src/nss-myhostname/nss-myhostname.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <net/if.h>
   5 #include <netdb.h>
   6 #include <nss.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9
  10 #include "alloc-util.h"
  11 #include "hostname-util.h"
  12 #include "local-addresses.h"
  13 #include "macro.h"
  14 #include "nss-util.h"
  15 #include "signal-util.h"
  16 #include "string-util.h"
  17 #include "util.h"
  18
  19 /* We use 127.0.0.2 as IPv4 address. This has the advantage over
  20  * 127.0.0.1 that it can be translated back to the local hostname. For
  21  * IPv6 we use ::1 which unfortunately will not translate back to the
  22  * hostname but instead something like "localhost" or so. */
  23
  24 #define LOCALADDRESS_IPV4 (htobe32(0x7F000002))
  25 #define LOCALADDRESS_IPV6 &in6addr_loopback
  26
  27 NSS_GETHOSTBYNAME_PROTOTYPES(myhostname);
  28 NSS_GETHOSTBYADDR_PROTOTYPES(myhostname);
  29
  30 enum nss_status _nss_myhostname_gethostbyname4_r(
  31                 const char *name,
  32                 struct gaih_addrtuple **pat,
  33                 char *buffer, size_t buflen,
  34                 int *errnop, int *h_errnop,
  35                 int32_t *ttlp) {
  36
  37         struct gaih_addrtuple *r_tuple, *r_tuple_prev = NULL;
  38         _cleanup_free_ struct local_address *addresses = NULL;
  39         _cleanup_free_ char *hn = NULL;
  40         const char *canonical = NULL;
  41         int n_addresses = 0;
  42         uint32_t local_address_ipv4;
  43         struct local_address *a;
  44         size_t l, idx, ms;
  45         char *r_name;
  46         unsigned n;
  47
  48         PROTECT_ERRNO;
  49         BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
  50
  51         assert(name);
  52         assert(pat);
  53         assert(buffer);
  54         assert(errnop);
  55         assert(h_errnop);
  56
  57         if (is_localhost(name)) {
  58                 /* We respond to 'localhost', so that /etc/hosts
  59                  * is optional */
  60
  61                 canonical = "localhost";
  62                 local_address_ipv4 = htobe32(INADDR_LOOPBACK);
  63
  64         } else if (is_gateway_hostname(name)) {
  65
  66                 n_addresses = local_gateways(NULL, 0, AF_UNSPEC, &addresses);
  67                 if (n_addresses <= 0) {
  68                         *h_errnop = HOST_NOT_FOUND;
  69                         return NSS_STATUS_NOTFOUND;
  70                 }
  71
  72                 canonical = "_gateway";
  73
  74         } else {
  75                 hn = gethostname_malloc();
  76                 if (!hn) {
  77                         *errnop = ENOMEM;
  78                         *h_errnop = NO_RECOVERY;
  79                         return NSS_STATUS_TRYAGAIN;
  80                 }
  81
  82                 /* We respond to our local host name, our hostname suffixed with a single dot. */
  83                 if (!streq(name, hn) && !streq_ptr(startswith(name, hn), ".")) {
  84                         *h_errnop = HOST_NOT_FOUND;
  85                         return NSS_STATUS_NOTFOUND;
  86                 }
  87
  88                 n_addresses = local_addresses(NULL, 0, AF_UNSPEC, &addresses);
  89                 if (n_addresses < 0)
  90                         n_addresses = 0;
  91
  92                 canonical = hn;
  93                 local_address_ipv4 = LOCALADDRESS_IPV4;
  94         }
  95
  96         l = strlen(canonical);
  97         ms = ALIGN(l+1) + ALIGN(sizeof(struct gaih_addrtuple)) * (n_addresses > 0 ? n_addresses : 2);
  98         if (buflen < ms) {
  99                 *errnop = ERANGE;
 100                 *h_errnop = NETDB_INTERNAL;
 101                 return NSS_STATUS_TRYAGAIN;
 102         }
 103
 104         /* First, fill in hostname */
 105         r_name = buffer;
 106         memcpy(r_name, canonical, l+1);
 107         idx = ALIGN(l+1);
 108
 109         assert(n_addresses >= 0);
 110         if (n_addresses == 0) {
 111                 /* Second, fill in IPv6 tuple */
 112                 r_tuple = (struct gaih_addrtuple*) (buffer + idx);
 113                 r_tuple->next = r_tuple_prev;
 114                 r_tuple->name = r_name;
 115                 r_tuple->family = AF_INET6;
 116                 memcpy(r_tuple->addr, LOCALADDRESS_IPV6, 16);
 117                 r_tuple->scopeid = 0;
 118
 119                 idx += ALIGN(sizeof(struct gaih_addrtuple));
 120                 r_tuple_prev = r_tuple;
 121
 122                 /* Third, fill in IPv4 tuple */
 123                 r_tuple = (struct gaih_addrtuple*) (buffer + idx);
 124                 r_tuple->next = r_tuple_prev;
 125                 r_tuple->name = r_name;
 126                 r_tuple->family = AF_INET;
 127                 *(uint32_t*) r_tuple->addr = local_address_ipv4;
 128                 r_tuple->scopeid = 0;
 129
 130                 idx += ALIGN(sizeof(struct gaih_addrtuple));
 131                 r_tuple_prev = r_tuple;
 132         }
 133
 134         /* Fourth, fill actual addresses in, but in backwards order */
 135         for (a = addresses + n_addresses - 1, n = 0; (int) n < n_addresses; n++, a--) {
 136                 r_tuple = (struct gaih_addrtuple*) (buffer + idx);
 137                 r_tuple->next = r_tuple_prev;
 138                 r_tuple->name = r_name;
 139                 r_tuple->family = a->family;
 140                 r_tuple->scopeid = a->family == AF_INET6 && IN6_IS_ADDR_LINKLOCAL(&a->address.in6) ? a->ifindex : 0;
 141                 memcpy(r_tuple->addr, &a->address, 16);
 142
 143                 idx += ALIGN(sizeof(struct gaih_addrtuple));
 144                 r_tuple_prev = r_tuple;
 145         }
 146
 147         /* Verify the size matches */
 148         assert(idx == ms);
 149
 150         /* Nscd expects us to store the first record in **pat. */
 151         if (*pat)
 152                 **pat = *r_tuple_prev;
 153         else
 154                 *pat = r_tuple_prev;
 155
 156         if (ttlp)
 157                 *ttlp = 0;
 158
 159         /* Explicitly reset both *h_errnop and h_errno to work around
 160          * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
 161         *h_errnop = NETDB_SUCCESS;
 162         h_errno = 0;
 163
 164         return NSS_STATUS_SUCCESS;
 165 }
 166
 167 static enum nss_status fill_in_hostent(
 168                 const char *canonical, const char *additional,
 169                 int af,
 170                 struct local_address *addresses, unsigned n_addresses,
 171                 uint32_t local_address_ipv4,
 172                 struct hostent *result,
 173                 char *buffer, size_t buflen,
 174                 int *errnop, int *h_errnop,
 175                 int32_t *ttlp,
 176                 char **canonp) {
 177
 178         size_t l_canonical, l_additional, idx, ms, alen;
 179         char *r_addr, *r_name, *r_aliases, *r_alias = NULL, *r_addr_list;
 180         struct local_address *a;
 181         unsigned n, c;
 182
 183         assert(canonical);
 184         assert(result);
 185         assert(buffer);
 186         assert(errnop);
 187         assert(h_errnop);
 188
 189         alen = FAMILY_ADDRESS_SIZE(af);
 190
 191         for (a = addresses, n = 0, c = 0; n < n_addresses; a++, n++)
 192                 if (af == a->family)
 193                         c++;
 194
 195         l_canonical = strlen(canonical);
 196         l_additional = strlen_ptr(additional);
 197         ms = ALIGN(l_canonical+1)+
 198                 (additional ? ALIGN(l_additional+1) : 0) +
 199                 sizeof(char*) +
 200                 (additional ? sizeof(char*) : 0) +
 201                 (c > 0 ? c : 1) * ALIGN(alen) +
 202                 (c > 0 ? c+1 : 2) * sizeof(char*);
 203
 204         if (buflen < ms) {
 205                 *errnop = ERANGE;
 206                 *h_errnop = NETDB_INTERNAL;
 207                 return NSS_STATUS_TRYAGAIN;
 208         }
 209
 210         /* First, fill in hostnames */
 211         r_name = buffer;
 212         memcpy(r_name, canonical, l_canonical+1);
 213         idx = ALIGN(l_canonical+1);
 214
 215         if (additional) {
 216                 r_alias = buffer + idx;
 217                 memcpy(r_alias, additional, l_additional+1);
 218                 idx += ALIGN(l_additional+1);
 219         }
 220
 221         /* Second, create aliases array */
 222         r_aliases = buffer + idx;
 223         if (additional) {
 224                 ((char**) r_aliases)[0] = r_alias;
 225                 ((char**) r_aliases)[1] = NULL;
 226                 idx += 2*sizeof(char*);
 227         } else {
 228                 ((char**) r_aliases)[0] = NULL;
 229                 idx += sizeof(char*);
 230         }
 231
 232         /* Third, add addresses */
 233         r_addr = buffer + idx;
 234         if (c > 0) {
 235                 unsigned i = 0;
 236
 237                 for (a = addresses, n = 0; n < n_addresses; a++, n++) {
 238                         if (af != a->family)
 239                                 continue;
 240
 241                         memcpy(r_addr + i*ALIGN(alen), &a->address, alen);
 242                         i++;
 243                 }
 244
 245                 assert(i == c);
 246                 idx += c*ALIGN(alen);
 247         } else {
 248                 if (af == AF_INET)
 249                         *(uint32_t*) r_addr = local_address_ipv4;
 250                 else
 251                         memcpy(r_addr, LOCALADDRESS_IPV6, 16);
 252
 253                 idx += ALIGN(alen);
 254         }
 255
 256         /* Fourth, add address pointer array */
 257         r_addr_list = buffer + idx;
 258         if (c > 0) {
 259                 unsigned i;
 260
 261                 for (i = 0; i < c; i++)
 262                         ((char**) r_addr_list)[i] = r_addr + i*ALIGN(alen);
 263
 264                 ((char**) r_addr_list)[i] = NULL;
 265                 idx += (c+1) * sizeof(char*);
 266
 267         } else {
 268                 ((char**) r_addr_list)[0] = r_addr;
 269                 ((char**) r_addr_list)[1] = NULL;
 270                 idx += 2 * sizeof(char*);
 271         }
 272
 273         /* Verify the size matches */
 274         assert(idx == ms);
 275
 276         result->h_name = r_name;
 277         result->h_aliases = (char**) r_aliases;
 278         result->h_addrtype = af;
 279         result->h_length = alen;
 280         result->h_addr_list = (char**) r_addr_list;
 281
 282         if (ttlp)
 283                 *ttlp = 0;
 284
 285         if (canonp)
 286                 *canonp = r_name;
 287
 288         /* Explicitly reset both *h_errnop and h_errno to work around
 289          * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
 290         *h_errnop = NETDB_SUCCESS;
 291         h_errno = 0;
 292
 293         return NSS_STATUS_SUCCESS;
 294 }
 295
 296 enum nss_status _nss_myhostname_gethostbyname3_r(
 297                 const char *name,
 298                 int af,
 299                 struct hostent *host,
 300                 char *buffer, size_t buflen,
 301                 int *errnop, int *h_errnop,
 302                 int32_t *ttlp,
 303                 char **canonp) {
 304
 305         _cleanup_free_ struct local_address *addresses = NULL;
 306         const char *canonical, *additional = NULL;
 307         _cleanup_free_ char *hn = NULL;
 308         uint32_t local_address_ipv4 = 0;
 309         int n_addresses = 0;
 310
 311         PROTECT_ERRNO;
 312         BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
 313
 314         assert(name);
 315         assert(host);
 316         assert(buffer);
 317         assert(errnop);
 318         assert(h_errnop);
 319
 320         if (af == AF_UNSPEC)
 321                 af = AF_INET;
 322
 323         if (!IN_SET(af, AF_INET, AF_INET6)) {
 324                 *errnop = EAFNOSUPPORT;
 325                 *h_errnop = NO_DATA;
 326                 return NSS_STATUS_UNAVAIL;
 327         }
 328
 329         if (is_localhost(name)) {
 330                 canonical = "localhost";
 331                 local_address_ipv4 = htobe32(INADDR_LOOPBACK);
 332
 333         } else if (is_gateway_hostname(name)) {
 334
 335                 n_addresses = local_gateways(NULL, 0, af, &addresses);
 336                 if (n_addresses <= 0) {
 337                         *h_errnop = HOST_NOT_FOUND;
 338                         return NSS_STATUS_NOTFOUND;
 339                 }
 340
 341                 canonical = "_gateway";
 342
 343         } else {
 344                 hn = gethostname_malloc();
 345                 if (!hn) {
 346                         *errnop = ENOMEM;
 347                         *h_errnop = NO_RECOVERY;
 348                         return NSS_STATUS_TRYAGAIN;
 349                 }
 350
 351                 if (!streq(name, hn) && !streq_ptr(startswith(name, hn), ".")) {
 352                         *h_errnop = HOST_NOT_FOUND;
 353                         return NSS_STATUS_NOTFOUND;
 354                 }
 355
 356                 n_addresses = local_addresses(NULL, 0, af, &addresses);
 357                 if (n_addresses < 0)
 358                         n_addresses = 0;
 359
 360                 canonical = hn;
 361                 additional = n_addresses <= 0 && af == AF_INET6 ? "localhost" : NULL;
 362                 local_address_ipv4 = LOCALADDRESS_IPV4;
 363         }
 364
 365         return fill_in_hostent(
 366                         canonical, additional,
 367                         af,
 368                         addresses, n_addresses,
 369                         local_address_ipv4,
 370                         host,
 371                         buffer, buflen,
 372                         errnop, h_errnop,
 373                         ttlp,
 374                         canonp);
 375 }
 376
 377 enum nss_status _nss_myhostname_gethostbyaddr2_r(
 378                 const void* addr, socklen_t len,
 379                 int af,
 380                 struct hostent *host,
 381                 char *buffer, size_t buflen,
 382                 int *errnop, int *h_errnop,
 383                 int32_t *ttlp) {
 384
 385         const char *canonical = NULL, *additional = NULL;
 386         uint32_t local_address_ipv4 = LOCALADDRESS_IPV4;
 387         _cleanup_free_ struct local_address *addresses = NULL;
 388         _cleanup_free_ char *hn = NULL;
 389         int n_addresses = 0;
 390         struct local_address *a;
 391         bool additional_from_hostname = false;
 392         unsigned n;
 393
 394         PROTECT_ERRNO;
 395         BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
 396
 397         assert(addr);
 398         assert(host);
 399         assert(buffer);
 400         assert(errnop);
 401         assert(h_errnop);
 402
 403         if (!IN_SET(af, AF_INET, AF_INET6)) {
 404                 *errnop = EAFNOSUPPORT;
 405                 *h_errnop = NO_DATA;
 406                 return NSS_STATUS_UNAVAIL;
 407         }
 408
 409         if (len != FAMILY_ADDRESS_SIZE(af)) {
 410                 *errnop = EINVAL;
 411                 *h_errnop = NO_RECOVERY;
 412                 return NSS_STATUS_UNAVAIL;
 413         }
 414
 415         if (af == AF_INET) {
 416                 if ((*(uint32_t*) addr) == LOCALADDRESS_IPV4)
 417                         goto found;
 418
 419                 if ((*(uint32_t*) addr) == htobe32(INADDR_LOOPBACK)) {
 420                         canonical = "localhost";
 421                         local_address_ipv4 = htobe32(INADDR_LOOPBACK);
 422                         goto found;
 423                 }
 424
 425         } else {
 426                 assert(af == AF_INET6);
 427
 428                 if (memcmp(addr, LOCALADDRESS_IPV6, 16) == 0) {
 429                         canonical = "localhost";
 430                         additional_from_hostname = true;
 431                         goto found;
 432                 }
 433         }
 434
 435         n_addresses = local_addresses(NULL, 0, AF_UNSPEC, &addresses);
 436         for (a = addresses, n = 0; (int) n < n_addresses; n++, a++) {
 437                 if (af != a->family)
 438                         continue;
 439
 440                 if (memcmp(addr, &a->address, FAMILY_ADDRESS_SIZE(af)) == 0)
 441                         goto found;
 442         }
 443
 444         addresses = mfree(addresses);
 445
 446         n_addresses = local_gateways(NULL, 0, AF_UNSPEC, &addresses);
 447         for (a = addresses, n = 0; (int) n < n_addresses; n++, a++) {
 448                 if (af != a->family)
 449                         continue;
 450
 451                 if (memcmp(addr, &a->address, FAMILY_ADDRESS_SIZE(af)) == 0) {
 452                         canonical = "_gateway";
 453                         goto found;
 454                 }
 455         }
 456
 457         *h_errnop = HOST_NOT_FOUND;
 458         return NSS_STATUS_NOTFOUND;
 459
 460 found:
 461         if (!canonical || additional_from_hostname) {
 462                 hn = gethostname_malloc();
 463                 if (!hn) {
 464                         *errnop = ENOMEM;
 465                         *h_errnop = NO_RECOVERY;
 466                         return NSS_STATUS_TRYAGAIN;
 467                 }
 468
 469                 if (!canonical)
 470                         canonical = hn;
 471                 else
 472                         additional = hn;
 473         }
 474
 475         return fill_in_hostent(
 476                         canonical, additional,
 477                         af,
 478                         addresses, n_addresses,
 479                         local_address_ipv4,
 480                         host,
 481                         buffer, buflen,
 482                         errnop, h_errnop,
 483                         ttlp,
 484                         NULL);
 485 }
 486
 487 NSS_GETHOSTBYNAME_FALLBACKS(myhostname);
 488 NSS_GETHOSTBYADDR_FALLBACKS(myhostname);