iodine/src/dns.c

/*
 * Copyright (c) 2006 Bjorn Andersson <flex@kryo.se>, Erik Ekman <yarrick@kryo.se>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <arpa/inet.h>
#include <arpa/nameser.h>
#ifdef DARWIN
#include <arpa/nameser8_compat.h>
#endif
#include <time.h>
#include <err.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <ctype.h>

#include "dns.h"
#include "encoding.h"
#include "read.h"

int
dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen)
{
	HEADER *header;
	short name;
	char *p;
	int len;

	memset(buf, 0, buflen);
	
	header = (HEADER*)buf;
	
	header->id = htons(q->id);
	header->qr = (qr == QR_ANSWER);
	header->opcode = 0;
	header->aa = (qr == QR_ANSWER);
	header->tc = 0;
	header->rd = (qr == QR_QUERY);
	header->ra = 0;

	p = buf + sizeof(HEADER);

	switch (qr) {
	case QR_ANSWER:
		header->ancount = htons(1);
		header->qdcount = htons(1);
	
		name = 0xc000 | ((p - buf) & 0x3fff);
		p += dns_encode_hostname(q->name, p, strlen(q->name));
		putshort(&p, q->type);
		putshort(&p, C_IN);

		putshort(&p, name);	
		putshort(&p, q->type);
		putshort(&p, C_IN);
		putlong(&p, 0);

		/* 
		 * XXX: This is jidder! This is used to detect if there's packets to be sent. 
		 */
		q->id = 0;

		putshort(&p, datalen);
		putdata(&p, data, datalen);
		break;
	case QR_QUERY:
		header->qdcount = htons(1);
		header->arcount = htons(1);
	
		p += dns_encode_hostname(data, p, datalen);	

		putshort(&p, q->type);
		putshort(&p, C_IN);

		// EDNS0
		putbyte(&p, 0x00); //Root
		putshort(&p, 0x0029); // OPT
		putshort(&p, 0x1000); // Payload size: 4096
		putshort(&p, 0x0000); // Higher bits/edns version
		putshort(&p, 0x8000); // Z
		putshort(&p, 0x0000); // Data length
		break;
	}
	
	len = p - buf;

	return len;
}

int
dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, size_t packetlen)
{
	char rdata[4*1024];
	HEADER *header;
	short qdcount;
	short ancount;
	char name[255];
	uint32_t ttl;
	short class;
	short type;
	char *data;
	short rlen;
	int id; 
	int rv;

	rv = 0;
	header = (HEADER*)packet;

	// Reject short packets
	if (packetlen < sizeof(HEADER)) 
		return 0;
	
	if (header->qr != qr) {
		warnx("header->qr does not match the requested qr");
		return -1;
	}

	data = packet + sizeof(HEADER);
	qdcount = ntohs(header->qdcount);
	ancount = ntohs(header->ancount);
	
	id = ntohs(header->id);
		
	rlen = 0;

	switch (qr) {
	case QR_ANSWER:
		if(qdcount != 1 || ancount != 1) {
			warnx("no query or answer in answer");
			return -1;
		}

		if (q != NULL) 
			q->id = id;

		readname(packet, packetlen, &data, name, sizeof(name));
		readshort(packet, &data, &type);
		readshort(packet, &data, &class);
		
		readname(packet, packetlen, &data, name, sizeof(name));
		readshort(packet, &data, &type);
		readshort(packet, &data, &class);
		readlong(packet, &data, &ttl);
		readshort(packet, &data, &rlen);
		rv = MIN(rlen, sizeof(rdata));
		rv = readdata(packet, &data, rdata, rv);

		if(type == T_NULL && rv > 2) {
			rv = MIN(rv, buflen);
			memcpy(buf, rdata, rv);
		}
		break;
	case QR_QUERY:
		if (qdcount != 1) {
			warnx("no query on query");
			return -1;
		}

		readname(packet, packetlen, &data, name, sizeof(name) -1);
		name[256] = 0;
		readshort(packet, &data, &type);
		readshort(packet, &data, &class);

		if(type != T_NULL) {
			rv = 0;
			break;
		}

		strncpy(q->name, name, 257);
		q->type = type;
		q->id = id;

		rv = strlen(q->name);
		break;
	}

	return rv;
}

int
dns_build_hostname(char *buf, size_t buflen, 
				   const char *data, const size_t datalen, 
				   const char *topdomain)
{
	int avail;
	int written;
	int encoded;
	char *b;

	avail = MIN(0xFF, buflen) - strlen(topdomain) - 2;
	memset(buf, 0, buflen);
	b = buf;
	written = encode_data(data, datalen, avail, b);
	encoded = strlen(buf);
	b += encoded;
	if (*b != '.') {
		*b++ = '.';
	}
	strncpy(b, topdomain, strlen(topdomain)+1);
	
	return written;
}

int
dns_encode_hostname(const char *host, char *buffer, int size)
{
	char *h;
	char *p;
	char *word;
	int left;

	h = strdup(host);
	memset(buffer, 0, size);
	p = buffer;
	left = size;
	
	word = strtok(h, ".");
	while(word) {
		if (strlen(word) > 63 || strlen(word) > left) {
			free(h);
			return -1;
		}
		left -= (strlen(word) + 1);
		*p++ = (char)strlen(word);
		memcpy(p, word, strlen(word));
		p += strlen(word);

		word = strtok(NULL, ".");
	}

	*p++ = 0;

	free(h);

	return p - buffer;
}