src/resolve/resolved-dns-stub.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2016 Lennart Poettering
   6 ***/
   7
   8 #include "fd-util.h"
   9 #include "resolved-dns-stub.h"
  10 #include "socket-util.h"
  11
  12 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
  13  * IP and UDP header sizes */
  14 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
  15
  16 static int manager_dns_stub_udp_fd(Manager *m);
  17 static int manager_dns_stub_tcp_fd(Manager *m);
  18
  19 static int dns_stub_make_reply_packet(
  20                 DnsPacket **p,
  21                 size_t max_size,
  22                 DnsQuestion *q,
  23                 DnsAnswer *answer,
  24                 bool *ret_truncated) {
  25
  26         bool truncated = false;
  27         DnsResourceRecord *rr;
  28         unsigned c = 0;
  29         int r;
  30
  31         assert(p);
  32
  33         /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
  34          * roundtrips aren't expensive. */
  35
  36         if (!*p) {
  37                 r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0, max_size);
  38                 if (r < 0)
  39                         return r;
  40
  41                 r = dns_packet_append_question(*p, q);
  42                 if (r < 0)
  43                         return r;
  44
  45                 DNS_PACKET_HEADER(*p)->qdcount = htobe16(dns_question_size(q));
  46         }
  47
  48         DNS_ANSWER_FOREACH(rr, answer) {
  49
  50                 r = dns_question_matches_rr(q, rr, NULL);
  51                 if (r < 0)
  52                         return r;
  53                 if (r > 0)
  54                         goto add;
  55
  56                 r = dns_question_matches_cname_or_dname(q, rr, NULL);
  57                 if (r < 0)
  58                         return r;
  59                 if (r > 0)
  60                         goto add;
  61
  62                 continue;
  63         add:
  64                 r = dns_packet_append_rr(*p, rr, 0, NULL, NULL);
  65                 if (r == -EMSGSIZE) {
  66                         truncated = true;
  67                         break;
  68                 }
  69                 if (r < 0)
  70                         return r;
  71
  72                 c++;
  73         }
  74
  75         if (ret_truncated)
  76                 *ret_truncated = truncated;
  77         else if (truncated)
  78                 return -EMSGSIZE;
  79
  80         DNS_PACKET_HEADER(*p)->ancount = htobe16(be16toh(DNS_PACKET_HEADER(*p)->ancount) + c);
  81
  82         return 0;
  83 }
  84
  85 static int dns_stub_finish_reply_packet(
  86                 DnsPacket *p,
  87                 uint16_t id,
  88                 int rcode,
  89                 bool tc,        /* set the Truncated bit? */
  90                 bool add_opt,   /* add an OPT RR to this packet? */
  91                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
  92                 bool ad) {      /* set the DNSSEC authenticated data bit? */
  93
  94         int r;
  95
  96         assert(p);
  97
  98         if (!add_opt) {
  99                 /* If the client can't to EDNS0, don't do DO either */
 100                 edns0_do = false;
 101
 102                 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
 103                 if (rcode > 0xF)
 104                         rcode = DNS_RCODE_SERVFAIL;
 105         }
 106
 107         /* Don't set the AD bit unless DO is on, too */
 108         if (!edns0_do)
 109                 ad = false;
 110
 111         DNS_PACKET_HEADER(p)->id = id;
 112
 113         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 114                                                               1  /* qr */,
 115                                                               0  /* opcode */,
 116                                                               0  /* aa */,
 117                                                               tc /* tc */,
 118                                                               1  /* rd */,
 119                                                               1  /* ra */,
 120                                                               ad /* ad */,
 121                                                               0  /* cd */,
 122                                                               rcode));
 123
 124         if (add_opt) {
 125                 r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
 126                 if (r < 0)
 127                         return r;
 128         }
 129
 130         return 0;
 131 }
 132
 133 static void dns_stub_detach_stream(DnsStream *s) {
 134         assert(s);
 135
 136         s->complete = NULL;
 137         s->on_packet = NULL;
 138         s->query = NULL;
 139 }
 140
 141 static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
 142         int r;
 143
 144         assert(m);
 145         assert(p);
 146         assert(reply);
 147
 148         if (s)
 149                 r = dns_stream_write_packet(s, reply);
 150         else {
 151                 int fd;
 152
 153                 fd = manager_dns_stub_udp_fd(m);
 154                 if (fd < 0)
 155                         return log_debug_errno(fd, "Failed to get reply socket: %m");
 156
 157                 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
 158                  * is because otherwise the kernel will choose it automatically based on the routing table and will
 159                  * thus pick 127.0.0.1 rather than 127.0.0.53. */
 160
 161                 r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
 162         }
 163         if (r < 0)
 164                 return log_debug_errno(r, "Failed to send reply packet: %m");
 165
 166         return 0;
 167 }
 168
 169 static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode, bool authenticated) {
 170         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 171         int r;
 172
 173         assert(m);
 174         assert(p);
 175
 176         r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL);
 177         if (r < 0)
 178                 return log_debug_errno(r, "Failed to make failure packet: %m");
 179
 180         r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, false, !!p->opt, DNS_PACKET_DO(p), authenticated);
 181         if (r < 0)
 182                 return log_debug_errno(r, "Failed to build failure packet: %m");
 183
 184         return dns_stub_send(m, s, p, reply);
 185 }
 186
 187 static void dns_stub_query_complete(DnsQuery *q) {
 188         int r;
 189
 190         assert(q);
 191         assert(q->request_dns_packet);
 192
 193         switch (q->state) {
 194
 195         case DNS_TRANSACTION_SUCCESS: {
 196                 bool truncated;
 197
 198                 r = dns_stub_make_reply_packet(&q->reply_dns_packet, DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_dns_packet), q->question_idna, q->answer, &truncated);
 199                 if (r < 0) {
 200                         log_debug_errno(r, "Failed to build reply packet: %m");
 201                         break;
 202                 }
 203
 204                 r = dns_query_process_cname(q);
 205                 if (r == -ELOOP) {
 206                         (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
 207                         break;
 208                 }
 209                 if (r < 0) {
 210                         log_debug_errno(r, "Failed to process CNAME: %m");
 211                         break;
 212                 }
 213                 if (r == DNS_QUERY_RESTARTED)
 214                         return;
 215
 216                 r = dns_stub_finish_reply_packet(
 217                                 q->reply_dns_packet,
 218                                 DNS_PACKET_ID(q->request_dns_packet),
 219                                 q->answer_rcode,
 220                                 truncated,
 221                                 !!q->request_dns_packet->opt,
 222                                 DNS_PACKET_DO(q->request_dns_packet),
 223                                 dns_query_fully_authenticated(q));
 224                 if (r < 0) {
 225                         log_debug_errno(r, "Failed to finish reply packet: %m");
 226                         break;
 227                 }
 228
 229                 (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
 230                 break;
 231         }
 232
 233         case DNS_TRANSACTION_RCODE_FAILURE:
 234                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
 235                 break;
 236
 237         case DNS_TRANSACTION_NOT_FOUND:
 238                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
 239                 break;
 240
 241         case DNS_TRANSACTION_TIMEOUT:
 242         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 243                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 244                 break;
 245
 246         case DNS_TRANSACTION_NO_SERVERS:
 247         case DNS_TRANSACTION_INVALID_REPLY:
 248         case DNS_TRANSACTION_ERRNO:
 249         case DNS_TRANSACTION_ABORTED:
 250         case DNS_TRANSACTION_DNSSEC_FAILED:
 251         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 252         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 253         case DNS_TRANSACTION_NETWORK_DOWN:
 254                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
 255                 break;
 256
 257         case DNS_TRANSACTION_NULL:
 258         case DNS_TRANSACTION_PENDING:
 259         case DNS_TRANSACTION_VALIDATING:
 260         default:
 261                 assert_not_reached("Impossible state");
 262         }
 263
 264         /* If there's a packet to write set, let's leave the stream around */
 265         if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
 266
 267                 /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
 268                  * default completion action of the stream will drop the reference. */
 269
 270                 dns_stub_detach_stream(q->request_dns_stream);
 271                 q->request_dns_stream = NULL;
 272         }
 273
 274         dns_query_free(q);
 275 }
 276
 277 static int dns_stub_stream_complete(DnsStream *s, int error) {
 278         assert(s);
 279
 280         log_debug_errno(error, "DNS TCP connection terminated, destroying query: %m");
 281
 282         assert(s->query);
 283         dns_query_free(s->query);
 284
 285         return 0;
 286 }
 287
 288 static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
 289         DnsQuery *q = NULL;
 290         int r;
 291
 292         assert(m);
 293         assert(p);
 294         assert(p->protocol == DNS_PROTOCOL_DNS);
 295
 296         /* Takes ownership of the *s stream object */
 297
 298         if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 299             in_addr_is_localhost(p->family, &p->destination) <= 0) {
 300                 log_error("Got packet on unexpected IP range, refusing.");
 301                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 302                 goto fail;
 303         }
 304
 305         r = dns_packet_extract(p);
 306         if (r < 0) {
 307                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 308                 dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
 309                 goto fail;
 310         }
 311
 312         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 313                 log_debug("Got EDNS OPT field with unsupported version number.");
 314                 dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
 315                 goto fail;
 316         }
 317
 318         if (dns_type_is_obsolete(p->question->keys[0]->type)) {
 319                 log_debug("Got message with obsolete key type, refusing.");
 320                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 321                 goto fail;
 322         }
 323
 324         if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
 325                 log_debug("Got request for zone transfer, refusing.");
 326                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 327                 goto fail;
 328         }
 329
 330         if (!DNS_PACKET_RD(p))  {
 331                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 332                 log_debug("Got request with recursion disabled, refusing.");
 333                 dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
 334                 goto fail;
 335         }
 336
 337         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
 338                 log_debug("Got request with DNSSEC CD bit set, refusing.");
 339                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 340                 goto fail;
 341         }
 342
 343         r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH);
 344         if (r < 0) {
 345                 log_error_errno(r, "Failed to generate query object: %m");
 346                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 347                 goto fail;
 348         }
 349
 350         /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
 351         q->clamp_ttl = true;
 352
 353         q->request_dns_packet = dns_packet_ref(p);
 354         q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 355         q->complete = dns_stub_query_complete;
 356
 357         if (s) {
 358                 s->on_packet = NULL;
 359                 s->complete = dns_stub_stream_complete;
 360                 s->query = q;
 361         }
 362
 363         r = dns_query_go(q);
 364         if (r < 0) {
 365                 log_error_errno(r, "Failed to start query: %m");
 366                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 367                 goto fail;
 368         }
 369
 370         log_debug("Processing query...");
 371         return;
 372
 373 fail:
 374         if (s && DNS_STREAM_QUEUED(s))
 375                 dns_stub_detach_stream(s);
 376
 377         dns_query_free(q);
 378 }
 379
 380 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 381         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 382         Manager *m = userdata;
 383         int r;
 384
 385         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
 386         if (r <= 0)
 387                 return r;
 388
 389         if (dns_packet_validate_query(p) > 0) {
 390                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
 391
 392                 dns_stub_process_query(m, NULL, p);
 393         } else
 394                 log_debug("Invalid DNS stub UDP packet, ignoring.");
 395
 396         return 0;
 397 }
 398
 399 static int manager_dns_stub_udp_fd(Manager *m) {
 400         static const int one = 1;
 401         union sockaddr_union sa = {
 402                 .in.sin_family = AF_INET,
 403                 .in.sin_port = htobe16(53),
 404                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
 405         };
 406         _cleanup_close_ int fd = -1;
 407         int r;
 408
 409         if (m->dns_stub_udp_fd >= 0)
 410                 return m->dns_stub_udp_fd;
 411
 412         fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 413         if (fd < 0)
 414                 return -errno;
 415
 416         if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
 417                 return -errno;
 418
 419         if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
 420                 return -errno;
 421
 422         if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
 423                 return -errno;
 424
 425         /* Make sure no traffic from outside the local host can leak to onto this socket */
 426         if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
 427                 return -errno;
 428
 429         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
 430                 return -errno;
 431
 432         r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
 433         if (r < 0)
 434                 return r;
 435
 436         (void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
 437
 438         return m->dns_stub_udp_fd = TAKE_FD(fd);
 439 }
 440
 441 static int on_dns_stub_stream_packet(DnsStream *s) {
 442         assert(s);
 443         assert(s->read_packet);
 444
 445         if (dns_packet_validate_query(s->read_packet) > 0) {
 446                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 447
 448                 dns_stub_process_query(s->manager, s, s->read_packet);
 449         } else
 450                 log_debug("Invalid DNS stub TCP packet, ignoring.");
 451
 452         /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
 453          * or that didn't happen in which case we want to free the stream */
 454         dns_stream_unref(s);
 455
 456         return 0;
 457 }
 458
 459 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 460         DnsStream *stream;
 461         Manager *m = userdata;
 462         int cfd, r;
 463
 464         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 465         if (cfd < 0) {
 466                 if (IN_SET(errno, EAGAIN, EINTR))
 467                         return 0;
 468
 469                 return -errno;
 470         }
 471
 472         r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd);
 473         if (r < 0) {
 474                 safe_close(cfd);
 475                 return r;
 476         }
 477
 478         stream->on_packet = on_dns_stub_stream_packet;
 479
 480         /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
 481          * of the stream, or by our packet callback, or when the manager is shut down. */
 482
 483         return 0;
 484 }
 485
 486 static int manager_dns_stub_tcp_fd(Manager *m) {
 487         static const int one = 1;
 488         union sockaddr_union sa = {
 489                 .in.sin_family = AF_INET,
 490                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
 491                 .in.sin_port = htobe16(53),
 492         };
 493         _cleanup_close_ int fd = -1;
 494         int r;
 495
 496         if (m->dns_stub_tcp_fd >= 0)
 497                 return m->dns_stub_tcp_fd;
 498
 499         fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 500         if (fd < 0)
 501                 return -errno;
 502
 503         if (setsockopt(fd, IPPROTO_IP, IP_TTL, &one, sizeof one) < 0)
 504                 return -errno;
 505
 506         if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
 507                 return -errno;
 508
 509         if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
 510                 return -errno;
 511
 512         if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
 513                 return -errno;
 514
 515         /* Make sure no traffic from outside the local host can leak to onto this socket */
 516         if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
 517                 return -errno;
 518
 519         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
 520                 return -errno;
 521
 522         if (listen(fd, SOMAXCONN) < 0)
 523                 return -errno;
 524
 525         r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
 526         if (r < 0)
 527                 return r;
 528
 529         (void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
 530
 531         return m->dns_stub_tcp_fd = TAKE_FD(fd);
 532 }
 533
 534 int manager_dns_stub_start(Manager *m) {
 535         const char *t = "UDP";
 536         int r = 0;
 537
 538         assert(m);
 539
 540         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
 541                 log_debug("Not creating stub listener.");
 542         else
 543                 log_debug("Creating stub listener using %s.",
 544                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
 545                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
 546                           "UDP/TCP");
 547
 548         if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
 549                 r = manager_dns_stub_udp_fd(m);
 550
 551         if (r >= 0 &&
 552             IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
 553                 t = "TCP";
 554                 r = manager_dns_stub_tcp_fd(m);
 555         }
 556
 557         if (IN_SET(r, -EADDRINUSE, -EPERM)) {
 558                 if (r == -EADDRINUSE)
 559                         log_warning_errno(r,
 560                                           "Another process is already listening on %s socket 127.0.0.53:53.\n"
 561                                           "Turning off local DNS stub support.", t);
 562                 else
 563                         log_warning_errno(r,
 564                                           "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
 565                                           "Turning off local DNS stub support.", t);
 566                 manager_dns_stub_stop(m);
 567         } else if (r < 0)
 568                 return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
 569
 570         return 0;
 571 }
 572
 573 void manager_dns_stub_stop(Manager *m) {
 574         assert(m);
 575
 576         m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
 577         m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);
 578
 579         m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
 580         m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
 581 }