resolv/res_hconf.c

   1 /* Copyright (C) 1993-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by David Mosberger (davidm@azstarnet.com).
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* This file provides a Linux /etc/host.conf compatible front end to
  20    the various name resolvers (/etc/hosts, named, NIS server, etc.).
  21    Though mostly compatibly, the following differences exist compared
  22    to the original implementation:
  23
  24         - new command "spoof" takes an arguments like RESOLV_SPOOF_CHECK
  25           environment variable (i.e., `off', `nowarn', or `warn').
  26
  27         - line comments can appear anywhere (not just at the beginning of
  28           a line)
  29 */
  30
  31 #include <assert.h>
  32 #include <errno.h>
  33 #include <ctype.h>
  34 #include <libintl.h>
  35 #include <memory.h>
  36 #include <stdio.h>
  37 #include <stdio_ext.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40 #include <net/if.h>
  41 #include <sys/ioctl.h>
  42 #include <unistd.h>
  43 #include <netinet/in.h>
  44 #include <bits/libc-lock.h>
  45 #include "ifreq.h"
  46 #include "res_hconf.h"
  47 #include <wchar.h>
  48
  49 #define _PATH_HOSTCONF  "/etc/host.conf"
  50
  51 /* Environment vars that all user to override default behavior:  */
  52 #define ENV_HOSTCONF    "RESOLV_HOST_CONF"
  53 #define ENV_SPOOF       "RESOLV_SPOOF_CHECK"
  54 #define ENV_TRIM_OVERR  "RESOLV_OVERRIDE_TRIM_DOMAINS"
  55 #define ENV_TRIM_ADD    "RESOLV_ADD_TRIM_DOMAINS"
  56 #define ENV_MULTI       "RESOLV_MULTI"
  57 #define ENV_REORDER     "RESOLV_REORDER"
  58
  59 enum parse_cbs
  60   {
  61     CB_none,
  62     CB_arg_trimdomain_list,
  63     CB_arg_spoof,
  64     CB_arg_bool
  65   };
  66
  67 static const struct cmd
  68 {
  69   const char name[11];
  70   uint8_t cb;
  71   unsigned int arg;
  72 } cmd[] =
  73 {
  74   {"order",             CB_none,                0},
  75   {"trim",              CB_arg_trimdomain_list, 0},
  76   {"spoof",             CB_arg_spoof,           0},
  77   {"multi",             CB_arg_bool,            HCONF_FLAG_MULTI},
  78   {"nospoof",           CB_arg_bool,            HCONF_FLAG_SPOOF},
  79   {"spoofalert",        CB_arg_bool,            HCONF_FLAG_SPOOFALERT},
  80   {"reorder",           CB_arg_bool,            HCONF_FLAG_REORDER}
  81 };
  82
  83 /* Structure containing the state.  */
  84 struct hconf _res_hconf;
  85
  86 /* Skip white space.  */
  87 static const char *
  88 skip_ws (const char *str)
  89 {
  90   while (isspace (*str)) ++str;
  91   return str;
  92 }
  93
  94
  95 /* Skip until whitespace, comma, end of line, or comment character.  */
  96 static const char *
  97 skip_string (const char *str)
  98 {
  99   while (*str && !isspace (*str) && *str != '#' && *str != ',')
 100     ++str;
 101   return str;
 102 }
 103
 104
 105 static const char *
 106 arg_trimdomain_list (const char *fname, int line_num, const char *args)
 107 {
 108   const char * start;
 109   size_t len;
 110
 111   do
 112     {
 113       start = args;
 114       args = skip_string (args);
 115       len = args - start;
 116
 117       if (_res_hconf.num_trimdomains >= TRIMDOMAINS_MAX)
 118         {
 119           char *buf;
 120
 121           if (__asprintf (&buf, _("\
 122 %s: line %d: cannot specify more than %d trim domains"),
 123                           fname, line_num, TRIMDOMAINS_MAX) < 0)
 124             return 0;
 125
 126           __fxprintf (NULL, "%s", buf);
 127
 128           free (buf);
 129           return 0;
 130         }
 131       _res_hconf.trimdomain[_res_hconf.num_trimdomains++] =
 132         __strndup (start, len);
 133       args = skip_ws (args);
 134       switch (*args)
 135         {
 136         case ',': case ';': case ':':
 137           args = skip_ws (++args);
 138           if (!*args || *args == '#')
 139             {
 140               char *buf;
 141
 142               if (__asprintf (&buf, _("\
 143 %s: line %d: list delimiter not followed by domain"),
 144                               fname, line_num) < 0)
 145                 return 0;
 146
 147               __fxprintf (NULL, "%s", buf);
 148
 149               free (buf);
 150               return 0;
 151             }
 152         default:
 153           break;
 154         }
 155     }
 156   while (*args && *args != '#');
 157   return args;
 158 }
 159
 160
 161 static const char *
 162 arg_spoof (const char *fname, int line_num, const char *args)
 163 {
 164   const char *start = args;
 165   size_t len;
 166
 167   args = skip_string (args);
 168   len = args - start;
 169
 170   if (len == 3 && __strncasecmp (start, "off", len) == 0)
 171     _res_hconf.flags &= ~(HCONF_FLAG_SPOOF | HCONF_FLAG_SPOOFALERT);
 172   else
 173     {
 174       _res_hconf.flags |= (HCONF_FLAG_SPOOF | HCONF_FLAG_SPOOFALERT);
 175       if ((len == 6 && __strncasecmp (start, "nowarn", len) == 0)
 176           || !(len == 4 && __strncasecmp (start, "warn", len) == 0))
 177         _res_hconf.flags &= ~HCONF_FLAG_SPOOFALERT;
 178     }
 179   return args;
 180 }
 181
 182
 183 static const char *
 184 arg_bool (const char *fname, int line_num, const char *args, unsigned flag)
 185 {
 186   if (__strncasecmp (args, "on", 2) == 0)
 187     {
 188       args += 2;
 189       _res_hconf.flags |= flag;
 190     }
 191   else if (__strncasecmp (args, "off", 3) == 0)
 192     {
 193       args += 3;
 194       _res_hconf.flags &= ~flag;
 195     }
 196   else
 197     {
 198       char *buf;
 199
 200       if (__asprintf (&buf,
 201                       _("%s: line %d: expected `on' or `off', found `%s'\n"),
 202                       fname, line_num, args) < 0)
 203         return 0;
 204
 205       __fxprintf (NULL, "%s", buf);
 206
 207       free (buf);
 208       return 0;
 209     }
 210   return args;
 211 }
 212
 213
 214 static void
 215 parse_line (const char *fname, int line_num, const char *str)
 216 {
 217   const char *start;
 218   const struct cmd *c = 0;
 219   size_t len;
 220   size_t i;
 221
 222   str = skip_ws (str);
 223
 224   /* skip line comment and empty lines: */
 225   if (*str == '\0' || *str == '#') return;
 226
 227   start = str;
 228   str = skip_string (str);
 229   len = str - start;
 230
 231   for (i = 0; i < sizeof (cmd) / sizeof (cmd[0]); ++i)
 232     {
 233       if (__strncasecmp (start, cmd[i].name, len) == 0
 234           && strlen (cmd[i].name) == len)
 235         {
 236           c = &cmd[i];
 237           break;
 238         }
 239     }
 240   if (c == NULL)
 241     {
 242       char *buf;
 243
 244       if (__asprintf (&buf, _("%s: line %d: bad command `%s'\n"),
 245                       fname, line_num, start) < 0)
 246         return;
 247
 248       __fxprintf (NULL, "%s", buf);
 249
 250       free (buf);
 251       return;
 252     }
 253
 254   /* process args: */
 255   str = skip_ws (str);
 256
 257   if (c->cb == CB_arg_trimdomain_list)
 258     str = arg_trimdomain_list (fname, line_num, str);
 259   else if (c->cb == CB_arg_spoof)
 260     str = arg_spoof (fname, line_num, str);
 261   else if (c->cb == CB_arg_bool)
 262     str = arg_bool (fname, line_num, str, c->arg);
 263   else
 264     /* Ignore the line.  */
 265     return;
 266
 267   if (!str)
 268     return;
 269
 270   /* rest of line must contain white space or comment only: */
 271   while (*str)
 272     {
 273       if (!isspace (*str)) {
 274         if (*str != '#')
 275           {
 276             char *buf;
 277
 278             if (__asprintf (&buf,
 279                             _("%s: line %d: ignoring trailing garbage `%s'\n"),
 280                             fname, line_num, str) < 0)
 281               break;
 282
 283             __fxprintf (NULL, "%s", buf);
 284
 285             free (buf);
 286           }
 287         break;
 288       }
 289       ++str;
 290     }
 291 }
 292
 293
 294 static void
 295 do_init (void)
 296 {
 297   const char *hconf_name;
 298   int line_num = 0;
 299   char buf[256], *envval;
 300   FILE *fp;
 301
 302   memset (&_res_hconf, '\0', sizeof (_res_hconf));
 303
 304   hconf_name = getenv (ENV_HOSTCONF);
 305   if (hconf_name == NULL)
 306     hconf_name = _PATH_HOSTCONF;
 307
 308   fp = fopen (hconf_name, "rce");
 309   if (fp)
 310     {
 311       /* No threads using this stream.  */
 312       __fsetlocking (fp, FSETLOCKING_BYCALLER);
 313
 314       while (fgets_unlocked (buf, sizeof (buf), fp))
 315         {
 316           ++line_num;
 317           *__strchrnul (buf, '\n') = '\0';
 318           parse_line (hconf_name, line_num, buf);
 319         }
 320       fclose (fp);
 321     }
 322
 323   envval = getenv (ENV_SPOOF);
 324   if (envval)
 325     arg_spoof (ENV_SPOOF, 1, envval);
 326
 327   envval = getenv (ENV_MULTI);
 328   if (envval)
 329     arg_bool (ENV_MULTI, 1, envval, HCONF_FLAG_MULTI);
 330
 331   envval = getenv (ENV_REORDER);
 332   if (envval)
 333     arg_bool (ENV_REORDER, 1, envval, HCONF_FLAG_REORDER);
 334
 335   envval = getenv (ENV_TRIM_ADD);
 336   if (envval)
 337     arg_trimdomain_list (ENV_TRIM_ADD, 1, envval);
 338
 339   envval = getenv (ENV_TRIM_OVERR);
 340   if (envval)
 341     {
 342       _res_hconf.num_trimdomains = 0;
 343       arg_trimdomain_list (ENV_TRIM_OVERR, 1, envval);
 344     }
 345
 346   _res_hconf.initialized = 1;
 347 }
 348
 349
 350 /* Initialize hconf datastructure by reading host.conf file and
 351    environment variables.  */
 352 void
 353 _res_hconf_init (void)
 354 {
 355   __libc_once_define (static, once);
 356
 357   __libc_once (once, do_init);
 358 }
 359
 360
 361 #if IS_IN (libc)
 362 # if defined SIOCGIFCONF && defined SIOCGIFNETMASK
 363 /* List of known interfaces.  */
 364 libc_freeres_ptr (
 365 static struct netaddr
 366 {
 367   int addrtype;
 368   union
 369   {
 370     struct
 371     {
 372       u_int32_t addr;
 373       u_int32_t mask;
 374     } ipv4;
 375   } u;
 376 } *ifaddrs);
 377 # endif
 378
 379 /* Reorder addresses returned in a hostent such that the first address
 380    is an address on the local subnet, if there is such an address.
 381    Otherwise, nothing is changed.
 382
 383    Note that this function currently only handles IPv4 addresses.  */
 384
 385 void
 386 _res_hconf_reorder_addrs (struct hostent *hp)
 387 {
 388 #if defined SIOCGIFCONF && defined SIOCGIFNETMASK
 389   int i, j;
 390   /* Number of interfaces.  */
 391   static int num_ifs = -1;
 392   /* We need to protect the dynamic buffer handling.  */
 393   __libc_lock_define_initialized (static, lock);
 394
 395   /* Only reorder if we're supposed to.  */
 396   if ((_res_hconf.flags & HCONF_FLAG_REORDER) == 0)
 397     return;
 398
 399   /* Can't deal with anything but IPv4 for now...  */
 400   if (hp->h_addrtype != AF_INET)
 401     return;
 402
 403   if (num_ifs <= 0)
 404     {
 405       struct ifreq *ifr, *cur_ifr;
 406       int sd, num, i;
 407       /* Save errno.  */
 408       int save = errno;
 409
 410       /* Initialize interface table.  */
 411
 412       /* The SIOCGIFNETMASK ioctl will only work on an AF_INET socket.  */
 413       sd = __socket (AF_INET, SOCK_DGRAM, 0);
 414       if (sd < 0)
 415         return;
 416
 417       /* Get lock.  */
 418       __libc_lock_lock (lock);
 419
 420       /* Recheck, somebody else might have done the work by done.  */
 421       if (num_ifs <= 0)
 422         {
 423           int new_num_ifs = 0;
 424
 425           /* Get a list of interfaces.  */
 426           __ifreq (&ifr, &num, sd);
 427           if (!ifr)
 428             goto cleanup;
 429
 430           ifaddrs = malloc (num * sizeof (ifaddrs[0]));
 431           if (!ifaddrs)
 432             goto cleanup1;
 433
 434           /* Copy usable interfaces in ifaddrs structure.  */
 435           for (cur_ifr = ifr, i = 0; i < num;
 436                cur_ifr = __if_nextreq (cur_ifr), ++i)
 437             {
 438               if (cur_ifr->ifr_addr.sa_family != AF_INET)
 439                 continue;
 440
 441               ifaddrs[new_num_ifs].addrtype = AF_INET;
 442               ifaddrs[new_num_ifs].u.ipv4.addr =
 443                 ((struct sockaddr_in *) &cur_ifr->ifr_addr)->sin_addr.s_addr;
 444
 445               if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0)
 446                 continue;
 447
 448               ifaddrs[new_num_ifs].u.ipv4.mask =
 449                 ((struct sockaddr_in *) &cur_ifr->ifr_netmask)->sin_addr.s_addr;
 450
 451               /* Now we're committed to this entry.  */
 452               ++new_num_ifs;
 453             }
 454           /* Just keep enough memory to hold all the interfaces we want.  */
 455           ifaddrs = realloc (ifaddrs, new_num_ifs * sizeof (ifaddrs[0]));
 456           assert (ifaddrs != NULL);
 457
 458         cleanup1:
 459           __if_freereq (ifr, num);
 460
 461         cleanup:
 462           /* Release lock, preserve error value, and close socket.  */
 463           errno = save;
 464
 465           num_ifs = new_num_ifs;
 466
 467           __libc_lock_unlock (lock);
 468         }
 469
 470       __close (sd);
 471     }
 472
 473   if (num_ifs == 0)
 474     return;
 475
 476   /* Find an address for which we have a direct connection.  */
 477   for (i = 0; hp->h_addr_list[i]; ++i)
 478     {
 479       struct in_addr *haddr = (struct in_addr *) hp->h_addr_list[i];
 480
 481       for (j = 0; j < num_ifs; ++j)
 482         {
 483           u_int32_t if_addr    = ifaddrs[j].u.ipv4.addr;
 484           u_int32_t if_netmask = ifaddrs[j].u.ipv4.mask;
 485
 486           if (((haddr->s_addr ^ if_addr) & if_netmask) == 0)
 487             {
 488               void *tmp;
 489
 490               tmp = hp->h_addr_list[i];
 491               hp->h_addr_list[i] = hp->h_addr_list[0];
 492               hp->h_addr_list[0] = tmp;
 493               return;
 494             }
 495         }
 496     }
 497 #endif /* defined(SIOCGIFCONF) && ... */
 498 }
 499
 500
 501 /* If HOSTNAME has a postfix matching any of the trimdomains, trim away
 502    that postfix.  Notice that HOSTNAME is modified inplace.  Also, the
 503    original code applied all trimdomains in order, meaning that the
 504    same domainname could be trimmed multiple times.  I believe this
 505    was unintentional.  */
 506 void
 507 _res_hconf_trim_domain (char *hostname)
 508 {
 509   size_t hostname_len, trim_len;
 510   int i;
 511
 512   hostname_len = strlen (hostname);
 513
 514   for (i = 0; i < _res_hconf.num_trimdomains; ++i)
 515     {
 516       const char *trim = _res_hconf.trimdomain[i];
 517
 518       trim_len = strlen (trim);
 519       if (hostname_len > trim_len
 520           && __strcasecmp (&hostname[hostname_len - trim_len], trim) == 0)
 521         {
 522           hostname[hostname_len - trim_len] = '\0';
 523           break;
 524         }
 525     }
 526 }
 527
 528
 529 /* Trim all hostnames/aliases in HP according to the trimdomain list.
 530    Notice that HP is modified inplace!  */
 531 void
 532 _res_hconf_trim_domains (struct hostent *hp)
 533 {
 534   int i;
 535
 536   if (_res_hconf.num_trimdomains == 0)
 537     return;
 538
 539   _res_hconf_trim_domain (hp->h_name);
 540   for (i = 0; hp->h_aliases[i]; ++i)
 541     _res_hconf_trim_domain (hp->h_aliases[i]);
 542 }
 543 #endif