src/resolve/resolved-etc-hosts.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   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 "string-util.h"
  13 #include "strv.h"
  14 #include "time-util.h"
  15
  16 /* Recheck /etc/hosts at most once every 2s */
  17 #define ETC_HOSTS_RECHECK_USEC (2*USEC_PER_SEC)
  18
  19 static void etc_hosts_item_free(EtcHostsItem *item) {
  20         strv_free(item->names);
  21         free(item);
  22 }
  23
  24 static void etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
  25         free(item->name);
  26         free(item->addresses);
  27         free(item);
  28 }
  29
  30 void etc_hosts_free(EtcHosts *hosts) {
  31         hosts->by_address = hashmap_free_with_destructor(hosts->by_address, etc_hosts_item_free);
  32         hosts->by_name = hashmap_free_with_destructor(hosts->by_name, etc_hosts_item_by_name_free);
  33         hosts->no_address = set_free_free(hosts->no_address);
  34 }
  35
  36 void manager_etc_hosts_flush(Manager *m) {
  37         etc_hosts_free(&m->etc_hosts);
  38         m->etc_hosts_mtime = USEC_INFINITY;
  39 }
  40
  41 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
  42         _cleanup_free_ char *address_str = NULL;
  43         struct in_addr_data address = {};
  44         bool found = false;
  45         EtcHostsItem *item;
  46         int r;
  47
  48         assert(hosts);
  49         assert(line);
  50
  51         r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
  52         if (r < 0)
  53                 return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
  54         assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
  55
  56         r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
  57         if (r < 0) {
  58                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  59                 return 0;
  60         }
  61
  62         r = in_addr_is_null(address.family, &address.address);
  63         if (r < 0) {
  64                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  65                 return 0;
  66         }
  67         if (r > 0)
  68                 /* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
  69                  * nothing. */
  70                 item = NULL;
  71         else {
  72                 /* If this is a normal address, then simply add entry mapping it to the specified names */
  73
  74                 item = hashmap_get(hosts->by_address, &address);
  75                 if (!item) {
  76                         r = hashmap_ensure_allocated(&hosts->by_address, &in_addr_data_hash_ops);
  77                         if (r < 0)
  78                                 return log_oom();
  79
  80                         item = new0(EtcHostsItem, 1);
  81                         if (!item)
  82                                 return log_oom();
  83
  84                         item->address = address;
  85
  86                         r = hashmap_put(hosts->by_address, &item->address, item);
  87                         if (r < 0) {
  88                                 free(item);
  89                                 return log_oom();
  90                         }
  91                 }
  92         }
  93
  94         for (;;) {
  95                 _cleanup_free_ char *name = NULL;
  96                 EtcHostsItemByName *bn;
  97
  98                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
  99                 if (r < 0)
 100                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract host name: %m", nr);
 101                 if (r == 0)
 102                         break;
 103
 104                 found = true;
 105
 106                 r = dns_name_is_valid_ldh(name);
 107                 if (r <= 0) {
 108                         log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 109                         continue;
 110                 }
 111
 112                 if (is_localhost(name))
 113                         /* Suppress the "localhost" line that is often seen */
 114                         continue;
 115
 116                 if (!item) {
 117                         /* Optimize the case where we don't need to store any addresses, by storing
 118                          * only the name in a dedicated Set instead of the hashmap */
 119
 120                         r = set_ensure_allocated(&hosts->no_address, &dns_name_hash_ops);
 121                         if (r < 0)
 122                                 return log_oom();
 123
 124                         r = set_put(hosts->no_address, name);
 125                         if (r < 0)
 126                                 return r;
 127
 128                         TAKE_PTR(name);
 129                         continue;
 130                 }
 131
 132                 r = strv_extend(&item->names, name);
 133                 if (r < 0)
 134                         return log_oom();
 135
 136                 bn = hashmap_get(hosts->by_name, name);
 137                 if (!bn) {
 138                         r = hashmap_ensure_allocated(&hosts->by_name, &dns_name_hash_ops);
 139                         if (r < 0)
 140                                 return log_oom();
 141
 142                         bn = new0(EtcHostsItemByName, 1);
 143                         if (!bn)
 144                                 return log_oom();
 145
 146                         r = hashmap_put(hosts->by_name, name, bn);
 147                         if (r < 0) {
 148                                 free(bn);
 149                                 return log_oom();
 150                         }
 151
 152                         bn->name = TAKE_PTR(name);
 153                 }
 154
 155                 if (!GREEDY_REALLOC(bn->addresses, bn->n_allocated, bn->n_addresses + 1))
 156                         return log_oom();
 157
 158                 bn->addresses[bn->n_addresses++] = &item->address;
 159         }
 160
 161         if (!found)
 162                 log_warning("/etc/hosts:%u: line is missing any host names", nr);
 163
 164         return 0;
 165 }
 166
 167 int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
 168         _cleanup_(etc_hosts_free) EtcHosts t = {};
 169         unsigned nr = 0;
 170         int r;
 171
 172         for (;;) {
 173                 _cleanup_free_ char *line = NULL;
 174                 char *l;
 175
 176                 r = read_line(f, LONG_LINE_MAX, &line);
 177                 if (r < 0)
 178                         return log_error_errno(r, "Failed to read /etc/hosts: %m");
 179                 if (r == 0)
 180                         break;
 181
 182                 nr++;
 183
 184                 l = strchr(line, '#');
 185                 if (l)
 186                         *l = '\0';
 187
 188                 l = strstrip(line);
 189                 if (isempty(l))
 190                         continue;
 191
 192                 r = parse_line(&t, nr, l);
 193                 if (r < 0)
 194                         return r;
 195         }
 196
 197         etc_hosts_free(hosts);
 198         *hosts = t;
 199         t = (EtcHosts) {}; /* prevent cleanup */
 200         return 0;
 201 }
 202
 203 static int manager_etc_hosts_read(Manager *m) {
 204         _cleanup_fclose_ FILE *f = NULL;
 205         struct stat st;
 206         usec_t ts;
 207         int r;
 208
 209         assert_se(sd_event_now(m->event, clock_boottime_or_monotonic(), &ts) >= 0);
 210
 211         /* See if we checked /etc/hosts recently already */
 212         if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
 213                 return 0;
 214
 215         m->etc_hosts_last = ts;
 216
 217         if (m->etc_hosts_mtime != USEC_INFINITY) {
 218                 if (stat("/etc/hosts", &st) < 0) {
 219                         if (errno != ENOENT)
 220                                 return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
 221
 222                         manager_etc_hosts_flush(m);
 223                         return 0;
 224                 }
 225
 226                 /* Did the mtime change? If not, there's no point in re-reading the file. */
 227                 if (timespec_load(&st.st_mtim) == m->etc_hosts_mtime)
 228                         return 0;
 229         }
 230
 231         f = fopen("/etc/hosts", "re");
 232         if (!f) {
 233                 if (errno != ENOENT)
 234                         return log_error_errno(errno, "Failed to open /etc/hosts: %m");
 235
 236                 manager_etc_hosts_flush(m);
 237                 return 0;
 238         }
 239
 240         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 241          * invocation */
 242         r = fstat(fileno(f), &st);
 243         if (r < 0)
 244                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 245
 246         r = etc_hosts_parse(&m->etc_hosts, f);
 247         if (r < 0)
 248                 return r;
 249
 250         m->etc_hosts_mtime = timespec_load(&st.st_mtim);
 251         m->etc_hosts_last = ts;
 252
 253         return 1;
 254 }
 255
 256 int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
 257         bool found_a = false, found_aaaa = false;
 258         struct in_addr_data k = {};
 259         EtcHostsItemByName *bn;
 260         DnsResourceKey *t;
 261         const char *name;
 262         unsigned i;
 263         int r;
 264
 265         assert(m);
 266         assert(q);
 267         assert(answer);
 268
 269         if (!m->read_etc_hosts)
 270                 return 0;
 271
 272         (void) manager_etc_hosts_read(m);
 273
 274         name = dns_question_first_name(q);
 275         if (!name)
 276                 return 0;
 277
 278         r = dns_name_address(name, &k.family, &k.address);
 279         if (r > 0) {
 280                 EtcHostsItem *item;
 281                 DnsResourceKey *found_ptr = NULL;
 282
 283                 item = hashmap_get(m->etc_hosts.by_address, &k);
 284                 if (!item)
 285                         return 0;
 286
 287                 /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 288                  * we'll only return if the request was for PTR. */
 289
 290                 DNS_QUESTION_FOREACH(t, q) {
 291                         if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 292                                 continue;
 293                         if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 294                                 continue;
 295
 296                         r = dns_name_equal(dns_resource_key_name(t), name);
 297                         if (r < 0)
 298                                 return r;
 299                         if (r > 0) {
 300                                 found_ptr = t;
 301                                 break;
 302                         }
 303                 }
 304
 305                 if (found_ptr) {
 306                         char **n;
 307
 308                         r = dns_answer_reserve(answer, strv_length(item->names));
 309                         if (r < 0)
 310                                 return r;
 311
 312                         STRV_FOREACH(n, item->names) {
 313                                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 314
 315                                 rr = dns_resource_record_new(found_ptr);
 316                                 if (!rr)
 317                                         return -ENOMEM;
 318
 319                                 rr->ptr.name = strdup(*n);
 320                                 if (!rr->ptr.name)
 321                                         return -ENOMEM;
 322
 323                                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 324                                 if (r < 0)
 325                                         return r;
 326                         }
 327                 }
 328
 329                 return 1;
 330         }
 331
 332         bn = hashmap_get(m->etc_hosts.by_name, name);
 333         if (bn) {
 334                 r = dns_answer_reserve(answer, bn->n_addresses);
 335                 if (r < 0)
 336                         return r;
 337         } else {
 338                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 339                 if (!set_contains(m->etc_hosts.no_address, name))
 340                         return 0;
 341         }
 342
 343         DNS_QUESTION_FOREACH(t, q) {
 344                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 345                         continue;
 346                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 347                         continue;
 348
 349                 r = dns_name_equal(dns_resource_key_name(t), name);
 350                 if (r < 0)
 351                         return r;
 352                 if (r == 0)
 353                         continue;
 354
 355                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 356                         found_a = true;
 357                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 358                         found_aaaa = true;
 359
 360                 if (found_a && found_aaaa)
 361                         break;
 362         }
 363
 364         for (i = 0; bn && i < bn->n_addresses; i++) {
 365                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 366
 367                 if ((!found_a && bn->addresses[i]->family == AF_INET) ||
 368                     (!found_aaaa && bn->addresses[i]->family == AF_INET6))
 369                         continue;
 370
 371                 r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
 372                 if (r < 0)
 373                         return r;
 374
 375                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 376                 if (r < 0)
 377                         return r;
 378         }
 379
 380         return found_a || found_aaaa;
 381 }