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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>
#include <netdb.h>
#include <time.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "dns.h"
#include "read.h"
static int host2dns(const char *, 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 outid;
int outbuflen;
char outbuf[64*1024];
char delayed_q_name[256];
short delayed_q_type;
short delayed_q_id;
struct sockaddr_in delayed_q_from;
int delayed_q_fromlen;
int
open_dns(const char *host, const char *domain)
{
int fd;
int flag;
struct sockaddr_in addr;
struct hostent *h;
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(0);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
fd = socket(AF_INET, SOCK_DGRAM, 0);
if(fd < 0) {
warn("socket");
return 0;
}
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 0;
}
printf("Opened UDP socket\n");
// Init dns target struct
h = gethostbyname(host);
if (!h) {
perror("gethostbyname");
}
bzero(&peer, sizeof(peer));
peer.sin_family = AF_INET;
peer.sin_port = htons(53);
peer.sin_addr = *((struct in_addr *) h->h_addr);
// Save top domain used
strncpy(topdomain, domain, sizeof(topdomain) - 2);
topdomain[sizeof(topdomain) - 1] = 0;
// Init chunk id
chunkid = 0;
pingid = 0;
return fd;
}
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);
//printf("Sent %d bytes of %d remaining\n", lastlen, avail);
}
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()) {
// printf("No reply on chunk, discarding\n");
lastlen = 0;
packetpos = 0;
packetlen = 0;
}
data[0] = (pingid & 0xFF00) >> 8;
data[1] = (pingid & 0xFF);
dns_write(dns_fd, ++pingid, data, 2, 1);
}
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 += host2dns(host, p, strlen(host));
PUTSHORT(type, p);
PUTSHORT(C_IN, p);
// EDNS0
*p++ = 0x00; //Root
PUTSHORT(0x0029, p); // OPT
PUTSHORT(0x1000, p); // Payload size: 4096
PUTSHORT(0x0000, p); // Higher bits/ edns version
PUTSHORT(0x8000, p); // Z
PUTSHORT(0x0000, p); // Data length
peerlen = sizeof(peer);
len = p - buf;
sendto(fd, buf, len, 0, (struct sockaddr*)&peer, peerlen);
}
static char to_hex[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
static void
put_hex(char *p, char h)
{
int t;
t = (h & 0xF0) >> 4;
p[0] = to_hex[t];
t = h & 0x0F;
p[1] = to_hex[t];
}
int
dns_write(int fd, int id, char *buf, int len, int ping)
{
int avail;
int i;
int final;
char data[257];
char *d;
#define CHUNK 31
// 31 bytes expands to 62 chars in domain
// We just use hex as encoding right now
avail = 0xFF - strlen(topdomain) - 2;
avail /= 2; // use two chars per byte in encoding
avail -= (avail/CHUNK); // make space for parts
avail = MIN(avail, len); // do not use more bytes than is available;
final = (avail == len); // is this the last block?
bzero(data, sizeof(data));
d = data;
if (ping) {
*d = 'P';
} else {
// First byte is 0 for middle packet and 1 for last packet
*d = '0' + final;
}
d++;
if (len > 0) {
for (i = 0; i < avail; i++) {
if (i > 0 && i % 31 == 0) {
*d = '.';
d++;
}
put_hex(d, buf[i]);
d += 2;
}
}
if (*d != '.') {
*d++ = '.';
}
strncpy(d, topdomain, strlen(topdomain)+1);
//printf("Resolving %s\n", data);
dns_query(fd, id, data, T_NULL);
return avail;
}
int
dns_read(int fd, char *buf, int buflen)
{
int r;
long ttl;
short rlen;
short type;
short class;
short qdcount;
short ancount;
char *data;
char name[255];
char rdata[4*1024];
HEADER *header;
char packet[64*1024];
r = recv(fd, packet, sizeof(packet), 0);
//printf("Read %d bytes DNS reply\n", r);
if(r == -1) {
perror("recv");
} else {
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, name, data);
READSHORT(type, data);
READSHORT(class, data);
}
if(ancount == 1) {
READNAME(packet, name, data);
READSHORT(type, data);
READSHORT(class, data);
READLONG(ttl, data);
READSHORT(rlen, data);
READDATA(rdata, data, rlen);
}
if (dns_sending() && chunkid == ntohs(header->id)) {
// Got ACK on sent packet
packetpos += lastlen;
if (packetpos == packetlen) {
// Packet completed
// printf("IP packet size %d sent successfully!\n", packetlen);
packetpos = 0;
packetlen = 0;
lastlen = 0;
} else {
// More to send
dns_send_chunk(fd);
}
}
if(type == T_NULL && rlen > 2) {
memcpy(buf, rdata, rlen);
return rlen;
} else {
return 0;
}
}
}
return 0;
}
static int
host2dns(const char *host, char *buffer, int size)
{
char *h;
char *p;
char *word;
h = strdup(host);
memset(buffer, 0, size);
p = buffer;
word = strtok(h, ".");
while(word) {
*p++ = (char)strlen(word);
memcpy(p, word, strlen(word));
p += strlen(word);
word = strtok(NULL, ".");
}
*p++ = 0;
free(h);
return p - buffer;
}
int
dnsd_haspacket()
{
return (outbuflen > 0);
}
int
dnsd_hasack()
{
return (delayed_q_id != 0);
}
void
dnsd_queuepacket(const char *buf, const int buflen)
{
memcpy(outbuf, buf, buflen);
outbuflen = buflen;
outid++;
}
static void
dnsd_send(int fd, char *name, short type, short id, struct sockaddr_in from)
{
int len;
char *p;
char buf[64*1024];
HEADER *header;
memset(buf, 0, sizeof(buf));
len = 0;
header = (HEADER*)buf;
header->id = htons(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);
p += host2dns(name, p, strlen(name));
PUTSHORT(type, p);
PUTSHORT(C_IN, p);
p += host2dns(name, p, strlen(name));
PUTSHORT(type, p);
PUTSHORT(C_IN, p);
PUTLONG(0, p);
if(outbuflen > 0) {
PUTSHORT(outbuflen, p);
memcpy(p, outbuf, outbuflen);
p += outbuflen;
} else {
PUTSHORT(0, p);
}
len = p - buf;
// printf("Responding with %d\n", len);
sendto(fd, buf, len, 0, (struct sockaddr*)&from, sizeof(from));
outbuflen = 0;
}
void
dnsd_forceack(int fd)
{
dnsd_send(fd, delayed_q_name, delayed_q_type, delayed_q_id, delayed_q_from);
delayed_q_id = 0;
}
struct packet
{
int len;
int offset;
char data[64*1024];
};
static int
decodepacket(const char *name, struct packet *packet)
{
int r;
int len;
int last;
int ping;
char *dp;
char *domain;
const char *np;
len = 0;
last = (name[0] == '1');
ping = (name[0] == 'p' || name[0] == 'P');
domain = strstr(name, topdomain);
if (!ping && domain) {
np = name + 1;
dp = packet->data + packet->offset;
while(np < domain) {
if(*np == '.') {
np++;
continue;
}
sscanf(np, "%02X", &r);
*dp++ = (char)r;
np+=2;
len++;
}
packet->len += len;
packet->offset += len;
}
if(last) {
len = packet->len;
packet->len = packet->offset = 0;
} else {
len = 0;
}
return len;
}
int
open_dnsd(const char *domain)
{
int fd;
int flag;
struct sockaddr_in addr;
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(53);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
fd = socket(AF_INET, SOCK_DGRAM, 0);
if(fd < 0) {
warn("socket");
return 0;
}
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 0;
}
printf("Opened UDP socket\n");
// Save top domain used
strncpy(topdomain, domain, sizeof(topdomain) - 2);
topdomain[sizeof(topdomain) - 1] = 0;
packetlen = 0;
delayed_q_type = 0;
delayed_q_id = 0;
delayed_q_fromlen = 0;
return fd;
}
void
close_dnsd(int fd)
{
close(fd);
}
struct packet packetbuf;
int
dnsd_read(int fd, char *buf, int buflen)
{
int r;
short id;
short type;
short class;
short qdcount;
char *data;
char name[255];
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);
//printf("Read %d bytes DNS query from %s\n", r, inet_ntoa(from.sin_addr));
if(r == -1) {
perror("recvfrom");
} else {
header = (HEADER*)packet;
id = ntohs(header->id);
data = packet + sizeof(HEADER);
if(!header->qr) {
qdcount = ntohs(header->qdcount);
if(qdcount == 1) {
bzero(name, sizeof(name));
READNAME(packet, name, data);
READSHORT(type, data);
READSHORT(class, data);
if (dnsd_haspacket()) {
dnsd_send(fd, name, type, id, from);
} else {
// Store needed info about delayed response
strncpy(delayed_q_name, name, 256);
delayed_q_type = type;
delayed_q_id = id;
delayed_q_fromlen = addrlen;
memcpy((struct sockaddr*)&delayed_q_from, (struct sockaddr*)&from, addrlen);
}
r = decodepacket(name, &packetbuf);
memcpy(buf, packetbuf.data, r);
return r;
}
}
}
return 0;
}
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