src/resolve/resolved-dns-stub.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2016 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include "fd-util.h"
  21 #include "resolved-dns-stub.h"
  22 #include "socket-util.h"
  23
  24 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
  25  * IP and UDP header sizes */
  26 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
  27
  28 static int manager_dns_stub_udp_fd(Manager *m);
  29 static int manager_dns_stub_tcp_fd(Manager *m);
  30
  31 static int dns_stub_make_reply_packet(
  32                 DnsPacket **p,
  33                 DnsQuestion *q,
  34                 DnsAnswer *answer) {
  35
  36         DnsResourceRecord *rr;
  37         unsigned c = 0;
  38         int r;
  39
  40         assert(p);
  41
  42         /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
  43          * roundtrips aren't expensive. */
  44
  45         if (!*p) {
  46                 r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0);
  47                 if (r < 0)
  48                         return r;
  49
  50                 r = dns_packet_append_question(*p, q);
  51                 if (r < 0)
  52                         return r;
  53
  54                 DNS_PACKET_HEADER(*p)->qdcount = htobe16(dns_question_size(q));
  55         }
  56
  57         DNS_ANSWER_FOREACH(rr, answer) {
  58
  59                 r = dns_question_matches_rr(q, rr, NULL);
  60                 if (r < 0)
  61                         return r;
  62                 if (r > 0)
  63                         goto add;
  64
  65                 r = dns_question_matches_cname_or_dname(q, rr, NULL);
  66                 if (r < 0)
  67                         return r;
  68                 if (r > 0)
  69                         goto add;
  70
  71                 continue;
  72         add:
  73                 r = dns_packet_append_rr(*p, rr, 0, NULL, NULL);
  74                 if (r < 0)
  75                         return r;
  76
  77                 c++;
  78         }
  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 add_opt,   /* add an OPT RR to this packet? */
  90                 bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
  91                 bool ad) {      /* set the DNSSEC authenticated data bit? */
  92
  93         int r;
  94
  95         assert(p);
  96
  97         if (!add_opt) {
  98                 /* If the client can't to EDNS0, don't do DO either */
  99                 edns0_do = false;
 100
 101                 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
 102                 if (rcode > 0xF)
 103                         rcode = DNS_RCODE_SERVFAIL;
 104         }
 105
 106         /* Don't set the AD bit unless DO is on, too */
 107         if (!edns0_do)
 108                 ad = false;
 109
 110         DNS_PACKET_HEADER(p)->id = id;
 111
 112         DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
 113                                                               1 /* qr */,
 114                                                               0 /* opcode */,
 115                                                               0 /* aa */,
 116                                                               0 /* tc */,
 117                                                               1 /* rd */,
 118                                                               1 /* ra */,
 119                                                               ad /* ad */,
 120                                                               0 /* cd */,
 121                                                               rcode));
 122
 123         if (add_opt) {
 124                 r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
 125                 if (r < 0)
 126                         return r;
 127         }
 128
 129         return 0;
 130 }
 131
 132 static void dns_stub_detach_stream(DnsStream *s) {
 133         assert(s);
 134
 135         s->complete = NULL;
 136         s->on_packet = NULL;
 137         s->query = NULL;
 138 }
 139
 140 static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
 141         int r;
 142
 143         assert(m);
 144         assert(p);
 145         assert(reply);
 146
 147         if (s)
 148                 r = dns_stream_write_packet(s, reply);
 149         else {
 150                 int fd;
 151
 152                 /* Truncate the message to the right size */
 153                 if (reply->size > DNS_PACKET_PAYLOAD_SIZE_MAX(p)) {
 154                         dns_packet_truncate(reply, DNS_PACKET_UNICAST_SIZE_MAX);
 155                         DNS_PACKET_HEADER(reply)->flags = htobe16(be16toh(DNS_PACKET_HEADER(reply)->flags) | DNS_PACKET_FLAG_TC);
 156                 }
 157
 158                 fd = manager_dns_stub_udp_fd(m);
 159                 if (fd < 0)
 160                         return log_debug_errno(fd, "Failed to get reply socket: %m");
 161
 162                 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
 163                  * is because otherwise the kernel will choose it automatically based on the routing table and will
 164                  * thus pick 127.0.0.1 rather than 127.0.0.53. */
 165
 166                 r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
 167         }
 168         if (r < 0)
 169                 return log_debug_errno(r, "Failed to send reply packet: %m");
 170
 171         return 0;
 172 }
 173
 174 static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode, bool authenticated) {
 175         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
 176         int r;
 177
 178         assert(m);
 179         assert(p);
 180
 181         r = dns_stub_make_reply_packet(&reply, p->question, NULL);
 182         if (r < 0)
 183                 return log_debug_errno(r, "Failed to make failure packet: %m");
 184
 185         r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, !!p->opt, DNS_PACKET_DO(p), authenticated);
 186         if (r < 0)
 187                 return log_debug_errno(r, "Failed to build failure packet: %m");
 188
 189         return dns_stub_send(m, s, p, reply);
 190 }
 191
 192 static void dns_stub_query_complete(DnsQuery *q) {
 193         int r;
 194
 195         assert(q);
 196         assert(q->request_dns_packet);
 197
 198         switch (q->state) {
 199
 200         case DNS_TRANSACTION_SUCCESS:
 201
 202                 r = dns_stub_make_reply_packet(&q->reply_dns_packet, q->question_idna, q->answer);
 203                 if (r < 0) {
 204                         log_debug_errno(r, "Failed to build reply packet: %m");
 205                         break;
 206                 }
 207
 208                 r = dns_query_process_cname(q);
 209                 if (r == -ELOOP) {
 210                         (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
 211                         break;
 212                 }
 213                 if (r < 0) {
 214                         log_debug_errno(r, "Failed to process CNAME: %m");
 215                         break;
 216                 }
 217                 if (r == DNS_QUERY_RESTARTED)
 218                         return;
 219
 220                 r = dns_stub_finish_reply_packet(
 221                                 q->reply_dns_packet,
 222                                 DNS_PACKET_ID(q->request_dns_packet),
 223                                 q->answer_rcode,
 224                                 !!q->request_dns_packet->opt,
 225                                 DNS_PACKET_DO(q->request_dns_packet),
 226                                 dns_query_fully_authenticated(q));
 227                 if (r < 0) {
 228                         log_debug_errno(r, "Failed to finish reply packet: %m");
 229                         break;
 230                 }
 231
 232                 (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
 233                 break;
 234
 235         case DNS_TRANSACTION_RCODE_FAILURE:
 236                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
 237                 break;
 238
 239         case DNS_TRANSACTION_NOT_FOUND:
 240                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
 241                 break;
 242
 243         case DNS_TRANSACTION_TIMEOUT:
 244         case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
 245                 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
 246                 break;
 247
 248         case DNS_TRANSACTION_NO_SERVERS:
 249         case DNS_TRANSACTION_INVALID_REPLY:
 250         case DNS_TRANSACTION_ERRNO:
 251         case DNS_TRANSACTION_ABORTED:
 252         case DNS_TRANSACTION_DNSSEC_FAILED:
 253         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
 254         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
 255         case DNS_TRANSACTION_NETWORK_DOWN:
 256                 (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
 257                 break;
 258
 259         case DNS_TRANSACTION_NULL:
 260         case DNS_TRANSACTION_PENDING:
 261         case DNS_TRANSACTION_VALIDATING:
 262         default:
 263                 assert_not_reached("Impossible state");
 264         }
 265
 266         /* If there's a packet to write set, let's leave the stream around */
 267         if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
 268
 269                 /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
 270                  * default completion action of the stream will drop the reference. */
 271
 272                 dns_stub_detach_stream(q->request_dns_stream);
 273                 q->request_dns_stream = NULL;
 274         }
 275
 276         dns_query_free(q);
 277 }
 278
 279 static int dns_stub_stream_complete(DnsStream *s, int error) {
 280         assert(s);
 281
 282         log_debug_errno(error, "DNS TCP connection terminated, destroying query: %m");
 283
 284         assert(s->query);
 285         dns_query_free(s->query);
 286
 287         return 0;
 288 }
 289
 290 static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
 291         DnsQuery *q = NULL;
 292         int r;
 293
 294         assert(m);
 295         assert(p);
 296         assert(p->protocol == DNS_PROTOCOL_DNS);
 297
 298         /* Takes ownership of the *s stream object */
 299
 300         if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
 301             in_addr_is_localhost(p->family, &p->destination) <= 0) {
 302                 log_error("Got packet on unexpected IP range, refusing.");
 303                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 304                 goto fail;
 305         }
 306
 307         r = dns_packet_extract(p);
 308         if (r < 0) {
 309                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
 310                 dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
 311                 goto fail;
 312         }
 313
 314         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
 315                 log_debug("Got EDNS OPT field with unsupported version number.");
 316                 dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
 317                 goto fail;
 318         }
 319
 320         if (dns_type_is_obsolete(p->question->keys[0]->type)) {
 321                 log_debug("Got message with obsolete key type, refusing.");
 322                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 323                 goto fail;
 324         }
 325
 326         if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
 327                 log_debug("Got request for zone transfer, refusing.");
 328                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 329                 goto fail;
 330         }
 331
 332         if (!DNS_PACKET_RD(p))  {
 333                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
 334                 log_debug("Got request with recursion disabled, refusing.");
 335                 dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
 336                 goto fail;
 337         }
 338
 339         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
 340                 log_debug("Got request with DNSSEC CD bit set, refusing.");
 341                 dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
 342                 goto fail;
 343         }
 344
 345         r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH);
 346         if (r < 0) {
 347                 log_error_errno(r, "Failed to generate query object: %m");
 348                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 349                 goto fail;
 350         }
 351
 352         /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
 353         q->clamp_ttl = true;
 354
 355         q->request_dns_packet = dns_packet_ref(p);
 356         q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
 357         q->complete = dns_stub_query_complete;
 358
 359         if (s) {
 360                 s->on_packet = NULL;
 361                 s->complete = dns_stub_stream_complete;
 362                 s->query = q;
 363         }
 364
 365         r = dns_query_go(q);
 366         if (r < 0) {
 367                 log_error_errno(r, "Failed to start query: %m");
 368                 dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
 369                 goto fail;
 370         }
 371
 372         log_debug("Processing query...");
 373         return;
 374
 375 fail:
 376         if (s && DNS_STREAM_QUEUED(s))
 377                 dns_stub_detach_stream(s);
 378
 379         dns_query_free(q);
 380 }
 381
 382 static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 383         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 384         Manager *m = userdata;
 385         int r;
 386
 387         r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
 388         if (r <= 0)
 389                 return r;
 390
 391         if (dns_packet_validate_query(p) > 0) {
 392                 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
 393
 394                 dns_stub_process_query(m, NULL, p);
 395         } else
 396                 log_debug("Invalid DNS stub UDP packet, ignoring.");
 397
 398         return 0;
 399 }
 400
 401 static int manager_dns_stub_udp_fd(Manager *m) {
 402         static const int one = 1;
 403         union sockaddr_union sa = {
 404                 .in.sin_family = AF_INET,
 405                 .in.sin_port = htobe16(53),
 406                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
 407         };
 408         _cleanup_close_ int fd = -1;
 409         int r;
 410
 411         if (m->dns_stub_udp_fd >= 0)
 412                 return m->dns_stub_udp_fd;
 413
 414         fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 415         if (fd < 0)
 416                 return -errno;
 417
 418         if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
 419                 return -errno;
 420
 421         if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
 422                 return -errno;
 423
 424         if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
 425                 return -errno;
 426
 427         /* Make sure no traffic from outside the local host can leak to onto this socket */
 428         if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
 429                 return -errno;
 430
 431         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
 432                 return -errno;
 433
 434         r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
 435         if (r < 0)
 436                 return r;
 437
 438         (void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
 439         m->dns_stub_udp_fd = fd;
 440         fd = -1;
 441
 442         return m->dns_stub_udp_fd;
 443 }
 444
 445 static int on_dns_stub_stream_packet(DnsStream *s) {
 446         assert(s);
 447         assert(s->read_packet);
 448
 449         if (dns_packet_validate_query(s->read_packet) > 0) {
 450                 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 451
 452                 dns_stub_process_query(s->manager, s, s->read_packet);
 453         } else
 454                 log_debug("Invalid DNS stub TCP packet, ignoring.");
 455
 456         /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
 457          * or that didn't happen in which case we want to free the stream */
 458         dns_stream_unref(s);
 459
 460         return 0;
 461 }
 462
 463 static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 464         DnsStream *stream;
 465         Manager *m = userdata;
 466         int cfd, r;
 467
 468         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 469         if (cfd < 0) {
 470                 if (IN_SET(errno, EAGAIN, EINTR))
 471                         return 0;
 472
 473                 return -errno;
 474         }
 475
 476         r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd);
 477         if (r < 0) {
 478                 safe_close(cfd);
 479                 return r;
 480         }
 481
 482         stream->on_packet = on_dns_stub_stream_packet;
 483
 484         /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
 485          * of the stream, or by our packet callback, or when the manager is shut down. */
 486
 487         return 0;
 488 }
 489
 490 static int manager_dns_stub_tcp_fd(Manager *m) {
 491         static const int one = 1;
 492         union sockaddr_union sa = {
 493                 .in.sin_family = AF_INET,
 494                 .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
 495                 .in.sin_port = htobe16(53),
 496         };
 497         _cleanup_close_ int fd = -1;
 498         int r;
 499
 500         if (m->dns_stub_tcp_fd >= 0)
 501                 return m->dns_stub_tcp_fd;
 502
 503         fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 504         if (fd < 0)
 505                 return -errno;
 506
 507         if (setsockopt(fd, IPPROTO_IP, IP_TTL, &one, sizeof one) < 0)
 508                 return -errno;
 509
 510         if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
 511                 return -errno;
 512
 513         if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
 514                 return -errno;
 515
 516         if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
 517                 return -errno;
 518
 519         /* Make sure no traffic from outside the local host can leak to onto this socket */
 520         if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
 521                 return -errno;
 522
 523         if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
 524                 return -errno;
 525
 526         if (listen(fd, SOMAXCONN) < 0)
 527                 return -errno;
 528
 529         r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
 530         if (r < 0)
 531                 return r;
 532
 533         (void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
 534         m->dns_stub_tcp_fd = fd;
 535         fd = -1;
 536
 537         return m->dns_stub_tcp_fd;
 538 }
 539
 540 int manager_dns_stub_start(Manager *m) {
 541         const char *t = "UDP";
 542         int r = 0;
 543
 544         assert(m);
 545
 546         if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
 547                 log_debug("Not creating stub listener.");
 548         else
 549                 log_debug("Creating stub listener using %s.",
 550                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
 551                           m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
 552                           "UDP/TCP");
 553
 554         if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
 555                 r = manager_dns_stub_udp_fd(m);
 556
 557         if (r >= 0 &&
 558             IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
 559                 t = "TCP";
 560                 r = manager_dns_stub_tcp_fd(m);
 561         }
 562
 563         if (IN_SET(r, -EADDRINUSE, -EPERM)) {
 564                 if (r == -EADDRINUSE)
 565                         log_warning_errno(r,
 566                                           "Another process is already listening on %s socket 127.0.0.53:53.\n"
 567                                           "Turning off local DNS stub support.", t);
 568                 else
 569                         log_warning_errno(r,
 570                                           "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
 571                                           "Turning off local DNS stub support.", t);
 572                 manager_dns_stub_stop(m);
 573         } else if (r < 0)
 574                 return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
 575
 576         return 0;
 577 }
 578
 579 void manager_dns_stub_stop(Manager *m) {
 580         assert(m);
 581
 582         m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
 583         m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);
 584
 585         m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
 586         m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
 587 }