src/resolve/resolved-etc-hosts.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include "fd-util.h"
   4 #include "fileio.h"
   5 #include "hostname-util.h"
   6 #include "resolved-dns-synthesize.h"
   7 #include "resolved-etc-hosts.h"
   8 #include "string-util.h"
   9 #include "strv.h"
  10 #include "time-util.h"
  11
  12 /* Recheck /etc/hosts at most once every 2s */
  13 #define ETC_HOSTS_RECHECK_USEC (2*USEC_PER_SEC)
  14
  15 static void etc_hosts_item_free(EtcHostsItem *item) {
  16         strv_free(item->names);
  17         free(item);
  18 }
  19
  20 static void etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
  21         free(item->name);
  22         free(item->addresses);
  23         free(item);
  24 }
  25
  26 void etc_hosts_free(EtcHosts *hosts) {
  27         hosts->by_address = hashmap_free_with_destructor(hosts->by_address, etc_hosts_item_free);
  28         hosts->by_name = hashmap_free_with_destructor(hosts->by_name, etc_hosts_item_by_name_free);
  29         hosts->no_address = set_free_free(hosts->no_address);
  30 }
  31
  32 void manager_etc_hosts_flush(Manager *m) {
  33         etc_hosts_free(&m->etc_hosts);
  34         m->etc_hosts_mtime = USEC_INFINITY;
  35 }
  36
  37 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
  38         _cleanup_free_ char *address_str = NULL;
  39         struct in_addr_data address = {};
  40         bool found = false;
  41         EtcHostsItem *item;
  42         int r;
  43
  44         assert(hosts);
  45         assert(line);
  46
  47         r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
  48         if (r < 0)
  49                 return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
  50         assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
  51
  52         r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
  53         if (r < 0) {
  54                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  55                 return 0;
  56         }
  57
  58         r = in_addr_is_null(address.family, &address.address);
  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         if (r > 0)
  64                 /* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
  65                  * nothing. */
  66                 item = NULL;
  67         else {
  68                 /* If this is a normal address, then simply add entry mapping it to the specified names */
  69
  70                 item = hashmap_get(hosts->by_address, &address);
  71                 if (!item) {
  72                         r = hashmap_ensure_allocated(&hosts->by_address, &in_addr_data_hash_ops);
  73                         if (r < 0)
  74                                 return log_oom();
  75
  76                         item = new0(EtcHostsItem, 1);
  77                         if (!item)
  78                                 return log_oom();
  79
  80                         item->address = address;
  81
  82                         r = hashmap_put(hosts->by_address, &item->address, item);
  83                         if (r < 0) {
  84                                 free(item);
  85                                 return log_oom();
  86                         }
  87                 }
  88         }
  89
  90         for (;;) {
  91                 _cleanup_free_ char *name = NULL;
  92                 EtcHostsItemByName *bn;
  93
  94                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
  95                 if (r < 0)
  96                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract host name: %m", nr);
  97                 if (r == 0)
  98                         break;
  99
 100                 found = true;
 101
 102                 r = dns_name_is_valid_ldh(name);
 103                 if (r <= 0) {
 104                         log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 105                         continue;
 106                 }
 107
 108                 if (is_localhost(name))
 109                         /* Suppress the "localhost" line that is often seen */
 110                         continue;
 111
 112                 if (!item) {
 113                         /* Optimize the case where we don't need to store any addresses, by storing
 114                          * only the name in a dedicated Set instead of the hashmap */
 115
 116                         r = set_ensure_allocated(&hosts->no_address, &dns_name_hash_ops);
 117                         if (r < 0)
 118                                 return log_oom();
 119
 120                         r = set_put(hosts->no_address, name);
 121                         if (r < 0)
 122                                 return r;
 123
 124                         TAKE_PTR(name);
 125                         continue;
 126                 }
 127
 128                 r = strv_extend(&item->names, name);
 129                 if (r < 0)
 130                         return log_oom();
 131
 132                 bn = hashmap_get(hosts->by_name, name);
 133                 if (!bn) {
 134                         r = hashmap_ensure_allocated(&hosts->by_name, &dns_name_hash_ops);
 135                         if (r < 0)
 136                                 return log_oom();
 137
 138                         bn = new0(EtcHostsItemByName, 1);
 139                         if (!bn)
 140                                 return log_oom();
 141
 142                         r = hashmap_put(hosts->by_name, name, bn);
 143                         if (r < 0) {
 144                                 free(bn);
 145                                 return log_oom();
 146                         }
 147
 148                         bn->name = TAKE_PTR(name);
 149                 }
 150
 151                 if (!GREEDY_REALLOC(bn->addresses, bn->n_allocated, bn->n_addresses + 1))
 152                         return log_oom();
 153
 154                 bn->addresses[bn->n_addresses++] = &item->address;
 155         }
 156
 157         if (!found)
 158                 log_warning("/etc/hosts:%u: line is missing any host names", nr);
 159
 160         return 0;
 161 }
 162
 163 int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
 164         _cleanup_(etc_hosts_free) EtcHosts t = {};
 165         unsigned nr = 0;
 166         int r;
 167
 168         for (;;) {
 169                 _cleanup_free_ char *line = NULL;
 170                 char *l;
 171
 172                 r = read_line(f, LONG_LINE_MAX, &line);
 173                 if (r < 0)
 174                         return log_error_errno(r, "Failed to read /etc/hosts: %m");
 175                 if (r == 0)
 176                         break;
 177
 178                 nr++;
 179
 180                 l = strchr(line, '#');
 181                 if (l)
 182                         *l = '\0';
 183
 184                 l = strstrip(line);
 185                 if (isempty(l))
 186                         continue;
 187
 188                 r = parse_line(&t, nr, l);
 189                 if (r < 0)
 190                         return r;
 191         }
 192
 193         etc_hosts_free(hosts);
 194         *hosts = t;
 195         t = (EtcHosts) {}; /* prevent cleanup */
 196         return 0;
 197 }
 198
 199 static int manager_etc_hosts_read(Manager *m) {
 200         _cleanup_fclose_ FILE *f = NULL;
 201         struct stat st;
 202         usec_t ts;
 203         int r;
 204
 205         assert_se(sd_event_now(m->event, clock_boottime_or_monotonic(), &ts) >= 0);
 206
 207         /* See if we checked /etc/hosts recently already */
 208         if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
 209                 return 0;
 210
 211         m->etc_hosts_last = ts;
 212
 213         if (m->etc_hosts_mtime != USEC_INFINITY) {
 214                 if (stat("/etc/hosts", &st) < 0) {
 215                         if (errno != ENOENT)
 216                                 return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
 217
 218                         manager_etc_hosts_flush(m);
 219                         return 0;
 220                 }
 221
 222                 /* Did the mtime change? If not, there's no point in re-reading the file. */
 223                 if (timespec_load(&st.st_mtim) == m->etc_hosts_mtime)
 224                         return 0;
 225         }
 226
 227         f = fopen("/etc/hosts", "re");
 228         if (!f) {
 229                 if (errno != ENOENT)
 230                         return log_error_errno(errno, "Failed to open /etc/hosts: %m");
 231
 232                 manager_etc_hosts_flush(m);
 233                 return 0;
 234         }
 235
 236         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 237          * invocation */
 238         r = fstat(fileno(f), &st);
 239         if (r < 0)
 240                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 241
 242         r = etc_hosts_parse(&m->etc_hosts, f);
 243         if (r < 0)
 244                 return r;
 245
 246         m->etc_hosts_mtime = timespec_load(&st.st_mtim);
 247         m->etc_hosts_last = ts;
 248
 249         return 1;
 250 }
 251
 252 int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
 253         bool found_a = false, found_aaaa = false;
 254         struct in_addr_data k = {};
 255         EtcHostsItemByName *bn;
 256         DnsResourceKey *t;
 257         const char *name;
 258         unsigned i;
 259         int r;
 260
 261         assert(m);
 262         assert(q);
 263         assert(answer);
 264
 265         if (!m->read_etc_hosts)
 266                 return 0;
 267
 268         (void) manager_etc_hosts_read(m);
 269
 270         name = dns_question_first_name(q);
 271         if (!name)
 272                 return 0;
 273
 274         r = dns_name_address(name, &k.family, &k.address);
 275         if (r > 0) {
 276                 EtcHostsItem *item;
 277                 DnsResourceKey *found_ptr = NULL;
 278
 279                 item = hashmap_get(m->etc_hosts.by_address, &k);
 280                 if (!item)
 281                         return 0;
 282
 283                 /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 284                  * we'll only return if the request was for PTR. */
 285
 286                 DNS_QUESTION_FOREACH(t, q) {
 287                         if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 288                                 continue;
 289                         if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 290                                 continue;
 291
 292                         r = dns_name_equal(dns_resource_key_name(t), name);
 293                         if (r < 0)
 294                                 return r;
 295                         if (r > 0) {
 296                                 found_ptr = t;
 297                                 break;
 298                         }
 299                 }
 300
 301                 if (found_ptr) {
 302                         char **n;
 303
 304                         r = dns_answer_reserve(answer, strv_length(item->names));
 305                         if (r < 0)
 306                                 return r;
 307
 308                         STRV_FOREACH(n, item->names) {
 309                                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 310
 311                                 rr = dns_resource_record_new(found_ptr);
 312                                 if (!rr)
 313                                         return -ENOMEM;
 314
 315                                 rr->ptr.name = strdup(*n);
 316                                 if (!rr->ptr.name)
 317                                         return -ENOMEM;
 318
 319                                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 320                                 if (r < 0)
 321                                         return r;
 322                         }
 323                 }
 324
 325                 return 1;
 326         }
 327
 328         bn = hashmap_get(m->etc_hosts.by_name, name);
 329         if (bn) {
 330                 r = dns_answer_reserve(answer, bn->n_addresses);
 331                 if (r < 0)
 332                         return r;
 333         } else {
 334                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 335                 if (!set_contains(m->etc_hosts.no_address, name))
 336                         return 0;
 337         }
 338
 339         DNS_QUESTION_FOREACH(t, q) {
 340                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 341                         continue;
 342                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 343                         continue;
 344
 345                 r = dns_name_equal(dns_resource_key_name(t), name);
 346                 if (r < 0)
 347                         return r;
 348                 if (r == 0)
 349                         continue;
 350
 351                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 352                         found_a = true;
 353                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 354                         found_aaaa = true;
 355
 356                 if (found_a && found_aaaa)
 357                         break;
 358         }
 359
 360         for (i = 0; bn && i < bn->n_addresses; i++) {
 361                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 362
 363                 if ((!found_a && bn->addresses[i]->family == AF_INET) ||
 364                     (!found_aaaa && bn->addresses[i]->family == AF_INET6))
 365                         continue;
 366
 367                 r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
 368                 if (r < 0)
 369                         return r;
 370
 371                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 372                 if (r < 0)
 373                         return r;
 374         }
 375
 376         return found_a || found_aaaa;
 377 }