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 void etc_hosts_item_free(EtcHostsItem *item) {
  22         strv_free(item->names);
  23         free(item);
  24 }
  25
  26 static void etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
  27         free(item->name);
  28         free(item->addresses);
  29         free(item);
  30 }
  31
  32 void etc_hosts_free(EtcHosts *hosts) {
  33         hosts->by_address = hashmap_free_with_destructor(hosts->by_address, etc_hosts_item_free);
  34         hosts->by_name = hashmap_free_with_destructor(hosts->by_name, etc_hosts_item_by_name_free);
  35         hosts->no_address = set_free_free(hosts->no_address);
  36 }
  37
  38 void manager_etc_hosts_flush(Manager *m) {
  39         etc_hosts_free(&m->etc_hosts);
  40         m->etc_hosts_stat = (struct stat) {};
  41 }
  42
  43 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
  44         _cleanup_free_ char *address_str = NULL;
  45         struct in_addr_data address = {};
  46         bool found = false;
  47         EtcHostsItem *item;
  48         int r;
  49
  50         assert(hosts);
  51         assert(line);
  52
  53         r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
  54         if (r < 0)
  55                 return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
  56         assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
  57
  58         r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
  59         if (r < 0) {
  60                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  61                 return 0;
  62         }
  63
  64         r = in_addr_data_is_null(&address);
  65         if (r < 0) {
  66                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  67                 return 0;
  68         }
  69         if (r > 0)
  70                 /* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
  71                  * nothing. */
  72                 item = NULL;
  73         else {
  74                 /* If this is a normal address, then simply add entry mapping it to the specified names */
  75
  76                 item = hashmap_get(hosts->by_address, &address);
  77                 if (!item) {
  78                         r = hashmap_ensure_allocated(&hosts->by_address, &in_addr_data_hash_ops);
  79                         if (r < 0)
  80                                 return log_oom();
  81
  82                         item = new(EtcHostsItem, 1);
  83                         if (!item)
  84                                 return log_oom();
  85
  86                         *item = (EtcHostsItem) {
  87                                 .address = address,
  88                         };
  89
  90                         r = hashmap_put(hosts->by_address, &item->address, item);
  91                         if (r < 0) {
  92                                 free(item);
  93                                 return log_oom();
  94                         }
  95                 }
  96         }
  97
  98         for (;;) {
  99                 _cleanup_free_ char *name = NULL;
 100                 EtcHostsItemByName *bn;
 101
 102                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
 103                 if (r < 0)
 104                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract hostname: %m", nr);
 105                 if (r == 0)
 106                         break;
 107
 108                 found = true;
 109
 110                 r = dns_name_is_valid_ldh(name);
 111                 if (r <= 0) {
 112                         if (r < 0)
 113                                 log_warning_errno(r, "/etc/hosts:%u: Failed to check the validity of hostname \"%s\", ignoring: %m", nr, name);
 114                         else
 115                                 log_warning("/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 116                         continue;
 117                 }
 118
 119                 if (!item) {
 120                         /* Optimize the case where we don't need to store any addresses, by storing
 121                          * only the name in a dedicated Set instead of the hashmap */
 122
 123                         r = set_ensure_consume(&hosts->no_address, &dns_name_hash_ops, TAKE_PTR(name));
 124                         if (r < 0)
 125                                 return r;
 126
 127                         continue;
 128                 }
 129
 130                 r = strv_extend(&item->names, name);
 131                 if (r < 0)
 132                         return log_oom();
 133
 134                 bn = hashmap_get(hosts->by_name, name);
 135                 if (!bn) {
 136                         r = hashmap_ensure_allocated(&hosts->by_name, &dns_name_hash_ops);
 137                         if (r < 0)
 138                                 return log_oom();
 139
 140                         bn = new0(EtcHostsItemByName, 1);
 141                         if (!bn)
 142                                 return log_oom();
 143
 144                         r = hashmap_put(hosts->by_name, name, bn);
 145                         if (r < 0) {
 146                                 free(bn);
 147                                 return log_oom();
 148                         }
 149
 150                         bn->name = TAKE_PTR(name);
 151                 }
 152
 153                 if (!GREEDY_REALLOC(bn->addresses, bn->n_addresses + 1))
 154                         return log_oom();
 155
 156                 bn->addresses[bn->n_addresses++] = &item->address;
 157         }
 158
 159         if (!found)
 160                 log_warning("/etc/hosts:%u: line is missing any hostnames", nr);
 161
 162         return 0;
 163 }
 164
 165 static void strip_localhost(EtcHosts *hosts) {
 166         static const struct in_addr_data local_in_addrs[] = {
 167                 {
 168                         .family = AF_INET,
 169 #if __BYTE_ORDER == __LITTLE_ENDIAN
 170                         /* We want constant expressions here, that's why we don't use htole32() here */
 171                         .address.in.s_addr = UINT32_C(0x0100007F),
 172 #else
 173                         .address.in.s_addr = UINT32_C(0x7F000001),
 174 #endif
 175                 },
 176                 {
 177                         .family = AF_INET6,
 178                         .address.in6 = IN6ADDR_LOOPBACK_INIT,
 179                 },
 180         };
 181
 182         EtcHostsItem *item;
 183
 184         assert(hosts);
 185
 186         /* Removes the 'localhost' entry from what we loaded. But only if the mapping is exclusively between
 187          * 127.0.0.1 and localhost (or aliases to that we recognize). If there's any other name assigned to
 188          * it, we leave the entry in.
 189          *
 190          * This way our regular synthesizing can take over, but only if it would result in the exact same
 191          * mappings.  */
 192
 193         for (size_t j = 0; j < ELEMENTSOF(local_in_addrs); j++) {
 194                 bool all_localhost, in_order;
 195
 196                 item = hashmap_get(hosts->by_address, local_in_addrs + j);
 197                 if (!item)
 198                         continue;
 199
 200                 /* Check whether all hostnames the loopback address points to are localhost ones */
 201                 all_localhost = true;
 202                 STRV_FOREACH(i, item->names)
 203                         if (!is_localhost(*i)) {
 204                                 all_localhost = false;
 205                                 break;
 206                         }
 207
 208                 if (!all_localhost) /* Not all names are localhost, hence keep the entries for this address. */
 209                         continue;
 210
 211                 /* Now check if the names listed for this address actually all point back just to this
 212                  * address (or the other loopback address). If not, let's stay away from this too. */
 213                 in_order = true;
 214                 STRV_FOREACH(i, item->names) {
 215                         EtcHostsItemByName *n;
 216                         bool all_local_address;
 217
 218                         n = hashmap_get(hosts->by_name, *i);
 219                         if (!n) /* No reverse entry? Then almost certainly the entry already got deleted from
 220                                  * the previous iteration of this loop, i.e. via the other protocol */
 221                                 break;
 222
 223                         /* Now check if the addresses of this item are all localhost addresses */
 224                         all_local_address = true;
 225                         for (size_t m = 0; m < n->n_addresses; m++)
 226                                 if (!in_addr_is_localhost(n->addresses[m]->family, &n->addresses[m]->address)) {
 227                                         all_local_address = false;
 228                                         break;
 229                                 }
 230
 231                         if (!all_local_address) {
 232                                 in_order = false;
 233                                 break;
 234                         }
 235                 }
 236
 237                 if (!in_order)
 238                         continue;
 239
 240                 STRV_FOREACH(i, item->names) {
 241                         EtcHostsItemByName *n;
 242
 243                         n = hashmap_remove(hosts->by_name, *i);
 244                         if (n)
 245                                 etc_hosts_item_by_name_free(n);
 246                 }
 247
 248                 assert_se(hashmap_remove(hosts->by_address, local_in_addrs + j) == item);
 249                 etc_hosts_item_free(item);
 250         }
 251 }
 252
 253 int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
 254         _cleanup_(etc_hosts_free) EtcHosts t = {};
 255         unsigned nr = 0;
 256         int r;
 257
 258         for (;;) {
 259                 _cleanup_free_ char *line = NULL;
 260                 char *l;
 261
 262                 r = read_line(f, LONG_LINE_MAX, &line);
 263                 if (r < 0)
 264                         return log_error_errno(r, "Failed to read /etc/hosts: %m");
 265                 if (r == 0)
 266                         break;
 267
 268                 nr++;
 269
 270                 l = strchr(line, '#');
 271                 if (l)
 272                         *l = '\0';
 273
 274                 l = strstrip(line);
 275                 if (isempty(l))
 276                         continue;
 277
 278                 r = parse_line(&t, nr, l);
 279                 if (r < 0)
 280                         return r;
 281         }
 282
 283         strip_localhost(&t);
 284
 285         etc_hosts_free(hosts);
 286         *hosts = t;
 287         t = (EtcHosts) {}; /* prevent cleanup */
 288         return 0;
 289 }
 290
 291 static int manager_etc_hosts_read(Manager *m) {
 292         _cleanup_fclose_ FILE *f = NULL;
 293         struct stat st;
 294         usec_t ts;
 295         int r;
 296
 297         assert_se(sd_event_now(m->event, CLOCK_BOOTTIME, &ts) >= 0);
 298
 299         /* See if we checked /etc/hosts recently already */
 300         if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
 301                 return 0;
 302
 303         m->etc_hosts_last = ts;
 304
 305         if (m->etc_hosts_stat.st_mode != 0) {
 306                 if (stat("/etc/hosts", &st) < 0) {
 307                         if (errno != ENOENT)
 308                                 return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
 309
 310                         manager_etc_hosts_flush(m);
 311                         return 0;
 312                 }
 313
 314                 /* Did the mtime or ino/dev change? If not, there's no point in re-reading the file. */
 315                 if (stat_inode_unmodified(&m->etc_hosts_stat, &st))
 316                         return 0;
 317         }
 318
 319         f = fopen("/etc/hosts", "re");
 320         if (!f) {
 321                 if (errno != ENOENT)
 322                         return log_error_errno(errno, "Failed to open /etc/hosts: %m");
 323
 324                 manager_etc_hosts_flush(m);
 325                 return 0;
 326         }
 327
 328         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 329          * invocation */
 330         r = fstat(fileno(f), &st);
 331         if (r < 0)
 332                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 333
 334         r = etc_hosts_parse(&m->etc_hosts, f);
 335         if (r < 0)
 336                 return r;
 337
 338         m->etc_hosts_stat = st;
 339         m->etc_hosts_last = ts;
 340
 341         return 1;
 342 }
 343
 344 int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
 345         bool found_a = false, found_aaaa = false;
 346         struct in_addr_data k = {};
 347         EtcHostsItemByName *bn;
 348         DnsResourceKey *t;
 349         const char *name;
 350         unsigned i;
 351         int r;
 352
 353         assert(m);
 354         assert(q);
 355         assert(answer);
 356
 357         if (!m->read_etc_hosts)
 358                 return 0;
 359
 360         (void) manager_etc_hosts_read(m);
 361
 362         name = dns_question_first_name(q);
 363         if (!name)
 364                 return 0;
 365
 366         r = dns_name_address(name, &k.family, &k.address);
 367         if (r > 0) {
 368                 EtcHostsItem *item;
 369                 DnsResourceKey *found_ptr = NULL;
 370
 371                 item = hashmap_get(m->etc_hosts.by_address, &k);
 372                 if (!item)
 373                         return 0;
 374
 375                 /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 376                  * we'll only return if the request was for PTR. */
 377
 378                 DNS_QUESTION_FOREACH(t, q) {
 379                         if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 380                                 continue;
 381                         if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 382                                 continue;
 383
 384                         r = dns_name_equal(dns_resource_key_name(t), name);
 385                         if (r < 0)
 386                                 return r;
 387                         if (r > 0) {
 388                                 found_ptr = t;
 389                                 break;
 390                         }
 391                 }
 392
 393                 if (found_ptr) {
 394                         r = dns_answer_reserve(answer, strv_length(item->names));
 395                         if (r < 0)
 396                                 return r;
 397
 398                         STRV_FOREACH(n, item->names) {
 399                                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 400
 401                                 rr = dns_resource_record_new(found_ptr);
 402                                 if (!rr)
 403                                         return -ENOMEM;
 404
 405                                 rr->ptr.name = strdup(*n);
 406                                 if (!rr->ptr.name)
 407                                         return -ENOMEM;
 408
 409                                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED, NULL);
 410                                 if (r < 0)
 411                                         return r;
 412                         }
 413                 }
 414
 415                 return 1;
 416         }
 417
 418         bn = hashmap_get(m->etc_hosts.by_name, name);
 419         if (bn) {
 420                 r = dns_answer_reserve(answer, bn->n_addresses);
 421                 if (r < 0)
 422                         return r;
 423         } else {
 424                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 425                 if (!set_contains(m->etc_hosts.no_address, name))
 426                         return 0;
 427         }
 428
 429         DNS_QUESTION_FOREACH(t, q) {
 430                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 431                         continue;
 432                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 433                         continue;
 434
 435                 r = dns_name_equal(dns_resource_key_name(t), name);
 436                 if (r < 0)
 437                         return r;
 438                 if (r == 0)
 439                         continue;
 440
 441                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 442                         found_a = true;
 443                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 444                         found_aaaa = true;
 445
 446                 if (found_a && found_aaaa)
 447                         break;
 448         }
 449
 450         for (i = 0; bn && i < bn->n_addresses; i++) {
 451                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 452
 453                 if ((!found_a && bn->addresses[i]->family == AF_INET) ||
 454                     (!found_aaaa && bn->addresses[i]->family == AF_INET6))
 455                         continue;
 456
 457                 r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
 458                 if (r < 0)
 459                         return r;
 460
 461                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED, NULL);
 462                 if (r < 0)
 463                         return r;
 464         }
 465
 466         return found_a || found_aaaa;
 467 }