iodine/dns.c

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/*
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* Copyright (c) 2006 Bjorn Andersson <flex@kryo.se>, Erik Ekman <yarrick@kryo.se>
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*
* 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>
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#include <netdb.h>
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#include <time.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "dns.h"
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static int host2dns(const char *, char *, int);
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struct sockaddr_in peer;
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char topdomain[256];
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// Current IP packet
char activepacket[4096];
int lastlen;
int packetpos;
int packetlen;
uint16_t chunkid;
uint16_t pingid;
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static int
readname(char *packet, char *dst, char *src)
{
char l;
int len;
int offset;
len = 0;
while(*src) {
l = *src++;
len++;
if(l & 0x80 && l & 0x40) {
offset = ((src[-1] & 0x3f) << 8) | src[0];
readname(packet, dst, packet + offset);
dst += strlen(dst);
break;
}
while(l) {
*dst++ = *src++;
l--;
len++;
}
*dst++ = '.';
}
*dst = '\0';
src++;
len++;
return len;
}
#define READNAME(packet, dst, src) (src) += readname((packet), (dst), (src));
#define READSHORT(dst, src) \
(dst) = ntohs(*(short*)(src)); (src)+=2;
#define READLONG(dst, src) \
(dst) = ntohl(*(long*)(src)); (src)+=4;
#define READDATA(dst, src, len) \
memcpy((dst), (src), (len)); (src)+=(len);
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int
open_dns(const char *host, const char *domain)
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{
int fd;
int flag;
struct sockaddr_in addr;
struct hostent *h;
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bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
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addr.sin_port = htons(0);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
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fd = socket(AF_INET, SOCK_DGRAM, 0);
if(fd < 0) {
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warn("socket");
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return 0;
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}
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) {
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warn("bind");
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return 0;
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}
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;
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// Init chunk id
chunkid = 0;
pingid = 0;
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return fd;
}
void
close_dns(int fd)
{
close(fd);
}
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int
dns_sending()
{
return (packetlen != 0);
}
static void
dns_send_chunk(int fd)
{
int avail;
char *p;
p = activepacket;
p += packetpos;
avail = packetlen - packetpos;
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lastlen = dns_write(fd, ++chunkid, p, avail, 0);
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//printf("Sent %d bytes of %d remaining\n", lastlen, avail);
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}
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);
}
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void
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dns_ping(int dns_fd)
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{
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char data[3];
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if (dns_sending()) {
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// printf("No reply on chunk, discarding\n");
lastlen = 0;
packetpos = 0;
packetlen = 0;
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}
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snprintf(data, 3, "%02X", pingid);
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dns_write(dns_fd, ++pingid, data, 2, 1);
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}
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void
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dns_query(int fd, int id, char *host, int type)
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{
char *p;
int len;
int peerlen;
char buf[1024];
HEADER *header;
len = 0;
memset(buf, 0, sizeof(buf));
header = (HEADER*)buf;
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header->id = htons(id);
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header->qr = 0;
header->opcode = 0;
header->aa = 0;
header->tc = 0;
header->rd = 1;
header->ra = 0;
header->qdcount = htons(1);
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header->arcount = htons(1);
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p = buf + sizeof(HEADER);
p += host2dns(host, p, strlen(host));
PUTSHORT(type, p);
PUTSHORT(C_IN, p);
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// 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
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peerlen = sizeof(peer);
len = p - buf;
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sendto(fd, buf, len, 0, (struct sockaddr*)&peer, peerlen);
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}
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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];
}
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int
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dns_write(int fd, int id, char *buf, int len, int ping)
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{
int avail;
int i;
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int final;
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char data[257];
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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;
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final = (avail == len); // is this the last block?
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bzero(data, sizeof(data));
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d = data;
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if (ping) {
*d = 'P';
} else {
// First byte is 0 for middle packet and 1 for last packet
*d = '0' + final;
}
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d++;
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if (len > 0) {
for (i = 0; i < avail; i++) {
if (i > 0 && i % 31 == 0) {
*d = '.';
d++;
}
put_hex(d, buf[i]);
d += 2;
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}
}
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if (*d != '.') {
*d++ = '.';
}
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strncpy(d, topdomain, strlen(topdomain)+1);
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//printf("Resolving %s\n", data);
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dns_query(fd, id, data, T_NULL);
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return avail;
}
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int
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dns_read(int fd, char *buf, int buflen)
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{
int r;
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long ttl;
short rlen;
short type;
short class;
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short qdcount;
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short ancount;
char *data;
char name[255];
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char rdata[4*1024];
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HEADER *header;
char packet[64*1024];
r = recv(fd, packet, sizeof(packet), 0);
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//printf("Read %d bytes DNS reply\n", r);
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if(r == -1) {
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perror("recv");
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} else {
header = (HEADER*)packet;
data = packet + sizeof(HEADER);
if(header->qr) { /* qr=1 => response */
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qdcount = ntohs(header->qdcount);
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ancount = ntohs(header->ancount);
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rlen = 0;
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if(qdcount == 1) {
READNAME(packet, name, data);
READSHORT(type, data);
READSHORT(class, data);
}
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if(ancount == 1) {
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READNAME(packet, name, data);
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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
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// printf("IP packet size %d sent successfully!\n", packetlen);
packetpos = 0;
packetlen = 0;
lastlen = 0;
} else {
// More to send
dns_send_chunk(fd);
}
}
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if(type == T_NULL && rlen > 2) {
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memcpy(buf, rdata, rlen);
return rlen;
} else {
return 0;
}
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}
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}
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return 0;
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}
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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;
}