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.
 */
 
 
/*! \li \ref dnsmgr.c uses the configuration file \ref dnsmgr.conf
 * \addtogroup configuration_file Configuration Files
 */
 
/*!
 * \page dnsmgr.conf dnsmgr.conf
 * \verbinclude dnsmgr.conf.sample
 */
 
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/_private.h"
#include <regex.h>
#include <signal.h>
 
#include "asterisk/module.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"
            "       Performs 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 int unload_module(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);
 
    return 0;
}
 
static int load_module(void)
{
    if (!(sched = ast_sched_context_create())) {
        ast_log(LOG_ERROR, "Unable to create schedule context.\n");
        return AST_MODULE_LOAD_FAILURE;
    }
    ast_cli_register(&cli_reload);
    ast_cli_register(&cli_status);
    ast_cli_register(&cli_refresh);
 
    return do_reload(1) ? AST_MODULE_LOAD_FAILURE : AST_MODULE_LOAD_SUCCESS;
}
 
static int reload_module(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);
 
    return 0;
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "DNS Manager",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
    .reload = reload_module,
    .load_pri = AST_MODPRI_CORE,
    .requires = "extconfig",
);