366 lines
12 KiB
C
366 lines
12 KiB
C
#include <stdio.h>
|
|
#include <string.h>
|
|
#include <stdlib.h>
|
|
#include <sys/socket.h>
|
|
#include <netinet/in.h>
|
|
#include <stdint.h>
|
|
#include <sys/types.h>
|
|
#include <arpa/inet.h>
|
|
#include <time.h>
|
|
#include <ctype.h>
|
|
|
|
#define BUFLEN 512
|
|
|
|
int port = 53;
|
|
int datattl = 60;
|
|
int nsttl = 30583;
|
|
char *host = "seedtest.bitcoin.sipa.be";
|
|
char *ns = "vps.sipa.be";
|
|
char *mbox = "sipa.ulyssis.org";
|
|
|
|
extern int GetIPList(struct in_addr *addr, int max, int ipv4only);
|
|
|
|
typedef enum {
|
|
CLASS_IN = 1,
|
|
QCLASS_ANY = 255
|
|
} dns_class;
|
|
|
|
typedef enum {
|
|
TYPE_A = 1,
|
|
TYPE_NS = 2,
|
|
TYPE_CNAME = 5,
|
|
TYPE_SOA = 6,
|
|
TYPE_MX = 15,
|
|
TYPE_AAAA = 28,
|
|
TYPE_SRV = 33,
|
|
QTYPE_ANY = 255
|
|
} dns_type;
|
|
|
|
|
|
// 0: ok
|
|
// -1: premature end of input, forward reference, component > 63 char, invalid character
|
|
// -2: insufficient space in output
|
|
int static parse_name(const unsigned char **inpos, const unsigned char *inend, const unsigned char *inbuf, char *buf, size_t bufsize) {
|
|
size_t bufused = 0;
|
|
int init = 1;
|
|
do {
|
|
if (*inpos == inend)
|
|
return -1;
|
|
// read length of next component
|
|
int octet = *((*inpos)++);
|
|
if (octet == 0) {
|
|
buf[bufused] = 0;
|
|
return 0;
|
|
}
|
|
// add dot in output
|
|
if (!init) {
|
|
if (bufused == bufsize-1)
|
|
return -2;
|
|
buf[bufused++] = '.';
|
|
} else
|
|
init = 0;
|
|
// handle references
|
|
if ((octet & 0xC0) == 0xC0) {
|
|
if (*inpos == inend)
|
|
return -1;
|
|
int ref = ((octet - 0xC0) << 8) + *((*inpos)++);
|
|
if (ref < 0 || ref >= (*inpos)-inbuf) return -1;
|
|
const unsigned char *newbuf = inbuf + ref;
|
|
return parse_name(&newbuf, *inpos, inbuf, buf+bufused, bufsize-bufused);
|
|
}
|
|
if (octet > 63) return -1;
|
|
// copy label
|
|
while (octet) {
|
|
if (*inpos == inend)
|
|
return -1;
|
|
if (bufused == bufsize-1)
|
|
return -2;
|
|
int c = *((*inpos)++);
|
|
if (c == '.')
|
|
return -1;
|
|
octet--;
|
|
buf[bufused++] = c;
|
|
}
|
|
} while(1);
|
|
}
|
|
|
|
// 0: k
|
|
// -1: component > 63 characters
|
|
// -2: insufficent space in output
|
|
// -3: two subsequent dots
|
|
int static write_name(unsigned char** outpos, unsigned char *outend, char *name, int offset) {
|
|
while (*name != 0) {
|
|
char *dot = strchr(name, '.');
|
|
char *fin = dot;
|
|
if (!dot) fin = name + strlen(name);
|
|
if (fin - name > 63) return -1;
|
|
if (fin == name) return -3;
|
|
if (outend - *outpos < fin - name + 2) return -2;
|
|
*((*outpos)++) = fin - name;
|
|
memcpy(*outpos, name, fin - name);
|
|
*outpos += fin - name;
|
|
if (!dot) break;
|
|
name = dot + 1;
|
|
}
|
|
if (offset < 0) {
|
|
// no reference
|
|
if (outend == *outpos) return -2;
|
|
*((*outpos)++) = 0;
|
|
} else {
|
|
if (outend - *outpos < 2) return -2;
|
|
*((*outpos)++) = (offset >> 8) | 0xC0;
|
|
*((*outpos)++) = offset & 0xFF;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
int static write_record(unsigned char** outpos, unsigned char *outend, char *name, int offset, dns_type typ, dns_class cls, int ttl) {
|
|
unsigned char *oldpos = *outpos;
|
|
int error = 0;
|
|
// name
|
|
int ret = write_name(outpos, outend, name, offset);
|
|
if (ret) { error = ret; goto error; }
|
|
if (outend - *outpos < 8) { error = -4; goto error; }
|
|
// type
|
|
*((*outpos)++) = typ >> 8; *((*outpos)++) = typ & 0xFF;
|
|
// class
|
|
*((*outpos)++) = cls >> 8; *((*outpos)++) = cls & 0xFF;
|
|
// ttl
|
|
*((*outpos)++) = (ttl >> 24) & 0xFF; *((*outpos)++) = (ttl >> 16) & 0xFF; *((*outpos)++) = (ttl >> 8) & 0xFF; *((*outpos)++) = ttl & 0xFF;
|
|
return 0;
|
|
error:
|
|
*outpos = oldpos;
|
|
return error;
|
|
}
|
|
|
|
|
|
int static write_record_a(unsigned char** outpos, unsigned char *outend, char *name, int offset, dns_class cls, int ttl, const struct in_addr *ip) {
|
|
unsigned char *oldpos = *outpos;
|
|
int error = 0;
|
|
int ret = write_record(outpos, outend, name, offset, TYPE_A, cls, ttl);
|
|
if (ret) return ret;
|
|
if (outend - *outpos < 6) { error = -5; goto error; }
|
|
// rdlength
|
|
*((*outpos)++) = 0; *((*outpos)++) = 4;
|
|
// rdata
|
|
const unsigned char *pd = (const unsigned char*)ip;
|
|
for (int i=0; i<4; i++)
|
|
*((*outpos)++) = pd[i];
|
|
return 0;
|
|
error:
|
|
*outpos = oldpos;
|
|
return error;
|
|
}
|
|
|
|
int static write_record_aaaa(unsigned char** outpos, unsigned char *outend, char *name, int offset, dns_class cls, int ttl, const struct in6_addr *ip) {
|
|
unsigned char *oldpos = *outpos;
|
|
int error = 0;
|
|
int ret = write_record(outpos, outend, name, offset, TYPE_AAAA, cls, ttl);
|
|
if (ret) return ret;
|
|
if (outend - *outpos < 6) { error = -5; goto error; }
|
|
// rdlength
|
|
*((*outpos)++) = 0; *((*outpos)++) = 16;
|
|
// rdata
|
|
const unsigned char *pd = (const unsigned char*)ip;
|
|
for (int i=0; i<16; i++)
|
|
*((*outpos)++) = pd[i];
|
|
return 0;
|
|
error:
|
|
*outpos = oldpos;
|
|
return error;
|
|
}
|
|
|
|
int static write_record_ns(unsigned char** outpos, unsigned char *outend, char *name, int offset, dns_class cls, int ttl, char *ns) {
|
|
unsigned char *oldpos = *outpos;
|
|
int ret = write_record(outpos, outend, name, offset, TYPE_NS, cls, ttl);
|
|
if (ret) return ret;
|
|
int error = 0;
|
|
if (outend - *outpos < 2) { error = -5; goto error; }
|
|
(*outpos) += 2;
|
|
unsigned char *curpos = *outpos;
|
|
ret = write_name(outpos, outend, ns, -1);
|
|
if (ret) { error = ret; goto error; }
|
|
curpos[-2] = (*outpos - curpos) >> 8;
|
|
curpos[-1] = (*outpos - curpos) & 0xFF;
|
|
return 0;
|
|
error:
|
|
*outpos = oldpos;
|
|
return error;
|
|
}
|
|
|
|
int static write_record_soa(unsigned char** outpos, unsigned char *outend, char *name, int offset, dns_class cls, int ttl, char* mname, char *rname,
|
|
uint32_t serial, uint32_t refresh, uint32_t retry, uint32_t expire, uint32_t minimum) {
|
|
unsigned char *oldpos = *outpos;
|
|
int ret = write_record(outpos, outend, name, offset, TYPE_SOA, cls, ttl);
|
|
if (ret) return ret;
|
|
int error = 0;
|
|
if (outend - *outpos < 2) { error = -5; goto error; }
|
|
(*outpos) += 2;
|
|
unsigned char *curpos = *outpos;
|
|
ret = write_name(outpos, outend, mname, -1);
|
|
if (ret) { error = ret; goto error; }
|
|
ret = write_name(outpos, outend, rname, -1);
|
|
if (ret) { error = ret; goto error; }
|
|
if (outend - *outpos < 20) { error = -5; goto error; }
|
|
*((*outpos)++) = (serial >> 24) & 0xFF; *((*outpos)++) = (serial >> 16) & 0xFF; *((*outpos)++) = (serial >> 8) & 0xFF; *((*outpos)++) = serial & 0xFF;
|
|
*((*outpos)++) = (refresh >> 24) & 0xFF; *((*outpos)++) = (refresh >> 16) & 0xFF; *((*outpos)++) = (refresh >> 8) & 0xFF; *((*outpos)++) = refresh & 0xFF;
|
|
*((*outpos)++) = (retry >> 24) & 0xFF; *((*outpos)++) = (retry >> 16) & 0xFF; *((*outpos)++) = (retry >> 8) & 0xFF; *((*outpos)++) = retry & 0xFF;
|
|
*((*outpos)++) = (expire >> 24) & 0xFF; *((*outpos)++) = (expire >> 16) & 0xFF; *((*outpos)++) = (expire >> 8) & 0xFF; *((*outpos)++) = expire & 0xFF;
|
|
*((*outpos)++) = (minimum >> 24) & 0xFF; *((*outpos)++) = (minimum >> 16) & 0xFF; *((*outpos)++) = (minimum >> 8) & 0xFF; *((*outpos)++) = minimum & 0xFF;
|
|
curpos[-2] = (*outpos - curpos) >> 8;
|
|
curpos[-1] = (*outpos - curpos) & 0xFF;
|
|
return 0;
|
|
error:
|
|
*outpos = oldpos;
|
|
return error;
|
|
}
|
|
|
|
ssize_t static dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outbuf) {
|
|
int error = 0;
|
|
if (insize < 12) // DNS header
|
|
return -1;
|
|
// copy id
|
|
outbuf[0] = inbuf[0];
|
|
outbuf[1] = inbuf[1];
|
|
// copy flags;
|
|
outbuf[2] = inbuf[2];
|
|
outbuf[3] = inbuf[3];
|
|
// clear error
|
|
outbuf[3] &= ~15;
|
|
// check qr
|
|
if (inbuf[2] & 128) { /* printf("Got response?\n"); */ error = 1; goto error; }
|
|
// check opcode
|
|
if (((inbuf[2] & 120) >> 3) != 0) { /* printf("Opcode nonzero?\n"); */ error = 4; goto error; }
|
|
// check Z
|
|
if (((inbuf[3] & 112) >> 4) != 0) { /* printf("Z nonzero?\n"); */ error = 1; goto error; }
|
|
// unset TC
|
|
outbuf[2] &= ~2;
|
|
// unset RA
|
|
outbuf[3] &= ~128;
|
|
// check questions
|
|
int nquestion = (inbuf[4] << 8) + inbuf[5];
|
|
if (nquestion == 0) { /* printf("No questions?\n"); */ error = 0; goto error; }
|
|
if (nquestion > 1) { /* printf("Multiple questions %i?\n", nquestion); */ error = 4; goto error; }
|
|
const unsigned char *inpos = inbuf + 12;
|
|
const unsigned char *inend = inbuf + insize;
|
|
char name[256];
|
|
int offset = inpos - inbuf;
|
|
int ret = parse_name(&inpos, inend, inbuf, name, 256);
|
|
if (ret == -1) { error = 1; goto error; }
|
|
if (ret == -2) { error = 5; goto error; }
|
|
int namel = strlen(name), hostl = strlen(host);
|
|
if (strcmp(name, host) && (namel<hostl+2 || name[namel-hostl-1]!='.' || strcmp(name+namel-hostl,host))) { error = 5; goto error; }
|
|
if (inend - inpos < 4) { error = 1; goto error; }
|
|
// copy question to output
|
|
memcpy(outbuf+12, inbuf+12, inpos+4 - (inbuf+12));
|
|
// set counts
|
|
outbuf[4] = 0; outbuf[5] = 1;
|
|
outbuf[6] = 0; outbuf[7] = 0;
|
|
outbuf[8] = 0; outbuf[9] = 0;
|
|
outbuf[10] = 0; outbuf[11] = 0;
|
|
// set qr
|
|
outbuf[2] |= 128;
|
|
|
|
int typ = (inpos[0] << 8) + inpos[1];
|
|
int cls = (inpos[2] << 8) + inpos[3];
|
|
inpos += 4;
|
|
|
|
unsigned char *outpos = outbuf+(inpos-inbuf);
|
|
unsigned char *outend = outbuf + BUFLEN;
|
|
|
|
printf("Request host='%s' type=%i class=%i\n", name, typ, cls);
|
|
|
|
// calculate size of authority section
|
|
|
|
int auth_size = 0;
|
|
|
|
if (!((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY))) {
|
|
// authority section will be necessary
|
|
unsigned char *oldpos = outpos;
|
|
write_record_ns(&oldpos, outend, "", offset, CLASS_IN, 0, ns);
|
|
auth_size = oldpos - outpos;
|
|
// printf("Authority section will claim %i bytes\n", auth_size);
|
|
}
|
|
|
|
// Answer section
|
|
|
|
int have_ns = 0;
|
|
|
|
// NS records
|
|
if ((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
|
|
int ret2 = write_record_ns(&outpos, outend - auth_size, "", offset, CLASS_IN, nsttl, ns);
|
|
// printf("wrote NS record: %i\n", ret2);
|
|
if (!ret2) { outbuf[7]++; have_ns++; }
|
|
}
|
|
|
|
// SOA records
|
|
if ((typ == TYPE_SOA || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
|
|
int ret2 = write_record_soa(&outpos, outend - auth_size, "", offset, CLASS_IN, nsttl, ns, mbox, time(NULL), 604800, 86400, 2592000, 604800);
|
|
// printf("wrote SOA record: %i\n", ret2);
|
|
if (!ret2) { outbuf[7]++; }
|
|
}
|
|
|
|
// A records
|
|
if ((typ == TYPE_A || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
|
|
struct in_addr addr[20];
|
|
int naddr = GetIPList(addr, 20, 1);
|
|
int n = 0;
|
|
while (n < naddr) {
|
|
int ret = write_record_a(&outpos, outend - auth_size, "", offset, CLASS_IN, datattl, &addr[n]);
|
|
// printf("wrote A record: %i\n", ret);
|
|
if (!ret) {
|
|
n++;
|
|
outbuf[7]++;
|
|
} else
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Authority section
|
|
if (!have_ns) {
|
|
int ret2 = write_record_ns(&outpos, outend, "", offset, CLASS_IN, nsttl, ns);
|
|
// printf("wrote NS record: %i\n", ret2);
|
|
if (!ret2) {
|
|
outbuf[9]++;
|
|
}
|
|
}
|
|
|
|
// set AA
|
|
outbuf[2] |= 4;
|
|
|
|
return outpos - outbuf;
|
|
error:
|
|
// set error
|
|
outbuf[3] |= error & 0xF;
|
|
// set counts
|
|
outbuf[4] = 0; outbuf[5] = 0;
|
|
outbuf[6] = 0; outbuf[7] = 0;
|
|
outbuf[8] = 0; outbuf[9] = 0;
|
|
outbuf[10] = 0; outbuf[11] = 0;
|
|
return 12;
|
|
}
|
|
|
|
int dnsserver(void) {
|
|
struct sockaddr_in si_me, si_other;
|
|
socklen_t s, slen=sizeof(si_other);
|
|
unsigned char inbuf[BUFLEN], outbuf[BUFLEN];
|
|
if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
|
|
return -1;
|
|
memset((char *) &si_me, 0, sizeof(si_me));
|
|
si_me.sin_family = AF_INET;
|
|
si_me.sin_port = htons(port);
|
|
si_me.sin_addr.s_addr = INADDR_ANY;
|
|
if (bind(s, (struct sockaddr*)&si_me, sizeof(si_me))==-1)
|
|
return -2;
|
|
do {
|
|
ssize_t insize = recvfrom(s, inbuf, BUFLEN, 0, (struct sockaddr*)&si_other, &slen);
|
|
unsigned char *addr = (unsigned char*)&si_other.sin_addr.s_addr;
|
|
printf("Request from %i.%i.%i.%i:%i of %i bytes\n", addr[0], addr[1], addr[2], addr[3], ntohs(si_other.sin_port), (int)insize);
|
|
if (insize > 0) {
|
|
ssize_t ret = dnshandle(inbuf, insize, outbuf);
|
|
if (ret > 0)
|
|
sendto(s, outbuf, ret, 0, (struct sockaddr*)&si_other, slen);
|
|
}
|
|
} while(1);
|
|
return 0;
|
|
}
|