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