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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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()
{
int fd;
int flag;
struct sockaddr_in addr;
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");
return fd;
}
void
close_dns(int fd)
{
close(fd);
}
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void
dns_set_peer(const char *host)
{
struct hostent *h;
h = gethostbyname(host);
bzero(&peer, sizeof(peer));
peer.sin_family = AF_INET;
peer.sin_port = htons(53);
peer.sin_addr = *((struct in_addr *) h->h_addr);
}
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void
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dns_ping(int dns_fd)
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{
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dns_query(dns_fd, "kryo.se", 1);
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}
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void
dns_query(int fd, 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 = 0;
header->qr = 0;
header->opcode = 0;
header->aa = 0;
header->tc = 0;
header->rd = 1;
header->ra = 0;
header->qdcount = htons(1);
p = buf + sizeof(HEADER);
p += host2dns(host, p, strlen(host));
PUTSHORT(type, p);
PUTSHORT(C_IN, p);
peerlen = sizeof(peer);
len = p - buf;
sendto(fd, buf, len+1, 0, (struct sockaddr*)&peer, peerlen);
}
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int
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dns_read(int fd, char *buf, int buflen)
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{
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int i;
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int r;
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long ttl;
short rlen;
short type;
short class;
short port;
short ancount;
char *data;
char name[255];
char host[255];
char rdata[256];
HEADER *header;
char packet[64*1024];
r = recv(fd, packet, sizeof(packet), 0);
printf("Read %d bytes DNS reply\n", r);
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if(r == -1) {
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perror("recvfrom");
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} else {
header = (HEADER*)packet;
data = packet + sizeof(HEADER);
if(header->qr) { /* qr=1 => response */
ancount = ntohs(header->ancount);
for(i=0;i<ancount;i++) {
READNAME(buf, name, data);
READSHORT(type, data);
READSHORT(class, data);
READLONG(ttl, data);
READSHORT(rlen, data);
READDATA(rdata, data, rlen);
if(type == T_SRV && rlen > 6) {
char *r;
short priority;
short weight;
r = rdata;
READSHORT(priority, r);
READSHORT(weight, r);
READSHORT(port, r);
READNAME(buf, host, r);
}
printf("%s\n", name);
}
}
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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;
}