app_followme.c: Grab reference on nativeformats before using it

Fixes a crash due to a lack of proper reference on the nativeformats
object before passing it into ast_request().  Also found potentially
similar use case bugs in app_chanisavail.c, bridge.c, and bridge_basic.c

Fixes: #388
(cherry picked from commit b5c31b55c9)

apps/app_chanisavail.c

@@ -117,6 +117,7 @@ static int chanavail_exec(struct ast_channel *chan, const char *data)
 	struct ast_str *tmp_availcause = ast_str_alloca(2048);
 	struct ast_channel *tempchan;
 	struct ast_custom_function *cdr_prop_func = ast_custom_function_find("CDR_PROP");
+	struct ast_format_cap *caps = NULL;
 	AST_DECLARE_APP_ARGS(args,
 		AST_APP_ARG(reqchans);
 		AST_APP_ARG(options);
@@ -126,6 +127,10 @@ static int chanavail_exec(struct ast_channel *chan, const char *data)
 
 	AST_STANDARD_APP_ARGS(args, info);
 
+	ao2_lock(chan);
+	caps = ao2_bump(ast_channel_nativeformats(chan));
+	ao2_unlock(chan);
+
 	if (args.options) {
 		if (strchr(args.options, 'a')) {
 			option_all_avail = 1;
@@ -174,10 +179,11 @@ static int chanavail_exec(struct ast_channel *chan, const char *data)
 			snprintf(trychan, sizeof(trychan), "%s/%s", tech, number);
 			status = inuse = ast_device_state(trychan);
 		}
-		ast_str_append(&tmp_availstat, 0, "%s%d",
-			ast_str_strlen(tmp_availstat) ? "&" : "", status);
+		ast_str_append(&tmp_availstat, 0, "%s%d", ast_str_strlen(tmp_availstat) ? "&" : "", status);
+
 		if ((inuse <= (int) AST_DEVICE_NOT_INUSE)
-			&& (tempchan = ast_request(tech, ast_channel_nativeformats(chan), NULL, chan, number, &status))) {
+			&& (tempchan = ast_request(tech, caps, NULL, chan, number, &status))) {
+
 			ast_str_append(&tmp_availchan, 0, "%s%s",
 				ast_str_strlen(tmp_availchan) ? "&" : "", ast_channel_name(tempchan));
 
@@ -199,8 +205,11 @@ static int chanavail_exec(struct ast_channel *chan, const char *data)
 				break;
 			}
 		}
+
 	}
 
+	ao2_cleanup(caps);
+
 	pbx_builtin_setvar_helper(chan, "AVAILCHAN", ast_str_buffer(tmp_availchan));
 	/* Store the originally used channel too */
 	pbx_builtin_setvar_helper(chan, "AVAILORIGCHAN", ast_str_buffer(tmp_availorig));

apps/app_followme.c

@@ -1068,6 +1068,7 @@ static struct ast_channel *findmeexec(struct fm_args *tpargs, struct ast_channel
 		ast_copy_string(num, nm->number, sizeof(num));
 		for (number = num; number; number = rest) {
 			struct ast_channel *outbound;
+			struct ast_format_cap *caps;
 
 			rest = strchr(number, '&');
 			if (rest) {
@@ -1097,8 +1098,15 @@ static struct ast_channel *findmeexec(struct fm_args *tpargs, struct ast_channel
 						? "/n" : "/m");
 			}
 
-			outbound = ast_request("Local", ast_channel_nativeformats(caller), NULL, caller,
-				tmpuser->dialarg, &dg);
+			/* Capture nativeformats reference in case it gets changed */
+			ast_channel_lock(caller);
+			caps = ao2_bump(ast_channel_nativeformats(caller));
+			ast_channel_unlock(caller);
+
+			outbound = ast_request("Local", caps, NULL, caller, tmpuser->dialarg, &dg);
+
+			ao2_cleanup(caps);
+
 			if (!outbound) {
 				ast_log(LOG_WARNING, "Unable to allocate a channel for Local/%s cause: %s\n",
 					tmpuser->dialarg, ast_cause2str(dg));

main/bridge.c

@@ -4118,10 +4118,18 @@ static enum ast_transfer_result blind_transfer_bridge(int is_external,
 	struct ast_channel *local;
 	char chan_name[AST_MAX_EXTENSION + AST_MAX_CONTEXT + 2];
 	int cause;
+	struct ast_format_cap *caps;
+
+	ast_channel_lock(transferer);
+	caps = ao2_bump(ast_channel_nativeformats(transferer));
+	ast_channel_unlock(transferer);
 
 	snprintf(chan_name, sizeof(chan_name), "%s@%s", exten, context);
-	local = ast_request("Local", ast_channel_nativeformats(transferer), NULL, transferer,
+	local = ast_request("Local", caps, NULL, transferer,
 			chan_name, &cause);
+
+	ao2_cleanup(caps);
+
 	if (!local) {
 		return AST_BRIDGE_TRANSFER_FAIL;
 	}
@@ -4228,9 +4236,16 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
 	int cause;
 	int res;
 	const char *app = NULL;
+	struct ast_format_cap *caps;
+
+	ast_channel_lock(chan1);
+	caps = ao2_bump(ast_channel_nativeformats(chan1));
+	ast_channel_unlock(chan1);
+
+	local_chan = ast_request("Local", caps, NULL, chan1, dest, &cause);
+
+	ao2_cleanup(caps);
 
-	local_chan = ast_request("Local", ast_channel_nativeformats(chan1), NULL, chan1,
-			dest, &cause);
 	if (!local_chan) {
 		return AST_BRIDGE_TRANSFER_FAIL;
 	}

main/bridge_basic.c

@@ -3288,10 +3288,17 @@ static struct ast_channel *dial_transfer(struct ast_channel *caller, const char
 {
 	struct ast_channel *chan;
 	int cause;
+	struct ast_format_cap *caps;
+
+	ast_channel_lock(caller);
+	caps = ao2_bump(ast_channel_nativeformats(caller));
+	ast_channel_unlock(caller);
 
 	/* Now we request a local channel to prepare to call the destination */
-	chan = ast_request("Local", ast_channel_nativeformats(caller), NULL, caller, destination,
-		&cause);
+	chan = ast_request("Local", caps, NULL, caller, destination, &cause);
+
+	ao2_cleanup(caps);
+
 	if (!chan) {
 		return NULL;
 	}