/* $NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $ */
/*-
* Copyright (c) 2013 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Andreas Gustafsson.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/
/*
* A minimal DNS server capable of providing canned answers to the
* specific queries issued by t_hostent.sh and nothing more.
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $");
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#ifdef __NetBSD__
#include <netinet6/in6.h>
#endif
#ifdef __FreeBSD__
#include <paths.h>
#endif
union sockaddr_either {
struct sockaddr s;
struct sockaddr_in sin;
struct sockaddr_in6 sin6;
};
#ifdef DEBUG
#define DPRINTF(...) fprintf(stderr, __VA_ARGS__)
#else
#define DPRINTF(...)
#endif
/* A DNS question and its corresponding answer */
struct dns_data {
size_t qname_size;
const char *qname; /* Wire-encode question name */
int qtype;
size_t answer_size;
const char *answer; /* One wire-encoded answer RDATA */
};
/* Convert C string constant to length + data pair */
#define STR_DATA(s) sizeof(s) - 1, s
/* Canned DNS queestion-answer pairs */
struct dns_data data[] = {
/* Forward mappings */
/* localhost IN A -> 127.0.0.1 */
{ STR_DATA("\011localhost\000"), 1,
STR_DATA("\177\000\000\001") },
/* localhost IN AAAA -> ::1 */
{ STR_DATA("\011localhost\000"), 28,
STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") },
/* sixthavenue.astron.com IN A -> 38.117.134.16 */
{ STR_DATA("\013sixthavenue\006astron\003com\000"), 1,
STR_DATA("\046\165\206\020") },
/* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */
{ STR_DATA("\013sixthavenue\006astron\003com\000"), 28,
STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") },
/* Reverse mappings */
{ STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12,
STR_DATA("\011localhost\000") },
{ STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010"
"\0010\0010\0010\0010\0010\0010\0010\0010"
"\0010\0010\0010\0010\0010\0010\0010\0010"
"\0010\0010\0010\0010\0010\0010\0010\0010"
"\003ip6\004arpa\000"), 12,
STR_DATA("\011localhost\000") },
{ STR_DATA("\00216\003134\003117\00238"
"\007in-addr\004arpa\000"), 12,
STR_DATA("\013sixthavenue\006astron\003com\000") },
{ STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f"
"\001f\001f\0012\0019\001a\0014\001e\0013"
"\0010\0010\001f\0011\0013\0010\0010\0013"
"\0016\0010\0011\0010\0010\0012\0016\0012"
"\003ip6\004arpa\000"), 12,
STR_DATA("\013sixthavenue\006astron\003com\000") },
/* End marker */
{ STR_DATA(""), 0, STR_DATA("") }
};
/*
* Compare two DNS names for equality. If equal, return their
* length, and if not, return zero. Does not handle compression.
*/
static int
name_eq(const unsigned char *a, const unsigned char *b) {
const unsigned char *a_save = a;
for (;;) {
int i;
int lena = *a++;
int lenb = *b++;
if (lena != lenb)
return 0;
if (lena == 0)
return a - a_save;
for (i = 0; i < lena; i++)
if (tolower(a[i]) != tolower(b[i]))
return 0;
a += lena;
b += lena;
}
}
#ifdef DEBUG
static char *
name2str(const void *v, char *buf, size_t buflen) {
const unsigned char *a = v;
char *b = buf;
char *eb = buf + buflen;
#define ADDC(c) do { \
if (b < eb) \
*b++ = c; \
else \
return NULL; \
} while (/*CONSTCOND*/0)
for (int did = 0;; did++) {
int lena = *a++;
if (lena == 0) {
ADDC('\0');
return buf;
}
if (did)
ADDC('.');
for (int i = 0; i < lena; i++)
ADDC(a[i]);
a += lena;
}
}
#endif
#ifdef __FreeBSD__
/* XXX the daemon2_* functions should be in a library */
int __daemon2_detach_pipe[2];
static int
daemon2_fork(void)
{
int r;
int fd;
int i;
/*
* Set up the pipe, making sure the write end does not
* get allocated one of the file descriptors that will
* be closed in daemon2_detach().
*/
for (i = 0; i < 3; i++) {
r = pipe(__daemon2_detach_pipe);
if (r < 0)
return -1;
if (__daemon2_detach_pipe[1] <= STDERR_FILENO &&
(fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
(void)dup2(fd, __daemon2_detach_pipe[0]);
(void)dup2(fd, __daemon2_detach_pipe[1]);
if (fd > STDERR_FILENO)
(void)close(fd);
continue;
}
break;
}
r = fork();
if (r < 0) {
return -1;
} else if (r == 0) {
/* child */
close(__daemon2_detach_pipe[0]);
return 0;
}
/* Parent */
(void) close(__daemon2_detach_pipe[1]);
for (;;) {
char dummy;
r = read(__daemon2_detach_pipe[0], &dummy, 1);
if (r < 0) {
if (errno == EINTR)
continue;
_exit(1);
} else if (r == 0) {
_exit(1);
} else { /* r > 0 */
_exit(0);
}
}
}
static int
daemon2_detach(int nochdir, int noclose)
{
int r;
int fd;
if (setsid() == -1)
return -1;
if (!nochdir)
(void)chdir("/");
if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
(void)dup2(fd, STDIN_FILENO);
(void)dup2(fd, STDOUT_FILENO);
(void)dup2(fd, STDERR_FILENO);
if (fd > STDERR_FILENO)
(void)close(fd);
}
while (1) {
r = write(__daemon2_detach_pipe[1], "", 1);
if (r < 0) {
if (errno == EINTR)
continue;
/* May get "broken pipe" here if parent is killed */
return -1;
} else if (r == 0) {
/* Should not happen */
return -1;
} else {
break;
}
}
(void) close(__daemon2_detach_pipe[1]);
return 0;
}
#endif
int main(int argc, char **argv) {
int s, r, protocol;
union sockaddr_either saddr;
struct dns_data *dp;
unsigned char *p;
char pidfile_name[40];
FILE *f;
int one = 1;
#ifdef DEBUG
char buf1[1024], buf2[1024];
#endif
#ifdef __FreeBSD__
daemon2_fork();
#endif
if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6'))
errx(1, "usage: dns_server 4 | 6");
s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP);
if (s < 0)
err(1, "socket");
if (protocol == '4') {
memset(&saddr.sin, 0, sizeof(saddr.sin));
saddr.sin.sin_family = AF_INET;
saddr.sin.sin_len = sizeof(saddr.sin);
saddr.sin.sin_port = htons(53);
saddr.sin.sin_addr.s_addr = INADDR_ANY;
} else {
static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT;
memset(&saddr.sin6, 0, sizeof(saddr.sin6));
saddr.sin6.sin6_family = AF_INET6;
saddr.sin6.sin6_len = sizeof(saddr.sin6);
saddr.sin6.sin6_port = htons(53);
saddr.sin6.sin6_addr = loopback;
}
r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one);
if (r < 0)
err(1, "setsockopt");
r = bind(s,
(struct sockaddr *) &saddr,
protocol == '4' ? sizeof(struct sockaddr_in) :
sizeof(struct sockaddr_in6));
if (r < 0)
err(1, "bind");
snprintf(pidfile_name, sizeof pidfile_name,
"dns_server_%c.pid", protocol);
f = fopen(pidfile_name, "w");
fprintf(f, "%d", getpid());
fclose(f);
#ifdef __FreeBSD__
#ifdef DEBUG
daemon2_detach(0, 1);
#else
daemon2_detach(0, 0);
#endif
#else
#ifdef DEBUG
daemon(0, 1);
#else
daemon(0, 0);
#endif
#endif
for (;;) {
unsigned char buf[512];
union sockaddr_either from;
ssize_t nrecv, nsent;
socklen_t fromlen =
protocol == '4' ? sizeof(struct sockaddr_in) :
sizeof(struct sockaddr_in6);
memset(buf, 0, sizeof buf);
nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen);
if (nrecv < 0)
err(1, "recvfrom");
if (nrecv < 12) {
DPRINTF("Too short %zd\n", nrecv);
continue;
}
if ((buf[2] & 0x80) != 0) {
DPRINTF("Not a query 0x%x\n", buf[2]);
continue;
}
if (!(buf[4] == 0 && buf[5] == 1)) {
DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]);
continue; /* QDCOUNT is not 1 */
}
for (dp = data; dp->qname_size != 0; dp++) {
int qtype, qclass;
p = buf + 12; /* Point to QNAME */
int n = name_eq(p, (const unsigned char *) dp->qname);
if (n == 0) {
DPRINTF("no match name %s != %s\n",
name2str(p, buf1, sizeof(buf1)),
name2str(dp->qname, buf2, sizeof(buf2)));
continue; /* Name does not match */
}
DPRINTF("match name %s\n",
name2str(p, buf1, sizeof(buf1)));
p += n; /* Skip QNAME */
qtype = *p++ << 8;
qtype |= *p++;
if (qtype != dp->qtype) {
DPRINTF("no match name 0x%x != 0x%x\n",
qtype, dp->qtype);
continue;
}
DPRINTF("match type 0x%x\n", qtype);
qclass = *p++ << 8;
qclass |= *p++;
if (qclass != 1) { /* IN */
DPRINTF("no match class %d != 1\n", qclass);
continue;
}
DPRINTF("match class %d\n", qclass);
goto found;
}
continue;
found:
buf[2] |= 0x80; /* QR */
buf[3] |= 0x80; /* RA */
memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */
buf[7] = 1; /* ANCOUNT */
memcpy(p, dp->qname, dp->qname_size);
p += dp->qname_size;
*p++ = dp->qtype >> 8;
*p++ = dp->qtype & 0xFF;
*p++ = 0;
*p++ = 1; /* IN */
memset(p, 0, 4); /* TTL = 0 */
p += 4;
*p++ = 0; /* RDLENGTH MSB */
*p++ = dp->answer_size; /* RDLENGTH LSB */
memcpy(p, dp->answer, dp->answer_size);
p += dp->answer_size;
nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen);
DPRINTF("sent %zd\n", nsent);
if (nsent != p - buf)
warn("sendto");
}
}