src/resolve/resolved-etc-hosts.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <sys/stat.h>
   4 #include "sd-event.h"
   5
   6 #include "alloc-util.h"
   7 #include "dns-domain.h"
   8 #include "extract-word.h"
   9 #include "fd-util.h"
  10 #include "fileio.h"
  11 #include "hostname-util.h"
  12 #include "log.h"
  13 #include "resolved-dns-answer.h"
  14 #include "resolved-dns-question.h"
  15 #include "resolved-dns-rr.h"
  16 #include "resolved-etc-hosts.h"
  17 #include "resolved-manager.h"
  18 #include "set.h"
  19 #include "socket-netlink.h"
  20 #include "stat-util.h"
  21 #include "string-util.h"
  22 #include "time-util.h"
  23
  24 /* Recheck /etc/hosts at most once every 2s */
  25 #define ETC_HOSTS_RECHECK_USEC (2*USEC_PER_SEC)
  26
  27 static EtcHostsItemByAddress *etc_hosts_item_by_address_free(EtcHostsItemByAddress *item) {
  28         if (!item)
  29                 return NULL;
  30
  31         set_free(item->names);
  32         return mfree(item);
  33 }
  34
  35 DEFINE_TRIVIAL_CLEANUP_FUNC(EtcHostsItemByAddress*, etc_hosts_item_by_address_free);
  36
  37 DEFINE_PRIVATE_HASH_OPS_WITH_VALUE_DESTRUCTOR(
  38         by_address_hash_ops,
  39         struct in_addr_data,
  40         in_addr_data_hash_func,
  41         in_addr_data_compare_func,
  42         EtcHostsItemByAddress,
  43         etc_hosts_item_by_address_free);
  44
  45 static EtcHostsItemByName *etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
  46         if (!item)
  47                 return NULL;
  48
  49         free(item->name);
  50         set_free(item->addresses);
  51         return mfree(item);
  52 }
  53
  54 DEFINE_TRIVIAL_CLEANUP_FUNC(EtcHostsItemByName*, etc_hosts_item_by_name_free);
  55
  56 DEFINE_PRIVATE_HASH_OPS_WITH_VALUE_DESTRUCTOR(
  57         by_name_hash_ops,
  58         char,
  59         dns_name_hash_func,
  60         dns_name_compare_func,
  61         EtcHostsItemByName,
  62         etc_hosts_item_by_name_free);
  63
  64 void etc_hosts_clear(EtcHosts *hosts) {
  65         assert(hosts);
  66
  67         hosts->by_address = hashmap_free(hosts->by_address);
  68         hosts->by_name = hashmap_free(hosts->by_name);
  69         hosts->no_address = set_free(hosts->no_address);
  70 }
  71
  72 void manager_etc_hosts_flush(Manager *m) {
  73         etc_hosts_clear(&m->etc_hosts);
  74         m->etc_hosts_stat = (struct stat) {};
  75 }
  76
  77 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
  78         _cleanup_free_ char *address_str = NULL;
  79         struct in_addr_data address = {};
  80         bool found = false;
  81         EtcHostsItemByAddress *item;
  82         int r;
  83
  84         assert(hosts);
  85         assert(line);
  86
  87         r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
  88         if (r < 0)
  89                 return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
  90         assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
  91
  92         r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
  93         if (r < 0) {
  94                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  95                 return 0;
  96         }
  97
  98         r = in_addr_data_is_null(&address);
  99         if (r < 0) {
 100                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
 101                 return 0;
 102         }
 103         if (r > 0)
 104                 /* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
 105                  * nothing. */
 106                 item = NULL;
 107         else {
 108                 /* If this is a normal address, then simply add entry mapping it to the specified names */
 109
 110                 item = hashmap_get(hosts->by_address, &address);
 111                 if (!item) {
 112                         _cleanup_(etc_hosts_item_by_address_freep) EtcHostsItemByAddress *new_item = NULL;
 113
 114                         new_item = new(EtcHostsItemByAddress, 1);
 115                         if (!new_item)
 116                                 return log_oom();
 117
 118                         *new_item = (EtcHostsItemByAddress) {
 119                                 .address = address,
 120                         };
 121
 122                         r = hashmap_ensure_put(&hosts->by_address, &by_address_hash_ops, &new_item->address, new_item);
 123                         if (r < 0)
 124                                 return log_oom();
 125
 126                         item = TAKE_PTR(new_item);
 127                 }
 128         }
 129
 130         for (;;) {
 131                 _cleanup_free_ char *name = NULL;
 132                 EtcHostsItemByName *bn;
 133
 134                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
 135                 if (r < 0)
 136                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract hostname: %m", nr);
 137                 if (r == 0)
 138                         break;
 139
 140                 r = dns_name_is_valid_ldh(name);
 141                 if (r <= 0) {
 142                         if (r < 0)
 143                                 log_warning_errno(r, "/etc/hosts:%u: Failed to check the validity of hostname \"%s\", ignoring: %m", nr, name);
 144                         else
 145                                 log_warning("/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 146                         continue;
 147                 }
 148
 149                 found = true;
 150
 151                 if (!item) {
 152                         /* Optimize the case where we don't need to store any addresses, by storing
 153                          * only the name in a dedicated Set instead of the hashmap */
 154
 155                         r = set_ensure_consume(&hosts->no_address, &dns_name_hash_ops_free, TAKE_PTR(name));
 156                         if (r < 0)
 157                                 return log_oom();
 158
 159                         continue;
 160                 }
 161
 162                 bn = hashmap_get(hosts->by_name, name);
 163                 if (!bn) {
 164                         _cleanup_(etc_hosts_item_by_name_freep) EtcHostsItemByName *new_item = NULL;
 165                         _cleanup_free_ char *name_copy = NULL;
 166
 167                         name_copy = strdup(name);
 168                         if (!name_copy)
 169                                 return log_oom();
 170
 171                         new_item = new(EtcHostsItemByName, 1);
 172                         if (!new_item)
 173                                 return log_oom();
 174
 175                         *new_item = (EtcHostsItemByName) {
 176                                 .name = TAKE_PTR(name_copy),
 177                         };
 178
 179                         r = hashmap_ensure_put(&hosts->by_name, &by_name_hash_ops, new_item->name, new_item);
 180                         if (r < 0)
 181                                 return log_oom();
 182
 183                         bn = TAKE_PTR(new_item);
 184                 }
 185
 186                 if (!set_contains(bn->addresses, &address)) {
 187                         _cleanup_free_ struct in_addr_data *address_copy = NULL;
 188
 189                         address_copy = newdup(struct in_addr_data, &address, 1);
 190                         if (!address_copy)
 191                                 return log_oom();
 192
 193                         r = set_ensure_consume(&bn->addresses, &in_addr_data_hash_ops_free, TAKE_PTR(address_copy));
 194                         if (r < 0)
 195                                 return log_oom();
 196                 }
 197
 198                 r = set_ensure_put(&item->names, &dns_name_hash_ops_free, name);
 199                 if (r < 0)
 200                         return log_oom();
 201                 if (r == 0) /* the name is already listed */
 202                         continue;
 203                 /*
 204                  * Keep track of the first name listed for this address.
 205                  * This name will be used in responses as the canonical name.
 206                  */
 207                 if (!item->canonical_name)
 208                         item->canonical_name = name;
 209                 TAKE_PTR(name);
 210         }
 211
 212         if (!found)
 213                 log_warning("/etc/hosts:%u: line is missing any valid hostnames", nr);
 214
 215         return 0;
 216 }
 217
 218 static void strip_localhost(EtcHosts *hosts) {
 219         static const struct in_addr_data local_in_addrs[] = {
 220                 {
 221                         .family = AF_INET,
 222 #if __BYTE_ORDER == __LITTLE_ENDIAN
 223                         /* We want constant expressions here, that's why we don't use htole32() here */
 224                         .address.in.s_addr = UINT32_C(0x0100007F),
 225 #else
 226                         .address.in.s_addr = UINT32_C(0x7F000001),
 227 #endif
 228                 },
 229                 {
 230                         .family = AF_INET6,
 231                         .address.in6 = IN6ADDR_LOOPBACK_INIT,
 232                 },
 233         };
 234
 235         assert(hosts);
 236
 237         /* Removes the 'localhost' entry from what we loaded. But only if the mapping is exclusively between
 238          * 127.0.0.1 and localhost (or aliases to that we recognize). If there's any other name assigned to
 239          * it, we leave the entry in.
 240          *
 241          * This way our regular synthesizing can take over, but only if it would result in the exact same
 242          * mappings.  */
 243
 244         FOREACH_ELEMENT(local_in_addr, local_in_addrs) {
 245                 bool all_localhost, all_local_address;
 246                 EtcHostsItemByAddress *item;
 247                 const char *name;
 248
 249                 item = hashmap_get(hosts->by_address, local_in_addr);
 250                 if (!item)
 251                         continue;
 252
 253                 /* Check whether all hostnames the loopback address points to are localhost ones */
 254                 all_localhost = true;
 255                 SET_FOREACH(name, item->names)
 256                         if (!is_localhost(name)) {
 257                                 all_localhost = false;
 258                                 break;
 259                         }
 260
 261                 if (!all_localhost) /* Not all names are localhost, hence keep the entries for this address. */
 262                         continue;
 263
 264                 /* Now check if the names listed for this address actually all point back just to this
 265                  * address (or the other loopback address). If not, let's stay away from this too. */
 266                 all_local_address = true;
 267                 SET_FOREACH(name, item->names) {
 268                         EtcHostsItemByName *n;
 269                         struct in_addr_data *a;
 270
 271                         n = hashmap_get(hosts->by_name, name);
 272                         if (!n) /* No reverse entry? Then almost certainly the entry already got deleted from
 273                                  * the previous iteration of this loop, i.e. via the other protocol */
 274                                 break;
 275
 276                         /* Now check if the addresses of this item are all localhost addresses */
 277                         SET_FOREACH(a, n->addresses)
 278                                 if (!in_addr_is_localhost(a->family, &a->address)) {
 279                                         all_local_address = false;
 280                                         break;
 281                                 }
 282
 283                         if (!all_local_address)
 284                                 break;
 285                 }
 286
 287                 if (!all_local_address)
 288                         continue;
 289
 290                 SET_FOREACH(name, item->names)
 291                         etc_hosts_item_by_name_free(hashmap_remove(hosts->by_name, name));
 292
 293                 assert_se(hashmap_remove(hosts->by_address, local_in_addr) == item);
 294                 etc_hosts_item_by_address_free(item);
 295         }
 296 }
 297
 298 int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
 299         _cleanup_(etc_hosts_clear) EtcHosts t = {};
 300         unsigned nr = 0;
 301         int r;
 302
 303         assert(hosts);
 304
 305         for (;;) {
 306                 _cleanup_free_ char *line = NULL;
 307                 char *l;
 308
 309                 r = read_line(f, LONG_LINE_MAX, &line);
 310                 if (r < 0)
 311                         return log_error_errno(r, "Failed to read /etc/hosts: %m");
 312                 if (r == 0)
 313                         break;
 314
 315                 nr++;
 316
 317                 l = strchr(line, '#');
 318                 if (l)
 319                         *l = '\0';
 320
 321                 l = strstrip(line);
 322                 if (isempty(l))
 323                         continue;
 324
 325                 r = parse_line(&t, nr, l);
 326                 if (r < 0)
 327                         return r;
 328         }
 329
 330         strip_localhost(&t);
 331
 332         etc_hosts_clear(hosts);
 333         *hosts = TAKE_STRUCT(t);
 334         return 0;
 335 }
 336
 337 static int manager_etc_hosts_read(Manager *m) {
 338         _cleanup_fclose_ FILE *f = NULL;
 339         struct stat st;
 340         usec_t ts;
 341         int r;
 342
 343         assert_se(sd_event_now(m->event, CLOCK_BOOTTIME, &ts) >= 0);
 344
 345         /* See if we checked /etc/hosts recently already */
 346         if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
 347                 return 0;
 348
 349         m->etc_hosts_last = ts;
 350
 351         if (stat_is_set(&m->etc_hosts_stat)) {
 352                 if (stat("/etc/hosts", &st) < 0) {
 353                         if (errno != ENOENT)
 354                                 return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
 355
 356                         manager_etc_hosts_flush(m);
 357                         return 0;
 358                 }
 359
 360                 /* Did the mtime or ino/dev change? If not, there's no point in re-reading the file. */
 361                 if (stat_inode_unmodified(&m->etc_hosts_stat, &st))
 362                         return 0;
 363         }
 364
 365         f = fopen("/etc/hosts", "re");
 366         if (!f) {
 367                 if (errno != ENOENT)
 368                         return log_error_errno(errno, "Failed to open %s: %m", "/etc/hosts");
 369
 370                 manager_etc_hosts_flush(m);
 371                 return 0;
 372         }
 373
 374         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 375          * invocation */
 376         r = fstat(fileno(f), &st);
 377         if (r < 0)
 378                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 379
 380         r = etc_hosts_parse(&m->etc_hosts, f);
 381         if (r < 0)
 382                 return r;
 383
 384         m->etc_hosts_stat = st;
 385         m->etc_hosts_last = ts;
 386
 387         return 1;
 388 }
 389
 390 static int answer_add_ptr(DnsAnswer *answer, DnsResourceKey *key, const char *name) {
 391         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 392
 393         rr = dns_resource_record_new(key);
 394         if (!rr)
 395                 return -ENOMEM;
 396
 397         rr->ptr.name = strdup(name);
 398         if (!rr->ptr.name)
 399                 return -ENOMEM;
 400
 401         return dns_answer_add(answer, rr, 0, DNS_ANSWER_AUTHENTICATED, NULL);
 402 }
 403
 404 static int answer_add_cname(DnsAnswer *answer, const char *name, const char *cname) {
 405         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 406
 407         rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_CNAME, name);
 408         if (!rr)
 409                 return -ENOMEM;
 410
 411         rr->cname.name = strdup(cname);
 412         if (!rr->cname.name)
 413                 return -ENOMEM;
 414
 415         return dns_answer_add(answer, rr, 0, DNS_ANSWER_AUTHENTICATED, NULL);
 416 }
 417
 418 static int answer_add_addr(DnsAnswer *answer, const char *name, const struct in_addr_data *a) {
 419         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 420         int r;
 421
 422         r = dns_resource_record_new_address(&rr, a->family, &a->address, name);
 423         if (r < 0)
 424                 return r;
 425
 426         return dns_answer_add(answer, rr, 0, DNS_ANSWER_AUTHENTICATED, NULL);
 427 }
 428
 429 static int etc_hosts_lookup_by_address(
 430                 EtcHosts *hosts,
 431                 DnsQuestion *q,
 432                 const char *name,
 433                 const struct in_addr_data *address,
 434                 DnsAnswer **answer) {
 435
 436         DnsResourceKey *t, *found_ptr = NULL;
 437         EtcHostsItemByAddress *item;
 438         int r;
 439
 440         assert(hosts);
 441         assert(q);
 442         assert(name);
 443         assert(address);
 444         assert(answer);
 445
 446         item = hashmap_get(hosts->by_address, address);
 447         if (!item)
 448                 return 0;
 449
 450         /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 451          * we'll only return if the request was for PTR. */
 452
 453         DNS_QUESTION_FOREACH(t, q) {
 454                 if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 455                         continue;
 456                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 457                         continue;
 458
 459                 r = dns_name_equal(dns_resource_key_name(t), name);
 460                 if (r < 0)
 461                         return r;
 462                 if (r > 0) {
 463                         found_ptr = t;
 464                         break;
 465                 }
 466         }
 467
 468         if (found_ptr) {
 469                 const char *n;
 470
 471                 r = dns_answer_reserve(answer, set_size(item->names));
 472                 if (r < 0)
 473                         return r;
 474
 475                 if (item->canonical_name) {
 476                         r = answer_add_ptr(*answer, found_ptr, item->canonical_name);
 477                         if (r < 0)
 478                                 return r;
 479                 }
 480
 481                 SET_FOREACH(n, item->names) {
 482                         if (n == item->canonical_name)
 483                                 continue;
 484
 485                         r = answer_add_ptr(*answer, found_ptr, n);
 486                         if (r < 0)
 487                                 return r;
 488                 }
 489         }
 490
 491         return 1;
 492 }
 493
 494 static int etc_hosts_lookup_by_name(
 495                 EtcHosts *hosts,
 496                 DnsQuestion *q,
 497                 const char *name,
 498                 DnsAnswer **answer) {
 499
 500         bool question_for_a = false, question_for_aaaa = false;
 501         const struct in_addr_data *a;
 502         EtcHostsItemByName *item;
 503         DnsResourceKey *t;
 504         int r;
 505
 506         assert(hosts);
 507         assert(q);
 508         assert(name);
 509         assert(answer);
 510
 511         item = hashmap_get(hosts->by_name, name);
 512         if (item) {
 513                 r = dns_answer_reserve(answer, set_size(item->addresses));
 514                 if (r < 0)
 515                         return r;
 516         } else {
 517                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 518                 if (!set_contains(hosts->no_address, name))
 519                         return 0;
 520         }
 521
 522         /* Determine whether we are looking for A and/or AAAA RRs */
 523         DNS_QUESTION_FOREACH(t, q) {
 524                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 525                         continue;
 526                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 527                         continue;
 528
 529                 r = dns_name_equal(dns_resource_key_name(t), name);
 530                 if (r < 0)
 531                         return r;
 532                 if (r == 0)
 533                         continue;
 534
 535                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 536                         question_for_a = true;
 537                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 538                         question_for_aaaa = true;
 539
 540                 if (question_for_a && question_for_aaaa)
 541                         break; /* We are looking for both, no need to continue loop */
 542         }
 543
 544         SET_FOREACH(a, item ? item->addresses : NULL) {
 545                 EtcHostsItemByAddress *item_by_addr;
 546                 const char *canonical_name;
 547
 548                 if ((!question_for_a && a->family == AF_INET) ||
 549                     (!question_for_aaaa && a->family == AF_INET6))
 550                         continue;
 551
 552                 item_by_addr = hashmap_get(hosts->by_address, a);
 553                 if (item_by_addr && item_by_addr->canonical_name)
 554                         canonical_name = item_by_addr->canonical_name;
 555                 else
 556                         canonical_name = item->name;
 557
 558                 if (!streq(item->name, canonical_name)) {
 559                         r = answer_add_cname(*answer, item->name, canonical_name);
 560                         if (r < 0)
 561                                 return r;
 562                 }
 563
 564                 r = answer_add_addr(*answer, canonical_name, a);
 565                 if (r < 0)
 566                         return r;
 567         }
 568
 569         return true; /* We consider ourselves authoritative for the whole name, all RR types, not just A/AAAA */
 570 }
 571
 572 int manager_etc_hosts_lookup(Manager *m, DnsQuestion *q, DnsAnswer **answer) {
 573         struct in_addr_data k;
 574         const char *name;
 575
 576         assert(m);
 577         assert(q);
 578         assert(answer);
 579
 580         if (!m->read_etc_hosts)
 581                 return 0;
 582
 583         (void) manager_etc_hosts_read(m);
 584
 585         name = dns_question_first_name(q);
 586         if (!name)
 587                 return 0;
 588
 589         if (dns_name_address(name, &k.family, &k.address) > 0)
 590                 return etc_hosts_lookup_by_address(&m->etc_hosts, q, name, &k, answer);
 591
 592         return etc_hosts_lookup_by_name(&m->etc_hosts, q, name, answer);
 593 }