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/* dns.c
Domain Name Service subroutines. */
/*
* Copyright (C) 1992 by Ted Lemon.
* Copyright (c) 1997 The Internet Software Consortium.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of The Internet Software Consortium nor the names
* of its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This file is based on software written in 1992 by Ted Lemon for
* a portable network boot loader. That original code base has been
* substantially modified for use in the Internet Software Consortium
* DHCP suite.
*
* These later modifications were done on behalf of the Internet
* Software Consortium by Ted Lemon <mellon@fugue.com> in cooperation
* with Vixie Enterprises. To learn more about the Internet Software
* Consortium, see ``http://www.vix.com/isc''. To learn more about
* Vixie Enterprises, see ``http://www.vix.com''.
*/
#ifndef lint
static char copyright[] =
"$Id: dns.c,v 1.4 1997/06/08 04:05:20 mellon Exp $ Copyright (c) 1997 The Internet Software Consortium. All rights reserved.\n";
#endif /* not lint */
#include "dhcpd.h"
#include "arpa/nameser.h"
int dns_protocol_initialized;
int dns_protocol_fd;
static int addlabel PROTO ((u_int8_t *, char *));
static int skipname PROTO ((u_int8_t *));
static int copy_out_name PROTO ((u_int8_t *, u_int8_t *, char *));
static int nslookup PROTO ((u_int8_t, char *, int, u_int16_t, u_int16_t));
static int zonelookup PROTO ((u_int8_t, char *, int, u_int16_t));
u_int16_t dns_port;
/* Initialize the DNS protocol. */
void dns_startup ()
{
struct servent *srv;
struct sockaddr_in from;
/* Only initialize icmp once. */
if (dns_protocol_initialized)
error ("attempted to reinitialize dns protocol");
dns_protocol_initialized = 1;
/* Get the protocol number (should be 1). */
srv = getservbyname ("domain", "tcp");
if (srv)
dns_port = srv -> s_port;
else
dns_port = htons (53);
/* Get a socket for the DNS protocol. */
dns_protocol_fd = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (!dns_protocol_fd)
error ("unable to create dns socket: %m");
pick_name_server ();
add_protocol ("dns", dns_protocol_fd, dns_packet, 0);
}
/* Label manipulation stuff; see RFC1035, page 28 section 4.1.2 and
page 30, section 4.1.4. */
/* addlabel copies a label into the specified buffer, putting the length of
the label in the first character, the contents of the label in subsequent
characters, and returning the length of the conglomeration. */
static int addlabel (buf, label)
u_int8_t *buf;
char *label;
{
*buf = strlen (label);
memcpy (buf + 1, label, *buf);
return *buf + 1;
}
/* skipname skips over all of the labels in a single domain name,
returning the length of the domain name. */
static int skipname (label)
u_int8_t *label;
{
if (*label & INDIR_MASK)
return 2;
if (*label == 0)
return 1;
return *label + 1 + skipname (label + *label + 1);
}
/* copy_out_name copies out the name appearing at the specified location
into a string, stored as fields seperated by dots rather than lengths
and labels. The length of the label-formatted name is returned. */
static int copy_out_name (base, name, buf)
u_int8_t *base;
u_int8_t *name;
char *buf;
{
if (*name & INDIR_MASK) {
int offset = (*name & ~INDIR_MASK) + (*name + 1);
return copy_out_name (base, base + offset, buf);
}
if (!*name) {
*buf = 0;
return 1;
}
memcpy (buf, name + 1, *name);
*(buf + *name) = '.';
return (*name + 1
+ copy_out_name (base, name + *name + 1, buf + *name + 1));
}
/* ns_inaddr_lookup constructs a PTR lookup query for an internet address -
e.g., 1.200.9.192.in-addr.arpa. If the specified timeout period passes
before the query is satisfied, or if the query fails, the callback is
called with a null pointer. Otherwise, the callback is called with the
address of the string returned by the name server. */
int ns_inaddr_lookup (id, inaddr)
u_int16_t id;
struct iaddr inaddr;
{
unsigned char namebuf [512];
unsigned char *s = namebuf;
unsigned char *label;
int i;
unsigned char c;
for (i = 3; i >= 0; --i) {
label = s++;
*label = 1;
c = inaddr.iabuf [i];
if (c > 100) {
++*label;
*s++ = '0' + c / 100;
}
if (c > 10) {
++*label;
*s++ = '0' + ((c / 10) % 10);
}
*s++ = '0' + (c % 10);
}
s += addlabel (s, "in-addr");
s += addlabel (s, "arpa");
*s++ = 0;
/* return nslookup (id, namebuf, s - namebuf, T_PTR, C_IN); */
return zonelookup (id, namebuf, s - namebuf, C_IN);
}
/* Construct and transmit a name server query. */
static int nslookup (id, qname, namelen, qtype, qclass)
u_int8_t id;
char *qname;
int namelen;
u_int16_t qtype;
u_int16_t qclass;
{
HEADER *hdr;
unsigned char query [512];
u_int8_t *s;
int len;
int i, status;
struct sockaddr_in *server = pick_name_server ();
if (!server)
return 0;
/* Construct a header... */
hdr = (HEADER *)query;
memset (hdr, 0, sizeof *hdr);
hdr -> id = htons (id);
hdr -> rd = 1;
hdr -> opcode = QUERY;
hdr -> qdcount = htons (1);
/* Copy in the name we're looking up. */
s = (u_int8_t *)(hdr + 1);
memcpy (s, qname, namelen);
s += namelen;
/* Set the query type. */
putUShort (s, qtype);
s += sizeof (u_int16_t);
/* Set the query class. */
putUShort (s, qclass);
s += sizeof (u_int16_t);
/* Send the query. */
status = sendto (dns_protocol_fd, query, s - query, 0,
(struct sockaddr *)server, sizeof *server);
/* If the send failed, report the failure. */
if (status < 0)
return 0;
return 1;
}
/* Construct a query for the SOA for a specified name.
Try every possible SOA name starting from the name specified and going
to the root name - e.g., for
215.5.5.192.in-addr.arpa, look for SOAs matching:
215.5.5.5.192.in-addr.arpa
5.5.192.in-addr.arpa
5.192.in-addr.arpa
192.in-addr.arpa
in-addr.arpa
arpa */
static int zonelookup (id, qname, namelen, qclass)
u_int8_t id;
char *qname;
int namelen;
u_int16_t qclass;
{
HEADER *hdr;
unsigned char query [512];
u_int8_t *s, *nptr;
int len;
int i, status, count;
struct sockaddr_in *server = pick_name_server ();
if (!server)
return 0;
/* Construct a header... */
hdr = (HEADER *)query;
memset (hdr, 0, sizeof *hdr);
hdr -> id = htons (id);
hdr -> rd = 1;
hdr -> opcode = QUERY;
/* Copy in the name we're looking up. */
s = (u_int8_t *)(hdr + 1);
memcpy (s, qname, namelen);
s += namelen;
/* Set the query type. */
putUShort (s, T_SOA);
s += sizeof (u_int16_t);
/* Set the query class. */
putUShort (s, qclass);
s += sizeof (u_int16_t);
count = 1;
/* Now query up the hierarchy. */
nptr = (u_int8_t *)(hdr + 1);
while (*(nptr += *nptr + 1)) {
/* Store a compressed reference from the full name. */
putUShort (s, ntohs (htons (0xC000) |
htons (nptr - &query [0])));
s += sizeof (u_int16_t);
/* Store the query type. */
putUShort (s, T_SOA);
s += sizeof (u_int16_t);
putUShort (s, qclass);
s += sizeof (u_int16_t);
/* Increment the query count... */
++count;
break;
}
hdr -> qdcount = htons (count);
dump_raw (query, s - query);
/* Send the query. */
status = sendto (dns_protocol_fd, query, s - query, 0,
(struct sockaddr *)server, sizeof *server);
/* If the send failed, report the failure. */
if (status < 0)
return 0;
return 1;
}
/* Process a reply from a name server. */
void dns_packet (protocol)
struct protocol *protocol;
{
HEADER *ns_header;
struct sockaddr_in from;
int fl;
unsigned char buf [4096];
unsigned char nbuf [512];
unsigned char *base;
unsigned char *dptr;
u_int16_t type;
u_int16_t class;
TIME ttl;
u_int16_t rdlength;
int len, status;
int i;
len = sizeof from;
status = recvfrom (protocol -> fd, buf, sizeof buf, 0,
(struct sockaddr *)&from, &len);
if (status < 0) {
warn ("icmp_echoreply: %m");
return;
}
ns_header = (HEADER *)buf;
base = (unsigned char *)(ns_header + 1);
#if 0
/* Ignore invalid packets... */
if (ntohs (ns_header -> id) > ns_query_max) {
printf ("Out-of-range NS message; id = %d\n",
ntohs (ns_header -> id));
return;
}
#endif
/* Parse the response... */
dptr = base;
/* Skip over the queries... */
for (i = 0; i < ntohs (ns_header -> qdcount); i++) {
dptr += skipname (dptr);
/* Skip over the query type and query class. */
dptr += 2 * sizeof (u_int16_t);
}
/* Process the answers... */
for (i = 0; i < ntohs (ns_header -> ancount); i++) {
/* Skip over the name we looked up. */
dptr += skipname (dptr);
/* Get the type. */
type = getUShort (dptr);
dptr += sizeof type;
/* Get the class. */
class = getUShort (dptr);
dptr += sizeof class;
/* Get the time-to-live. */
ttl = getULong (dptr);
dptr += sizeof ttl;
/* Get the length of the reply. */
rdlength = getUShort (dptr);
dptr += sizeof rdlength;
switch (type) {
case T_A:
note ("A record; value is %d.%d.%d.%d",
dptr [0], dptr [1], dptr [2], dptr [3]);
break;
case T_CNAME:
case T_PTR:
copy_out_name (base, dptr, nbuf);
note ("Domain name; value is %s\n", nbuf);
return;
default:
note ("unhandled type: %x", type);
}
}
}
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