dnsmgr.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2005-2006, Kevin P. Fleming
 *
 * Kevin P. Fleming <kpfleming@digium.com>
 *
 * 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 Background DNS update manager
 *
 * \author Kevin P. Fleming <kpfleming@digium.com>
 *
 * \bug There is a minor race condition.  In the event that an IP address
 * of a dnsmgr managed host changes, there is the potential for the consumer
 * of that address to access the in_addr data at the same time that the dnsmgr
 * thread is in the middle of updating it to the new address.
 */

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

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 377706 $")

#include "asterisk/_private.h"
#include <regex.h>
#include <signal.h>

#include "asterisk/dnsmgr.h"
#include "asterisk/linkedlists.h"
#include "asterisk/utils.h"
#include "asterisk/config.h"
#include "asterisk/sched.h"
#include "asterisk/cli.h"
#include "asterisk/manager.h"
#include "asterisk/acl.h"

static struct ast_sched_context *sched;
static int refresh_sched = -1;
static pthread_t refresh_thread = AST_PTHREADT_NULL;

struct ast_dnsmgr_entry {
   /*! where we will store the resulting IP address and port number */
   struct ast_sockaddr *result;
   /*! SRV record to lookup, if provided. Composed of service, protocol, and domain name: _Service._Proto.Name */
   char *service;
   /*! Address family to filter DNS responses. */
   unsigned int family;
   /*! Set to 1 if the entry changes */
   unsigned int changed:1;
   /*! Data to pass back to update_func */
   void *data;
   /*! The callback function to execute on address update */
   dns_update_func update_func;
   ast_mutex_t lock;
   AST_RWLIST_ENTRY(ast_dnsmgr_entry) list;
   /*! just 1 here, but we use calloc to allocate the correct size */
   char name[1];
};

static AST_RWLIST_HEAD_STATIC(entry_list, ast_dnsmgr_entry);

AST_MUTEX_DEFINE_STATIC(refresh_lock);

#define REFRESH_DEFAULT 300

static int enabled;
static int refresh_interval;

struct refresh_info {
   struct entry_list *entries;
   int verbose;
   unsigned int regex_present:1;
   regex_t filter;
};

static struct refresh_info master_refresh_info = {
   .entries = &entry_list,
   .verbose = 0,
};

struct ast_dnsmgr_entry *ast_dnsmgr_get_family(const char *name, struct ast_sockaddr *result, const char *service, unsigned int family)
{
   struct ast_dnsmgr_entry *entry;
   int total_size = sizeof(*entry) + strlen(name) + (service ? strlen(service) + 1 : 0);

   if (!result || ast_strlen_zero(name) || !(entry = ast_calloc(1, total_size))) {
      return NULL;
   }

   entry->result = result;
   ast_mutex_init(&entry->lock);
   strcpy(entry->name, name);
   if (service) {
      entry->service = ((char *) entry) + sizeof(*entry) + strlen(name);
      strcpy(entry->service, service);
   }
   entry->family = family;

   AST_RWLIST_WRLOCK(&entry_list);
   AST_RWLIST_INSERT_HEAD(&entry_list, entry, list);
   AST_RWLIST_UNLOCK(&entry_list);

   return entry;
}

struct ast_dnsmgr_entry *ast_dnsmgr_get(const char *name, struct ast_sockaddr *result, const char *service)
{
   return ast_dnsmgr_get_family(name, result, service, 0);
}

void ast_dnsmgr_release(struct ast_dnsmgr_entry *entry)
{
   if (!entry) {
      return;
   }

   AST_RWLIST_WRLOCK(&entry_list);
   AST_RWLIST_REMOVE(&entry_list, entry, list);
   AST_RWLIST_UNLOCK(&entry_list);
   ast_debug(6, "removing dns manager for '%s'\n", entry->name);

   ast_mutex_destroy(&entry->lock);
   ast_free(entry);
}

static int internal_dnsmgr_lookup(const char *name, struct ast_sockaddr *result, struct ast_dnsmgr_entry **dnsmgr, const char *service, dns_update_func func, void *data)
{
   unsigned int family;

   if (ast_strlen_zero(name) || !result || !dnsmgr) {
      return -1;
   }

   if (*dnsmgr && !strcasecmp((*dnsmgr)->name, name)) {
      return 0;
   }

   /* Lookup address family filter. */
   family = result->ss.ss_family;

   /*
    * If it's actually an IP address and not a name, there's no
    * need for a managed lookup.
    */
   if (ast_sockaddr_parse(result, name, PARSE_PORT_FORBID)) {
      return 0;
   }

   ast_debug(6, "doing dnsmgr_lookup for '%s'\n", name);

   /* do a lookup now but add a manager so it will automagically get updated in the background */
   ast_get_ip_or_srv(result, name, service);

   /* if dnsmgr is not enable don't bother adding an entry */
   if (!enabled) {
      return 0;
   }

   ast_debug(6, "adding dns manager for '%s'\n", name);
   *dnsmgr = ast_dnsmgr_get_family(name, result, service, family);
   (*dnsmgr)->update_func = func;
   (*dnsmgr)->data = data;
   return !*dnsmgr;
}

int ast_dnsmgr_lookup(const char *name, struct ast_sockaddr *result, struct ast_dnsmgr_entry **dnsmgr, const char *service)
{
   return internal_dnsmgr_lookup(name, result, dnsmgr, service, NULL, NULL);
}

int ast_dnsmgr_lookup_cb(const char *name, struct ast_sockaddr *result, struct ast_dnsmgr_entry **dnsmgr, const char *service, dns_update_func func, void *data)
{
   return internal_dnsmgr_lookup(name, result, dnsmgr, service, func, data);
}

/*
 * Refresh a dnsmgr entry
 */
static int dnsmgr_refresh(struct ast_dnsmgr_entry *entry, int verbose)
{
   struct ast_sockaddr tmp = { .len = 0, };
   int changed = 0;

   ast_mutex_lock(&entry->lock);

   ast_debug(6, "refreshing '%s'\n", entry->name);

   tmp.ss.ss_family = entry->family;
   if (!ast_get_ip_or_srv(&tmp, entry->name, entry->service)) {
      if (!ast_sockaddr_port(&tmp)) {
         ast_sockaddr_set_port(&tmp, ast_sockaddr_port(entry->result));
      }
      if (ast_sockaddr_cmp(&tmp, entry->result)) {
         const char *old_addr = ast_strdupa(ast_sockaddr_stringify(entry->result));
         const char *new_addr = ast_strdupa(ast_sockaddr_stringify(&tmp));

         if (entry->update_func) {
            entry->update_func(entry->result, &tmp, entry->data);
         } else {
            ast_log(LOG_NOTICE, "dnssrv: host '%s' changed from %s to %s\n",
                  entry->name, old_addr, new_addr);

            ast_sockaddr_copy(entry->result, &tmp);
            changed = entry->changed = 1;
         }
      }
   }

   ast_mutex_unlock(&entry->lock);

   return changed;
}

int ast_dnsmgr_refresh(struct ast_dnsmgr_entry *entry)
{
   return dnsmgr_refresh(entry, 0);
}

/*
 * Check if dnsmgr entry has changed from since last call to this function
 */
int ast_dnsmgr_changed(struct ast_dnsmgr_entry *entry)
{
   int changed;

   ast_mutex_lock(&entry->lock);

   changed = entry->changed;
   entry->changed = 0;

   ast_mutex_unlock(&entry->lock);

   return changed;
}

static void *do_refresh(void *data)
{
   for (;;) {
      pthread_testcancel();
      usleep((ast_sched_wait(sched)*1000));
      pthread_testcancel();
      ast_sched_runq(sched);
   }
   return NULL;
}

static int refresh_list(const void *data)
{
   struct refresh_info *info = (struct refresh_info *)data;
   struct ast_dnsmgr_entry *entry;

   /* if a refresh or reload is already in progress, exit now */
   if (ast_mutex_trylock(&refresh_lock)) {
      if (info->verbose) {
         ast_log(LOG_WARNING, "DNS Manager refresh already in progress.\n");
      }
      return -1;
   }

   ast_debug(6, "Refreshing DNS lookups.\n");
   AST_RWLIST_RDLOCK(info->entries);
   AST_RWLIST_TRAVERSE(info->entries, entry, list) {
      if (info->regex_present && regexec(&info->filter, entry->name, 0, NULL, 0)) {
         continue;
      }

      dnsmgr_refresh(entry, info->verbose);
   }
   AST_RWLIST_UNLOCK(info->entries);

   ast_mutex_unlock(&refresh_lock);

   /* automatically reschedule based on the interval */
   return refresh_interval * 1000;
}

void dnsmgr_start_refresh(void)
{
   if (refresh_sched > -1) {
      AST_SCHED_DEL(sched, refresh_sched);
      refresh_sched = ast_sched_add_variable(sched, 100, refresh_list, &master_refresh_info, 1);
   }
}

static int do_reload(int loading);

static char *handle_cli_reload(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   switch (cmd) {
   case CLI_INIT:
      e->command = "dnsmgr reload";
      e->usage =
         "Usage: dnsmgr reload\n"
         "       Reloads the DNS manager configuration.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }
   if (a->argc > 2) {
      return CLI_SHOWUSAGE;
   }

   do_reload(0);
   return CLI_SUCCESS;
}

static char *handle_cli_refresh(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct refresh_info info = {
      .entries = &entry_list,
      .verbose = 1,
   };
   switch (cmd) {
   case CLI_INIT:
      e->command = "dnsmgr refresh";
      e->usage =
         "Usage: dnsmgr refresh [pattern]\n"
         "       Peforms an immediate refresh of the managed DNS entries.\n"
         "       Optional regular expression pattern is used to filter the entries to refresh.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (!enabled) {
      ast_cli(a->fd, "DNS Manager is disabled.\n");
      return 0;
   }

   if (a->argc > 3) {
      return CLI_SHOWUSAGE;
   }

   if (a->argc == 3) {
      if (regcomp(&info.filter, a->argv[2], REG_EXTENDED | REG_NOSUB)) {
         return CLI_SHOWUSAGE;
      } else {
         info.regex_present = 1;
      }
   }

   refresh_list(&info);

   if (info.regex_present) {
      regfree(&info.filter);
   }

   return CLI_SUCCESS;
}

static char *handle_cli_status(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   int count = 0;
   struct ast_dnsmgr_entry *entry;
   switch (cmd) {
   case CLI_INIT:
      e->command = "dnsmgr status";
      e->usage =
         "Usage: dnsmgr status\n"
         "       Displays the DNS manager status.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc > 2) {
      return CLI_SHOWUSAGE;
   }

   ast_cli(a->fd, "DNS Manager: %s\n", enabled ? "enabled" : "disabled");
   ast_cli(a->fd, "Refresh Interval: %d seconds\n", refresh_interval);
   AST_RWLIST_RDLOCK(&entry_list);
   AST_RWLIST_TRAVERSE(&entry_list, entry, list)
      count++;
   AST_RWLIST_UNLOCK(&entry_list);
   ast_cli(a->fd, "Number of entries: %d\n", count);

   return CLI_SUCCESS;
}

static struct ast_cli_entry cli_reload = AST_CLI_DEFINE(handle_cli_reload, "Reloads the DNS manager configuration");
static struct ast_cli_entry cli_refresh = AST_CLI_DEFINE(handle_cli_refresh, "Performs an immediate refresh");
static struct ast_cli_entry cli_status = AST_CLI_DEFINE(handle_cli_status, "Display the DNS manager status");

static void dnsmgr_shutdown(void)
{
   ast_cli_unregister(&cli_reload);
   ast_cli_unregister(&cli_status);
   ast_cli_unregister(&cli_refresh);

   /* Destroy refresh thread. */
   ast_mutex_lock(&refresh_lock);
   if (refresh_thread != AST_PTHREADT_NULL) {
      /* wake up the thread so it will exit */
      pthread_cancel(refresh_thread);
      pthread_kill(refresh_thread, SIGURG);
      pthread_join(refresh_thread, NULL);
      refresh_thread = AST_PTHREADT_NULL;
   }
   ast_mutex_unlock(&refresh_lock);

   ast_sched_context_destroy(sched);
}

int dnsmgr_init(void)
{
   if (!(sched = ast_sched_context_create())) {
      ast_log(LOG_ERROR, "Unable to create schedule context.\n");
      return -1;
   }
   ast_cli_register(&cli_reload);
   ast_cli_register(&cli_status);
   ast_cli_register(&cli_refresh);

   ast_register_atexit(dnsmgr_shutdown);

   return do_reload(1);
}

int dnsmgr_reload(void)
{
   return do_reload(0);
}

static int do_reload(int loading)
{
   struct ast_config *config;
   struct ast_variable *v;
   struct ast_flags config_flags = { loading ? 0 : CONFIG_FLAG_FILEUNCHANGED };
   int interval;
   int was_enabled;

   if ((config = ast_config_load2("dnsmgr.conf", "dnsmgr", config_flags)) == CONFIG_STATUS_FILEUNCHANGED) {
      return 0;
   }

   /* ensure that no refresh cycles run while the reload is in progress */
   ast_mutex_lock(&refresh_lock);

   /* reset defaults in preparation for reading config file */
   refresh_interval = REFRESH_DEFAULT;
   was_enabled = enabled;
   enabled = 0;

   if (config == CONFIG_STATUS_FILEMISSING || config == CONFIG_STATUS_FILEINVALID) {
      ast_mutex_unlock(&refresh_lock);
      return 0;
   }

   AST_SCHED_DEL(sched, refresh_sched);

   for (v = ast_variable_browse(config, "general"); v; v = v->next) {
      if (!strcasecmp(v->name, "enable")) {
         enabled = ast_true(v->value);
      } else if (!strcasecmp(v->name, "refreshinterval")) {
         if (sscanf(v->value, "%30d", &interval) < 1) {
            ast_log(LOG_WARNING, "Unable to convert '%s' to a numeric value.\n", v->value);
         } else if (interval < 0) {
            ast_log(LOG_WARNING, "Invalid refresh interval '%d' specified, using default\n", interval);
         } else {
            refresh_interval = interval;
         }
      }
   }
   ast_config_destroy(config);

   if (enabled && refresh_interval) {
      ast_log(LOG_NOTICE, "Managed DNS entries will be refreshed every %d seconds.\n", refresh_interval);
   }

   /* if this reload enabled the manager, create the background thread
      if it does not exist */
   if (enabled) {
      if (!was_enabled && (refresh_thread == AST_PTHREADT_NULL)) {
         if (ast_pthread_create_background(&refresh_thread, NULL, do_refresh, NULL) < 0) {
            ast_log(LOG_ERROR, "Unable to start refresh thread.\n");
         }
      }
      /* make a background refresh happen right away */
      refresh_sched = ast_sched_add_variable(sched, 100, refresh_list, &master_refresh_info, 1);
   /* if this reload disabled the manager and there is a background thread, kill it */
   } else if (!enabled && was_enabled && (refresh_thread != AST_PTHREADT_NULL)) {
      /* wake up the thread so it will exit */
      pthread_cancel(refresh_thread);
      pthread_kill(refresh_thread, SIGURG);
      pthread_join(refresh_thread, NULL);
      refresh_thread = AST_PTHREADT_NULL;
   }

   ast_mutex_unlock(&refresh_lock);
   manager_event(EVENT_FLAG_SYSTEM, "Reload", "Module: DNSmgr\r\nStatus: %s\r/nMessage: DNSmgr reload Requested\r\n", enabled ? "Enabled" : "Disabled");

   return 0;
}