303 lines
5.7 KiB
C
303 lines
5.7 KiB
C
/*
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* Copyright (c) 2006 Bjorn Andersson <flex@kryo.se>, Erik Ekman <yarrick@kryo.se>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <arpa/nameser.h>
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#include <netdb.h>
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#include <time.h>
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#include <err.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <ctype.h>
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#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
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int packetlen;
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char activepacket[4096];
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int outbuflen;
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char outbuf[64*1024];
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static int
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readname(char *packet, char *dst, char *src)
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{
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char l;
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int len;
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int offset;
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len = 0;
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while(*src) {
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l = *src++;
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len++;
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if(l & 0x80 && l & 0x40) {
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offset = ((src[-1] & 0x3f) << 8) | src[0];
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readname(packet, dst, packet + offset);
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dst += strlen(dst);
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break;
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}
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while(l) {
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*dst++ = *src++;
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l--;
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len++;
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}
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*dst++ = '.';
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}
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*dst = '\0';
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src++;
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len++;
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return len;
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}
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#define READNAME(packet, dst, src) (src) += readname((packet), (dst), (src));
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#define READSHORT(dst, src) \
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(dst) = ntohs(*(short*)(src)); (src)+=2;
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#define READLONG(dst, src) \
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(dst) = ntohl(*(long*)(src)); (src)+=4;
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#define READDATA(dst, src, len) \
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memcpy((dst), (src), (len)); (src)+=(len);
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int
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open_dnsd(const char *domain)
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{
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int fd;
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int flag;
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struct sockaddr_in addr;
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bzero(&addr, sizeof(addr));
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addr.sin_family = AF_INET;
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addr.sin_port = htons(53);
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addr.sin_addr.s_addr = htonl(INADDR_ANY);
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fd = socket(AF_INET, SOCK_DGRAM, 0);
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if(fd < 0) {
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warn("socket");
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return 0;
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}
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flag = 1;
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#ifdef SO_REUSEPORT
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setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &flag, sizeof(flag));
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#endif
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setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag));
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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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}
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printf("Opened UDP socket\n");
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// Save top domain used
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strncpy(topdomain, domain, sizeof(topdomain) - 2);
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topdomain[sizeof(topdomain) - 1] = 0;
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packetlen = 0;
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return fd;
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}
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void
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close_dnsd(int fd)
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{
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close(fd);
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}
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static int
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host2dns(const char *host, char *buffer, int size)
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{
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char *h;
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char *p;
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char *word;
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h = strdup(host);
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memset(buffer, 0, size);
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p = buffer;
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word = strtok(h, ".");
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while(word) {
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*p++ = (char)strlen(word);
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memcpy(p, word, strlen(word));
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p += strlen(word);
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word = strtok(NULL, ".");
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}
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*p++ = 0;
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free(h);
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return p - buffer;
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}
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int
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dnsd_haspacket()
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{
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return (outbuflen > 0);
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}
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void
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dnsd_queuepacket(const char *buf, const int buflen)
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{
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memcpy(outbuf, buf, buflen);
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outbuflen = buflen;
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}
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static void
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dnsd_respond(int fd, short id, struct sockaddr_in from)
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{
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int len;
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int size;
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HEADER *header;
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char *p;
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char buf[1024];
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memset(buf, 0, sizeof(buf));
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len = 0;
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header = (HEADER*)buf;
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header->id = id;
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header->qr = 1;
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header->opcode = 0;
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header->aa = 1;
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header->tc = 0;
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header->rd = 0;
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header->ra = 0;
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header->ancount = htons(1);
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p = buf + sizeof(HEADER);
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p += host2dns("fluff", p, 5);
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PUTSHORT(T_PTR, p);
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PUTSHORT(C_IN, p);
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PUTLONG(htons(3600), p);
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size = host2dns("mupp", p+2, 4);
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PUTSHORT(size, p);
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p += size;
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len = p - buf;
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printf("%d\n", len);
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sendto(fd, buf, len, 0, (struct sockaddr*)&from, sizeof(from));
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}
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int
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dnsd_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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short id;
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short type;
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short class;
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short qdcount;
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char *data;
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char name[255];
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HEADER *header;
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socklen_t addrlen;
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char packet[64*1024];
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struct sockaddr_in from;
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char lastblock;
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char *np;
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char *domainstart;
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int namelen;
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char *packetp;
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int datalen;
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addrlen = sizeof(struct sockaddr);
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r = recvfrom(fd, packet, sizeof(packet), 0, (struct sockaddr*)&from, &addrlen);
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printf("Read %d bytes DNS query from %s\n", r, inet_ntoa(from.sin_addr));
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if(r == -1) {
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perror("recvfrom");
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} else {
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header = (HEADER*)packet;
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id = ntohs(header->id);
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data = packet + sizeof(HEADER);
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if(!header->qr) {
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qdcount = ntohs(header->qdcount);
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for(i=0;i<qdcount;i++) {
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bzero(name, sizeof(name));
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READNAME(packet, name, data);
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READSHORT(type, data);
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READSHORT(class, data);
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lastblock = name[0] - '0';
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np = name;
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np++; // skip first byte, it has only fragmentation info
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domainstart = strstr(np, topdomain);
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if (!domainstart) {
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fprintf(stderr, "Resolved domain does not end with %s! Ignoring packet\n", topdomain);
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return 0;
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}
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namelen = (int) domainstart - (int) np;
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*domainstart = '\0';
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packetp = activepacket;
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packetp += packetlen;
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while (np < domainstart && packetlen < sizeof(activepacket)) {
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if (*np == '.') {
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np++;
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}
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sscanf(np, "%02X", &r);
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*packetp = r & 0xFF;
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np += 2;
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packetp++;
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packetlen++;
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}
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dnsd_respond(fd, id, from);
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if (lastblock) {
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datalen = MIN(packetlen, buflen);
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memcpy(buf, activepacket, datalen);
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packetlen = 0;
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printf("Got full packet, returning %d bytes!\n", datalen);
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return datalen;
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} else {
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return 0;
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}
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}
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}
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}
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return 0;
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}
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