;
 893         }
 894
 895         if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
 896                 log_debug("Got request for zone transfer, refusing.");
 897                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 898                 return;
 899         }
 900
 901         if (!DNS_PACKET_RD(p))  {
 902                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 903                 log_debug("Got request with recursion disabled, refusing.");
 904                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 905                 return;
 906         }
 907
 908         r = hashmap_ensure_allocated(queries_by_packet, &stub_packet_hash_ops);
 909         if (r < 0) {
 910                 log_oom();
 911                 return;
 912         }
 913
 914         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
 915                 log_debug("Got request with DNSSEC checking disabled, enabling bypass logic.");
 916
 917                 r = dns_query_new(m, &q, NULL, NULL, p, 0,
 918                                   SD_RESOLVED_PROTOCOLS_ALL|
 919                                   SD_RESOLVED_NO_CNAME|
 920                                   SD_RESOLVED_NO_SEARCH|
 921                                   SD_RESOLVED_NO_VALIDATE|
 922                                   SD_RESOLVED_REQUIRE_PRIMARY|
 923                                   SD_RESOLVED_CLAMP_TTL);
 924         } else
 925                 r = dns_query_new(m, &q, p->question, p->question, NULL, 0,
 926                                   SD_RESOLVED_PROTOCOLS_ALL|
 927                                   SD_RESOLVED_NO_SEARCH|
 928                                   (DNS_PACKET_DO(p) ? SD_RESOLVED_REQUIRE_PRIMARY : 0)|
 929                                   SD_RESOLVED_CLAMP_TTL);
 930         if (r < 0) {
 931                 log_error_errno(r, "Failed to generate query object: %m");
 932                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 933                 return;
 934         }
 935
 936         q->request_packet = dns_packet_ref(p);
 937         q->request_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 938         q->stub_listener_extra = l;
 939         q->complete = dns_stub_query_complete;
 940
 941         if (s) {
 942                 /* Remember which queries belong to this stream, so that we can cancel them when the stream
 943                  * is disconnected early */
 944
 945                 r = set_ensure_put(&s->queries, NULL, q);
 946                 if (r < 0) {
 947                         log_oom();
 948                         return;
 949                 }
 950                 assert(r > 0);
 951         }
 952
 953         /* Add the query to the hash table we use to determine repeat packets now. We don't care about
 954          * failures here, since in the worst case we'll not recognize duplicate incoming requests, which
 955          * isn't particularly bad. */
 956         (void) hashmap_put(*queries_by_packet, q->request_packet, q);
 957
 958         r = dns_query_go(q);
 959         if (r < 0) {
 960                 log_error_errno(r, "Failed to start query: %m");
 961                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 962                 return;
 963         }
 964
 965         log_debug("Processing query...");
 966         TAKE_PTR(q);
 967 }
 968
 969 static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
 970         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 971         int r;
 972
 973         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
 974         if (r <= 0)
 975                 return r;
 976
 977         if (dns_packet_validate_query(p) > 0) {
 978                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
 979
 980                 dns_stub_process_query(m, l, NULL, p);
 981         } else
 982                 log_debug("Invalid DNS stub UDP packet, ignoring.");
 983
 984         return 0;
 985 }
 986
 987 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 988         return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL);
 989 }
 990
 991 static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 992         DnsStubListenerExtra *l = userdata;
 993
 994         assert(l);
 995
 996         return on_dns_stub_packet_internal(s, fd, revents, l->manager, l);
 997 }
 998
 999 static int on_dns_stub_stream_packet(DnsStream *s) {
1000         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
1001
1002         assert(s);
1003
1004         p = dns_stream_take_read_packet(s);
1005         assert(p);
1006
1007         if (dns_packet_validate_query(p) > 0) {
1008                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
1009
1010                 dns_stub_process_query(s->manager, s->stub_listener_extra, s, p);
1011         } else
1012                 log_debug("Invalid DNS stub TCP packet, ignoring.");
1013
1014         return 0;
1015 }
1016
1017 static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
1018         DnsStream *stream;
1019         int cfd, r;
1020
1021         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
1022         if (cfd < 0) {
1023                 if (ERRNO_IS_ACCEPT_AGAIN(errno))
1024                         return 0;
1025
1026                 return -errno;
1027         }
1028
1029         r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
1030         if (r < 0) {
1031                 safe_close(cfd);
1032                 return r;
1033         }
1034
1035         stream->stub_listener_extra = l;
1036         stream->on_packet = on_dns_stub_stream_packet;
1037         stream->complete = dns_stub_stream_complete;
1038
1039         /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
1040
1041         return 0;
1042 }
1043
1044 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1045         return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL);
1046 }
1047
1048 static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1049         DnsStubListenerExtra *l = userdata;
1050
1051         assert(l);
1052         return on_dns_stub_stream_internal(s, fd, revents, l->manager, l);
1053 }
1054
1055 static int set_dns_stub_common_socket_options(int fd, int family) {
1056         int r;
1057
1058         assert(fd >= 0);
1059         assert(IN_SET(family, AF_INET, AF_INET6));
1060
1061         r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
1062         if (r < 0)
1063                 return r;
1064
1065         r = socket_set_recvpktinfo(fd, family, true);
1066         if (r < 0)
1067                 return r;
1068
1069         r = socket_set_recvttl(fd, family, true);
1070         if (r < 0)
1071                 return r;
1072
1073         return 0;
1074 }
1075
1076 static int set_dns_stub_common_tcp_socket_options(int fd) {
1077         int r;
1078
1079         assert(fd >= 0);
1080
1081         r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */
1082         if (r < 0)
1083                 log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m");
1084
1085         r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true);
1086         if (r < 0)
1087                 log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m");
1088
1089         return 0;
1090 }
1091
1092 static int manager_dns_stub_fd(Manager *m, int type) {
1093         union sockaddr_union sa = {
1094                 .in.sin_family = AF_INET,
1095                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
1096                 .in.sin_port = htobe16(53),
1097         };
1098         _cleanup_close_ int fd = -1;
1099         int r;
1100
1101         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1102
1103         sd_event_source **event_source = type == SOCK_DGRAM ? &m->dns_stub_udp_event_source : &m->dns_stub_tcp_event_source;
1104         if (*event_source)
1105                 return sd_event_source_get_io_fd(*event_source);
1106
1107         fd = socket(AF_INET, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1108         if (fd < 0)
1109                 return -errno;
1110
1111         r = set_dns_stub_common_socket_options(fd, AF_INET);
1112         if (r < 0)
1113                 return r;
1114
1115         if (type == SOCK_STREAM) {
1116                 r = set_dns_stub_common_tcp_socket_options(fd);
1117                 if (r < 0)
1118                         return r;
1119         }
1120
1121         /* Make sure no traffic from outside the local host can leak to onto this socket */
1122         r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX);
1123         if (r < 0)
1124                 return r;
1125
1126         r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, 1);
1127         if (r < 0)
1128                 return r;
1129
1130         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
1131                 return -errno;
1132
1133         if (type == SOCK_STREAM &&
1134             listen(fd, SOMAXCONN) < 0)
1135                 return -errno;
1136
1137         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1138                             type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream,
1139                             m);
1140         if (r < 0)
1141                 return r;
1142
1143         r = sd_event_source_set_io_fd_own(*event_source, true);
1144         if (r < 0)
1145                 return r;
1146
1147         (void) sd_event_source_set_description(*event_source,
1148                                                type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp");
1149
1150         return TAKE_FD(fd);
1151 }
1152
1153 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) {
1154         _cleanup_free_ char *pretty = NULL;
1155         _cleanup_close_ int fd = -1;
1156         union sockaddr_union sa;
1157         int r;
1158
1159         assert(m);
1160         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1161
1162         if (!l)
1163                 return manager_dns_stub_fd(m, type);
1164
1165         sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source;
1166         if (*event_source)
1167                 return sd_event_source_get_io_fd(*event_source);
1168
1169         if (l->family == AF_INET)
1170                 sa = (union sockaddr_union) {
1171                         .in.sin_family = l->family,
1172                         .in.sin_port = htobe16(dns_stub_listener_extra_port(l)),
1173                         .in.sin_addr = l->address.in,
1174                 };
1175         else
1176                 sa = (union sockaddr_union) {
1177                         .in6.sin6_family = l->family,
1178                         .in6.sin6_port = htobe16(dns_stub_listener_extra_port(l)),
1179                         .in6.sin6_addr = l->address.in6,
1180                 };
1181
1182         fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1183         if (fd < 0) {
1184                 r = -errno;
1185                 goto fail;
1186         }
1187
1188         r = set_dns_stub_common_socket_options(fd, l->family);
1189         if (r < 0)
1190                 goto fail;
1191
1192         if (type == SOCK_STREAM) {
1193                 r = set_dns_stub_common_tcp_socket_options(fd);
1194                 if (r < 0)
1195                         goto fail;
1196         }
1197
1198         /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case
1199          * people may want ttl > 1. */
1200
1201         r = socket_set_freebind(fd, l->family, true);
1202         if (r < 0)
1203                 goto fail;
1204
1205         if (type == SOCK_DGRAM) {
1206                 r = socket_disable_pmtud(fd, l->family);
1207                 if (r < 0)
1208                         log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m");
1209
1210                 r = socket_set_recvfragsize(fd, l->family, true);
1211                 if (r < 0)
1212                         log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m");
1213         }
1214
1215         if (bind(fd, &sa.sa, SOCKADDR_LEN(sa)) < 0) {
1216                 r = -errno;
1217                 goto fail;
1218         }
1219
1220         if (type == SOCK_STREAM &&
1221             listen(fd, SOMAXCONN) < 0) {
1222                 r = -errno;
1223                 goto fail;
1224         }
1225
1226         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1227                             type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra,
1228                             l);
1229         if (r < 0)
1230                 goto fail;
1231
1232         r = sd_event_source_set_io_fd_own(*event_source, true);
1233         if (r < 0)
1234                 goto fail;
1235
1236         (void) sd_event_source_set_description(*event_source,
1237                                                type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra");
1238
1239         if (DEBUG_LOGGING) {
1240                 (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1241                 log_debug("Listening on %s socket %s.",
1242                           type == SOCK_DGRAM ? "UDP" : "TCP",
1243                           strnull(pretty));
1244         }
1245
1246         return TAKE_FD(fd);
1247
1248 fail:
1249         assert(r < 0);
1250         (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1251         return log_warning_errno(r,
1252                                  r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" :
1253                                                     "Failed to listen on %s socket %s: %m",
1254                                  type == SOCK_DGRAM ? "UDP" : "TCP",
1255                                  strnull(pretty));
1256 }
1257
1258 int manager_dns_stub_start(Manager *m) {
1259         const char *t = "UDP";
1260         int r = 0;
1261
1262         assert(m);
1263
1264         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
1265                 log_debug("Not creating stub listener.");
1266         else
1267                 log_debug("Creating stub listener using %s.",
1268                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
1269                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
1270                           "UDP/TCP");
1271
1272         if (FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_UDP))
1273                 r = manager_dns_stub_fd(m, SOCK_DGRAM);
1274
1275         if (r >= 0 &&
1276             FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_TCP)) {
1277                 t = "TCP";
1278                 r = manager_dns_stub_fd(m, SOCK_STREAM);
1279         }
1280
1281         if (IN_SET(r, -EADDRINUSE, -EPERM)) {
1282                 log_warning_errno(r,
1283                                   r == -EADDRINUSE ? "Another process is already listening on %s socket 127.0.0.53:53.\n"
1284                                                      "Turning off local DNS stub support." :
1285                                                      "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
1286                                                      "Turning off local DNS stub support.",
1287                                   t);
1288                 manager_dns_stub_stop(m);
1289         } else if (r < 0)
1290                 return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
1291
1292         if (!ordered_set_isempty(m->dns_extra_stub_listeners)) {
1293                 DnsStubListenerExtra *l;
1294
1295                 log_debug("Creating extra stub listeners.");
1296
1297                 ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) {
1298                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP))
1299                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM);
1300                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP))
1301                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM);
1302                 }
1303         }
1304
1305         return 0;
1306 }
1307
1308 void manager_dns_stub_stop(Manager *m) {
1309         assert(m);
1310
1311         m->dns_stub_udp_event_source = sd_event_source_disable_unref(m->dns_stub_udp_event_source);
1312         m->dns_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_stub_tcp_event_source);
1313 }
1314
1315 static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = {
1316         [DNS_STUB_LISTENER_NO]  = "no",
1317         [DNS_STUB_LISTENER_UDP] = "udp",
1318         [DNS_STUB_LISTENER_TCP] = "tcp",
1319         [DNS_STUB_LISTENER_YES] = "yes",
1320 };
1321 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);