Fix issue #33, respond to NS requests

CHANGELOG

@@ -19,6 +19,8 @@ CHANGES:
 	- Added capability to forward DNS queries outside tunnel domain to
 		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.
 
 2008-08-06: 0.4.2 "Opened Zone"
 	- Applied a few small patches from Maxim Bourmistrov and Gregor Herrmann

src/dns.c

@@ -98,6 +98,85 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
 	return len;
 }
 
+int
+dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain)
+{
+	HEADER *header;
+	int len;
+	short name;
+	short topname;
+	short nsname;
+	char *domain;
+	int domain_len;
+	char *p;
+
+	memset(buf, 0, buflen);
+	
+	header = (HEADER*)buf;
+	
+	header->id = htons(q->id);
+	header->qr = 1;
+	header->opcode = 0;
+	header->aa = 1;
+	header->tc = 0;
+	header->rd = 0;
+	header->ra = 0;
+
+	p = buf + sizeof(HEADER);
+
+	header->qdcount = htons(1);
+	header->ancount = htons(1);
+	header->arcount = htons(1);
+
+	/* pointer to start of name */
+	name = 0xc000 | ((p - buf) & 0x3fff);
+
+	domain = strstr(q->name, topdomain);
+	if (domain) {
+		domain_len = (int) (domain - q->name); 
+	} else {
+		return -1;
+	}
+	/* pointer to start of topdomain */
+	topname = 0xc000 | ((p - buf + domain_len) & 0x3fff);
+
+	/* Query section */
+	putname(&p, sizeof(q->name), q->name);	/* Name */
+	putshort(&p, q->type);			/* Type */
+	putshort(&p, C_IN);			/* Class */
+
+	/* Answer section */
+	putshort(&p, name);			/* Name */
+	putshort(&p, q->type);			/* Type */
+	putshort(&p, C_IN);			/* Class */
+	putlong(&p, 0x3ea7d011);		/* TTL */
+	putshort(&p, 5);			/* Data length */
+
+	/* pointer to ns.topdomain */
+	nsname = 0xc000 | ((p - buf) & 0x3fff);
+	putbyte(&p, 2);
+	putbyte(&p, 'n');
+	putbyte(&p, 's');
+	putshort(&p, topname);			/* Name Server */
+
+	/* Additional data (A-record of NS server) */
+	putshort(&p, nsname);			/* Name Server */
+	putshort(&p, T_A);			/* Type */
+	putshort(&p, C_IN);			/* Class */
+	putlong(&p, 0x3ea7d011);		/* TTL */
+	putshort(&p, 4);			/* Data length */
+
+	/* ugly hack to output IP address */
+	domain = (char *) &q->destination;
+	putbyte(&p, *domain++);
+	putbyte(&p, *domain++);
+	putbyte(&p, *domain++);
+	putbyte(&p, *domain);
+
+	len = p - buf;
+	return len;
+}
+
 short
 dns_get_id(char *packet, size_t packetlen)
 {

src/dns.h

@@ -25,6 +25,7 @@ typedef enum {
 } qr_t;
 
 int dns_encode(char *, size_t, struct query *, qr_t, char *, size_t);
+int dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain);
 short dns_get_id(char *packet, size_t packetlen);
 int dns_decode(char *, size_t, struct query *, qr_t, char *, size_t);
 

src/iodined.c

@@ -333,6 +333,19 @@ handle_null_request(int tun_fd, int dns_fd, struct query *q, int domain_len)
 	}
 }
 
+static void
+handle_ns_request(int dns_fd, struct query *q)
+{
+	char buf[64*1024];
+	int len;
+
+	len = dns_encode_ns_response(buf, sizeof(buf), q, topdomain);
+	
+	if (sendto(dns_fd, buf, len, 0, (struct sockaddr*)&q->from, q->fromlen) <= 0) {
+		warn("ns reply send error");
+	}
+}
+
 static void
 forward_query(int bind_fd, struct query *q)
 {
@@ -443,6 +456,9 @@ tunnel_dns(int tun_fd, int dns_fd, int bind_fd)
 		case T_NULL:
 			handle_null_request(tun_fd, dns_fd, &q, domain_len);
 			break;
+		case T_NS:
+			handle_ns_request(dns_fd, &q);
+			break;
 		default:
 			break;
 		}