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 "capability-util.h"
   7 #include "errno-util.h"
   8 #include "fd-util.h"
   9 #include "missing_network.h"
  10 #include "missing_socket.h"
  11 #include "resolved-dns-stub.h"
  12 #include "socket-netlink.h"
  13 #include "socket-util.h"
  14 #include "stdio-util.h"
  15 #include "string-table.h"
  16
  17 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
  18  * IP and UDP header sizes */
  19 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
  20
  21 /* On the extra stubs, use a more conservative choice */
  22 #define ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX DNS_PACKET_UNICAST_SIZE_LARGE_MAX
  23
  24 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type);
  25 static int manager_dns_stub_fd(Manager *m, int family, const union in_addr_union *listen_address, int type);
  26
  27 static void dns_stub_listener_extra_hash_func(const DnsStubListenerExtra *a, struct siphash *state) {
  28         assert(a);
  29
  30         siphash24_compress(&a->mode, sizeof(a->mode), state);
  31         siphash24_compress(&a->family, sizeof(a->family), state);
  32         siphash24_compress(&a->address, FAMILY_ADDRESS_SIZE(a->family), state);
  33         siphash24_compress(&a->port, sizeof(a->port), state);
  34 }
  35
  36 static int dns_stub_listener_extra_compare_func(const DnsStubListenerExtra *a, const DnsStubListenerExtra *b) {
  37         int r;
  38
  39         assert(a);
  40         assert(b);
  41
  42         r = CMP(a->mode, b->mode);
  43         if (r != 0)
  44                 return r;
  45
  46         r = CMP(a->family, b->family);
  47         if (r != 0)
  48                 return r;
  49
  50         r = memcmp(&a->address, &b->address, FAMILY_ADDRESS_SIZE(a->family));
  51         if (r != 0)
  52                 return r;
  53
  54         return CMP(a->port, b->port);
  55 }
  56
  57 DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR(
  58                 dns_stub_listener_extra_hash_ops,
  59                 DnsStubListenerExtra,
  60                 dns_stub_listener_extra_hash_func,
  61                 dns_stub_listener_extra_compare_func,
  62                 dns_stub_listener_extra_free);
  63
  64 int dns_stub_listener_extra_new(
  65                 Manager *m,
  66                 DnsStubListenerExtra **ret) {
  67
  68         DnsStubListenerExtra *l;
  69
  70         l = new(DnsStubListenerExtra, 1);
  71         if (!l)
  72                 return -ENOMEM;
  73
  74         *l = (DnsStubListenerExtra) {
  75                 .manager = m,
  76         };
  77
  78         *ret = TAKE_PTR(l);
  79         return 0;
  80 }
  81
  82 DnsStubListenerExtra *dns_stub_listener_extra_free(DnsStubListenerExtra *p) {
  83         if (!p)
  84                 return NULL;
  85
  86         p->udp_event_source = sd_event_source_disable_unref(p->udp_event_source);
  87         p->tcp_event_source = sd_event_source_disable_unref(p->tcp_event_source);
  88
  89         hashmap_free(p->queries_by_packet);
  90
  91         return mfree(p);
  92 }
  93
  94 static void stub_packet_hash_func(const DnsPacket *p, struct siphash *state) {
  95         assert(p);
  96
  97         siphash24_compress(&p->protocol, sizeof(p->protocol), state);
  98         siphash24_compress(&p->family, sizeof(p->family), state);
  99         siphash24_compress(&p->sender, sizeof(p->sender), state);
 100         siphash24_compress(&p->ipproto, sizeof(p->ipproto), state);
 101         siphash24_compress(&p->sender_port, sizeof(p->sender_port), state);
 102         siphash24_compress(DNS_PACKET_HEADER(p), sizeof(DnsPacketHeader), state);
 103
 104         /* We don't bother hashing the full packet here, just the header */
 105 }
 106
 107 static int stub_packet_compare_func(const DnsPacket *x, const DnsPacket *y) {
 108         int r;
 109
 110         r = CMP(x->protocol, y->protocol);
 111         if (r != 0)
 112                 return r;
 113
 114         r = CMP(x->family, y->family);
 115         if (r != 0)
 116                 return r;
 117
 118         r = memcmp(&x->sender, &y->sender, sizeof(x->sender));
 119         if (r != 0)
 120                 return r;
 121
 122         r = CMP(x->ipproto, y->ipproto);
 123         if (r != 0)
 124                 return r;
 125
 126         r = CMP(x->sender_port, y->sender_port);
 127         if (r != 0)
 128                 return r;
 129
 130         return memcmp(DNS_PACKET_HEADER(x), DNS_PACKET_HEADER(y), sizeof(DnsPacketHeader));
 131 }
 132
 133 DEFINE_HASH_OPS(stub_packet_hash_ops, DnsPacket, stub_packet_hash_func, stub_packet_compare_func);
 134
 135 static int reply_add_with_rrsig(
 136                 DnsAnswer **reply,
 137                 DnsResourceRecord *rr,
 138                 int ifindex,
 139                 DnsAnswerFlags flags,
 140                 DnsResourceRecord *rrsig,
 141                 bool with_rrsig) {
 142         int r;
 143
 144         assert(reply);
 145         assert(rr);
 146
 147         r = dns_answer_add_extend(reply, rr, ifindex, flags, rrsig);
 148         if (r < 0)
 149                 return r;
 150
 151         if (with_rrsig && rrsig) {
 152                 r = dns_answer_add_extend(reply, rrsig, ifindex, flags, NULL);
 153                 if (r < 0)
 154                         return r;
 155         }
 156
 157         return 0;
 158 }
 159
 160 static int dns_stub_collect_answer_by_question(
 161                 DnsAnswer **reply,
 162                 DnsAnswer *answer,
 163                 DnsQuestion *question,
 164                 bool with_rrsig) { /* Add RRSIG RR matching each RR */
 165
 166         DnsAnswerItem *item;
 167         int r;
 168
 169         assert(reply);
 170
 171         /* Copies all RRs from 'answer' into 'reply', if they match 'question'. */
 172
 173         DNS_ANSWER_FOREACH_ITEM(item, answer) {
 174
 175                 /* We have a question, let's see if this RR matches it */
 176                 r = dns_question_matches_rr(question, item->rr, NULL);
 177                 if (r < 0)
 178                         return r;
 179                 if (!r) {
 180                         /* Maybe there's a CNAME/DNAME in here? If so, that's an answer too */
 181                         r = dns_question_matches_cname_or_dname(question, item->rr, NULL);
 182                         if (r < 0)
 183                                 return r;
 184                         if (!r)
 185                                 continue;
 186                 }
 187
 188                 /* Mask the section info, we want the primary answers to always go without section
 189                  * info, so that it is added to the answer section when we synthesize a reply. */
 190
 191                 r = reply_add_with_rrsig(
 192                                 reply,
 193                                 item->rr,
 194                                 item->ifindex,
 195                                 item->flags & ~DNS_ANSWER_MASK_SECTIONS,
 196                                 item->rrsig,
 197                                 with_rrsig);
 198                 if (r < 0)
 199                         return r;
 200         }
 201
 202         return 0;
 203 }
 204
 205 static int dns_stub_collect_answer_by_section(
 206                 DnsAnswer **reply,
 207                 DnsAnswer *answer,
 208                 DnsAnswerFlags section,
 209                 DnsAnswer *exclude1,
 210                 DnsAnswer *exclude2,
 211                 bool with_dnssec) { /* Include DNSSEC RRs. RRSIG, NSEC, … */
 212
 213         DnsAnswerItem *item;
 214         int r;
 215
 216         assert(reply);
 217
 218         /* Copies all RRs from 'answer' into 'reply', if they originate from the specified section. Also,
 219          * avoid any RRs listed in 'exclude'. */
 220
 221         DNS_ANSWER_FOREACH_ITEM(item, answer) {
 222
 223                 if (dns_answer_contains(exclude1, item->rr) ||
 224                     dns_answer_contains(exclude2, item->rr))
 225                         continue;
 226
 227                 if (!with_dnssec &&
 228                     dns_type_is_dnssec(item->rr->key->type))
 229                         continue;
 230
 231                 if (((item->flags ^ section) & DNS_ANSWER_MASK_SECTIONS) != 0)
 232                         continue;
 233
 234                 r = reply_add_with_rrsig(
 235                                 reply,
 236                                 item->rr,
 237                                 item->ifindex,
 238                                 item->flags,
 239                                 item->rrsig,
 240                                 with_dnssec);
 241                 if (r < 0)
 242                         return r;
 243         }
 244
 245         return 0;
 246 }
 247
 248 static int dns_stub_assign_sections(
 249                 DnsQuery *q,
 250                 DnsQuestion *question,
 251                 bool edns0_do) {
 252
 253         int r;
 254
 255         assert(q);
 256         assert(question);
 257
 258         /* Let's assign the 'answer' RRs we collected to their respective sections in the reply datagram. We
 259          * try to reproduce a section assignment similar to what the upstream DNS server responded to us. We
 260          * use the DNS_ANSWER_SECTION_xyz flags to match things up, which is where the original upstream's
 261          * packet section assignment is stored in the DnsAnswer object. Not all RRs in the 'answer' objects
 262          * come with section information though (for example, because they were synthesized locally, and not
 263          * from a DNS packet). To deal with that we extend the assignment logic a bit: anything from the
 264          * 'answer' object that directly matches the original question is always put in the ANSWER section,
 265          * regardless if it carries section info, or what that section info says. Then, anything from the
 266          * 'answer' objects that is from the ANSWER or AUTHORITY sections, and wasn't already added to the
 267          * ANSWER section is placed in the AUTHORITY section. Everything else from either object is added to
 268          * the ADDITIONAL section. */
 269
 270         /* Include all RRs that directly answer the question in the answer section */
 271         r = dns_stub_collect_answer_by_question(
 272                         &q->reply_answer,
 273                         q->answer,
 274                         question,
 275                         edns0_do);
 276         if (r < 0)
 277                 return r;
 278
 279         /* Include all RRs that originate from the authority sections, and aren't already listed in the
 280          * answer section, in the authority section */
 281         r = dns_stub_collect_answer_by_section(
 282                         &q->reply_authoritative,
 283                         q->answer,
 284                         DNS_ANSWER_SECTION_AUTHORITY,
 285                         q->reply_answer, NULL,
 286                         edns0_do);
 287         if (r < 0)
 288                 return r;
 289
 290         /* Include all RRs that originate from the answer or additional sections in the additional section
 291          * (except if already listed in the other two sections). Also add all RRs with no section marking. */
 292         r = dns_stub_collect_answer_by_section(
 293                         &q->reply_additional,
 294                         q->answer,
 295                         DNS_ANSWER_SECTION_ANSWER,
 296                         q->reply_answer, q->reply_authoritative,
 297                         edns0_do);
 298         if (r < 0)
 299                 return r;
 300         r = dns_stub_collect_answer_by_section(
 301                         &q->reply_additional,
 302                         q->answer,
 303                         DNS_ANSWER_SECTION_ADDITIONAL,
 304                         q->reply_answer, q->reply_authoritative,
 305                         edns0_do);
 306         if (r < 0)
 307                 return r;
 308         r = dns_stub_collect_answer_by_section(
 309                         &q->reply_additional,
 310                         q->answer,
 311                         0,
 312                         q->reply_answer, q->reply_authoritative,
 313                         edns0_do);
 314         if (r < 0)
 315                 return r;
 316
 317         return 0;
 318 }
 319
 320 static int dns_stub_make_reply_packet(
 321                 DnsPacket **ret,
 322                 size_t max_size,
 323                 DnsQuestion *q,
 324                 bool *ret_truncated) {
 325
 326         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 327         bool tc = false;
 328         int r;
 329
 330         assert(ret);
 331
 332         r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0, max_size);
 333         if (r < 0)
 334                 return r;
 335
 336         r = dns_packet_append_question(p, q);
 337         if (r == -EMSGSIZE)
 338                 tc = true;
 339         else if (r < 0)
 340                 return r;
 341
 342         if (ret_truncated)
 343                 *ret_truncated = tc;
 344         else if (tc)
 345                 return -EMSGSIZE;
 346
 347         DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
 348
 349         *ret = TAKE_PTR(p);
 350         return 0;
 351 }
 352
 353 static int dns_stub_add_reply_packet_body(
 354                 DnsPacket *p,
 355                 DnsAnswer *answer,
 356                 DnsAnswer *authoritative,
 357                 DnsAnswer *additional,
 358                 bool edns0_do, /* Client expects DNSSEC RRs? */
 359                 bool *truncated) {
 360
 361         unsigned n_answer = 0, n_authoritative = 0, n_additional = 0;
 362         bool tc = false;
 363         int r;
 364
 365         assert(p);
 366
 367         /* Add the three sections to the packet. If the answer section doesn't fit we'll signal that as
 368          * truncation. If the authoritative section doesn't fit and we are in DNSSEC mode, also signal
 369          * truncation. In all other cases where things don't fit don't signal truncation, as for those cases
 370          * the dropped RRs should not be essential. */
 371
 372         r = dns_packet_append_answer(p, answer, &n_answer);
 373         if (r == -EMSGSIZE)
 374                 tc = true;
 375         else if (r < 0)
 376                 return r;
 377         else {
 378                 r = dns_packet_append_answer(p, authoritative, &n_authoritative);
 379                 if (r == -EMSGSIZE) {
 380                         if (edns0_do)
 381                                 tc = true;
 382                 } else if (r < 0)
 383                         return r;
 384                 else {
 385                         r = dns_packet_append_answer(p, additional, &n_additional);
 386                         if (r < 0 && r != -EMSGSIZE)
 387                                 return r;
 388                 }
 389         }
 390
 391         if (tc) {
 392                 if (!truncated)
 393                         return -EMSGSIZE;
 394
 395                 *truncated = true;
 396         }
 397
 398         DNS_PACKET_HEADER(p)->ancount = htobe16(n_answer);
 399         DNS_PACKET_HEADER(p)->nscount = htobe16(n_authoritative);
 400         DNS_PACKET_HEADER(p)->arcount = htobe16(n_additional);
 401         return 0;
 402 }
 403
 404 static const char *nsid_string(void) {
 405         static char buffer[SD_ID128_STRING_MAX + STRLEN(".resolved.systemd.io")] = "";
 406         sd_id128_t id;
 407         int r;
 408
 409         /* Let's generate a string that we can use as RFC5001 NSID identifier. The string shall identify us
 410          * as systemd-resolved, and return a different string for each resolved instance without leaking host
 411          * identity. Hence let's use a fixed suffix that identifies resolved, and a prefix generated from the
 412          * machine ID but from which the machine ID cannot be determined.
 413          *
 414          * Clients can use this to determine whether an answer is originating locally or is proxied from
 415          * upstream. */
 416
 417         if (!isempty(buffer))
 418                 return buffer;
 419
 420         r = sd_id128_get_machine_app_specific(
 421                         SD_ID128_MAKE(ed,d3,12,5d,16,b9,41,f9,a1,49,5f,ab,15,62,ab,27),
 422                         &id);
 423         if (r < 0) {
 424                 log_debug_errno(r, "Failed to determine machine ID, ignoring: %m");
 425                 return NULL;
 426         }
 427
 428         xsprintf(buffer, SD_ID128_FORMAT_STR ".resolved.systemd.io", SD_ID128_FORMAT_VAL(id));
 429         return buffer;
 430 }
 431
 432 static int dns_stub_finish_reply_packet(
 433                 DnsPacket *p,
 434                 uint16_t id,
 435                 int rcode,
 436                 bool tc,        /* set the Truncated bit? */
 437                 bool aa,        /* set the Authoritative Answer bit? */
 438                 bool rd,        /* set the Recursion Desired bit? */
 439                 bool add_opt,   /* add an OPT RR to this packet? */
 440                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
 441                 bool ad,        /* set the DNSSEC authenticated data bit? */
 442                 bool cd,        /* set the DNSSEC checking disabled bit? */
 443                 uint16_t max_udp_size, /* The maximum UDP datagram size to advertise to clients */
 444                 bool nsid) {    /* whether to add NSID */
 445
 446         int r;
 447
 448         assert(p);
 449
 450         if (add_opt) {
 451                 r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, nsid ? nsid_string() : NULL, rcode, NULL);
 452                 if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */
 453                         tc = true;
 454                 else if (r < 0)
 455                         return r;
 456         } else {
 457                 /* If the client can't to EDNS0, don't do DO either */
 458                 edns0_do = false;
 459
 460                 /* If we don't do EDNS, clamp the rcode to 4 bit */
 461                 if (rcode > 0xF)
 462                         rcode = DNS_RCODE_SERVFAIL;
 463         }
 464
 465         /* Don't set the CD bit unless DO is on, too */
 466         if (!edns0_do)
 467                 cd = false;
 468
 469         /* Note that we allow the AD bit to be set even if client didn't signal DO, as per RFC 6840, section
 470          * 5.7 */
 471
 472         DNS_PACKET_HEADER(p)->id = id;
 473
 474         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 475                                                               1  /* qr */,
 476                                                               0  /* opcode */,
 477                                                               aa /* aa */,
 478                                                               tc /* tc */,
 479                                                               rd /* rd */,
 480                                                               1  /* ra */,
 481                                                               ad /* ad */,
 482                                                               cd /* cd */,
 483                                                               rcode));
 484
 485         return 0;
 486 }
 487
 488 static bool address_is_proxy(int family, const union in_addr_union *a) {
 489         assert(a);
 490
 491         /* Returns true if the specified address is the DNS "proxy" stub, i.e. where we unconditionally enable bypass mode */
 492
 493         if (family != AF_INET)
 494                 return false;
 495
 496         return be32toh(a->in.s_addr) == INADDR_DNS_PROXY_STUB;
 497 }
 498
 499 static int find_socket_fd(
 500                 Manager *m,
 501                 DnsStubListenerExtra *l,
 502                 int family,
 503                 const union in_addr_union *listen_address,
 504                 int type) {
 505
 506         assert(m);
 507
 508         /* Finds the right socket to use for sending. If we know the extra listener, otherwise go via the
 509          * address to send from */
 510         if (l)
 511                 return manager_dns_stub_fd_extra(m, l, type);
 512
 513         return manager_dns_stub_fd(m, family, listen_address, type);
 514 }
 515
 516 static int dns_stub_send(
 517                 Manager *m,
 518                 DnsStubListenerExtra *l,
 519                 DnsStream *s,
 520                 DnsPacket *p,
 521                 DnsPacket *reply) {
 522
 523         int r;
 524
 525         assert(m);
 526         assert(p);
 527         assert(reply);
 528
 529         if (s)
 530                 r = dns_stream_write_packet(s, reply);
 531         else {
 532                 int fd, ifindex;
 533
 534                 fd = find_socket_fd(m, l, p->family, &p->destination, SOCK_DGRAM);
 535                 if (fd < 0)
 536                         return fd;
 537
 538                 if (address_is_proxy(p->family, &p->destination))
 539                         /* Force loopback iface if this is the loopback proxy stub
 540                          * and ifindex was normalized to 0 by manager_recv(). */
 541                         ifindex = p->ifindex ?: LOOPBACK_IFINDEX;
 542                 else
 543                         /* Force loopback iface if this is the main listener stub. */
 544                         ifindex = l ? p->ifindex : LOOPBACK_IFINDEX;
 545
 546                 /* Note that it is essential here that we explicitly choose the source IP address for this
 547                  * packet. This is because otherwise the kernel will choose it automatically based on the
 548                  * routing table and will thus pick 127.0.0.1 rather than 127.0.0.53/54. */
 549                 r = manager_send(m,
 550                                  fd,
 551                                  ifindex,
 552                                  p->family, &p->sender, p->sender_port, &p->destination,
 553                                  reply);
 554         }
 555         if (r < 0)
 556                 return log_debug_errno(r, "Failed to send reply packet: %m");
 557
 558         return 0;
 559 }
 560
 561 static int dns_stub_reply_with_edns0_do(DnsQuery *q) {
 562          assert(q);
 563
 564         /* Reply with DNSSEC DO set? Only if client supports it; and we did any DNSSEC verification
 565          * ourselves, or consider the data fully authenticated because we generated it locally, or the client
 566          * set cd */
 567
 568          return DNS_PACKET_DO(q->request_packet) &&
 569                  (q->answer_dnssec_result >= 0 ||        /* we did proper DNSSEC validation … */
 570                   dns_query_fully_authenticated(q) ||    /* … or we considered it authentic otherwise … */
 571                   DNS_PACKET_CD(q->request_packet));     /* … or client set CD */
 572 }
 573
 574 static void dns_stub_suppress_duplicate_section_rrs(DnsQuery *q) {
 575         /* If we follow a CNAME/DNAME chain we might end up populating our sections with redundant RRs
 576          * because we built up the sections from multiple reply packets (one from each CNAME/DNAME chain
 577          * element). E.g. it could be that an RR that was included in the first reply's additional section
 578          * ends up being relevant as main answer in a subsequent reply in the chain. Let's clean this up, and
 579          * remove everything in the "higher priority" sections from the "lower priority" sections.
 580          *
 581          * Note that this removal matches by RR keys instead of the full RRs. This is because RRsets should
 582          * always end up in one section fully or not at all, but never be split among sections.
 583          *
 584          * Specifically: we remove ANSWER section RRs from the AUTHORITATIVE and ADDITIONAL sections, as well
 585          * as AUTHORITATIVE section RRs from the ADDITIONAL section. */
 586
 587         dns_answer_remove_by_answer_keys(&q->reply_authoritative, q->reply_answer);
 588         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_answer);
 589         dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_authoritative);
 590 }
 591
 592 static int dns_stub_send_reply(
 593                 DnsQuery *q,
 594                 int rcode) {
 595
 596         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 597         bool truncated, edns0_do;
 598         int r;
 599
 600         assert(q);
 601
 602         edns0_do = dns_stub_reply_with_edns0_do(q); /* let's check if we shall reply with EDNS0 DO? */
 603
 604         r = dns_stub_make_reply_packet(
 605                         &reply,
 606                         DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_packet),
 607                         q->request_packet->question,
 608                         &truncated);
 609         if (r < 0)
 610                 return log_debug_errno(r, "Failed to build reply packet: %m");
 611
 612         dns_stub_suppress_duplicate_section_rrs(q);
 613
 614         r = dns_stub_add_reply_packet_body(
 615                         reply,
 616                         q->reply_answer,
 617                         q->reply_authoritative,
 618                         q->reply_additional,
 619                         edns0_do,
 620                         &truncated);
 621         if (r < 0)
 622                 return log_debug_errno(r, "Failed to append reply packet body: %m");
 623
 624         r = dns_stub_finish_reply_packet(
 625                         reply,
 626                         DNS_PACKET_ID(q->request_packet),
 627                         rcode,
 628                         truncated,
 629                         dns_query_fully_authoritative(q),
 630                         DNS_PACKET_RD(q->request_packet),
 631                         !!q->request_packet->opt,
 632                         edns0_do,
 633                         (DNS_PACKET_AD(q->request_packet) || DNS_PACKET_DO(q->request_packet)) && dns_query_fully_authenticated(q),
 634                         DNS_PACKET_CD(q->request_packet),
 635                         q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 636                         dns_packet_has_nsid_request(q->request_packet) > 0 && !q->stub_listener_extra);
 637         if (r < 0)
 638                 return log_debug_errno(r, "Failed to build failure packet: %m");
 639
 640         return dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply);
 641 }
 642
 643 static int dns_stub_send_failure(
 644                 Manager *m,
 645                 DnsStubListenerExtra *l,
 646                 DnsStream *s,
 647                 DnsPacket *p,
 648                 int rcode,
 649                 bool authenticated) {
 650
 651         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 652         bool truncated;
 653         int r;
 654
 655         assert(m);
 656         assert(p);
 657
 658         r = dns_stub_make_reply_packet(
 659                         &reply,
 660                         DNS_PACKET_PAYLOAD_SIZE_MAX(p),
 661                         p->question,
 662                         &truncated);
 663         if (r < 0)
 664                 return log_debug_errno(r, "Failed to make failure packet: %m");
 665
 666         r = dns_stub_finish_reply_packet(
 667                         reply,
 668                         DNS_PACKET_ID(p),
 669                         rcode,
 670                         truncated,
 671                         false,
 672                         DNS_PACKET_RD(p),
 673                         !!p->opt,
 674                         DNS_PACKET_DO(p),
 675                         (DNS_PACKET_AD(p) || DNS_PACKET_DO(p)) && authenticated,
 676                         DNS_PACKET_CD(p),
 677                         l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX,
 678                         dns_packet_has_nsid_request(p) > 0 && !l);
 679         if (r < 0)
 680                 return log_debug_errno(r, "Failed to build failure packet: %m");
 681
 682         return dns_stub_send(m, l, s, p, reply);
 683 }
 684
 685 static int dns_stub_patch_bypass_reply_packet(
 686                 DnsPacket **ret,       /* Where to place the patched packet */
 687                 DnsPacket *original,   /* The packet to patch */
 688                 DnsPacket *request) {  /* The packet the patched packet shall look like a reply to */
 689         _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL;
 690         int r;
 691
 692         assert(ret);
 693         assert(original);
 694         assert(request);
 695
 696         r = dns_packet_dup(&c, original);
 697         if (r < 0)
 698                 return r;
 699
 700         /* Extract the packet, so that we know where the OPT field is */
 701         r = dns_packet_extract(c);
 702         if (r < 0)
 703                 return r;
 704
 705         /* Copy over the original client request ID, so that we can make the upstream query look like our own reply. */
 706         DNS_PACKET_HEADER(c)->id = DNS_PACKET_HEADER(request)->id;
 707
 708         /* Patch in our own maximum datagram size, if EDNS0 was on */
 709         r = dns_packet_patch_max_udp_size(c, ADVERTISE_DATAGRAM_SIZE_MAX);
 710         if (r < 0)
 711                 return r;
 712
 713         /* Lower all TTLs by the time passed since we received the datagram. */
 714         if (timestamp_is_set(original->timestamp)) {
 715                 r = dns_packet_patch_ttls(c, original->timestamp);
 716                 if (r < 0)
 717                         return r;
 718         }
 719
 720         /* Our upstream connection might have supported larger DNS requests than our downstream one, hence
 721          * set the TC bit if our reply is larger than what the client supports, and truncate. */
 722         if (c->size > DNS_PACKET_PAYLOAD_SIZE_MAX(request)) {
 723                 log_debug("Artificially truncating stub response, as advertised size of client is smaller than upstream one.");
 724                 dns_packet_truncate(c, DNS_PACKET_PAYLOAD_SIZE_MAX(request));
 725                 DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC);
 726         }
 727
 728         *ret = TAKE_PTR(c);
 729         return 0;
 730 }
 731
 732 static void dns_stub_query_complete(DnsQuery *query) {
 733         _cleanup_(dns_query_freep) DnsQuery *q = query;
 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                         return;
 755                 }
 756         }
 757
 758         /* Take all data from the current reply, and merge it into the three reply sections we are building
 759          * up. We do this before processing CNAME redirects, so that we gradually build up our sections, and
 760          * and keep adding all RRs in the CNAME chain. */
 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                 return (void) log_debug_errno(r, "Failed to assign sections: %m");
 767
 768         switch (q->state) {
 769
 770         case DNS_TRANSACTION_SUCCESS: {
 771                 bool first = true;
 772
 773                 for (;;) {
 774                         int cname_result;
 775
 776                         cname_result = dns_query_process_cname_one(q);
 777                         if (cname_result == -ELOOP) { /* CNAME loop, let's send what we already have */
 778                                 log_debug("Detected CNAME loop, returning what we already have.");
 779                                 (void) dns_stub_send_reply(q, q->answer_rcode);
 780                                 break;
 781                         }
 782                         if (cname_result < 0) {
 783                                 log_debug_errno(cname_result, "Failed to process CNAME: %m");
 784                                 break;
 785                         }
 786
 787                         if (cname_result == DNS_QUERY_NOMATCH) {
 788                                 /* This answer doesn't contain any RR that would answer our question
 789                                  * positively, i.e. neither directly nor via CNAME. */
 790
 791                                 if (first) /* We never followed a CNAME and the answer doesn't match our
 792                                             * question at all? Then this is final, the empty answer is the
 793                                             * answer. */
 794                                         break;
 795
 796                                 /* Otherwise, we already followed a CNAME once within this packet, and the
 797                                  * packet doesn't answer our question. In that case let's restart the query,
 798                                  * now with the redirected question. We'll */
 799                                 r = dns_query_go(q);
 800                                 if (r < 0)
 801                                         return (void) log_debug_errno(r, "Failed to restart query: %m");
 802
 803                                 TAKE_PTR(q);
 804                                 return;
 805                         }
 806
 807                         r = dns_stub_assign_sections(
 808                                         q,
 809                                         dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
 810                                         dns_stub_reply_with_edns0_do(q));
 811                         if (r < 0)
 812                                 return (void) log_debug_errno(r, "Failed to assign sections: %m");
 813
 814                         if (cname_result == DNS_QUERY_MATCH) /* A match? Then we are done, let's return what we got */
 815                                 break;
 816
 817                         /* We followed a CNAME. and collected the RRs that answer the redirected question
 818                          * successfully. Let's not try to do this again. */
 819                         assert(cname_result == DNS_QUERY_CNAME);
 820                         first = false;
 821                 }
 822
 823                 _fallthrough_;
 824         }
 825
 826         case DNS_TRANSACTION_RCODE_FAILURE:
 827                 (void) dns_stub_send_reply(q, q->answer_rcode);
 828                 break;
 829
 830         case DNS_TRANSACTION_NOT_FOUND:
 831                 (void) dns_stub_send_reply(q, DNS_RCODE_NXDOMAIN);
 832                 break;
 833
 834         case DNS_TRANSACTION_TIMEOUT:
 835         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 836                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 837                 break;
 838
 839         case DNS_TRANSACTION_NO_SERVERS:
 840         case DNS_TRANSACTION_INVALID_REPLY:
 841         case DNS_TRANSACTION_ERRNO:
 842         case DNS_TRANSACTION_ABORTED:
 843         case DNS_TRANSACTION_DNSSEC_FAILED:
 844         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 845         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 846         case DNS_TRANSACTION_NETWORK_DOWN:
 847         case DNS_TRANSACTION_NO_SOURCE:
 848         case DNS_TRANSACTION_STUB_LOOP:
 849                 (void) dns_stub_send_reply(q, DNS_RCODE_SERVFAIL);
 850                 break;
 851
 852         case DNS_TRANSACTION_NULL:
 853         case DNS_TRANSACTION_PENDING:
 854         case DNS_TRANSACTION_VALIDATING:
 855         default:
 856                 assert_not_reached();
 857         }
 858 }
 859
 860 static int dns_stub_stream_complete(DnsStream *s, int error) {
 861         assert(s);
 862
 863         log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");
 864
 865         for (;;) {
 866                 DnsQuery *q;
 867
 868                 q = set_first(s->queries);
 869                 if (!q)
 870                         break;
 871
 872                 dns_query_free(q);
 873         }
 874
 875         /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
 876          * should be kept as long as the client wants to. */
 877         dns_stream_unref(s);
 878         return 0;
 879 }
 880
 881 static void dns_stub_process_query(Manager *m, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) {
 882         uint64_t protocol_flags = SD_RESOLVED_PROTOCOLS_ALL;
 883         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
 884         Hashmap **queries_by_packet;
 885         DnsQuery *existing;
 886         bool bypass = false;
 887         int r;
 888
 889         assert(m);
 890         assert(p);
 891         assert(p->protocol == DNS_PROTOCOL_DNS);
 892
 893         if (!l && /* l == NULL if this is the main stub */
 894             !address_is_proxy(p->family, &p->destination) && /* don't restrict needlessly for 127.0.0.54 */
 895             (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 896              in_addr_is_localhost(p->family, &p->destination) <= 0)) {
 897                 log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring.");
 898                 return;
 899         }
 900
 901         if (manager_packet_from_our_transaction(m, p)) {
 902                 log_debug("Got our own packet looped back, ignoring.");
 903                 return;
 904         }
 905
 906         queries_by_packet = l ? &l->queries_by_packet : &m->stub_queries_by_packet;
 907         existing = hashmap_get(*queries_by_packet, p);
 908         if (existing && dns_packet_equal(existing->request_packet, p)) {
 909                 log_debug("Got repeat packet from client, ignoring.");
 910                 return;
 911         }
 912
 913         r = dns_packet_extract(p);
 914         if (r < 0) {
 915                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 916                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_FORMERR, false);
 917                 return;
 918         }
 919
 920         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 921                 log_debug("Got EDNS OPT field with unsupported version number.");
 922                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false);
 923                 return;
 924         }
 925
 926         if (dns_type_is_obsolete(dns_question_first_key(p->question)->type)) {
 927                 log_debug("Got message with obsolete key type, refusing.");
 928                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 929                 return;
 930         }
 931
 932         if (dns_type_is_zone_transfer(dns_question_first_key(p->question)->type)) {
 933                 log_debug("Got request for zone transfer, refusing.");
 934                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 935                 return;
 936         }
 937
 938         if (!DNS_PACKET_RD(p))  {
 939                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 940                 log_debug("Got request with recursion disabled, refusing.");
 941                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false);
 942                 return;
 943         }
 944
 945         r = hashmap_ensure_allocated(queries_by_packet, &stub_packet_hash_ops);
 946         if (r < 0) {
 947                 log_oom();
 948                 return;
 949         }
 950
 951         if (address_is_proxy(p->family, &p->destination)) {
 952                 _cleanup_free_ char *dipa = NULL;
 953
 954                 r = in_addr_to_string(p->family, &p->destination, &dipa);
 955                 if (r < 0)
 956                         return (void) log_error_errno(r, "Failed to format destination address: %m");
 957
 958                 log_debug("Got request to DNS proxy address 127.0.0.54, enabling bypass logic.");
 959                 bypass = true;
 960                 protocol_flags = SD_RESOLVED_DNS|SD_RESOLVED_NO_ZONE; /* Turn off mDNS/LLMNR for proxy stub. */
 961         } else if ((DNS_PACKET_DO(p) && DNS_PACKET_CD(p))) {
 962                 log_debug("Got request with DNSSEC checking disabled, enabling bypass logic.");
 963                 bypass = true;
 964         }
 965
 966         if (bypass)
 967                 r = dns_query_new(m, &q, NULL, NULL, p, 0,
 968                                   protocol_flags|
 969                                   SD_RESOLVED_NO_CNAME|
 970                                   SD_RESOLVED_NO_SEARCH|
 971                                   SD_RESOLVED_NO_VALIDATE|
 972                                   SD_RESOLVED_REQUIRE_PRIMARY|
 973                                   SD_RESOLVED_CLAMP_TTL);
 974         else
 975                 r = dns_query_new(m, &q, p->question, p->question, NULL, 0,
 976                                   protocol_flags|
 977                                   SD_RESOLVED_NO_SEARCH|
 978                                   (DNS_PACKET_DO(p) ? SD_RESOLVED_REQUIRE_PRIMARY : 0)|
 979                                   SD_RESOLVED_CLAMP_TTL);
 980         if (r < 0) {
 981                 log_error_errno(r, "Failed to generate query object: %m");
 982                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
 983                 return;
 984         }
 985
 986         q->request_packet = dns_packet_ref(p);
 987         q->request_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 988         q->stub_listener_extra = l;
 989         q->complete = dns_stub_query_complete;
 990
 991         if (s) {
 992                 /* Remember which queries belong to this stream, so that we can cancel them when the stream
 993                  * is disconnected early */
 994
 995                 r = set_ensure_put(&s->queries, NULL, q);
 996                 if (r < 0) {
 997                         log_oom();
 998                         return;
 999                 }
1000                 assert(r > 0);
1001         }
1002
1003         /* Add the query to the hash table we use to determine repeat packets now. We don't care about
1004          * failures here, since in the worst case we'll not recognize duplicate incoming requests, which
1005          * isn't particularly bad. */
1006         (void) hashmap_put(*queries_by_packet, q->request_packet, q);
1007
1008         r = dns_query_go(q);
1009         if (r < 0) {
1010                 log_error_errno(r, "Failed to start query: %m");
1011                 dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
1012                 return;
1013         }
1014
1015         log_debug("Processing query...");
1016         TAKE_PTR(q);
1017 }
1018
1019 static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
1020         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
1021         int r;
1022
1023         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
1024         if (r <= 0)
1025                 return r;
1026
1027         if (dns_packet_validate_query(p) > 0) {
1028                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
1029
1030                 dns_stub_process_query(m, l, NULL, p);
1031         } else
1032                 log_debug("Invalid DNS stub UDP packet, ignoring.");
1033
1034         return 0;
1035 }
1036
1037 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1038         return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL);
1039 }
1040
1041 static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1042         DnsStubListenerExtra *l = ASSERT_PTR(userdata);
1043
1044         return on_dns_stub_packet_internal(s, fd, revents, l->manager, l);
1045 }
1046
1047 static int on_dns_stub_stream_packet(DnsStream *s, DnsPacket *p) {
1048         assert(s);
1049         assert(s->manager);
1050         assert(p);
1051
1052         if (dns_packet_validate_query(p) > 0) {
1053                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
1054
1055                 dns_stub_process_query(s->manager, s->stub_listener_extra, s, p);
1056         } else
1057                 log_debug("Invalid DNS stub TCP packet, ignoring.");
1058
1059         return 0;
1060 }
1061
1062 static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
1063         DnsStream *stream;
1064         int cfd, r;
1065
1066         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
1067         if (cfd < 0) {
1068                 if (ERRNO_IS_ACCEPT_AGAIN(errno))
1069                         return 0;
1070
1071                 return -errno;
1072         }
1073
1074         r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL,
1075                            on_dns_stub_stream_packet, dns_stub_stream_complete, DNS_STREAM_STUB_TIMEOUT_USEC);
1076         if (r < 0) {
1077                 safe_close(cfd);
1078                 return r;
1079         }
1080
1081         stream->stub_listener_extra = l;
1082
1083         /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
1084
1085         return 0;
1086 }
1087
1088 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1089         return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL);
1090 }
1091
1092 static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
1093         DnsStubListenerExtra *l = ASSERT_PTR(userdata);
1094
1095         return on_dns_stub_stream_internal(s, fd, revents, l->manager, l);
1096 }
1097
1098 static int set_dns_stub_common_socket_options(int fd, int family) {
1099         int r;
1100
1101         assert(fd >= 0);
1102         assert(IN_SET(family, AF_INET, AF_INET6));
1103
1104         r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
1105         if (r < 0)
1106                 return r;
1107
1108         r = socket_set_recvpktinfo(fd, family, true);
1109         if (r < 0)
1110                 return r;
1111
1112         r = socket_set_recvttl(fd, family, true);
1113         if (r < 0)
1114                 return r;
1115
1116         return 0;
1117 }
1118
1119 static int set_dns_stub_common_tcp_socket_options(int fd) {
1120         int r;
1121
1122         assert(fd >= 0);
1123
1124         r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */
1125         if (r < 0)
1126                 log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m");
1127
1128         r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true);
1129         if (r < 0)
1130                 log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m");
1131
1132         return 0;
1133 }
1134
1135 static int manager_dns_stub_fd(
1136                 Manager *m,
1137                 int family,
1138                 const union in_addr_union *listen_addr,
1139                 int type) {
1140
1141         sd_event_source **event_source;
1142         _cleanup_close_ int fd = -EBADF;
1143         union sockaddr_union sa;
1144         int r;
1145
1146         assert(m);
1147         assert(listen_addr);
1148
1149         if (type == SOCK_DGRAM)
1150                 event_source = address_is_proxy(family, listen_addr) ? &m->dns_proxy_stub_udp_event_source : &m->dns_stub_udp_event_source;
1151         else if (type == SOCK_STREAM)
1152                 event_source = address_is_proxy(family, listen_addr) ? &m->dns_proxy_stub_tcp_event_source : &m->dns_stub_tcp_event_source;
1153         else
1154                 return -EPROTONOSUPPORT;
1155
1156         if (*event_source)
1157                 return sd_event_source_get_io_fd(*event_source);
1158
1159         fd = socket(family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1160         if (fd < 0)
1161                 return -errno;
1162
1163         r = set_dns_stub_common_socket_options(fd, family);
1164         if (r < 0)
1165                 return r;
1166
1167         if (type == SOCK_STREAM) {
1168                 r = set_dns_stub_common_tcp_socket_options(fd);
1169                 if (r < 0)
1170                         return r;
1171         }
1172
1173         /* Set slightly different socket options for the non-proxy and the proxy binding. The former we want
1174          * to be accessible only from the local host, for the latter it's OK if people use NAT redirects or
1175          * so to redirect external traffic to it. */
1176
1177         if (!address_is_proxy(family, listen_addr)) {
1178                 /* Make sure no traffic from outside the local host can leak to onto this socket */
1179                 r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX);
1180                 if (r < 0)
1181                         return r;
1182
1183                 r = socket_set_ttl(fd, family, 1);
1184                 if (r < 0)
1185                         return r;
1186         } else if (type == SOCK_DGRAM) {
1187                 /* Turn off Path MTU Discovery for UDP, for security reasons. See socket_disable_pmtud() for
1188                  * a longer discussion. (We only do this for sockets that are potentially externally
1189                  * accessible, i.e. the proxy stub one. For the non-proxy one we instead set the TTL to 1,
1190                  * see above, so that packets don't get routed at all.) */
1191                 r = socket_disable_pmtud(fd, family);
1192                 if (r < 0)
1193                         log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m");
1194
1195                 r = socket_set_recvfragsize(fd, family, true);
1196                 if (r < 0)
1197                         log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m");
1198         }
1199
1200         r = sockaddr_set_in_addr(&sa, family, listen_addr, 53);
1201         if (r < 0)
1202                 return r;
1203
1204         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
1205                 return -errno;
1206
1207         if (type == SOCK_STREAM &&
1208             listen(fd, SOMAXCONN_DELUXE) < 0)
1209                 return -errno;
1210
1211         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1212                             type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream,
1213                             m);
1214         if (r < 0)
1215                 return r;
1216
1217         r = sd_event_source_set_io_fd_own(*event_source, true);
1218         if (r < 0)
1219                 return r;
1220
1221         (void) sd_event_source_set_description(*event_source,
1222                                                type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp");
1223
1224         return TAKE_FD(fd);
1225 }
1226
1227 static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) {
1228         _cleanup_free_ char *pretty = NULL;
1229         _cleanup_close_ int fd = -EBADF;
1230         union sockaddr_union sa;
1231         int r;
1232
1233         assert(m);
1234         assert(l);
1235         assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
1236
1237         sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source;
1238         if (*event_source)
1239                 return sd_event_source_get_io_fd(*event_source);
1240
1241         if (!have_effective_cap(CAP_NET_BIND_SERVICE) && dns_stub_listener_extra_port(l) < 1024) {
1242                 log_warning("Missing CAP_NET_BIND_SERVICE capability, not creating extra stub listener on port %hu.",
1243                             dns_stub_listener_extra_port(l));
1244                 return 0;
1245         }
1246
1247         if (l->family == AF_INET)
1248                 sa = (union sockaddr_union) {
1249                         .in.sin_family = l->family,
1250                         .in.sin_port = htobe16(dns_stub_listener_extra_port(l)),
1251                         .in.sin_addr = l->address.in,
1252                 };
1253         else
1254                 sa = (union sockaddr_union) {
1255                         .in6.sin6_family = l->family,
1256                         .in6.sin6_port = htobe16(dns_stub_listener_extra_port(l)),
1257                         .in6.sin6_addr = l->address.in6,
1258                 };
1259
1260         fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
1261         if (fd < 0) {
1262                 r = -errno;
1263                 goto fail;
1264         }
1265
1266         r = set_dns_stub_common_socket_options(fd, l->family);
1267         if (r < 0)
1268                 goto fail;
1269
1270         if (type == SOCK_STREAM) {
1271                 r = set_dns_stub_common_tcp_socket_options(fd);
1272                 if (r < 0)
1273                         goto fail;
1274         }
1275
1276         /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case
1277          * people may want ttl > 1. */
1278
1279         r = socket_set_freebind(fd, l->family, true);
1280         if (r < 0)
1281                 goto fail;
1282
1283         if (type == SOCK_DGRAM) {
1284                 r = socket_disable_pmtud(fd, l->family);
1285                 if (r < 0)
1286                         log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m");
1287
1288                 r = socket_set_recvfragsize(fd, l->family, true);
1289                 if (r < 0)
1290                         log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m");
1291         }
1292
1293         r = RET_NERRNO(bind(fd, &sa.sa, SOCKADDR_LEN(sa)));
1294         if (r < 0)
1295                 goto fail;
1296
1297         if (type == SOCK_STREAM &&
1298             listen(fd, SOMAXCONN_DELUXE) < 0) {
1299                 r = -errno;
1300                 goto fail;
1301         }
1302
1303         r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
1304                             type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra,
1305                             l);
1306         if (r < 0)
1307                 goto fail;
1308
1309         r = sd_event_source_set_io_fd_own(*event_source, true);
1310         if (r < 0)
1311                 goto fail;
1312
1313         (void) sd_event_source_set_description(*event_source,
1314                                                type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra");
1315
1316         if (DEBUG_LOGGING) {
1317                 (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1318                 log_debug("Listening on %s socket %s.",
1319                           type == SOCK_DGRAM ? "UDP" : "TCP",
1320                           strnull(pretty));
1321         }
1322
1323         return TAKE_FD(fd);
1324
1325 fail:
1326         assert(r < 0);
1327         (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
1328         return log_warning_errno(r,
1329                                  r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" :
1330                                                     "Failed to listen on %s socket %s: %m",
1331                                  type == SOCK_DGRAM ? "UDP" : "TCP",
1332                                  strnull(pretty));
1333 }
1334
1335 int manager_dns_stub_start(Manager *m) {
1336         int r;
1337
1338         assert(m);
1339
1340         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
1341                 log_debug("Not creating stub listener.");
1342         else if (!have_effective_cap(CAP_NET_BIND_SERVICE))
1343                 log_warning("Missing CAP_NET_BIND_SERVICE capability, not creating stub listener on port 53.");
1344         else {
1345                 static const struct {
1346                         uint32_t addr;
1347                         int socket_type;
1348                 } stub_sockets[] = {
1349                         { INADDR_DNS_STUB,       SOCK_DGRAM  },
1350                         { INADDR_DNS_STUB,       SOCK_STREAM },
1351                         { INADDR_DNS_PROXY_STUB, SOCK_DGRAM  },
1352                         { INADDR_DNS_PROXY_STUB, SOCK_STREAM },
1353                 };
1354
1355                 log_debug("Creating stub listener using %s.",
1356                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
1357                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
1358                           "UDP/TCP");
1359
1360                 for (size_t i = 0; i < ELEMENTSOF(stub_sockets); i++) {
1361                         union in_addr_union a = {
1362                                 .in.s_addr = htobe32(stub_sockets[i].addr),
1363                         };
1364
1365                         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP && stub_sockets[i].socket_type == SOCK_STREAM)
1366                                 continue;
1367                         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP && stub_sockets[i].socket_type == SOCK_DGRAM)
1368                                 continue;
1369
1370                         r = manager_dns_stub_fd(m, AF_INET, &a, stub_sockets[i].socket_type);
1371                         if (r < 0) {
1372                                 _cleanup_free_ char *busy_socket = NULL;
1373
1374                                 if (asprintf(&busy_socket,
1375                                              "%s socket " IPV4_ADDRESS_FMT_STR ":53",
1376                                              stub_sockets[i].socket_type == SOCK_DGRAM ? "UDP" : "TCP",
1377                                              IPV4_ADDRESS_FMT_VAL(a.in)) < 0)
1378                                         return log_oom();
1379
1380                                 if (IN_SET(r, -EADDRINUSE, -EPERM)) {
1381                                         log_warning_errno(r,
1382                                                           r == -EADDRINUSE ? "Another process is already listening on %s.\n"
1383                                                           "Turning off local DNS stub support." :
1384                                                           "Failed to listen on %s: %m.\n"
1385                                           "Turning off local DNS stub support.",
1386                                                           busy_socket);
1387                                         manager_dns_stub_stop(m);
1388                                         break;
1389                                 }
1390
1391                                 return log_error_errno(r, "Failed to listen on %s: %m", busy_socket);
1392                         }
1393                 }
1394         }
1395
1396         if (!ordered_set_isempty(m->dns_extra_stub_listeners)) {
1397                 DnsStubListenerExtra *l;
1398
1399                 log_debug("Creating extra stub listeners.");
1400
1401                 ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) {
1402                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP))
1403                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM);
1404                         if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP))
1405                                 (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM);
1406                 }
1407         }
1408
1409         return 0;
1410 }
1411
1412 void manager_dns_stub_stop(Manager *m) {
1413         assert(m);
1414
1415         m->dns_stub_udp_event_source = sd_event_source_disable_unref(m->dns_stub_udp_event_source);
1416         m->dns_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_stub_tcp_event_source);
1417         m->dns_proxy_stub_udp_event_source = sd_event_source_disable_unref(m->dns_proxy_stub_udp_event_source);
1418         m->dns_proxy_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_proxy_stub_tcp_event_source);
1419 }
1420
1421 static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = {
1422         [DNS_STUB_LISTENER_NO]  = "no",
1423         [DNS_STUB_LISTENER_UDP] = "udp",
1424         [DNS_STUB_LISTENER_TCP] = "tcp",
1425         [DNS_STUB_LISTENER_YES] = "yes",
1426 };
1427 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);