dns.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006 Thorsten Lockert
 *
 * Written by Thorsten Lockert <[email protected]>
 *
 * Funding provided by Troll Phone Networks AS
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief DNS Support for Asterisk
 *
 * \author Thorsten Lockert <[email protected]>
 *
 * \par Reference
 * - DNR SRV records http://www.ietf.org/rfc/rfc2782.txt
 *
 */

/*** MODULEINFO
 <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include "asterisk/network.h"
#include <arpa/nameser.h> /* res_* functions */
#include <resolv.h>

#include "asterisk/channel.h"
#include "asterisk/dns.h"
#include "asterisk/endian.h"

/*! \brief The maximum size permitted for the answer from the DNS server */
#define MAX_SIZE 4096

#ifdef __PDP_ENDIAN
#if __BYTE_ORDER == __PDP_ENDIAN
#define DETERMINED_BYTE_ORDER __LITTLE_ENDIAN
#endif
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
#define DETERMINED_BYTE_ORDER __BIG_ENDIAN
#endif
#if __BYTE_ORDER == __LITTLE_ENDIAN
#define DETERMINED_BYTE_ORDER __LITTLE_ENDIAN
#endif

#ifndef HAVE_RES_NINIT
AST_MUTEX_DEFINE_STATIC(res_lock);
#endif

/* The dns_HEADER structure definition below originated
 in the arpa/nameser.h header file distributed with ISC
 BIND, which contains the following copyright and license
 notices:

 * ++Copyright++ 1983, 1989, 1993
 * -
 * Copyright (c) 1983, 1989, 1993
 * The Regents of the University of California. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 * must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * -
 * Portions Copyright (c) 1993 by Digital Equipment Corporation.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies, and that
 * the name of Digital Equipment Corporation not be used in advertising or
 * publicity pertaining to distribution of the document or software without
 * specific, written prior permission.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL DIGITAL EQUIPMENT
 * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 * -
 * --Copyright--
 */

typedef struct {
 unsigned id:16; /*!< query identification number */
#if DETERMINED_BYTE_ORDER == __BIG_ENDIAN
 /* fields in third byte */
 unsigned qr:1; /*!< response flag */
 unsigned opcode:4; /*!< purpose of message */
 unsigned aa:1; /*!< authoritive answer */
 unsigned tc:1; /*!< truncated message */
 unsigned rd:1; /*!< recursion desired */
 /* fields in fourth byte */
 unsigned ra:1; /*!< recursion available */
 unsigned unused:1; /*!< unused bits (MBZ as of 4.9.3a3) */
 unsigned ad:1; /*!< authentic data from named */
 unsigned cd:1; /*!< checking disabled by resolver */
 unsigned rcode:4; /*!< response code */
#endif
#if DETERMINED_BYTE_ORDER == __LITTLE_ENDIAN
 /* fields in third byte */
 unsigned rd:1; /*!< recursion desired */
 unsigned tc:1; /*!< truncated message */
 unsigned aa:1; /*!< authoritive answer */
 unsigned opcode:4; /*!< purpose of message */
 unsigned qr:1; /*!< response flag */
 /* fields in fourth byte */
 unsigned rcode:4; /*!< response code */
 unsigned cd:1; /*!< checking disabled by resolver */
 unsigned ad:1; /*!< authentic data from named */
 unsigned unused:1; /*!< unused bits (MBZ as of 4.9.3a3) */
 unsigned ra:1; /*!< recursion available */
#endif
 /* remaining bytes */
 unsigned qdcount:16; /*!< number of question entries */
 unsigned ancount:16; /*!< number of answer entries */
 unsigned nscount:16; /*!< number of authority entries */
 unsigned arcount:16; /*!< number of resource entries */
} dns_HEADER;

struct dn_answer {
 unsigned short rtype; /*!< The resource record type. */
 unsigned short class; /*!< The resource record class. */
 unsigned int ttl; /*!< The resource record time to live. */
 unsigned short size; /*!< The resource record size. */
} __attribute__((__packed__));

/*!
 * \brief Tries to find the position of the next field in the DNS response.
 *
 * \internal
 *
 * \param s A char pointer to the current frame in the DNS response.
 * \param len The remaining available length of the DNS response.
 *
 * \retval The position of the next field
 * \retval -1 if there are no remaining fields
 */
static int skip_name(unsigned char *s, int len)
{
 int x = 0;

 while (x < len) {
 if (*s == '\0') {
 s++;
 x++;
 break;
 }

 if ((*s & 0xc0) == 0xc0) {
 s += 2;
 x += 2;
 break;
 }

 x += *s + 1;
 s += *s + 1;
 }

 /* If we are out of room to search, return failure. */
 if (x >= len) {
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Return the value for the current position in the DNS response. This is the start
 position of the next field. */
 return x;
}

/*!
 * \brief Advances the position of the DNS response pointer by the size of the current field.
 *
 * \internal
 *
 * \param dns_response A pointer to a char pointer to the current field in the DNS response.
 * \param remaining_len The remaining available length in the DNS response to search.
 * \param field_size A positive value representing the size of the current field
 pointed to by the dns_response parameter.
 *
 * \retval The remaining length in the DNS response
 * \retval -1 there are no frames remaining in the DNS response
 */
static int dns_advance_field(unsigned char **dns_response, int remaining_len, int field_size)
{
 if (dns_response == NULL || field_size < 0 || remaining_len < field_size) {
 return AST_DNS_SEARCH_FAILURE;
 }

 *dns_response += field_size;
 remaining_len -= field_size;

 return remaining_len;
}

#ifndef HAVE_RES_NINIT
/*!
 * \brief Handles the DNS search if the system has RES_INIT.
 *
 * \internal
 *
 * \param dname Domain name to lookup (host, SRV domain, TXT record name).
 * \param rr_class Record Class (see "man res_search").
 * \param rr_type Record type (see "man res_search").
 * \param dns_response The full DNS response.
 * \param dns_response_len The length of the full DNS response.
 *
 * \retval The length of the DNS response
 * \retval -1 on search failure
 */
static int dns_search_res(const char *dname, int rr_class, int rr_type,
 unsigned char *dns_response, int dns_response_len)
{

 int ret = AST_DNS_SEARCH_FAILURE;

 ast_mutex_lock(&res_lock);
 res_init();
 ret = res_search(dname,
 rr_class,
 rr_type,
 dns_response,
 dns_response_len);

#ifdef HAVE_RES_CLOSE
 res_close();
#endif

 ast_mutex_unlock(&res_lock);

 return ret;
}
#else
/*!
 * \brief Handles the DNS search if the system has RES_NINIT.
 *
 * \internal
 *
 * \param dname Domain name to lookup (host, SRV domain, TXT record name).
 * \param rr_class Record Class (see "man res_search").
 * \param rr_type Record type (see "man res_search").
 * \param dns_response The full DNS response.
 * \param dns_response_len The length of the full DNS response.
 *
 * \retval The length of the DNS response
 * \retval -1 on search failure
 */
static int dns_search_res(const char *dname, int rr_class, int rr_type,
 unsigned char *dns_response, int dns_response_len)
{

 int ret = AST_DNS_SEARCH_FAILURE;
 struct __res_state dns_state;

 memset(&dns_state, 0, sizeof(dns_state));
 res_ninit(&dns_state);
 ret = res_nsearch(&dns_state,
 dname,
 rr_class,
 rr_type,
 dns_response,
 dns_response_len);

#ifdef HAVE_RES_NDESTROY
 res_ndestroy(&dns_state);
#else
 res_nclose(&dns_state);
#endif

 return ret;
}
#endif

/*!
 * \brief Parse DNS lookup result, call callback
 *
 * \internal
 *
 * \param context Void pointer containing data to use in the callback functions.
 * \param dname Domain name to lookup (host, SRV domain, TXT record name).
 * \param class Record Class (see "man res_search").
 * \param type Record type (see "man res_search").
 * \param answer The full DNS response.
 * \param len The length of the full DNS response.
 * \param callback Callback function for handling the discovered resource records from the DNS search.
 *
 * \retval -1 on search failure
 * \retval 0 on no records found
 * \retval 1 on success
 */
static int dns_parse_answer(void *context,
 int class, int type, unsigned char *answer, int len,
 int (*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
{
 unsigned char *fullanswer = answer;
 struct dn_answer *ans;
 dns_HEADER *h;
 int ret = 0;
 int res;
 int x;

 h = (dns_HEADER *)answer;
 answer += sizeof(dns_HEADER);
 len -= sizeof(dns_HEADER);

 for (x = 0; x < ntohs(h->qdcount); x++) {
 if ((res = skip_name(answer, len)) < 0) {
 ast_log(LOG_WARNING, "Couldn't skip over name\n");
 return -1;
 }
 answer += res + 4; /* Skip name and QCODE / QCLASS */
 len -= res + 4;
 if (len < 0) {
 ast_log(LOG_WARNING, "Strange query size\n");
 return -1;
 }
 }

 for (x = 0; x < ntohs(h->ancount); x++) {
 if ((res = skip_name(answer, len)) < 0) {
 ast_log(LOG_WARNING, "Failed skipping name\n");
 return -1;
 }
 answer += res;
 len -= res;
 ans = (struct dn_answer *)answer;
 answer += sizeof(struct dn_answer);
 len -= sizeof(struct dn_answer);
 if (len < 0) {
 ast_log(LOG_WARNING, "Length of DNS answer exceeds frame\n");
 return -1;
 }

 if (ntohs(ans->class) == class && ntohs(ans->rtype) == type) {
 if (callback) {
 if ((res = callback(context, answer, ntohs(ans->size), fullanswer)) < 0) {
 ast_log(LOG_WARNING, "Failed to parse result\n");
 return -1;
 }
 ret = 1;
 }
 }
 answer += ntohs(ans->size);
 len -= ntohs(ans->size);
 }
 return ret;
}

/*!
 * \brief Extended version of the DNS Parsing function.
 *
 * \details Parses the DNS lookup result and notifies the observer of each discovered
 * resource record with the provided callback.
 *
 * \internal
 *
 * \param context Void pointer containing data to use in the callback functions.
 * \param dname Domain name to lookup (host, SRV domain, TXT record name).
 * \param rr_class Record Class (see "man res_search").
 * \param rr_type Record type (see "man res_search").
 * \param answer The full DNS response.
 * \param answer_len The length of the full DNS response.
 * \param response_handler Callback function for handling the DNS response.
 * \param record_handler Callback function for handling the discovered resource records from the DNS search.
 *
 * \retval -1 on search failure
 * \retval 0 on no records found
 * \retval 1 on success
 */
static int dns_parse_answer_ex(void *context, int rr_class, int rr_type, unsigned char *answer, int answer_len,
 int (*response_handler)(void *context, unsigned char *dns_response, int dns_response_len, int rcode),
 int (*record_handler)(void *context, unsigned char *record, int record_len, int ttl))
{
 unsigned char *dns_response = answer;
 dns_HEADER *dns_header = (dns_HEADER *)answer;

 struct dn_answer *ans;
 int res, x, pos, dns_response_len, ret;

 dns_response_len = answer_len;
 ret = AST_DNS_SEARCH_NO_RECORDS;

 /* Invoke the response_handler callback to notify the observer of the raw DNS response */
 response_handler(context, dns_response, dns_response_len, ntohs(dns_header->rcode));

 /* Verify there is something to parse */
 if (answer_len == 0) {
 return ret;
 }

 /* Try advancing the cursor for the dns header */
 if ((pos = dns_advance_field(&answer, answer_len, sizeof(dns_HEADER))) < 0) {
 ast_log(LOG_WARNING, "Length of DNS answer exceeds available search frames\n");
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Skip domain name and QCODE / QCLASS */
 for (x = 0; x < ntohs(dns_header->qdcount); x++) {
 if ((res = skip_name(answer, pos)) < 0) {
 ast_log(LOG_WARNING, "Failed skipping name\n");
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Try advancing the cursor for the name and QCODE / QCLASS fields */
 if ((pos = dns_advance_field(&answer, pos, res + 4)) < 0) {
 return AST_DNS_SEARCH_FAILURE;
 }
 }

 /* Extract the individual records */
 for (x = 0; x < ntohs(dns_header->ancount); x++) {
 if ((res = skip_name(answer, pos)) < 0) {
 ast_log(LOG_WARNING, "Failed skipping name\n");
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Try advancing the cursor to the current record */
 if ((pos = dns_advance_field(&answer, pos, res)) < 0) {
 ast_log(LOG_WARNING, "Length of DNS answer exceeds available search frames\n");
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Cast the current value for the answer pointer as a dn_answer struct */
 ans = (struct dn_answer *) answer;

 /* Try advancing the cursor to the end of the current record */
 if ((pos = dns_advance_field(&answer, pos, sizeof(struct dn_answer))) < 0) {
 ast_log(LOG_WARNING, "Length of DNS answer exceeds available search frames\n");
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Skip over the records that do not have the same resource record class and type we care about */
 if (ntohs(ans->class) == rr_class && ntohs(ans->rtype) == rr_type) {
 /* Invoke the record handler callback to deliver the discovered record */
 record_handler(context, answer, ntohs(ans->size), ntohl(ans->ttl));
 /*At least one record was found */
 ret = AST_DNS_SEARCH_SUCCESS;
 }

 /* Try and update the field to the next record, but ignore any errors that come
 * back because this may be the end of the line. */
 pos = dns_advance_field(&answer, pos, ntohs(ans->size));
 }

 return ret;
}

/*!
 * \brief Lookup record in DNS
 *
 * \note Asterisk DNS is synchronus at this time. This means that if your DNS does not
 * work properly, Asterisk might not start properly or a channel may lock.
*/
int ast_search_dns(void *context,
 const char *dname, int class, int type,
 int (*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
{
#ifdef HAVE_RES_NINIT
 struct __res_state dnsstate;
#endif
 unsigned char answer[MAX_SIZE];
 int res, ret = -1;

#ifdef HAVE_RES_NINIT
 memset(&dnsstate, 0, sizeof(dnsstate));
 res_ninit(&dnsstate);
 res = res_nsearch(&dnsstate, dname, class, type, answer, sizeof(answer));
#else
 ast_mutex_lock(&res_lock);
 res_init();
 res = res_search(dname, class, type, answer, sizeof(answer));
#endif
 if (res > 0) {
 if ((res = dns_parse_answer(context, class, type, answer, res, callback)) < 0) {
 ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
 ret = -1;
 } else if (res == 0) {
 ast_debug(1, "No matches found in DNS for %s\n", dname);
 ret = 0;
 } else
 ret = 1;
 }
#ifdef HAVE_RES_NINIT
#ifdef HAVE_RES_NDESTROY
 res_ndestroy(&dnsstate);
#else
 res_nclose(&dnsstate);
#endif
#else
#ifdef HAVE_RES_CLOSE
 res_close();
#endif
 ast_mutex_unlock(&res_lock);
#endif

 return ret;
}

enum ast_dns_search_result ast_search_dns_ex(void *context, const char *dname, int rr_class, int rr_type,
 int (*response_handler)(void *context, unsigned char *dns_response, int dns_response_len, int rcode),
 int (*record_handler)(void *context, unsigned char *record, int record_len, int ttl))
{
 int ret, dns_response_len;
 unsigned char dns_response[MAX_SIZE];

 /* Assert that the callbacks are not NULL */
 ast_assert(response_handler != NULL);
 ast_assert(record_handler != NULL);

 /* Try the DNS search. */
 dns_response_len = dns_search_res(dname,
 rr_class,
 rr_type,
 dns_response,
 sizeof(dns_response));

 if (dns_response_len < 0) {
 ast_debug(1, "DNS search failed for %s\n", dname);
 response_handler(context, (unsigned char *)"", 0, NXDOMAIN);
 return AST_DNS_SEARCH_FAILURE;
 }

 /* Parse records from DNS response */
 ret = dns_parse_answer_ex(context,
 rr_class,
 rr_type,
 dns_response,
 dns_response_len,
 response_handler,
 record_handler);

 /* Handle the return code from parsing the DNS response */
 if (ret == AST_DNS_SEARCH_FAILURE) {
 /* Parsing Error */
 ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
 } else if (ret == AST_DNS_SEARCH_NO_RECORDS) {
 /* No results found */
 ast_debug(1, "DNS search yielded no results for %s\n", dname);
 }

 return ret;
}

struct ao2_container *ast_dns_get_nameservers(void)
{
#ifdef HAVE_RES_NINIT
 struct __res_state dnsstate;
#endif
 struct __res_state *state;
 struct ao2_container *nameservers;
 int i;

 nameservers = ast_str_container_alloc_options(AO2_ALLOC_OPT_LOCK_NOLOCK, 3);
 if (!nameservers) {
 return NULL;
 }

#ifdef HAVE_RES_NINIT
 memset(&dnsstate, 0, sizeof(dnsstate));
 res_ninit(&dnsstate);
 state = &dnsstate;
#else
 ast_mutex_lock(&res_lock);
 res_init();
 state = &_res;
#endif

 for (i = 0; i < state->nscount; i++) {
 ast_str_container_add(nameservers, ast_inet_ntoa(state->nsaddr_list[i].sin_addr));
 }

#ifdef HAVE_RES_NINIT
#ifdef HAVE_RES_NDESTROY
 res_ndestroy(&dnsstate);
#else
 res_nclose(&dnsstate);
#endif
#else
#ifdef HAVE_RES_CLOSE
 res_close();
#endif
 ast_mutex_unlock(&res_lock);
#endif

 return nameservers;
}