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 "socket-netlink.h"
  13 #include "string-util.h"
  14 #include "strv.h"
  15 #include "time-util.h"
  16
  17 /* Recheck /etc/hosts at most once every 2s */
  18 #define ETC_HOSTS_RECHECK_USEC (2*USEC_PER_SEC)
  19
  20 static void etc_hosts_item_free(EtcHostsItem *item) {
  21         strv_free(item->names);
  22         free(item);
  23 }
  24
  25 static void etc_hosts_item_by_name_free(EtcHostsItemByName *item) {
  26         free(item->name);
  27         free(item->addresses);
  28         free(item);
  29 }
  30
  31 void etc_hosts_free(EtcHosts *hosts) {
  32         hosts->by_address = hashmap_free_with_destructor(hosts->by_address, etc_hosts_item_free);
  33         hosts->by_name = hashmap_free_with_destructor(hosts->by_name, etc_hosts_item_by_name_free);
  34         hosts->no_address = set_free_free(hosts->no_address);
  35 }
  36
  37 void manager_etc_hosts_flush(Manager *m) {
  38         etc_hosts_free(&m->etc_hosts);
  39         m->etc_hosts_mtime = USEC_INFINITY;
  40         m->etc_hosts_ino = 0;
  41         m->etc_hosts_dev = 0;
  42 }
  43
  44 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
  45         _cleanup_free_ char *address_str = NULL;
  46         struct in_addr_data address = {};
  47         bool found = false;
  48         EtcHostsItem *item;
  49         int r;
  50
  51         assert(hosts);
  52         assert(line);
  53
  54         r = extract_first_word(&line, &address_str, NULL, EXTRACT_RELAX);
  55         if (r < 0)
  56                 return log_error_errno(r, "/etc/hosts:%u: failed to extract address: %m", nr);
  57         assert(r > 0); /* We already checked that the line is not empty, so it should contain *something* */
  58
  59         r = in_addr_ifindex_from_string_auto(address_str, &address.family, &address.address, NULL);
  60         if (r < 0) {
  61                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  62                 return 0;
  63         }
  64
  65         r = in_addr_is_null(address.family, &address.address);
  66         if (r < 0) {
  67                 log_warning_errno(r, "/etc/hosts:%u: address '%s' is invalid, ignoring: %m", nr, address_str);
  68                 return 0;
  69         }
  70         if (r > 0)
  71                 /* This is an 0.0.0.0 or :: item, which we assume means that we shall map the specified hostname to
  72                  * nothing. */
  73                 item = NULL;
  74         else {
  75                 /* If this is a normal address, then simply add entry mapping it to the specified names */
  76
  77                 item = hashmap_get(hosts->by_address, &address);
  78                 if (!item) {
  79                         r = hashmap_ensure_allocated(&hosts->by_address, &in_addr_data_hash_ops);
  80                         if (r < 0)
  81                                 return log_oom();
  82
  83                         item = new(EtcHostsItem, 1);
  84                         if (!item)
  85                                 return log_oom();
  86
  87                         *item = (EtcHostsItem) {
  88                                 .address = address,
  89                         };
  90
  91                         r = hashmap_put(hosts->by_address, &item->address, item);
  92                         if (r < 0) {
  93                                 free(item);
  94                                 return log_oom();
  95                         }
  96                 }
  97         }
  98
  99         for (;;) {
 100                 _cleanup_free_ char *name = NULL;
 101                 EtcHostsItemByName *bn;
 102
 103                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
 104                 if (r < 0)
 105                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract hostname: %m", nr);
 106                 if (r == 0)
 107                         break;
 108
 109                 found = true;
 110
 111                 r = dns_name_is_valid_ldh(name);
 112                 if (r <= 0) {
 113                         log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 114                         continue;
 115                 }
 116
 117                 if (is_localhost(name))
 118                         /* Suppress the "localhost" line that is often seen */
 119                         continue;
 120
 121                 if (!item) {
 122                         /* Optimize the case where we don't need to store any addresses, by storing
 123                          * only the name in a dedicated Set instead of the hashmap */
 124
 125                         r = set_ensure_consume(&hosts->no_address, &dns_name_hash_ops, TAKE_PTR(name));
 126                         if (r < 0)
 127                                 return r;
 128
 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 hostnames", 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 or ino/dev change? If not, there's no point in re-reading the file. */
 227                 if (timespec_load(&st.st_mtim) == m->etc_hosts_mtime &&
 228                     st.st_ino == m->etc_hosts_ino && st.st_dev == m->etc_hosts_dev)
 229                         return 0;
 230         }
 231
 232         f = fopen("/etc/hosts", "re");
 233         if (!f) {
 234                 if (errno != ENOENT)
 235                         return log_error_errno(errno, "Failed to open /etc/hosts: %m");
 236
 237                 manager_etc_hosts_flush(m);
 238                 return 0;
 239         }
 240
 241         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 242          * invocation */
 243         r = fstat(fileno(f), &st);
 244         if (r < 0)
 245                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 246
 247         r = etc_hosts_parse(&m->etc_hosts, f);
 248         if (r < 0)
 249                 return r;
 250
 251         m->etc_hosts_mtime = timespec_load(&st.st_mtim);
 252         m->etc_hosts_ino = st.st_ino;
 253         m->etc_hosts_dev = st.st_dev;
 254         m->etc_hosts_last = ts;
 255
 256         return 1;
 257 }
 258
 259 int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
 260         bool found_a = false, found_aaaa = false;
 261         struct in_addr_data k = {};
 262         EtcHostsItemByName *bn;
 263         DnsResourceKey *t;
 264         const char *name;
 265         unsigned i;
 266         int r;
 267
 268         assert(m);
 269         assert(q);
 270         assert(answer);
 271
 272         if (!m->read_etc_hosts)
 273                 return 0;
 274
 275         (void) manager_etc_hosts_read(m);
 276
 277         name = dns_question_first_name(q);
 278         if (!name)
 279                 return 0;
 280
 281         r = dns_name_address(name, &k.family, &k.address);
 282         if (r > 0) {
 283                 EtcHostsItem *item;
 284                 DnsResourceKey *found_ptr = NULL;
 285
 286                 item = hashmap_get(m->etc_hosts.by_address, &k);
 287                 if (!item)
 288                         return 0;
 289
 290                 /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 291                  * we'll only return if the request was for PTR. */
 292
 293                 DNS_QUESTION_FOREACH(t, q) {
 294                         if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 295                                 continue;
 296                         if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 297                                 continue;
 298
 299                         r = dns_name_equal(dns_resource_key_name(t), name);
 300                         if (r < 0)
 301                                 return r;
 302                         if (r > 0) {
 303                                 found_ptr = t;
 304                                 break;
 305                         }
 306                 }
 307
 308                 if (found_ptr) {
 309                         char **n;
 310
 311                         r = dns_answer_reserve(answer, strv_length(item->names));
 312                         if (r < 0)
 313                                 return r;
 314
 315                         STRV_FOREACH(n, item->names) {
 316                                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 317
 318                                 rr = dns_resource_record_new(found_ptr);
 319                                 if (!rr)
 320                                         return -ENOMEM;
 321
 322                                 rr->ptr.name = strdup(*n);
 323                                 if (!rr->ptr.name)
 324                                         return -ENOMEM;
 325
 326                                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 327                                 if (r < 0)
 328                                         return r;
 329                         }
 330                 }
 331
 332                 return 1;
 333         }
 334
 335         bn = hashmap_get(m->etc_hosts.by_name, name);
 336         if (bn) {
 337                 r = dns_answer_reserve(answer, bn->n_addresses);
 338                 if (r < 0)
 339                         return r;
 340         } else {
 341                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 342                 if (!set_contains(m->etc_hosts.no_address, name))
 343                         return 0;
 344         }
 345
 346         DNS_QUESTION_FOREACH(t, q) {
 347                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 348                         continue;
 349                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 350                         continue;
 351
 352                 r = dns_name_equal(dns_resource_key_name(t), name);
 353                 if (r < 0)
 354                         return r;
 355                 if (r == 0)
 356                         continue;
 357
 358                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 359                         found_a = true;
 360                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 361                         found_aaaa = true;
 362
 363                 if (found_a && found_aaaa)
 364                         break;
 365         }
 366
 367         for (i = 0; bn && i < bn->n_addresses; i++) {
 368                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 369
 370                 if ((!found_a && bn->addresses[i]->family == AF_INET) ||
 371                     (!found_aaaa && bn->addresses[i]->family == AF_INET6))
 372                         continue;
 373
 374                 r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
 375                 if (r < 0)
 376                         return r;
 377
 378                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 379                 if (r < 0)
 380                         return r;
 381         }
 382
 383         return found_a || found_aaaa;
 384 }