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 = new0(EtcHostsItem, 1);
  84                         if (!item)
  85                                 return log_oom();
  86
  87                         item->address = address;
  88
  89                         r = hashmap_put(hosts->by_address, &item->address, item);
  90                         if (r < 0) {
  91                                 free(item);
  92                                 return log_oom();
  93                         }
  94                 }
  95         }
  96
  97         for (;;) {
  98                 _cleanup_free_ char *name = NULL;
  99                 EtcHostsItemByName *bn;
 100
 101                 r = extract_first_word(&line, &name, NULL, EXTRACT_RELAX);
 102                 if (r < 0)
 103                         return log_error_errno(r, "/etc/hosts:%u: couldn't extract hostname: %m", nr);
 104                 if (r == 0)
 105                         break;
 106
 107                 found = true;
 108
 109                 r = dns_name_is_valid_ldh(name);
 110                 if (r <= 0) {
 111                         log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
 112                         continue;
 113                 }
 114
 115                 if (is_localhost(name))
 116                         /* Suppress the "localhost" line that is often seen */
 117                         continue;
 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_allocated, 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 int etc_hosts_parse(EtcHosts *hosts, FILE *f) {
 166         _cleanup_(etc_hosts_free) EtcHosts t = {};
 167         unsigned nr = 0;
 168         int r;
 169
 170         for (;;) {
 171                 _cleanup_free_ char *line = NULL;
 172                 char *l;
 173
 174                 r = read_line(f, LONG_LINE_MAX, &line);
 175                 if (r < 0)
 176                         return log_error_errno(r, "Failed to read /etc/hosts: %m");
 177                 if (r == 0)
 178                         break;
 179
 180                 nr++;
 181
 182                 l = strchr(line, '#');
 183                 if (l)
 184                         *l = '\0';
 185
 186                 l = strstrip(line);
 187                 if (isempty(l))
 188                         continue;
 189
 190                 r = parse_line(&t, nr, l);
 191                 if (r < 0)
 192                         return r;
 193         }
 194
 195         etc_hosts_free(hosts);
 196         *hosts = t;
 197         t = (EtcHosts) {}; /* prevent cleanup */
 198         return 0;
 199 }
 200
 201 static int manager_etc_hosts_read(Manager *m) {
 202         _cleanup_fclose_ FILE *f = NULL;
 203         struct stat st;
 204         usec_t ts;
 205         int r;
 206
 207         assert_se(sd_event_now(m->event, clock_boottime_or_monotonic(), &ts) >= 0);
 208
 209         /* See if we checked /etc/hosts recently already */
 210         if (m->etc_hosts_last != USEC_INFINITY && m->etc_hosts_last + ETC_HOSTS_RECHECK_USEC > ts)
 211                 return 0;
 212
 213         m->etc_hosts_last = ts;
 214
 215         if (m->etc_hosts_mtime != USEC_INFINITY) {
 216                 if (stat("/etc/hosts", &st) < 0) {
 217                         if (errno != ENOENT)
 218                                 return log_error_errno(errno, "Failed to stat /etc/hosts: %m");
 219
 220                         manager_etc_hosts_flush(m);
 221                         return 0;
 222                 }
 223
 224                 /* Did the mtime or ino/dev change? If not, there's no point in re-reading the file. */
 225                 if (timespec_load(&st.st_mtim) == m->etc_hosts_mtime &&
 226                     st.st_ino == m->etc_hosts_ino && st.st_dev == m->etc_hosts_dev)
 227                         return 0;
 228         }
 229
 230         f = fopen("/etc/hosts", "re");
 231         if (!f) {
 232                 if (errno != ENOENT)
 233                         return log_error_errno(errno, "Failed to open /etc/hosts: %m");
 234
 235                 manager_etc_hosts_flush(m);
 236                 return 0;
 237         }
 238
 239         /* Take the timestamp at the beginning of processing, so that any changes made later are read on the next
 240          * invocation */
 241         r = fstat(fileno(f), &st);
 242         if (r < 0)
 243                 return log_error_errno(errno, "Failed to fstat() /etc/hosts: %m");
 244
 245         r = etc_hosts_parse(&m->etc_hosts, f);
 246         if (r < 0)
 247                 return r;
 248
 249         m->etc_hosts_mtime = timespec_load(&st.st_mtim);
 250         m->etc_hosts_ino = st.st_ino;
 251         m->etc_hosts_dev = st.st_dev;
 252         m->etc_hosts_last = ts;
 253
 254         return 1;
 255 }
 256
 257 int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
 258         bool found_a = false, found_aaaa = false;
 259         struct in_addr_data k = {};
 260         EtcHostsItemByName *bn;
 261         DnsResourceKey *t;
 262         const char *name;
 263         unsigned i;
 264         int r;
 265
 266         assert(m);
 267         assert(q);
 268         assert(answer);
 269
 270         if (!m->read_etc_hosts)
 271                 return 0;
 272
 273         (void) manager_etc_hosts_read(m);
 274
 275         name = dns_question_first_name(q);
 276         if (!name)
 277                 return 0;
 278
 279         r = dns_name_address(name, &k.family, &k.address);
 280         if (r > 0) {
 281                 EtcHostsItem *item;
 282                 DnsResourceKey *found_ptr = NULL;
 283
 284                 item = hashmap_get(m->etc_hosts.by_address, &k);
 285                 if (!item)
 286                         return 0;
 287
 288                 /* We have an address in /etc/hosts that matches the queried name. Let's return successful. Actual data
 289                  * we'll only return if the request was for PTR. */
 290
 291                 DNS_QUESTION_FOREACH(t, q) {
 292                         if (!IN_SET(t->type, DNS_TYPE_PTR, DNS_TYPE_ANY))
 293                                 continue;
 294                         if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 295                                 continue;
 296
 297                         r = dns_name_equal(dns_resource_key_name(t), name);
 298                         if (r < 0)
 299                                 return r;
 300                         if (r > 0) {
 301                                 found_ptr = t;
 302                                 break;
 303                         }
 304                 }
 305
 306                 if (found_ptr) {
 307                         char **n;
 308
 309                         r = dns_answer_reserve(answer, strv_length(item->names));
 310                         if (r < 0)
 311                                 return r;
 312
 313                         STRV_FOREACH(n, item->names) {
 314                                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 315
 316                                 rr = dns_resource_record_new(found_ptr);
 317                                 if (!rr)
 318                                         return -ENOMEM;
 319
 320                                 rr->ptr.name = strdup(*n);
 321                                 if (!rr->ptr.name)
 322                                         return -ENOMEM;
 323
 324                                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 325                                 if (r < 0)
 326                                         return r;
 327                         }
 328                 }
 329
 330                 return 1;
 331         }
 332
 333         bn = hashmap_get(m->etc_hosts.by_name, name);
 334         if (bn) {
 335                 r = dns_answer_reserve(answer, bn->n_addresses);
 336                 if (r < 0)
 337                         return r;
 338         } else {
 339                 /* Check if name was listed with no address. If yes, continue to return an answer. */
 340                 if (!set_contains(m->etc_hosts.no_address, name))
 341                         return 0;
 342         }
 343
 344         DNS_QUESTION_FOREACH(t, q) {
 345                 if (!IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 346                         continue;
 347                 if (!IN_SET(t->class, DNS_CLASS_IN, DNS_CLASS_ANY))
 348                         continue;
 349
 350                 r = dns_name_equal(dns_resource_key_name(t), name);
 351                 if (r < 0)
 352                         return r;
 353                 if (r == 0)
 354                         continue;
 355
 356                 if (IN_SET(t->type, DNS_TYPE_A, DNS_TYPE_ANY))
 357                         found_a = true;
 358                 if (IN_SET(t->type, DNS_TYPE_AAAA, DNS_TYPE_ANY))
 359                         found_aaaa = true;
 360
 361                 if (found_a && found_aaaa)
 362                         break;
 363         }
 364
 365         for (i = 0; bn && i < bn->n_addresses; i++) {
 366                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 367
 368                 if ((!found_a && bn->addresses[i]->family == AF_INET) ||
 369                     (!found_aaaa && bn->addresses[i]->family == AF_INET6))
 370                         continue;
 371
 372                 r = dns_resource_record_new_address(&rr, bn->addresses[i]->family, &bn->addresses[i]->address, bn->name);
 373                 if (r < 0)
 374                         return r;
 375
 376                 r = dns_answer_add(*answer, rr, 0, DNS_ANSWER_AUTHENTICATED);
 377                 if (r < 0)
 378                         return r;
 379         }
 380
 381         return found_a || found_aaaa;
 382 }