Fix memory leak of SSL_CTX structures in TLS core.

SSL_CTX structures were allocated but never freed. This was a bigger
issue for clients than servers since new SSL_CTX structures could be
allocated for each connection. Servers, on the other hand, typically
set up a single SSL_CTX for their lifetime.

This is solved in two ways:

1. In __ssl_setup(), if a tcptls_cfg has an ssl_ctx on it, it is
freed so that a new one can take its place.
2. A companion to ast_ssl_setup() called ast_ssl_teardown() has
been added so that servers can properly free their SSL_CTXs.

(issue ASTERISK-19278)
........

Merged revisions 367002 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@367003 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -31545,6 +31545,7 @@ static int unload_module(void)
 	if (sip_tls_desc.master) {
 		ast_tcptls_server_stop(&sip_tls_desc);
 	}
+	ast_ssl_teardown(sip_tls_desc.tls_cfg);
 
 	/* Kill all existing TCP/TLS threads */
 	i = ao2_iterator_init(threadt, 0);

include/asterisk/tcptls.h

@@ -190,8 +190,25 @@ void ast_tcptls_server_start(struct ast_tcptls_session_args *desc);
  * \version 1.6.1 changed desc parameter to be of ast_tcptls_session_args type
  */
 void ast_tcptls_server_stop(struct ast_tcptls_session_args *desc);
+
+/*!
+ * \brief Set up an SSL server
+ *
+ * \param cfg Configuration for the SSL server
+ * \retval 1 Success
+ * \retval 0 Failure
+ */
 int ast_ssl_setup(struct ast_tls_config *cfg);
 
+/*!
+ * \brief free resources used by an SSL server
+ *
+ * \note This only needs to be called if ast_ssl_setup() was
+ * directly called first.
+ * \param cfg Configuration for the SSL server
+ */
+void ast_ssl_teardown(struct ast_tls_config *cfg);
+
 /*!
  * \brief Used to parse conf files containing tls/ssl options.
  */

main/tcptls.c

@@ -130,6 +130,9 @@ HOOK_T ast_tcptls_server_write(struct ast_tcptls_session_instance *tcptls_sessio
 static void session_instance_destructor(void *obj)
 {
 	struct ast_tcptls_session_instance *i = obj;
+	if (i->parent && i->parent->tls_cfg) {
+		ast_ssl_teardown(i->parent->tls_cfg);
+	}
 	ast_mutex_destroy(&i->lock);
 }
 
@@ -311,6 +314,14 @@ static int __ssl_setup(struct ast_tls_config *cfg, int client)
 	SSL_load_error_strings();
 	SSLeay_add_ssl_algorithms();
 
+	/* 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)) {
@@ -346,6 +357,8 @@ static int __ssl_setup(struct ast_tls_config *cfg, int client)
 				ast_verb(0, "SSL error loading cert file. <%s>", cfg->certfile);
 				sleep(2);
 				cfg->enabled = 0;
+				SSL_CTX_free(cfg->ssl_ctx);
+				cfg->ssl_ctx = NULL;
 				return 0;
 			}
 		}
@@ -355,6 +368,8 @@ static int __ssl_setup(struct ast_tls_config *cfg, int client)
 				ast_verb(0, "SSL error loading private key file. <%s>", tmpprivate);
 				sleep(2);
 				cfg->enabled = 0;
+				SSL_CTX_free(cfg->ssl_ctx);
+				cfg->ssl_ctx = NULL;
 				return 0;
 			}
 		}
@@ -365,6 +380,8 @@ static int __ssl_setup(struct ast_tls_config *cfg, int client)
 				ast_verb(0, "SSL cipher error <%s>", cfg->cipher);
 				sleep(2);
 				cfg->enabled = 0;
+				SSL_CTX_free(cfg->ssl_ctx);
+				cfg->ssl_ctx = NULL;
 				return 0;
 			}
 		}
@@ -384,6 +401,14 @@ int ast_ssl_setup(struct ast_tls_config *cfg)
 	return __ssl_setup(cfg, 0);
 }
 
+void ast_ssl_teardown(struct ast_tls_config *cfg)
+{
+	if (cfg->ssl_ctx) {
+		SSL_CTX_free(cfg->ssl_ctx);
+		cfg->ssl_ctx = NULL;
+	}
+}
+
 struct ast_tcptls_session_instance *ast_tcptls_client_start(struct ast_tcptls_session_instance *tcptls_session)
 {
 	struct ast_tcptls_session_args *desc;