dns_core.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2015, Digium, Inc.
 *
 * Joshua Colp <[email protected]>
 *
 * 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 Core DNS Functionality
 *
 * \author Joshua Colp <[email protected]>
 */

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

#include "asterisk.h"

#include "asterisk/_private.h"
#include "asterisk/linkedlists.h"
#include "asterisk/astobj2.h"
#include "asterisk/strings.h"
#include "asterisk/sched.h"
#include "asterisk/dns_core.h"
#include "asterisk/dns_srv.h"
#include "asterisk/dns_tlsa.h"
#include "asterisk/dns_recurring.h"
#include "asterisk/dns_resolver.h"
#include "asterisk/dns_internal.h"
#include "asterisk/netsock2.h"

#include <netinet/in.h>
#include <arpa/nameser.h>

AST_RWLIST_HEAD_STATIC(resolvers, ast_dns_resolver);

static struct ast_sched_context *sched;

struct ast_sched_context *ast_dns_get_sched(void)
{
   return sched;
}

const char *ast_dns_query_get_name(const struct ast_dns_query *query)
{
   return query->name;
}

int ast_dns_query_get_rr_type(const struct ast_dns_query *query)
{
   return query->rr_type;
}

int ast_dns_query_get_rr_class(const struct ast_dns_query *query)
{
   return query->rr_class;
}

void *ast_dns_query_get_data(const struct ast_dns_query *query)
{
   return query->user_data;
}

struct ast_dns_result *ast_dns_query_get_result(const struct ast_dns_query *query)
{
   return query->result;
}

unsigned int ast_dns_result_get_secure(const struct ast_dns_result *result)
{
   return result->secure;
}

unsigned int ast_dns_result_get_bogus(const struct ast_dns_result *result)
{
   return result->bogus;
}

unsigned int ast_dns_result_get_rcode(const struct ast_dns_result *result)
{
   return result->rcode;
}

const char *ast_dns_result_get_canonical(const struct ast_dns_result *result)
{
   return result->canonical;
}

const struct ast_dns_record *ast_dns_result_get_records(const struct ast_dns_result *result)
{
   return AST_LIST_FIRST(&result->records);
}

const char *ast_dns_result_get_answer(const struct ast_dns_result *result)
{
   return result->answer;
}

int ast_dns_result_get_lowest_ttl(const struct ast_dns_result *result)
{
   int ttl = 0;
   const struct ast_dns_record *record;

   if (ast_dns_result_get_rcode(result) == NXDOMAIN) {
      return 0;
   }

   for (record = ast_dns_result_get_records(result); record; record = ast_dns_record_get_next(record)) {
      if (!ttl || (ast_dns_record_get_ttl(record) && (ast_dns_record_get_ttl(record) < ttl))) {
         ttl = ast_dns_record_get_ttl(record);
      }
   }

   return ttl;
}

void ast_dns_result_free(struct ast_dns_result *result)
{
   struct ast_dns_record *record;

   if (!result) {
      return;
   }

   while ((record = AST_LIST_REMOVE_HEAD(&result->records, list))) {
      ast_free(record);
   }

   ast_free(result);
}

int ast_dns_record_get_rr_type(const struct ast_dns_record *record)
{
   return record->rr_type;
}

int ast_dns_record_get_rr_class(const struct ast_dns_record *record)
{
   return record->rr_class;
}

int ast_dns_record_get_ttl(const struct ast_dns_record *record)
{
   return record->ttl;
}

const char *ast_dns_record_get_data(const struct ast_dns_record *record)
{
   return record->data_ptr;
}

size_t ast_dns_record_get_data_size(const struct ast_dns_record *record)
{
   return record->data_len;
}

const struct ast_dns_record *ast_dns_record_get_next(const struct ast_dns_record *record)
{
   return AST_LIST_NEXT(record, list);
}

/*! \brief Destructor for an active DNS query */
static void dns_query_active_destroy(void *data)
{
   struct ast_dns_query_active *active = data;

   ao2_cleanup(active->query);
}

/*! \brief \brief Destructor for a DNS query */
static void dns_query_destroy(void *data)
{
   struct ast_dns_query *query = data;

   ao2_cleanup(query->user_data);
   ao2_cleanup(query->resolver_data);
   ast_dns_result_free(query->result);
}

struct ast_dns_query *dns_query_alloc(const char *name, int rr_type, int rr_class, ast_dns_resolve_callback callback, void *data)
{
   struct ast_dns_query *query;

   if (ast_strlen_zero(name)) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution, no name provided\n");
      return NULL;
   } else if (rr_type > 65536) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', resource record type '%d' exceeds maximum\n",
         name, rr_type);
      return NULL;
   } else if (rr_type < 0) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', invalid resource record type '%d'\n",
         name, rr_type);
      return NULL;
   } else if (rr_class > 65536) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', resource record class '%d' exceeds maximum\n",
         name, rr_class);
      return NULL;
   } else if (rr_class < 0) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', invalid resource class '%d'\n",
         name, rr_class);
      return NULL;
   } else if (!callback) {
      ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', no callback provided\n",
         name);
      return NULL;
   }

   query = ao2_alloc_options(sizeof(*query) + strlen(name) + 1, dns_query_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
   if (!query) {
      return NULL;
   }

   query->callback = callback;
   query->user_data = ao2_bump(data);
   query->rr_type = rr_type;
   query->rr_class = rr_class;
   strcpy(query->name, name); /* SAFE */

   AST_RWLIST_RDLOCK(&resolvers);
   query->resolver = AST_RWLIST_FIRST(&resolvers);
   AST_RWLIST_UNLOCK(&resolvers);

   if (!query->resolver) {
      ast_log(LOG_ERROR, "Attempted to do a DNS query for '%s' of class '%d' and type '%d' but no resolver is available\n",
         name, rr_class, rr_type);
      ao2_ref(query, -1);
      return NULL;
   }

   return query;
}

struct ast_dns_query_active *ast_dns_resolve_async(const char *name, int rr_type, int rr_class, ast_dns_resolve_callback callback, void *data)
{
   struct ast_dns_query_active *active;

   active = ao2_alloc_options(sizeof(*active), dns_query_active_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
   if (!active) {
      return NULL;
   }

   active->query = dns_query_alloc(name, rr_type, rr_class, callback, data);
   if (!active->query) {
      ao2_ref(active, -1);
      return NULL;
   }

   if (active->query->resolver->resolve(active->query)) {
      ast_log(LOG_ERROR, "Resolver '%s' returned an error when resolving '%s' of class '%d' and type '%d'\n",
         active->query->resolver->name, name, rr_class, rr_type);
      ao2_ref(active, -1);
      return NULL;
   }

   return active;
}

int ast_dns_resolve_cancel(struct ast_dns_query_active *active)
{
   return active->query->resolver->cancel(active->query);
}

/*! \brief Structure used for signaling back for synchronous resolution completion */
struct dns_synchronous_resolve {
   /*! \brief Lock used for signaling */
   ast_mutex_t lock;
   /*! \brief Condition used for signaling */
   ast_cond_t cond;
   /*! \brief Whether the query has completed */
   unsigned int completed;
   /*! \brief The result from the query */
   struct ast_dns_result *result;
};

/*! \brief Destructor for synchronous resolution structure */
static void dns_synchronous_resolve_destroy(void *data)
{
   struct dns_synchronous_resolve *synchronous = data;

   ast_mutex_destroy(&synchronous->lock);
   ast_cond_destroy(&synchronous->cond);

   /* This purposely does not unref result as it has been passed to the caller */
}

/*! \brief Callback used to implement synchronous resolution */
static void dns_synchronous_resolve_callback(const struct ast_dns_query *query)
{
   struct dns_synchronous_resolve *synchronous = ast_dns_query_get_data(query);

   synchronous->result = query->result;
   ((struct ast_dns_query *)query)->result = NULL;

   ast_mutex_lock(&synchronous->lock);
   synchronous->completed = 1;
   ast_cond_signal(&synchronous->cond);
   ast_mutex_unlock(&synchronous->lock);
}

int ast_dns_resolve(const char *name, int rr_type, int rr_class, struct ast_dns_result **result)
{
   struct dns_synchronous_resolve *synchronous;
   struct ast_dns_query_active *active;

   if (ast_strlen_zero(name)) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution, no name provided\n");
      return -1;
   } else if (rr_type > 65536) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', resource record type '%d' exceeds maximum\n",
         name, rr_type);
      return -1;
   } else if (rr_type < 0) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', invalid resource record type '%d'\n",
         name, rr_type);
      return -1;
   } else if (rr_class > 65536) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', resource record class '%d' exceeds maximum\n",
         name, rr_class);
      return -1;
   } else if (rr_class < 0) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', invalid resource class '%d'\n",
         name, rr_class);
      return -1;
   } else if (!result) {
      ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', no result pointer provided for storing results\n",
         name);
      return -1;
   }

   synchronous = ao2_alloc_options(sizeof(*synchronous), dns_synchronous_resolve_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
   if (!synchronous) {
      return -1;
   }

   ast_mutex_init(&synchronous->lock);
   ast_cond_init(&synchronous->cond, NULL);

   active = ast_dns_resolve_async(name, rr_type, rr_class, dns_synchronous_resolve_callback, synchronous);
   if (active) {
      /* Wait for resolution to complete */
      ast_mutex_lock(&synchronous->lock);
      while (!synchronous->completed) {
         ast_cond_wait(&synchronous->cond, &synchronous->lock);
      }
      ast_mutex_unlock(&synchronous->lock);
      ao2_ref(active, -1);
   }

   *result = synchronous->result;
   ao2_ref(synchronous, -1);

   return *result ? 0 : -1;
}

int ast_dns_resolve_ipv6_and_ipv4(struct ast_sockaddr *address, const char *host, const char *port)
{
   RAII_VAR(struct ast_dns_query_set *, queries, ast_dns_query_set_create(), ao2_cleanup);
   int i;
   int rc;

   if (!queries) {
      ast_log(LOG_ERROR, "Couldn't allocate DNS query structure\n");
      return -1;
   }
   rc = ast_dns_query_set_add(queries, host, ns_t_aaaa, ns_c_in);
   if (rc != 0) {
      ast_log(LOG_ERROR, "Couldn't add 'AAAA' DNS query for '%s'\n", host);
      return -1;
   }
   rc = ast_dns_query_set_add(queries, host, ns_t_a, ns_c_in);
   if (rc != 0) {
      ast_log(LOG_ERROR, "Couldn't add 'A' DNS query for '%s'\n", host);
      return -1;
   }
   rc = ast_query_set_resolve(queries);
   if (rc != 0) {
      ast_log(LOG_ERROR, "Query set resolve failure for '%s'\n", host);
      return -1;
   }
   for (i = 0; i < ast_dns_query_set_num_queries(queries); ++i) {
      struct ast_dns_query *query = ast_dns_query_set_get(queries, i);
      struct ast_dns_result *result = ast_dns_query_get_result(query);
      const struct ast_dns_record *record;
      in_port_t in_port = 0;

      if (!ast_strlen_zero(port)) {
         in_port = htons(atoi(port));
      }

      for (record = ast_dns_result_get_records(result); record; record = ast_dns_record_get_next(record)) {
         size_t data_size = ast_dns_record_get_data_size(record);
         const unsigned char *data = (unsigned char *)ast_dns_record_get_data(record);
         int rr_type = ast_dns_record_get_rr_type(record);

         if (rr_type == ns_t_aaaa && data_size == 16) {
            struct sockaddr_in6 sin6 = { 0, };

            sin6.sin6_port = in_port;
            memcpy(&sin6.sin6_addr, data, data_size);
            sin6.sin6_family = AF_INET6;
            memcpy(&address->ss, &sin6, sizeof(sin6));
            address->len = sizeof(sin6);

            return 0;
         } else if (rr_type == ns_t_a && data_size == 4) {
            struct sockaddr_in sin4 = { 0, };

            sin4.sin_port = in_port;
            memcpy(&sin4.sin_addr, data, data_size);
            sin4.sin_family = AF_INET;
            memcpy(&address->ss, &sin4, sizeof(sin4));
            address->len = sizeof(sin4);

            return 0;
         } else {
            ast_debug(3, "Unrecognized rr_type '%u' or data_size '%zu' from DNS query for host '%s'\n",
               rr_type, data_size, host);
            continue;
         }
      }
   }

   return -1;
}

int ast_dns_resolver_set_data(struct ast_dns_query *query, void *data)
{
   if (query->resolver_data) {
      return -1;
   }

   query->resolver_data = ao2_bump(data);

   return 0;
}

void *ast_dns_resolver_get_data(const struct ast_dns_query *query)
{
   return query->resolver_data;
}

int ast_dns_resolver_set_result(struct ast_dns_query *query, unsigned int secure, unsigned int bogus,
   unsigned int rcode, const char *canonical, const char *answer, size_t answer_size)
{
   char *buf_ptr;

   if (secure && bogus) {
      ast_debug(2, "Query '%p': Could not set result information, it can not be both secure and bogus\n",
         query);
      return -1;
   }

   if (ast_strlen_zero(canonical)) {
      ast_debug(2, "Query '%p': Could not set result information since no canonical name was provided\n",
         query);
      return -1;
   }

   if (!answer) {
      answer = "";
      answer_size = 0;
      ast_debug(2, "Query '%p': Assuming zero-sized answer on NULL input\n", query);
   }

   ast_dns_result_free(query->result);

   query->result = ast_calloc(1, sizeof(*query->result) + strlen(canonical) + 1 + answer_size);
   if (!query->result) {
      return -1;
   }

   query->result->secure = secure;
   query->result->bogus = bogus;
   query->result->rcode = rcode;

   buf_ptr = query->result->buf;
   strcpy(buf_ptr, canonical); /* SAFE */
   query->result->canonical = buf_ptr;

   buf_ptr += strlen(canonical) + 1;
   memcpy(buf_ptr, answer, answer_size); /* SAFE */
   query->result->answer = buf_ptr;
   query->result->answer_size = answer_size;

   return 0;
}

static struct ast_dns_record *generic_record_alloc(struct ast_dns_query *query, const char *data, const size_t size)
{
   struct ast_dns_record *record;

   record = ast_calloc(1, sizeof(*record) + size);
   if (!record) {
      return NULL;
   }

   record->data_ptr = record->data;

   return record;
}

typedef struct ast_dns_record *(*dns_alloc_fn)(struct ast_dns_query *query, const char *data, const size_t size);

static dns_alloc_fn dns_alloc_table [] = {
   [T_TXT]   = dns_txt_alloc,
   [T_NAPTR] = dns_naptr_alloc,
   [T_SRV]   = dns_srv_alloc,
};

static struct ast_dns_record *allocate_dns_record(unsigned int rr_type, struct ast_dns_query *query, const char *data, const size_t size)
{
   dns_alloc_fn allocator = generic_record_alloc;

   if (rr_type < ARRAY_LEN(dns_alloc_table) && dns_alloc_table[rr_type]) {
      allocator = dns_alloc_table[rr_type];
   }

   return allocator(query, data, size);
}

int ast_dns_resolver_add_record(struct ast_dns_query *query, int rr_type, int rr_class, int ttl, const char *data, const size_t size)
{
   struct ast_dns_record *record;

   if (rr_type < 0) {
      ast_debug(2, "Query '%p': Could not add record, invalid resource record type '%d'\n",
         query, rr_type);
      return -1;
   } else if (rr_type > 65536) {
      ast_debug(2, "Query '%p': Could not add record, resource record type '%d' exceeds maximum\n",
         query, rr_type);
      return -1;
   } else if (rr_class < 0) {
      ast_debug(2, "Query '%p': Could not add record, invalid resource record class '%d'\n",
         query, rr_class);
      return -1;
   } else if (rr_class > 65536) {
      ast_debug(2, "Query '%p': Could not add record, resource record class '%d' exceeds maximum\n",
         query, rr_class);
      return -1;
   } else if (ttl < 0) {
      ast_debug(2, "Query '%p': Could not add record, invalid TTL '%d'\n",
         query, ttl);
      return -1;
   } else if (!data || !size) {
      ast_debug(2, "Query '%p': Could not add record, no data specified\n",
         query);
      return -1;
   } else if (!query->result) {
      ast_debug(2, "Query '%p': No result was set on the query, thus records can not be added\n",
         query);
      return -1;
   }

   record = allocate_dns_record(rr_type, query, data, size);
   if (!record) {
      return -1;
   }

   record->rr_type = rr_type;
   record->rr_class = rr_class;
   record->ttl = ttl;
   record->data_len = size;
   memcpy(record->data_ptr, data, size);

   AST_LIST_INSERT_TAIL(&query->result->records, record, list);

   return 0;
}

typedef void (*dns_sort_fn)(struct ast_dns_result *result);

static dns_sort_fn dns_sort_table [] = {
   [T_NAPTR] = dns_naptr_sort,
   [T_SRV] = dns_srv_sort,
};

static void sort_result(int rr_type, struct ast_dns_result *result)
{
   if (dns_sort_table[rr_type]) {
      dns_sort_table[rr_type](result);
   }
}

void ast_dns_resolver_completed(struct ast_dns_query *query)
{
   sort_result(ast_dns_query_get_rr_type(query), query->result);

   query->callback(query);
}

static void dns_shutdown(void)
{
   if (sched) {
      ast_sched_context_destroy(sched);
      sched = NULL;
   }
}

int dns_core_init(void)
{
   sched = ast_sched_context_create();
   if (!sched) {
      return -1;
   }

   if (ast_sched_start_thread(sched)) {
      return -1;
   }

   ast_register_cleanup(dns_shutdown);

   return 0;
}

int ast_dns_resolver_register(struct ast_dns_resolver *resolver)
{
   struct ast_dns_resolver *iter;
   int inserted = 0;

   if (!resolver) {
      return -1;
   } else if (ast_strlen_zero(resolver->name)) {
      ast_log(LOG_ERROR, "Registration of DNS resolver failed as it does not have a name\n");
      return -1;
   } else if (!resolver->resolve) {
      ast_log(LOG_ERROR, "DNS resolver '%s' does not implement the resolve callback which is required\n",
         resolver->name);
      return -1;
   } else if (!resolver->cancel) {
      ast_log(LOG_ERROR, "DNS resolver '%s' does not implement the cancel callback which is required\n",
         resolver->name);
      return -1;
   }

   AST_RWLIST_WRLOCK(&resolvers);

   AST_LIST_TRAVERSE(&resolvers, iter, next) {
      if (!strcmp(iter->name, resolver->name)) {
         ast_log(LOG_ERROR, "A DNS resolver with the name '%s' is already registered\n", resolver->name);
         AST_RWLIST_UNLOCK(&resolvers);
         return -1;
      }
   }

   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&resolvers, iter, next) {
      if (iter->priority > resolver->priority) {
         AST_RWLIST_INSERT_BEFORE_CURRENT(resolver, next);
         inserted = 1;
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   if (!inserted) {
      AST_RWLIST_INSERT_TAIL(&resolvers, resolver, next);
   }

   AST_RWLIST_UNLOCK(&resolvers);

   ast_verb(2, "Registered DNS resolver '%s' with priority '%d'\n", resolver->name, resolver->priority);

   return 0;
}

void ast_dns_resolver_unregister(struct ast_dns_resolver *resolver)
{
   struct ast_dns_resolver *iter;

   if (!resolver) {
      return;
   }

   AST_RWLIST_WRLOCK(&resolvers);
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&resolvers, iter, next) {
      if (resolver == iter) {
         AST_RWLIST_REMOVE_CURRENT(next);
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;
   AST_RWLIST_UNLOCK(&resolvers);

   ast_verb(2, "Unregistered DNS resolver '%s'\n", resolver->name);
}

char *dns_find_record(const char *record, size_t record_size, const char *response, size_t response_size)
{
   size_t remaining_size = response_size;
   const char *search_base = response;
   char *record_offset;

   while (1) {
      record_offset = memchr(search_base, record[0], remaining_size);

      ast_assert(record_offset != NULL);
      ast_assert(search_base + remaining_size - record_offset >= record_size);

      if (!memcmp(record_offset, record, record_size)) {
         return record_offset;
      }

      remaining_size -= record_offset - search_base;
      search_base = record_offset + 1;
   }
}

int dns_parse_short(unsigned char *cur, uint16_t *val)
{
   /* This assignment takes a big-endian 16-bit value and stores it in the
    * machine's native byte order. Using this method allows us to avoid potential
    * alignment issues in case the order is not on a short-addressable boundary.
    * See http://commandcenter.blogspot.com/2012/04/byte-order-fallacy.html for
    * more information
    */
   *val = (cur[1] << 0) | (cur[0] << 8);
   return sizeof(*val);
}

int dns_parse_string(char *cur, uint8_t *size, char **val)
{
   *size = *cur++;
   *val = cur;
   return *size + 1;
}