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/* $OpenBSD: unpack_dns.c,v 1.1 2018/01/06 07:57:53 sunil Exp $ */
/*
* Copyright (c) 2011-2014 Eric Faurot <eric@faurot.net>
*
* 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 <arpa/inet.h>
#include <string.h>
#include "unpack_dns.h"
static int unpack_data(struct unpack *, void *, size_t);
static int unpack_u16(struct unpack *, uint16_t *);
static int unpack_u32(struct unpack *, uint32_t *);
static int unpack_inaddr(struct unpack *, struct in_addr *);
static int unpack_in6addr(struct unpack *, struct in6_addr *);
static int unpack_dname(struct unpack *, char *, size_t);
void
unpack_init(struct unpack *unpack, const char *buf, size_t len)
{
unpack->buf = buf;
unpack->len = len;
unpack->offset = 0;
unpack->err = NULL;
}
int
unpack_header(struct unpack *p, struct dns_header *h)
{
if (unpack_data(p, h, HFIXEDSZ) == -1)
return (-1);
h->flags = ntohs(h->flags);
h->qdcount = ntohs(h->qdcount);
h->ancount = ntohs(h->ancount);
h->nscount = ntohs(h->nscount);
h->arcount = ntohs(h->arcount);
return (0);
}
int
unpack_query(struct unpack *p, struct dns_query *q)
{
unpack_dname(p, q->q_dname, sizeof(q->q_dname));
unpack_u16(p, &q->q_type);
unpack_u16(p, &q->q_class);
return (p->err) ? (-1) : (0);
}
int
unpack_rr(struct unpack *p, struct dns_rr *rr)
{
uint16_t rdlen;
size_t save_offset;
unpack_dname(p, rr->rr_dname, sizeof(rr->rr_dname));
unpack_u16(p, &rr->rr_type);
unpack_u16(p, &rr->rr_class);
unpack_u32(p, &rr->rr_ttl);
unpack_u16(p, &rdlen);
if (p->err)
return (-1);
if (p->len - p->offset < rdlen) {
p->err = "too short";
return (-1);
}
save_offset = p->offset;
switch (rr->rr_type) {
case T_CNAME:
unpack_dname(p, rr->rr.cname.cname, sizeof(rr->rr.cname.cname));
break;
case T_MX:
unpack_u16(p, &rr->rr.mx.preference);
unpack_dname(p, rr->rr.mx.exchange, sizeof(rr->rr.mx.exchange));
break;
case T_NS:
unpack_dname(p, rr->rr.ns.nsname, sizeof(rr->rr.ns.nsname));
break;
case T_PTR:
unpack_dname(p, rr->rr.ptr.ptrname, sizeof(rr->rr.ptr.ptrname));
break;
case T_SOA:
unpack_dname(p, rr->rr.soa.mname, sizeof(rr->rr.soa.mname));
unpack_dname(p, rr->rr.soa.rname, sizeof(rr->rr.soa.rname));
unpack_u32(p, &rr->rr.soa.serial);
unpack_u32(p, &rr->rr.soa.refresh);
unpack_u32(p, &rr->rr.soa.retry);
unpack_u32(p, &rr->rr.soa.expire);
unpack_u32(p, &rr->rr.soa.minimum);
break;
case T_A:
if (rr->rr_class != C_IN)
goto other;
unpack_inaddr(p, &rr->rr.in_a.addr);
break;
case T_AAAA:
if (rr->rr_class != C_IN)
goto other;
unpack_in6addr(p, &rr->rr.in_aaaa.addr6);
break;
default:
other:
rr->rr.other.rdata = p->buf + p->offset;
rr->rr.other.rdlen = rdlen;
p->offset += rdlen;
}
if (p->err)
return (-1);
/* make sure that the advertised rdlen is really ok */
if (p->offset - save_offset != rdlen)
p->err = "bad dlen";
return (p->err) ? (-1) : (0);
}
ssize_t
dname_expand(const unsigned char *data, size_t len, size_t offset,
size_t *newoffset, char *dst, size_t max)
{
size_t n, count, end, ptr, start;
ssize_t res;
if (offset >= len)
return (-1);
res = 0;
end = start = offset;
for (; (n = data[offset]); ) {
if ((n & 0xc0) == 0xc0) {
if (offset + 2 > len)
return (-1);
ptr = 256 * (n & ~0xc0) + data[offset + 1];
if (ptr >= start)
return (-1);
if (end < offset + 2)
end = offset + 2;
offset = start = ptr;
continue;
}
if (offset + n + 1 > len)
return (-1);
/* copy n + at offset+1 */
if (dst != NULL && max != 0) {
count = (max < n + 1) ? (max) : (n + 1);
memmove(dst, data + offset, count);
dst += count;
max -= count;
}
res += n + 1;
offset += n + 1;
if (end < offset)
end = offset;
}
if (end < offset + 1)
end = offset + 1;
if (dst != NULL && max != 0)
dst[0] = 0;
if (newoffset)
*newoffset = end;
return (res + 1);
}
char *
print_dname(const char *_dname, char *buf, size_t max)
{
const unsigned char *dname = _dname;
char *res;
size_t left, n, count;
if (_dname[0] == 0) {
(void)strlcpy(buf, ".", max);
return buf;
}
res = buf;
left = max - 1;
for (n = 0; dname[0] && left; n += dname[0]) {
count = (dname[0] < (left - 1)) ? dname[0] : (left - 1);
memmove(buf, dname + 1, count);
dname += dname[0] + 1;
left -= count;
buf += count;
if (left) {
left -= 1;
*buf++ = '.';
}
}
buf[0] = 0;
return (res);
}
static int
unpack_data(struct unpack *p, void *data, size_t len)
{
if (p->err)
return (-1);
if (p->len - p->offset < len) {
p->err = "too short";
return (-1);
}
memmove(data, p->buf + p->offset, len);
p->offset += len;
return (0);
}
static int
unpack_u16(struct unpack *p, uint16_t *u16)
{
if (unpack_data(p, u16, 2) == -1)
return (-1);
*u16 = ntohs(*u16);
return (0);
}
static int
unpack_u32(struct unpack *p, uint32_t *u32)
{
if (unpack_data(p, u32, 4) == -1)
return (-1);
*u32 = ntohl(*u32);
return (0);
}
static int
unpack_inaddr(struct unpack *p, struct in_addr *a)
{
return (unpack_data(p, a, 4));
}
static int
unpack_in6addr(struct unpack *p, struct in6_addr *a6)
{
return (unpack_data(p, a6, 16));
}
static int
unpack_dname(struct unpack *p, char *dst, size_t max)
{
ssize_t e;
if (p->err)
return (-1);
e = dname_expand(p->buf, p->len, p->offset, &p->offset, dst, max);
if (e == -1) {
p->err = "bad domain name";
return (-1);
}
if (e < 0 || e > MAXDNAME) {
p->err = "domain name too long";
return (-1);
}
return (0);
}
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