res_rtp_asterisk: Allow ICE host candidates to be overriden

During ICE negotiation the IPs of the local interfaces are sent to the remote
peer as host candidates. In many cases Asterisk is behind a static one-to-one
NAT, so these host addresses will be internal IP addresses.

To help in hiding the topology of the internal network, this patch adds the
ability to override the host candidates by matching them against a
user-defined list of replacements.

Change-Id: I1c9541af97b83a4c690c8150d19bf7202c8bff1f

1 files changed, 81 insertions, 0 deletions

diff --git a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
index f6bf34211..611920e80 100644
--- a/res/res_rtp_asterisk.c
+++ b/res/res_rtp_asterisk.c
@@ -182,6 +182,16 @@ struct ast_rtp_ioqueue_thread {
 /*! \brief List of ioqueue threads */
 static AST_LIST_HEAD_STATIC(ioqueues, ast_rtp_ioqueue_thread);
 
+/*! \brief Structure which contains ICE host candidate mapping information */
+struct ast_ice_host_candidate {
+	pj_sockaddr local;
+	pj_sockaddr advertised;
+	AST_RWLIST_ENTRY(ast_ice_host_candidate) next;
+};
+
+/*! \brief List of ICE host candidate mappings */
+static AST_RWLIST_HEAD_STATIC(host_candidates, ast_ice_host_candidate);
+
 #endif
 
 #define FLAG_3389_WARNING               (1 << 0)
@@ -451,6 +461,38 @@ static void dtls_srtp_stop_timeout_timer(struct ast_rtp_instance *instance, stru
 static int __rtp_sendto(struct ast_rtp_instance *instance, void *buf, size_t size, int flags, struct ast_sockaddr *sa, int rtcp, int *ice, int use_srtp);
 
 #ifdef HAVE_PJPROJECT
+/*! \brief Helper function which clears the ICE host candidate mapping */
+static void host_candidate_overrides_clear(void)
+{
+	struct ast_ice_host_candidate *candidate;
+
+	AST_RWLIST_WRLOCK(&host_candidates);
+	AST_RWLIST_TRAVERSE_SAFE_BEGIN(&host_candidates, candidate, next) {
+		AST_RWLIST_REMOVE_CURRENT(next);
+		ast_free(candidate);
+	}
+	AST_RWLIST_TRAVERSE_SAFE_END;
+	AST_RWLIST_UNLOCK(&host_candidates);
+}
+
+/*! \brief Applies the ICE host candidate mapping */
+static void host_candidate_overrides_apply(unsigned int count, pj_sockaddr addrs[])
+{
+	int pos;
+	struct ast_ice_host_candidate *candidate;
+
+	AST_RWLIST_RDLOCK(&host_candidates);
+	for (pos = 0; pos < count; pos++) {
+		AST_LIST_TRAVERSE(&host_candidates, candidate, next) {
+			if (!pj_sockaddr_cmp(&candidate->local, &addrs[pos])) {
+				pj_sockaddr_copy_addr(&addrs[pos], &candidate->advertised);
+				break;
+			}
+		}
+	}
+	AST_RWLIST_UNLOCK(&host_candidates);
+}
+
 /*! \brief Helper function which updates an ast_sockaddr with the candidate used for the component */
 static void update_address_with_ice_candidate(struct ast_rtp *rtp, enum ast_rtp_ice_component_type component,
 	struct ast_sockaddr *cand_address)
@@ -2368,6 +2410,8 @@ static void rtp_add_candidates_to_ice(struct ast_rtp_instance *instance, struct
 		pj_enum_ip_interface(pj_AF_INET6(), &count, address);
 	}
 
+	host_candidate_overrides_apply(count, address);
+
 	for (pos = 0; pos < count; pos++) {
 		pj_sockaddr_set_port(&address[pos], port);
 		ast_rtp_ice_add_cand(rtp, component, transport, PJ_ICE_CAND_TYPE_HOST, 65535, &address[pos], &address[pos], NULL,
@@ -5257,6 +5301,11 @@ static int rtp_reload(int reload)
 	const char *s;
 	struct ast_flags config_flags = { reload ? CONFIG_FLAG_FILEUNCHANGED : 0 };
 
+#ifdef HAVE_PJPROJECT
+	struct ast_variable *var;
+	struct ast_ice_host_candidate *candidate;
+#endif
+
 	cfg = ast_config_load2("rtp.conf", "rtp", config_flags);
 	if (cfg == CONFIG_STATUS_FILEMISSING || cfg == CONFIG_STATUS_FILEUNCHANGED || cfg == CONFIG_STATUS_FILEINVALID) {
 		return 0;
@@ -5283,6 +5332,7 @@ static int rtp_reload(int reload)
 	turnaddr = pj_str(NULL);
 	turnusername = pj_str(NULL);
 	turnpassword = pj_str(NULL);
+	host_candidate_overrides_clear();
 #endif
 
 	if (cfg) {
@@ -5362,6 +5412,36 @@ static int rtp_reload(int reload)
 		if ((s = ast_variable_retrieve(cfg, "general", "turnpassword"))) {
 			pj_strdup2_with_null(pool, &turnpassword, s);
 		}
+
+		AST_RWLIST_WRLOCK(&host_candidates);
+		for (var = ast_variable_browse(cfg, "ice_host_candidates"); var; var = var->next) {
+			struct ast_sockaddr local_addr, advertised_addr;
+			pj_str_t address;
+
+			ast_sockaddr_setnull(&local_addr);
+			ast_sockaddr_setnull(&advertised_addr);
+
+			if (ast_parse_arg(var->name, PARSE_ADDR | PARSE_PORT_IGNORE, &local_addr)) {
+				ast_log(LOG_WARNING, "Invalid local ICE host address: %s\n", var->name);
+				continue;
+			}
+
+			if (ast_parse_arg(var->value, PARSE_ADDR | PARSE_PORT_IGNORE, &advertised_addr)) {
+				ast_log(LOG_WARNING, "Invalid advertised ICE host address: %s\n", var->value);
+				continue;
+			}
+
+			if (!(candidate = ast_calloc(1, sizeof(*candidate)))) {
+				ast_log(LOG_ERROR, "Failed to allocate ICE host candidate mapping.\n");
+				break;
+			}
+
+			pj_sockaddr_parse(pj_AF_UNSPEC(), 0, pj_cstr(&address, ast_sockaddr_stringify(&local_addr)), &candidate->local);
+			pj_sockaddr_parse(pj_AF_UNSPEC(), 0, pj_cstr(&address, ast_sockaddr_stringify(&advertised_addr)), &candidate->advertised);
+
+			AST_RWLIST_INSERT_TAIL(&host_candidates, candidate, next);
+		}
+		AST_RWLIST_UNLOCK(&host_candidates);
 #endif
 		ast_config_destroy(cfg);
 	}
@@ -5464,6 +5544,7 @@ static int unload_module(void)
 	ast_cli_unregister_multiple(cli_rtp, ARRAY_LEN(cli_rtp));
 
 #ifdef HAVE_PJPROJECT
+	host_candidate_overrides_clear();
 	pj_thread_register_check();
 	rtp_terminate_pjproject();
 #endif