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