OpenBSD-4.6/usr.sbin/rdate/ntp.c
/* $OpenBSD: ntp.c,v 1.29 2006/09/17 17:03:56 ckuethe Exp $ */
/*
* Copyright (c) 1996, 1997 by N.M. Maclaren. All rights reserved.
* Copyright (c) 1996, 1997 by University of Cambridge. All rights reserved.
* Copyright (c) 2002 by Thorsten "mirabile" Glaser.
*
* 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 author nor the university may be used to
* endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include "ntpleaps.h"
/*
* NTP definitions. Note that these assume 8-bit bytes - sigh. There
* is little point in parameterising everything, as it is neither
* feasible nor useful. It would be very useful if more fields could
* be defined as unspecified. The NTP packet-handling routines
* contain a lot of extra assumptions.
*/
#define JAN_1970 2208988800.0 /* 1970 - 1900 in seconds */
#define NTP_SCALE 4294967296.0 /* 2^32, of course! */
#define NTP_MODE_CLIENT 3 /* NTP client mode */
#define NTP_MODE_SERVER 4 /* NTP server mode */
#define NTP_VERSION 4 /* The current version */
#define NTP_VERSION_MIN 1 /* The minum valid version */
#define NTP_VERSION_MAX 4 /* The maximum valid version */
#define NTP_STRATUM_MAX 14 /* The maximum valid stratum */
#define NTP_INSANITY 3600.0 /* Errors beyond this are hopeless */
#define NTP_PACKET_MIN 48 /* Without authentication */
#define NTP_PACKET_MAX 68 /* With authentication (ignored) */
#define NTP_DISP_FIELD 8 /* Offset of dispersion field */
#define NTP_REFERENCE 16 /* Offset of reference timestamp */
#define NTP_ORIGINATE 24 /* Offset of originate timestamp */
#define NTP_RECEIVE 32 /* Offset of receive timestamp */
#define NTP_TRANSMIT 40 /* Offset of transmit timestamp */
#define STATUS_NOWARNING 0 /* No Leap Indicator */
#define STATUS_LEAPHIGH 1 /* Last Minute Has 61 Seconds */
#define STATUS_LEAPLOW 2 /* Last Minute Has 59 Seconds */
#define STATUS_ALARM 3 /* Server Clock Not Synchronized */
#define MAX_QUERIES 25
#define MAX_DELAY 15
#define MILLION_L 1000000l /* For conversion to/from timeval */
#define MILLION_D 1.0e6 /* Must be equal to MILLION_L */
struct ntp_data {
u_char status;
u_char version;
u_char mode;
u_char stratum;
double receive;
double transmit;
double current;
u_int64_t recvck;
/* Local State */
double originate;
u_int64_t xmitck;
};
void ntp_client(const char *, int, struct timeval *, struct timeval *, int);
int sync_ntp(int, const struct sockaddr *, double *, double *);
int write_packet(int, struct ntp_data *);
int read_packet(int, struct ntp_data *, double *, double *);
void unpack_ntp(struct ntp_data *, u_char *);
double current_time(double);
void create_timeval(double, struct timeval *, struct timeval *);
#ifdef DEBUG
void print_packet(const struct ntp_data *);
#endif
int corrleaps;
void
ntp_client(const char *hostname, int family, struct timeval *new,
struct timeval *adjust, int leapflag)
{
struct addrinfo hints, *res0, *res;
double offset, error;
int accept = 0, ret, s, ierror;
memset(&hints, 0, sizeof(hints));
hints.ai_family = family;
hints.ai_socktype = SOCK_DGRAM;
ierror = getaddrinfo(hostname, "ntp", &hints, &res0);
if (ierror) {
errx(1, "%s: %s", hostname, gai_strerror(ierror));
/*NOTREACHED*/
}
corrleaps = leapflag;
if (corrleaps)
ntpleaps_init();
s = -1;
for (res = res0; res; res = res->ai_next) {
s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (s < 0)
continue;
ret = sync_ntp(s, res->ai_addr, &offset, &error);
if (ret < 0) {
#ifdef DEBUG
fprintf(stderr, "try the next address\n");
#endif
close(s);
s = -1;
continue;
}
accept++;
break;
}
freeaddrinfo(res0);
#ifdef DEBUG
fprintf(stderr, "Correction: %.6f +/- %.6f\n", offset, error);
#endif
if (accept < 1)
errx(1, "Unable to get a reasonable time estimate");
create_timeval(offset, new, adjust);
}
int
sync_ntp(int fd, const struct sockaddr *peer, double *offset, double *error)
{
int attempts = 0, accepts = 0, rejects = 0;
int delay = MAX_DELAY, ret;
double deadline;
double a, b, x, y;
double minerr = 0.1; /* Maximum ignorable variation */
struct ntp_data data;
deadline = current_time(JAN_1970) + delay;
*offset = 0.0;
*error = NTP_INSANITY;
if (connect(fd, peer, SA_LEN(peer)) < 0) {
warn("Failed to connect to server");
return (-1);
}
while (accepts < MAX_QUERIES && attempts < 2 * MAX_QUERIES) {
memset(&data, 0, sizeof(data));
if (current_time(JAN_1970) > deadline) {
warnx("Not enough valid responses received in time");
return (-1);
}
if (write_packet(fd, &data) < 0)
return (-1);
ret = read_packet(fd, &data, &x, &y);
if (ret < 0)
return (-1);
else if (ret > 0) {
#ifdef DEBUG
print_packet(&data);
#endif
if (++rejects > MAX_QUERIES) {
warnx("Too many bad or lost packets");
return (-1);
} else
continue;
} else
++accepts;
#ifdef DEBUG
fprintf(stderr, "Offset: %.6f +/- %.6f\n", x, y);
#endif
if ((a = x - *offset) < 0.0)
a = -a;
if (accepts <= 1)
a = 0.0;
b = *error + y;
if (y < *error) {
*offset = x;
*error = y;
}
#ifdef DEBUG
fprintf(stderr, "Best: %.6f +/- %.6f\n", *offset, *error);
#endif
if (a > b) {
warnx("Inconsistent times received from NTP server");
return (-1);
}
if ((data.status & STATUS_ALARM) == STATUS_ALARM) {
warnx("Ignoring NTP server with alarm flag set");
return (-1);
}
if (*error <= minerr)
break;
}
return (accepts);
}
/* Send out NTP packet. */
int
write_packet(int fd, struct ntp_data *data)
{
u_char packet[NTP_PACKET_MIN];
ssize_t length;
memset(packet, 0, sizeof(packet));
packet[0] = (NTP_VERSION << 3) | (NTP_MODE_CLIENT);
data->xmitck = (u_int64_t)arc4random() << 32 | arc4random();
/*
* Send out a random 64-bit number as our transmit time. The NTP
* server will copy said number into the originate field on the
* response that it sends us. This is totally legal per the SNTP spec.
*
* The impact of this is two fold: we no longer send out the current
* system time for the world to see (which may aid an attacker), and
* it gives us a (not very secure) way of knowing that we're not
* getting spoofed by an attacker that can't capture our traffic
* but can spoof packets from the NTP server we're communicating with.
*
* No endian concerns here. Since we're running as a strict
* unicast client, we don't have to worry about anyone else finding
* the transmit field intelligible.
*/
*(u_int64_t *)(packet + NTP_TRANSMIT) = data->xmitck;
data->originate = current_time(JAN_1970);
length = write(fd, packet, sizeof(packet));
if (length != sizeof(packet)) {
warn("Unable to send NTP packet to server");
return (-1);
}
return (0);
}
/*
* Check the packet and work out the offset and optionally the error.
* Note that this contains more checking than xntp does. Return 0 for
* success, 1 for failure. Note that it must not change its arguments
* if it fails.
*/
int
read_packet(int fd, struct ntp_data *data, double *off, double *error)
{
u_char receive[NTP_PACKET_MAX];
struct timeval tv;
double x, y;
int length, r;
fd_set *rfds;
rfds = calloc(howmany(fd + 1, NFDBITS), sizeof(fd_mask));
if (rfds == NULL)
err(1, "calloc");
FD_SET(fd, rfds);
retry:
tv.tv_sec = 0;
tv.tv_usec = 1000000 * MAX_DELAY / MAX_QUERIES;
r = select(fd + 1, rfds, NULL, NULL, &tv);
if (r < 0) {
if (errno == EINTR)
goto retry;
else
warn("select");
free(rfds);
return (r);
}
if (r != 1 || !FD_ISSET(fd, rfds)) {
free(rfds);
return (1);
}
free(rfds);
length = read(fd, receive, NTP_PACKET_MAX);
if (length < 0) {
warn("Unable to receive NTP packet from server");
return (-1);
}
if (length < NTP_PACKET_MIN || length > NTP_PACKET_MAX) {
warnx("Invalid NTP packet size, packet rejected");
return (1);
}
unpack_ntp(data, receive);
if (data->recvck != data->xmitck) {
warnx("Invalid cookie received, packet rejected");
return (1);
}
if (data->version < NTP_VERSION_MIN ||
data->version > NTP_VERSION_MAX) {
warnx("Received NTP version %u, need %u or lower",
data->version, NTP_VERSION);
return (1);
}
if (data->mode != NTP_MODE_SERVER) {
warnx("Invalid NTP server mode, packet rejected");
return (1);
}
if (data->stratum > NTP_STRATUM_MAX) {
warnx("Invalid stratum received, packet rejected");
return (1);
}
if (data->transmit == 0.0) {
warnx("Server clock invalid, packet rejected");
return (1);
}
x = data->receive - data->originate;
y = data->transmit - data->current;
*off = (x + y) / 2;
*error = x - y;
x = (data->current - data->originate) / 2;
if (x > *error)
*error = x;
return (0);
}
/*
* Unpack the essential data from an NTP packet, bypassing struct
* layout and endian problems. Note that it ignores fields irrelevant
* to SNTP.
*/
void
unpack_ntp(struct ntp_data *data, u_char *packet)
{
int i;
double d;
data->current = current_time(JAN_1970);
data->status = (packet[0] >> 6);
data->version = (packet[0] >> 3) & 0x07;
data->mode = packet[0] & 0x07;
data->stratum = packet[1];
for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_RECEIVE+i];
data->receive = d / NTP_SCALE;
for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_TRANSMIT+i];
data->transmit = d / NTP_SCALE;
/* See write_packet for why this isn't an endian problem. */
data->recvck = *(u_int64_t *)(packet + NTP_ORIGINATE);
}
/*
* Get the current UTC time in seconds since the Epoch plus an offset
* (usually the time from the beginning of the century to the Epoch)
*/
double
current_time(double offset)
{
struct timeval current;
u_int64_t t;
if (gettimeofday(¤t, NULL))
err(1, "Could not get local time of day");
/*
* At this point, current has the current TAI time.
* Now subtract leap seconds to set the posix tick.
*/
t = SEC_TO_TAI64(current.tv_sec);
if (corrleaps)
ntpleaps_sub(&t);
return (offset + TAI64_TO_SEC(t) + 1.0e-6 * current.tv_usec);
}
/*
* Change offset into current UTC time. This is portable, even if
* struct timeval uses an unsigned long for tv_sec.
*/
void
create_timeval(double difference, struct timeval *new, struct timeval *adjust)
{
struct timeval old;
long n;
/* Start by converting to timeval format. Note that we have to
* cater for negative, unsigned values. */
if ((n = (long) difference) > difference)
--n;
adjust->tv_sec = n;
adjust->tv_usec = (long) (MILLION_D * (difference-n));
errno = 0;
if (gettimeofday(&old, NULL))
err(1, "Could not get local time of day");
new->tv_sec = old.tv_sec + adjust->tv_sec;
new->tv_usec = (n = (long) old.tv_usec + (long) adjust->tv_usec);
if (n < 0) {
new->tv_usec += MILLION_L;
--new->tv_sec;
} else if (n >= MILLION_L) {
new->tv_usec -= MILLION_L;
++new->tv_sec;
}
}
#ifdef DEBUG
void
print_packet(const struct ntp_data *data)
{
printf("status: %u\n", data->status);
printf("version: %u\n", data->version);
printf("mode: %u\n", data->mode);
printf("stratum: %u\n", data->stratum);
printf("originate: %f\n", data->originate);
printf("receive: %f\n", data->receive);
printf("transmit: %f\n", data->transmit);
printf("current: %f\n", data->current);
printf("xmitck: 0x%0llX\n", data->xmitck);
printf("recvck: 0x%0llX\n", data->recvck);
};
#endif