src/resolve/resolved-etc-hosts.c

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