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iodine/dns.c

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/*
* 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 <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#ifdef DARWIN
#include <arpa/nameser8_compat.h>
#endif
#include <netdb.h>
#include <time.h>
#include <err.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "structs.h"
#include "dns.h"
#include "encoding.h"
#include "read.h"
// For FreeBSD
#ifndef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))
#endif
static int dns_write(int, int, char *, int, char);
static void dns_query(int, int, char *, int);
struct sockaddr_in peer;
char topdomain[256];
// Current IP packet
char activepacket[4096];
int lastlen;
int packetpos;
int packetlen;
uint16_t chunkid;
uint16_t pingid;
int
open_dns(const char *domain, int localport, in_addr_t listen_ip)
{
int fd;
int flag;
struct sockaddr_in addr;
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(localport);
/* listen_ip already in network byte order from inet_addr, or 0 */
addr.sin_addr.s_addr = listen_ip;
fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(fd < 0) {
warn("socket");
return -1;
}
flag = 1;
#ifdef SO_REUSEPORT
setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &flag, sizeof(flag));
#endif
setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag));
if(bind(fd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
warn("bind");
return -1;
}
// Save top domain used
strncpy(topdomain, domain, sizeof(topdomain) - 1);
topdomain[sizeof(topdomain) - 1] = '\0';
printf("Opened UDP socket\n");
return fd;
}
int
dns_settarget(const char *host)
{
struct hostent *h;
// Init dns target struct
h = gethostbyname(host);
if (!h) {
printf("Could not resolve name %s, exiting\n", host);
return -1;
}
bzero(&peer, sizeof(peer));
peer.sin_family = AF_INET;
peer.sin_port = htons(53);
peer.sin_addr = *((struct in_addr *) h->h_addr);
// Init chunk id
chunkid = 0;
pingid = 0;
return 0;
}
void
close_dns(int fd)
{
close(fd);
}
int
dns_sending()
{
return (packetlen != 0);
}
static void
dns_send_chunk(int fd)
{
int avail;
char *p;
p = activepacket;
p += packetpos;
avail = packetlen - packetpos;
lastlen = dns_write(fd, ++chunkid, p, avail, 0);
}
void
dns_handle_tun(int fd, char *data, int len)
{
memcpy(activepacket, data, MIN(len, sizeof(activepacket)));
lastlen = 0;
packetpos = 0;
packetlen = len;
dns_send_chunk(fd);
}
void
dns_ping(int dns_fd)
{
char data[2];
if (dns_sending()) {
lastlen = 0;
packetpos = 0;
packetlen = 0;
}
data[0] = (pingid & 0xFF00) >> 8;
data[1] = (pingid & 0xFF);
dns_write(dns_fd, ++pingid, data, 2, 'P');
}
void
dns_handshake(int dns_fd)
{
char data[2];
data[0] = (pingid & 0xFF00) >> 8;
data[1] = (pingid & 0xFF);
dns_write(dns_fd, ++pingid, data, 2, 'H');
}
static void
dns_query(int fd, int id, char *host, int type)
{
char *p;
int len;
int peerlen;
char buf[1024];
HEADER *header;
len = 0;
memset(buf, 0, sizeof(buf));
header = (HEADER*)buf;
header->id = htons(id);
header->qr = 0;
header->opcode = 0;
header->aa = 0;
header->tc = 0;
header->rd = 1;
header->ra = 0;
header->qdcount = htons(1);
header->arcount = htons(1);
p = buf + sizeof(HEADER);
p += dns_encode_hostname(host, p, strlen(host));
putshort(&p, 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
peerlen = sizeof(peer);
len = p - buf;
sendto(fd, buf, len, 0, (struct sockaddr*)&peer, peerlen);
}
static int
dns_write(int fd, int id, char *buf, int len, char flag)
{
int avail;
int written;
int encoded;
char data[257];
char *d;
avail = 0xFF - strlen(topdomain) - 2;
bzero(data, sizeof(data));
d = data;
written = encode_data(buf, len, avail, d, flag);
encoded = strlen(data);
d += encoded;
if (*d != '.') {
*d++ = '.';
}
strncpy(d, topdomain, strlen(topdomain)+1);
dns_query(fd, id, data, T_NULL);
return written;
}
int
dns_read(int fd, char *buf, int buflen)
{
int r;
socklen_t addrlen;
char packet[64*1024];
struct sockaddr_in from;
HEADER *header;
addrlen = sizeof(struct sockaddr);
r = recvfrom(fd, packet, sizeof(packet), 0, (struct sockaddr*)&from, &addrlen);
if(r == -1) {
perror("recvfrom");
return 0;
}
header = (HEADER*)packet;
if (dns_sending() && chunkid == ntohs(header->id)) {
/* Got ACK on sent packet */
packetpos += lastlen;
if (packetpos == packetlen) {
/* Packet completed */
packetpos = 0;
packetlen = 0;
lastlen = 0;
} else {
/* More to send */
dns_send_chunk(fd);
}
}
return dns_parse_reply(buf, buflen, packet, r);
}
int
dns_parse_reply(char *outbuf, int buflen, char *packet, int packetlen)
{
int rv;
uint32_t ttl;
short rlen;
short type;
short class;
short qdcount;
short ancount;
char *data;
char name[255];
char rdata[4*1024];
HEADER *header;
rv = 0;
header = (HEADER*)packet;
data = packet + sizeof(HEADER);
if(header->qr) { /* qr=1 => response */
qdcount = ntohs(header->qdcount);
ancount = ntohs(header->ancount);
rlen = 0;
if(qdcount == 1) {
readname(packet, packetlen, &data, name, sizeof(name));
readshort(packet, &data, &type);
readshort(packet, &data, &class);
}
if(ancount == 1) {
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));
readdata(packet, &data, rdata, rv);
}
if(type == T_NULL && rv > 2) {
rv = MIN(rv, buflen);
memcpy(outbuf, rdata, rv);
}
}
return rv;
}
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) {
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;
}
void
dnsd_send(int fd, struct query *q, char *data, int datalen)
{
int len;
char *p;
char buf[64*1024];
short name;
HEADER *header;
memset(buf, 0, sizeof(buf));
len = 0;
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;
header->qdcount = htons(1);
header->ancount = htons(1);
p = buf + sizeof(HEADER);
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);
q->id = 0;
putshort(&p, datalen);
putdata(&p, data, datalen);
len = p - buf;
sendto(fd, buf, len, 0, (struct sockaddr*)&q->from, q->fromlen);
}
static int
decodepacket(const char *name, char *buf, int buflen)
{
int len;
char *domain;
domain = strstr(name, topdomain);
len = decode_data(buf, buflen, name, domain);
if (len == buflen)
return -1;
return len;
}
int
dnsd_read(int fd, struct query *q, char *buf, int buflen)
{
int r;
int rv;
short id;
short type;
short class;
short qdcount;
char *data;
char name[257];
HEADER *header;
socklen_t addrlen;
char packet[64*1024];
struct sockaddr_in from;
addrlen = sizeof(struct sockaddr);
r = recvfrom(fd, packet, sizeof(packet), 0, (struct sockaddr*)&from, &addrlen);
if (r >= sizeof(HEADER)) {
header = (HEADER*)packet;
id = ntohs(header->id);
data = packet + sizeof(HEADER);
if(!header->qr) {
qdcount = ntohs(header->qdcount);
if(qdcount == 1) {
readname(packet, r, &data, name, sizeof(name) -1);
name[256] = 0;
readshort(packet, &data, &type);
readshort(packet, &data, &class);
strncpy(q->name, name, 257);
q->type = type;
q->id = id;
q->fromlen = addrlen;
memcpy((struct sockaddr*)&q->from, (struct sockaddr*)&from, addrlen);
rv = decodepacket(name, buf, buflen);
}
}
} else if (r < 0) { // Error
perror("recvfrom");
rv = 0;
} else { // Packet too small to be dns protocol
rv = 0;
}
return rv;
}
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