main/dns.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 1999 - 2006 Thorsten Lockert
   5  *
   6  * Written by Thorsten Lockert <tholo@trollphone.org>
   7  *
   8  * Funding provided by Troll Phone Networks AS
   9  *
  10  * See http://www.asterisk.org for more information about
  11  * the Asterisk project. Please do not directly contact
  12  * any of the maintainers of this project for assistance;
  13  * the project provides a web site, mailing lists and IRC
  14  * channels for your use.
  15  *
  16  * This program is free software, distributed under the terms of
  17  * the GNU General Public License Version 2. See the LICENSE file
  18  * at the top of the source tree.
  19  */
  20
  21 /*! \file
  22  *
  23  * \brief DNS Support for Asterisk
  24  *
  25  * \author Thorsten Lockert <tholo@trollphone.org>
  26  *
  27  * \par Reference
  28  * - DNR SRV records http://www.ietf.org/rfc/rfc2782.txt
  29  *
  30  */
  31
  32 #include "asterisk.h"
  33
  34 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
  35
  36 #include <sys/types.h>
  37 #include <sys/socket.h>
  38 #include <netinet/in.h>
  39 #include <arpa/nameser.h>
  40 #include <resolv.h>
  41 #include <unistd.h>
  42
  43 #include "asterisk/logger.h"
  44 #include "asterisk/channel.h"
  45 #include "asterisk/dns.h"
  46 #include "asterisk/endian.h"
  47
  48 #define MAX_SIZE 4096
  49
  50 /* The dns_HEADER structure definition below originated
  51    in the arpa/nameser.h header file distributed with ISC
  52    BIND, which contains the following copyright and license
  53    notices:
  54
  55  * ++Copyright++ 1983, 1989, 1993
  56  * -
  57  * Copyright (c) 1983, 1989, 1993
  58  *    The Regents of the University of California.  All rights reserved.
  59  *
  60  * Redistribution and use in source and binary forms, with or without
  61  * modification, are permitted provided that the following conditions
  62  * are met:
  63  * 1. Redistributions of source code must retain the above copyright
  64  *    notice, this list of conditions and the following disclaimer.
  65  * 2. Redistributions in binary form must reproduce the above copyright
  66  *    notice, this list of conditions and the following disclaimer in the
  67  *    documentation and/or other materials provided with the distribution.
  68  * 3. All advertising materials mentioning features or use of this software
  69  *    must display the following acknowledgement:
  70  *      This product includes software developed by the University of
  71  *      California, Berkeley and its contributors.
  72  * 4. Neither the name of the University nor the names of its contributors
  73  *    may be used to endorse or promote products derived from this software
  74  *    without specific prior written permission.
  75  *
  76  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  77  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  78  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  79  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  80  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  81  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  82  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  83  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  84  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  85  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  86  * SUCH DAMAGE.
  87  * -
  88  * Portions Copyright (c) 1993 by Digital Equipment Corporation.
  89  *
  90  * Permission to use, copy, modify, and distribute this software for any
  91  * purpose with or without fee is hereby granted, provided that the above
  92  * copyright notice and this permission notice appear in all copies, and that
  93  * the name of Digital Equipment Corporation not be used in advertising or
  94  * publicity pertaining to distribution of the document or software without
  95  * specific, written prior permission.
  96  *
  97  * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
  98  * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
  99  * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
 100  * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 101  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 102  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 103  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 104  * SOFTWARE.
 105  * -
 106  * --Copyright--
 107  */
 108
 109 typedef struct {
 110         unsigned        id:16;          /*!< query identification number */
 111 #if __BYTE_ORDER == __BIG_ENDIAN
 112                         /* fields in third byte */
 113         unsigned        qr:1;           /*!< response flag */
 114         unsigned        opcode:4;       /*!< purpose of message */
 115         unsigned        aa:1;           /*!< authoritive answer */
 116         unsigned        tc:1;           /*!< truncated message */
 117         unsigned        rd:1;           /*!< recursion desired */
 118                         /* fields in fourth byte */
 119         unsigned        ra:1;           /*!< recursion available */
 120         unsigned        unused:1;       /*!< unused bits (MBZ as of 4.9.3a3) */
 121         unsigned        ad:1;           /*!< authentic data from named */
 122         unsigned        cd:1;           /*!< checking disabled by resolver */
 123         unsigned        rcode:4;        /*!< response code */
 124 #endif
 125 #if __BYTE_ORDER == __LITTLE_ENDIAN || __BYTE_ORDER == __PDP_ENDIAN
 126                         /* fields in third byte */
 127         unsigned        rd:1;           /*!< recursion desired */
 128         unsigned        tc:1;           /*!< truncated message */
 129         unsigned        aa:1;           /*!< authoritive answer */
 130         unsigned        opcode:4;       /*!< purpose of message */
 131         unsigned        qr:1;           /*!< response flag */
 132                         /* fields in fourth byte */
 133         unsigned        rcode:4;        /*!< response code */
 134         unsigned        cd:1;           /*!< checking disabled by resolver */
 135         unsigned        ad:1;           /*!< authentic data from named */
 136         unsigned        unused:1;       /*!< unused bits (MBZ as of 4.9.3a3) */
 137         unsigned        ra:1;           /*!< recursion available */
 138 #endif
 139                         /* remaining bytes */
 140         unsigned        qdcount:16;     /*!< number of question entries */
 141         unsigned        ancount:16;     /*!< number of answer entries */
 142         unsigned        nscount:16;     /*!< number of authority entries */
 143         unsigned        arcount:16;     /*!< number of resource entries */
 144 } dns_HEADER;
 145
 146 struct dn_answer {
 147         unsigned short rtype;
 148         unsigned short class;
 149         unsigned int ttl;
 150         unsigned short size;
 151 } __attribute__ ((__packed__));
 152
 153 static int skip_name(unsigned char *s, int len)
 154 {
 155         int x = 0;
 156
 157         while (x < len) {
 158                 if (*s == '\0') {
 159                         s++;
 160                         x++;
 161                         break;
 162                 }
 163                 if ((*s & 0xc0) == 0xc0) {
 164                         s += 2;
 165                         x += 2;
 166                         break;
 167                 }
 168                 x += *s + 1;
 169                 s += *s + 1;
 170         }
 171         if (x >= len)
 172                 return -1;
 173         return x;
 174 }
 175
 176 /*! \brief Parse DNS lookup result, call callback */
 177 static int dns_parse_answer(void *context,
 178         int class, int type, unsigned char *answer, int len,
 179         int (*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
 180 {
 181         unsigned char *fullanswer = answer;
 182         struct dn_answer *ans;
 183         dns_HEADER *h;
 184         int res;
 185         int x;
 186
 187         h = (dns_HEADER *)answer;
 188         answer += sizeof(dns_HEADER);
 189         len -= sizeof(dns_HEADER);
 190
 191         for (x = 0; x < ntohs(h->qdcount); x++) {
 192                 if ((res = skip_name(answer, len)) < 0) {
 193                         ast_log(LOG_WARNING, "Couldn't skip over name\n");
 194                         return -1;
 195                 }
 196                 answer += res + 4;      /* Skip name and QCODE / QCLASS */
 197                 len -= res + 4;
 198                 if (len < 0) {
 199                         ast_log(LOG_WARNING, "Strange query size\n");
 200                         return -1;
 201                 }
 202         }
 203
 204         for (x = 0; x < ntohs(h->ancount); x++) {
 205                 if ((res = skip_name(answer, len)) < 0) {
 206                         ast_log(LOG_WARNING, "Failed skipping name\n");
 207                         return -1;
 208                 }
 209                 answer += res;
 210                 len -= res;
 211                 ans = (struct dn_answer *)answer;
 212                 answer += sizeof(struct dn_answer);
 213                 len -= sizeof(struct dn_answer);
 214                 if (len < 0) {
 215                         ast_log(LOG_WARNING, "Strange result size\n");
 216                         return -1;
 217                 }
 218                 if (len < 0) {
 219                         ast_log(LOG_WARNING, "Length exceeds frame\n");
 220                         return -1;
 221                 }
 222
 223                 if (ntohs(ans->class) == class && ntohs(ans->rtype) == type) {
 224                         if (callback) {
 225                                 if ((res = callback(context, answer, ntohs(ans->size), fullanswer)) < 0) {
 226                                         ast_log(LOG_WARNING, "Failed to parse result\n");
 227                                         return -1;
 228                                 }
 229                                 if (res > 0)
 230                                         return 1;
 231                         }
 232                 }
 233                 answer += ntohs(ans->size);
 234                 len -= ntohs(ans->size);
 235         }
 236         return 0;
 237 }
 238
 239 #ifndef HAVE_RES_NINIT
 240 AST_MUTEX_DEFINE_STATIC(res_lock);
 241 #endif
 242
 243 /*! \brief Lookup record in DNS
 244 \note Asterisk DNS is synchronus at this time. This means that if your DNS does
 245 not work properly, Asterisk might not start properly or a channel may lock.
 246 */
 247 int ast_search_dns(void *context,
 248            const char *dname, int class, int type,
 249            int (*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
 250 {
 251 #ifdef HAVE_RES_NINIT
 252         struct __res_state dnsstate;
 253 #endif
 254         unsigned char answer[MAX_SIZE];
 255         int res, ret = -1;
 256
 257 #ifdef HAVE_RES_NINIT
 258         res_ninit(&dnsstate);
 259         res = res_nsearch(&dnsstate, dname, class, type, answer, sizeof(answer));
 260 #else
 261         ast_mutex_lock(&res_lock);
 262         res_init();
 263         res = res_search(dname, class, type, answer, sizeof(answer));
 264 #endif
 265         if (res > 0) {
 266                 if ((res = dns_parse_answer(context, class, type, answer, res, callback)) < 0) {
 267                         ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
 268                         ret = -1;
 269                 }
 270                 else if (res == 0) {
 271                         ast_log(LOG_DEBUG, "No matches found in DNS for %s\n", dname);
 272                         ret = 0;
 273                 }
 274                 else
 275                         ret = 1;
 276         }
 277 #ifdef HAVE_RES_NINIT
 278 #ifdef HAVE_RES_NDESTROY
 279         res_ndestroy(&dnsstate);
 280 #else
 281         res_nclose(&dnsstate);
 282 #endif
 283 #else
 284 #ifndef __APPLE__
 285         res_close();
 286 #endif
 287         ast_mutex_unlock(&res_lock);
 288 #endif
 289
 290         return ret;
 291 }