tcptls.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007 - 2008, Digium, Inc.
 *
 * Luigi Rizzo (TCP and TLS server code)
 * Brett Bryant <brettbryant@gmail.com> (updated for client support)
 *
 * 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 Code to support TCP and TLS server/client
 *
 * \author Luigi Rizzo
 * \author Brett Bryant <brettbryant@gmail.com>
 */

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

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 373061 $")

#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif

#include <signal.h>
#include <sys/signal.h>

#include "asterisk/compat.h"
#include "asterisk/tcptls.h"
#include "asterisk/http.h"
#include "asterisk/utils.h"
#include "asterisk/strings.h"
#include "asterisk/options.h"
#include "asterisk/manager.h"
#include "asterisk/astobj2.h"

/*! \brief
 * replacement read/write functions for SSL support.
 * We use wrappers rather than SSL_read/SSL_write directly so
 * we can put in some debugging.
 */

#ifdef DO_SSL
static HOOK_T ssl_read(void *cookie, char *buf, LEN_T len)
{
   int i = SSL_read(cookie, buf, len-1);
#if 0
   if (i >= 0)
      buf[i] = '\0';
   ast_verb(0, "ssl read size %d returns %d <%s>\n", (int)len, i, buf);
#endif
   return i;
}

static HOOK_T ssl_write(void *cookie, const char *buf, LEN_T len)
{
#if 0
   char *s = ast_alloca(len+1);
   strncpy(s, buf, len);
   s[len] = '\0';
   ast_verb(0, "ssl write size %d <%s>\n", (int)len, s);
#endif
   return SSL_write(cookie, buf, len);
}

static int ssl_close(void *cookie)
{
   int cookie_fd = SSL_get_fd(cookie);
   int ret;

   if (cookie_fd > -1) {
      /*
       * According to the TLS standard, it is acceptable for an application to only send its shutdown
       * alert and then close the underlying connection without waiting for the peer's response (this
       * way resources can be saved, as the process can already terminate or serve another connection).
       */
      if ((ret = SSL_shutdown(cookie)) < 0) {
         ast_log(LOG_ERROR, "SSL_shutdown() failed: %d\n", SSL_get_error(cookie, ret));
      }

      if (!((SSL*)cookie)->server) {
         /* For client threads, ensure that the error stack is cleared */
         ERR_remove_state(0);
      }

      SSL_free(cookie);
      /* adding shutdown(2) here has no added benefit */
      if (close(cookie_fd)) {
         ast_log(LOG_ERROR, "close() failed: %s\n", strerror(errno));
      }
   }
   return 0;
}
#endif   /* DO_SSL */

HOOK_T ast_tcptls_server_read(struct ast_tcptls_session_instance *tcptls_session, void *buf, size_t count)
{
   if (tcptls_session->fd == -1) {
      ast_log(LOG_ERROR, "server_read called with an fd of -1\n");
      errno = EIO;
      return -1;
   }

#ifdef DO_SSL
   if (tcptls_session->ssl)
      return ssl_read(tcptls_session->ssl, buf, count);
#endif
   return read(tcptls_session->fd, buf, count);
}

HOOK_T ast_tcptls_server_write(struct ast_tcptls_session_instance *tcptls_session, const void *buf, size_t count)
{
   if (tcptls_session->fd == -1) {
      ast_log(LOG_ERROR, "server_write called with an fd of -1\n");
      errno = EIO;
      return -1;
   }

#ifdef DO_SSL
   if (tcptls_session->ssl)
      return ssl_write(tcptls_session->ssl, buf, count);
#endif
   return write(tcptls_session->fd, buf, count);
}

static void session_instance_destructor(void *obj)
{
   struct ast_tcptls_session_instance *i = obj;
   ast_mutex_destroy(&i->lock);
}

/*! \brief
* creates a FILE * from the fd passed by the accept thread.
* This operation is potentially expensive (certificate verification),
* so we do it in the child thread context.
*
* \note must decrement ref count before returning NULL on error
*/
static void *handle_tcptls_connection(void *data)
{
   struct ast_tcptls_session_instance *tcptls_session = data;
#ifdef DO_SSL
   int (*ssl_setup)(SSL *) = (tcptls_session->client) ? SSL_connect : SSL_accept;
   int ret;
   char err[256];
#endif

   /*
   * open a FILE * as appropriate.
   */
   if (!tcptls_session->parent->tls_cfg) {
      if ((tcptls_session->f = fdopen(tcptls_session->fd, "w+"))) {
         if(setvbuf(tcptls_session->f, NULL, _IONBF, 0)) {
            ast_tcptls_close_session_file(tcptls_session);
         }
      }
   }
#ifdef DO_SSL
   else if ( (tcptls_session->ssl = SSL_new(tcptls_session->parent->tls_cfg->ssl_ctx)) ) {
      SSL_set_fd(tcptls_session->ssl, tcptls_session->fd);
      if ((ret = ssl_setup(tcptls_session->ssl)) <= 0) {
         ast_verb(2, "Problem setting up ssl connection: %s\n", ERR_error_string(ERR_get_error(), err));
      } else {
#if defined(HAVE_FUNOPEN)  /* the BSD interface */
         tcptls_session->f = funopen(tcptls_session->ssl, ssl_read, ssl_write, NULL, ssl_close);

#elif defined(HAVE_FOPENCOOKIE)  /* the glibc/linux interface */
         static const cookie_io_functions_t cookie_funcs = {
            ssl_read, ssl_write, NULL, ssl_close
         };
         tcptls_session->f = fopencookie(tcptls_session->ssl, "w+", cookie_funcs);
#else
         /* could add other methods here */
         ast_debug(2, "no tcptls_session->f methods attempted!\n");
#endif
         if ((tcptls_session->client && !ast_test_flag(&tcptls_session->parent->tls_cfg->flags, AST_SSL_DONT_VERIFY_SERVER))
            || (!tcptls_session->client && ast_test_flag(&tcptls_session->parent->tls_cfg->flags, AST_SSL_VERIFY_CLIENT))) {
            X509 *peer;
            long res;
            peer = SSL_get_peer_certificate(tcptls_session->ssl);
            if (!peer)
               ast_log(LOG_WARNING, "No peer SSL certificate\n");
            res = SSL_get_verify_result(tcptls_session->ssl);
            if (res != X509_V_OK)
               ast_log(LOG_ERROR, "Certificate did not verify: %s\n", X509_verify_cert_error_string(res));
            if (!ast_test_flag(&tcptls_session->parent->tls_cfg->flags, AST_SSL_IGNORE_COMMON_NAME)) {
               ASN1_STRING *str;
               unsigned char *str2;
               X509_NAME *name = X509_get_subject_name(peer);
               int pos = -1;
               int found = 0;

               for (;;) {
                  /* Walk the certificate to check all available "Common Name" */
                  /* XXX Probably should do a gethostbyname on the hostname and compare that as well */
                  pos = X509_NAME_get_index_by_NID(name, NID_commonName, pos);
                  if (pos < 0)
                     break;
                  str = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(name, pos));
                  ASN1_STRING_to_UTF8(&str2, str);
                  if (str2) {
                     if (!strcasecmp(tcptls_session->parent->hostname, (char *) str2))
                        found = 1;
                     ast_debug(3, "SSL Common Name compare s1='%s' s2='%s'\n", tcptls_session->parent->hostname, str2);
                     OPENSSL_free(str2);
                  }
                  if (found)
                     break;
               }
               if (!found) {
                  ast_log(LOG_ERROR, "Certificate common name did not match (%s)\n", tcptls_session->parent->hostname);
                  if (peer) {
                     X509_free(peer);
                  }
                  ast_tcptls_close_session_file(tcptls_session);
                  ao2_ref(tcptls_session, -1);
                  return NULL;
               }
            }
            if (peer)
               X509_free(peer);
         }
      }
      if (!tcptls_session->f) /* no success opening descriptor stacking */
         SSL_free(tcptls_session->ssl);
   }
#endif /* DO_SSL */

   if (!tcptls_session->f) {
      ast_tcptls_close_session_file(tcptls_session);
      ast_log(LOG_WARNING, "FILE * open failed!\n");
#ifndef DO_SSL
      if (tcptls_session->parent->tls_cfg) {
         ast_log(LOG_WARNING, "Attempted a TLS connection without OpenSSL support.  This will not work!\n");
      }
#endif
      ao2_ref(tcptls_session, -1);
      return NULL;
   }

   if (tcptls_session->parent->worker_fn) {
      return tcptls_session->parent->worker_fn(tcptls_session);
   } else {
      return tcptls_session;
   }
}

void *ast_tcptls_server_root(void *data)
{
   struct ast_tcptls_session_args *desc = data;
   int fd;
   struct ast_sockaddr addr;
   struct ast_tcptls_session_instance *tcptls_session;
   pthread_t launched;

   for (;;) {
      int i, flags;

      if (desc->periodic_fn)
         desc->periodic_fn(desc);
      i = ast_wait_for_input(desc->accept_fd, desc->poll_timeout);
      if (i <= 0)
         continue;
      fd = ast_accept(desc->accept_fd, &addr);
      if (fd < 0) {
         if ((errno != EAGAIN) && (errno != EINTR))
            ast_log(LOG_WARNING, "Accept failed: %s\n", strerror(errno));
         continue;
      }
      tcptls_session = ao2_alloc(sizeof(*tcptls_session), session_instance_destructor);
      if (!tcptls_session) {
         ast_log(LOG_WARNING, "No memory for new session: %s\n", strerror(errno));
         if (close(fd)) {
            ast_log(LOG_ERROR, "close() failed: %s\n", strerror(errno));
         }
         continue;
      }

      ast_mutex_init(&tcptls_session->lock);

      flags = fcntl(fd, F_GETFL);
      fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
      tcptls_session->fd = fd;
      tcptls_session->parent = desc;
      ast_sockaddr_copy(&tcptls_session->remote_address, &addr);

      tcptls_session->client = 0;

      /* This thread is now the only place that controls the single ref to tcptls_session */
      if (ast_pthread_create_detached_background(&launched, NULL, handle_tcptls_connection, tcptls_session)) {
         ast_log(LOG_WARNING, "Unable to launch helper thread: %s\n", strerror(errno));
         ast_tcptls_close_session_file(tcptls_session);
         ao2_ref(tcptls_session, -1);
      }
   }
   return NULL;
}

static int __ssl_setup(struct ast_tls_config *cfg, int client)
{
#ifndef DO_SSL
   cfg->enabled = 0;
   return 0;
#else
   if (!cfg->enabled)
      return 0;

   /* Get rid of an old SSL_CTX since we're about to
    * allocate a new one
    */
   if (cfg->ssl_ctx) {
      SSL_CTX_free(cfg->ssl_ctx);
      cfg->ssl_ctx = NULL;
   }

   if (client) {
#ifndef OPENSSL_NO_SSL2
      if (ast_test_flag(&cfg->flags, AST_SSL_SSLV2_CLIENT)) {
         cfg->ssl_ctx = SSL_CTX_new(SSLv2_client_method());
      } else
#endif
      if (ast_test_flag(&cfg->flags, AST_SSL_SSLV3_CLIENT)) {
         cfg->ssl_ctx = SSL_CTX_new(SSLv3_client_method());
      } else if (ast_test_flag(&cfg->flags, AST_SSL_TLSV1_CLIENT)) {
         cfg->ssl_ctx = SSL_CTX_new(TLSv1_client_method());
      } else {
         /* SSLv23_client_method() sends SSLv2, this was the original
          * default for ssl clients before the option was given to
          * pick what protocol a client should use.  In order not
          * to break expected behavior it remains the default. */
         cfg->ssl_ctx = SSL_CTX_new(SSLv23_client_method());
      }
   } else {
      /* SSLv23_server_method() supports TLSv1, SSLv2, and SSLv3 inbound connections. */
      cfg->ssl_ctx = SSL_CTX_new(SSLv23_server_method());
   }

   if (!cfg->ssl_ctx) {
      ast_debug(1, "Sorry, SSL_CTX_new call returned null...\n");
      cfg->enabled = 0;
      return 0;
   }
   if (!ast_strlen_zero(cfg->certfile)) {
      char *tmpprivate = ast_strlen_zero(cfg->pvtfile) ? cfg->certfile : cfg->pvtfile;
      if (SSL_CTX_use_certificate_file(cfg->ssl_ctx, cfg->certfile, SSL_FILETYPE_PEM) == 0) {
         if (!client) {
            /* Clients don't need a certificate, but if its setup we can use it */
            ast_verb(0, "SSL error loading cert file. <%s>", cfg->certfile);
            cfg->enabled = 0;
            SSL_CTX_free(cfg->ssl_ctx);
            cfg->ssl_ctx = NULL;
            return 0;
         }
      }
      if ((SSL_CTX_use_PrivateKey_file(cfg->ssl_ctx, tmpprivate, SSL_FILETYPE_PEM) == 0) || (SSL_CTX_check_private_key(cfg->ssl_ctx) == 0 )) {
         if (!client) {
            /* Clients don't need a private key, but if its setup we can use it */
            ast_verb(0, "SSL error loading private key file. <%s>", tmpprivate);
            cfg->enabled = 0;
            SSL_CTX_free(cfg->ssl_ctx);
            cfg->ssl_ctx = NULL;
            return 0;
         }
      }
   }
   if (!ast_strlen_zero(cfg->cipher)) {
      if (SSL_CTX_set_cipher_list(cfg->ssl_ctx, cfg->cipher) == 0 ) {
         if (!client) {
            ast_verb(0, "SSL cipher error <%s>", cfg->cipher);
            cfg->enabled = 0;
            SSL_CTX_free(cfg->ssl_ctx);
            cfg->ssl_ctx = NULL;
            return 0;
         }
      }
   }
   if (!ast_strlen_zero(cfg->cafile) || !ast_strlen_zero(cfg->capath)) {
      if (SSL_CTX_load_verify_locations(cfg->ssl_ctx, S_OR(cfg->cafile, NULL), S_OR(cfg->capath,NULL)) == 0)
         ast_verb(0, "SSL CA file(%s)/path(%s) error\n", cfg->cafile, cfg->capath);
   }

   ast_verb(0, "SSL certificate ok\n");
   return 1;
#endif
}

int ast_ssl_setup(struct ast_tls_config *cfg)
{
   return __ssl_setup(cfg, 0);
}

void ast_ssl_teardown(struct ast_tls_config *cfg)
{
#ifdef DO_SSL
   if (cfg->ssl_ctx) {
      SSL_CTX_free(cfg->ssl_ctx);
      cfg->ssl_ctx = NULL;
   }
#endif
}

struct ast_tcptls_session_instance *ast_tcptls_client_start(struct ast_tcptls_session_instance *tcptls_session)
{
   struct ast_tcptls_session_args *desc;
   int flags;

   if (!(desc = tcptls_session->parent)) {
      goto client_start_error;
   }

   if (ast_connect(desc->accept_fd, &desc->remote_address)) {
      ast_log(LOG_ERROR, "Unable to connect %s to %s: %s\n",
         desc->name,
         ast_sockaddr_stringify(&desc->remote_address),
         strerror(errno));
      goto client_start_error;
   }

   flags = fcntl(desc->accept_fd, F_GETFL);
   fcntl(desc->accept_fd, F_SETFL, flags & ~O_NONBLOCK);

   if (desc->tls_cfg) {
      desc->tls_cfg->enabled = 1;
      __ssl_setup(desc->tls_cfg, 1);
   }

   return handle_tcptls_connection(tcptls_session);

client_start_error:
   if (desc) {
      close(desc->accept_fd);
      desc->accept_fd = -1;
   }
   ao2_ref(tcptls_session, -1);
   return NULL;

}

struct ast_tcptls_session_instance *ast_tcptls_client_create(struct ast_tcptls_session_args *desc)
{
   int x = 1;
   struct ast_tcptls_session_instance *tcptls_session = NULL;

   /* Do nothing if nothing has changed */
   if (!ast_sockaddr_cmp(&desc->old_address, &desc->remote_address)) {
      ast_debug(1, "Nothing changed in %s\n", desc->name);
      return NULL;
   }

   /* If we return early, there is no connection */
   ast_sockaddr_setnull(&desc->old_address);

   if (desc->accept_fd != -1)
      close(desc->accept_fd);

   desc->accept_fd = socket(ast_sockaddr_is_ipv6(&desc->remote_address) ?
             AF_INET6 : AF_INET, SOCK_STREAM, IPPROTO_TCP);
   if (desc->accept_fd < 0) {
      ast_log(LOG_WARNING, "Unable to allocate socket for %s: %s\n",
         desc->name, strerror(errno));
      return NULL;
   }

   /* if a local address was specified, bind to it so the connection will
      originate from the desired address */
   if (!ast_sockaddr_isnull(&desc->local_address)) {
      setsockopt(desc->accept_fd, SOL_SOCKET, SO_REUSEADDR, &x, sizeof(x));
      if (ast_bind(desc->accept_fd, &desc->local_address)) {
         ast_log(LOG_ERROR, "Unable to bind %s to %s: %s\n",
            desc->name,
            ast_sockaddr_stringify(&desc->local_address),
            strerror(errno));
         goto error;
      }
   }

   if (!(tcptls_session = ao2_alloc(sizeof(*tcptls_session), session_instance_destructor)))
      goto error;

   ast_mutex_init(&tcptls_session->lock);
   tcptls_session->client = 1;
   tcptls_session->fd = desc->accept_fd;
   tcptls_session->parent = desc;
   tcptls_session->parent->worker_fn = NULL;
   ast_sockaddr_copy(&tcptls_session->remote_address,
           &desc->remote_address);

   /* Set current info */
   ast_sockaddr_copy(&desc->old_address, &desc->remote_address);
   return tcptls_session;

error:
   close(desc->accept_fd);
   desc->accept_fd = -1;
   if (tcptls_session)
      ao2_ref(tcptls_session, -1);
   return NULL;
}

void ast_tcptls_server_start(struct ast_tcptls_session_args *desc)
{
   int flags;
   int x = 1;

   /* Do nothing if nothing has changed */
   if (!ast_sockaddr_cmp(&desc->old_address, &desc->local_address)) {
      ast_debug(1, "Nothing changed in %s\n", desc->name);
      return;
   }

   /* If we return early, there is no one listening */
   ast_sockaddr_setnull(&desc->old_address);

   /* Shutdown a running server if there is one */
   if (desc->master != AST_PTHREADT_NULL) {
      pthread_cancel(desc->master);
      pthread_kill(desc->master, SIGURG);
      pthread_join(desc->master, NULL);
   }

   if (desc->accept_fd != -1)
      close(desc->accept_fd);

   /* If there's no new server, stop here */
   if (ast_sockaddr_isnull(&desc->local_address)) {
      ast_debug(2, "Server disabled:  %s\n", desc->name);
      return;
   }

   desc->accept_fd = socket(ast_sockaddr_is_ipv6(&desc->local_address) ?
             AF_INET6 : AF_INET, SOCK_STREAM, 0);
   if (desc->accept_fd < 0) {
      ast_log(LOG_ERROR, "Unable to allocate socket for %s: %s\n", desc->name, strerror(errno));
      return;
   }

   setsockopt(desc->accept_fd, SOL_SOCKET, SO_REUSEADDR, &x, sizeof(x));
   if (ast_bind(desc->accept_fd, &desc->local_address)) {
      ast_log(LOG_ERROR, "Unable to bind %s to %s: %s\n",
         desc->name,
         ast_sockaddr_stringify(&desc->local_address),
         strerror(errno));
      goto error;
   }
   if (listen(desc->accept_fd, 10)) {
      ast_log(LOG_ERROR, "Unable to listen for %s!\n", desc->name);
      goto error;
   }
   flags = fcntl(desc->accept_fd, F_GETFL);
   fcntl(desc->accept_fd, F_SETFL, flags | O_NONBLOCK);
   if (ast_pthread_create_background(&desc->master, NULL, desc->accept_fn, desc)) {
      ast_log(LOG_ERROR, "Unable to launch thread for %s on %s: %s\n",
         desc->name,
         ast_sockaddr_stringify(&desc->local_address),
         strerror(errno));
      goto error;
   }

   /* Set current info */
   ast_sockaddr_copy(&desc->old_address, &desc->local_address);

   return;

error:
   close(desc->accept_fd);
   desc->accept_fd = -1;
}

void ast_tcptls_close_session_file(struct ast_tcptls_session_instance *tcptls_session)
{
   if (tcptls_session->f) {
      if (fclose(tcptls_session->f)) {
         ast_log(LOG_ERROR, "fclose() failed: %s\n", strerror(errno));
      }
      tcptls_session->f = NULL;
      tcptls_session->fd = -1;
   } else if (tcptls_session->fd != -1) {
      if (close(tcptls_session->fd)) {
         ast_log(LOG_ERROR, "close() failed: %s\n", strerror(errno));
      }
      tcptls_session->fd = -1;
   } else {
      ast_log(LOG_ERROR, "ast_tcptls_close_session_file invoked on session instance without file or file descriptor\n");
   }
}

void ast_tcptls_server_stop(struct ast_tcptls_session_args *desc)
{
   if (desc->master != AST_PTHREADT_NULL) {
      pthread_cancel(desc->master);
      pthread_kill(desc->master, SIGURG);
      pthread_join(desc->master, NULL);
      desc->master = AST_PTHREADT_NULL;
   }
   if (desc->accept_fd != -1)
      close(desc->accept_fd);
   desc->accept_fd = -1;
   ast_debug(2, "Stopped server :: %s\n", desc->name);
}

int ast_tls_read_conf(struct ast_tls_config *tls_cfg, struct ast_tcptls_session_args *tls_desc, const char *varname, const char *value)
{
   if (!strcasecmp(varname, "tlsenable") || !strcasecmp(varname, "sslenable")) {
      tls_cfg->enabled = ast_true(value) ? 1 : 0;
   } else if (!strcasecmp(varname, "tlscertfile") || !strcasecmp(varname, "sslcert") || !strcasecmp(varname, "tlscert")) {
      ast_free(tls_cfg->certfile);
      tls_cfg->certfile = ast_strdup(value);
   } else if (!strcasecmp(varname, "tlsprivatekey") || !strcasecmp(varname, "sslprivatekey")) {
      ast_free(tls_cfg->pvtfile);
      tls_cfg->pvtfile = ast_strdup(value);
   } else if (!strcasecmp(varname, "tlscipher") || !strcasecmp(varname, "sslcipher")) {
      ast_free(tls_cfg->cipher);
      tls_cfg->cipher = ast_strdup(value);
   } else if (!strcasecmp(varname, "tlscafile")) {
      ast_free(tls_cfg->cafile);
      tls_cfg->cafile = ast_strdup(value);
   } else if (!strcasecmp(varname, "tlscapath") || !strcasecmp(varname, "tlscadir")) {
      ast_free(tls_cfg->capath);
      tls_cfg->capath = ast_strdup(value);
   } else if (!strcasecmp(varname, "tlsverifyclient")) {
      ast_set2_flag(&tls_cfg->flags, ast_true(value), AST_SSL_VERIFY_CLIENT);
   } else if (!strcasecmp(varname, "tlsdontverifyserver")) {
      ast_set2_flag(&tls_cfg->flags, ast_true(value), AST_SSL_DONT_VERIFY_SERVER);
   } else if (!strcasecmp(varname, "tlsbindaddr") || !strcasecmp(varname, "sslbindaddr")) {
      if (ast_parse_arg(value, PARSE_ADDR, &tls_desc->local_address))
         ast_log(LOG_WARNING, "Invalid %s '%s'\n", varname, value);
   } else if (!strcasecmp(varname, "tlsclientmethod") || !strcasecmp(varname, "sslclientmethod")) {
      if (!strcasecmp(value, "tlsv1")) {
         ast_set_flag(&tls_cfg->flags, AST_SSL_TLSV1_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_SSLV3_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_SSLV2_CLIENT);
      } else if (!strcasecmp(value, "sslv3")) {
         ast_set_flag(&tls_cfg->flags, AST_SSL_SSLV3_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_SSLV2_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_TLSV1_CLIENT);
      } else if (!strcasecmp(value, "sslv2")) {
         ast_set_flag(&tls_cfg->flags, AST_SSL_SSLV2_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_TLSV1_CLIENT);
         ast_clear_flag(&tls_cfg->flags, AST_SSL_SSLV3_CLIENT);
      }
   } else {
      return -1;
   }

   return 0;
}