Added -n to set NS ip, updated docs, added checks

CHANGELOG

@@ -13,7 +13,8 @@ CHANGES:
 		a nameserver on localhost. Use -b port to enable.
 	- iodine client now shuts down if it detects a server restart.
 	- iodined now replies to NS request on its own domain, fixes issue #33.
-		The destination IP address is sent as reply.
+		The destination IP address is sent as reply. Use -n to specify
+		a specific IP address to return (if behind NAT etc).
 	- Upstream data is now Base64 encoded if relay server preserves case and
 		supports the plus (+) character in domain names, fixes #16.
 

man/iodine.8

@@ -27,16 +27,22 @@ iodine, iodined \- tunnel IPv4 over DNS
 
 .B iodined [-c] [-s] [-f] [-D] [-u
 .I user
-.B ] [-P
-.I password
 .B ] [-t
 .I chrootdir
+.B ] [-d
+.I device
 .B ] [-m
 .I mtu
 .B ] [-l
 .I listen_ip
-.B ] [-d
-.I device
+.B ] [-p
+.I port
+.B ] [-n
+.I external ip
+.B ] [-b
+.I dnsport
+.B ] [-P
+.I password
 .B ] 
 .I tunnel_ip
 .I topdomain
@@ -68,14 +74,14 @@ Drop privileges and run as user 'user' after setting up tunnel.
 .B -t chrootdir
 Chroot to 'chrootdir' after setting up tunnel.
 .TP
+.B -d device
+Use the TUN device 'device' instead of the normal one, which is dnsX on Linux
+and otherwise tunX.
+.TP
 .B -P password
 Use 'password' to authenticate. If not used, 
 .B stdin
 will be used as input. Only the first 32 characters will be used.
-.TP
-.B -d device
-Use the TUN device 'device' instead of the normal one, which is dnsX on Linux
-and otherwise tunX.
 .SS Server Options:
 .TP
 .B -c
@@ -100,6 +106,14 @@ connections.
 Make the server listen on 'port' instead of 53 for traffic. 
 .B Note:
 You must make sure the dns requests are forwarded to this port yourself.
+.TP
+.B -n external ip
+The IP address to return in NS responses. Default is to return the address used
+as destination in the query.
+.TP
+.B -b dnsport
+If this port is specified, all incoming requests not inside the tunnel domain
+will be forwarded to this port on localhost, to be handled by a real dns.
 .SS Client Arguments:
 .TP
 .B nameserver

src/iodined.c

@@ -60,6 +60,8 @@ static int check_ip;
 static int my_mtu;
 static in_addr_t my_ip;
 
+static in_addr_t ns_ip;
+
 static int bind_port;
 static int debug;
 
@@ -353,6 +355,10 @@ handle_ns_request(int dns_fd, struct query *q)
 	char buf[64*1024];
 	int len;
 
+	if (ns_ip != INADDR_ANY) {
+		memcpy(&q->destination.s_addr, &ns_ip, sizeof(in_addr_t));
+	}
+
 	len = dns_encode_ns_response(buf, sizeof(buf), q, topdomain);
 	
 	if (debug >= 1) {
@@ -636,7 +642,7 @@ usage() {
 
 	printf("Usage: %s [-v] [-h] [-c] [-s] [-f] [-D] [-u user] "
 		"[-t chrootdir] [-d device] [-m mtu] "
-		"[-l ip address to listen on] [-p port] [-b port] [-P password]"
+		"[-l ip address to listen on] [-p port] [-n external ip] [-b dnsport] [-P password]"
 		" tunnel_ip topdomain\n", __progname);
 	exit(2);
 }
@@ -648,7 +654,7 @@ help() {
 	printf("iodine IP over DNS tunneling server\n");
 	printf("Usage: %s [-v] [-h] [-c] [-s] [-f] [-D] [-u user] "
 		"[-t chrootdir] [-d device] [-m mtu] "
-		"[-l ip address to listen on] [-p port] [-b port] [-P password]"
+		"[-l ip address to listen on] [-p port] [-n external ip] [-b dnsport] [-P password]"
 		" tunnel_ip topdomain\n", __progname);
 	printf("  -v to print version info and exit\n");
 	printf("  -h to print this help and exit\n");
@@ -664,6 +670,7 @@ help() {
 	printf("  -l ip address to listen on for incoming dns traffic "
 		"(default 0.0.0.0)\n");
 	printf("  -p port to listen on for incoming dns traffic (default 53)\n");
+	printf("  -n ip to respond with to NS queries\n");
 	printf("  -b port to forward normal DNS queries to (on localhost)\n");
 	printf("  -P password used for authentication (max 32 chars will be used)\n");
 	printf("tunnel_ip is the IP number of the local tunnel interface.\n");
@@ -711,6 +718,7 @@ main(int argc, char **argv)
 	mtu = 1024;
 	listen_ip = INADDR_ANY;
 	port = 53;
+	ns_ip = INADDR_ANY;
 	check_ip = 1;
 	skipipconfig = 0;
 	debug = 0;
@@ -729,7 +737,7 @@ main(int argc, char **argv)
 	srand(time(NULL));
 	fw_query_init();
 	
-	while ((choice = getopt(argc, argv, "vcsfhDu:t:d:m:l:p:b:P:")) != -1) {
+	while ((choice = getopt(argc, argv, "vcsfhDu:t:d:m:l:p:n:b:P:")) != -1) {
 		switch(choice) {
 		case 'v':
 			version();
@@ -767,6 +775,9 @@ main(int argc, char **argv)
 		case 'p':
 			port = atoi(optarg);
 			break;
+		case 'n':
+			ns_ip = inet_addr(optarg);
+			break;
 		case 'b':
 			bind_enable = 1;
 			bind_port = atoi(optarg);
@@ -795,6 +806,13 @@ main(int argc, char **argv)
 	if (argc != 2) 
 		usage();
 	
+	my_ip = inet_addr(argv[0]);
+	
+	if (my_ip == INADDR_NONE) {
+		warnx("Bad IP address to use inside tunnel.\n");
+		usage();
+	}
+
 	topdomain = strdup(argv[1]);
 	if(strlen(topdomain) <= 128) {
 		if(check_topdomain(topdomain)) {
@@ -849,6 +867,11 @@ main(int argc, char **argv)
 		usage();
 	}
 	
+	if (ns_ip == INADDR_NONE) {
+		warnx("Bad IP address to return as nameserver.\n");
+		usage();
+	}
+	
 	if (strlen(password) == 0)
 		read_password(password, sizeof(password));
 
@@ -863,7 +886,6 @@ main(int argc, char **argv)
 		if ((bind_fd = open_dns(0, INADDR_ANY)) == -1)
 			goto cleanup3;
 
-	my_ip = inet_addr(argv[0]);
 	my_mtu = mtu;
 	init_users(my_ip);