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asterisk/main/dns.c

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/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 1999 - 2006 Thorsten Lockert
*
* Written by Thorsten Lockert <tholo@trollphone.org>
*
* 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 <tholo@trollphone.org>
*
* \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; /*!< authoritative 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; /*!< authoritative 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.
*
* \return 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.
*
* \return 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.
*
* \return 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.
*
* \return 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 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 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++) {
char addr[INET6_ADDRSTRLEN];
const char *addrp = NULL;
/* glibc sets sin_family to 0 when the nameserver is an IPv6 address */
if (state->nsaddr_list[i].sin_family) {
addrp = inet_ntop(AF_INET, &state->nsaddr_list[i].sin_addr, addr, sizeof(addr));
#if defined(HAVE_RES_NINIT) && defined(HAVE_STRUCT___RES_STATE__U__EXT_NSADDRS)
} else if (state->_u._ext.nsaddrs[i]) {
addrp = inet_ntop(AF_INET6, &state->_u._ext.nsaddrs[i]->sin6_addr, addr, sizeof(addr));
#endif
}
if (addrp) {
ast_debug(1, "Discovered nameserver: %s\n", addrp);
ast_str_container_add(nameservers, addrp);
}
}
#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;
}
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