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clockdiff.c
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clockdiff.c
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/*-
* Copyright (c) 1985, 1993
* The Regents of the University of California. 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 University 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 REGENTS 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 REGENTS 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.
*/
#include <time.h>
#include <sys/types.h>
#include <sys/param.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#define TSPTYPES
#include <fcntl.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <errno.h>
#include <linux/types.h>
#ifdef CAPABILITIES
#include <sys/capability.h>
#endif
void usage(void) __attribute__((noreturn));
#define MAX_HOSTNAMELEN NI_MAXHOST
/*
* Checksum routine for Internet Protocol family headers.
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
*
* This implementation is TAHOE version.
*/
#undef ADDCARRY
#define ADDCARRY(sum) { \
if (sum & 0xffff0000) { \
sum &= 0xffff; \
sum++; \
} \
}
int in_cksum(unsigned short *addr, int len)
{
union word {
char c[2];
unsigned short s;
} u;
int sum = 0;
while (len > 0) {
/*
* add by words.
*/
while ((len -= 2) >= 0) {
if ((unsigned long)addr & 0x1) {
/* word is not aligned */
u.c[0] = *(char *)addr;
u.c[1] = *((char *)addr+1);
sum += u.s;
addr++;
} else
sum += *addr++;
ADDCARRY(sum);
}
if (len == -1)
/*
* Odd number of bytes.
*/
u.c[0] = *(unsigned char *)addr;
}
if (len == -1) {
/* The last mbuf has odd # of bytes. Follow the
standard (the odd byte is shifted left by 8 bits) */
u.c[1] = 0;
sum += u.s;
ADDCARRY(sum);
}
return (~sum & 0xffff);
}
#define ON 1
#define OFF 0
#define RANGE 1 /* best expected round-trip time, ms */
#define MSGS 50
#define TRIALS 10
#define GOOD 0
#define UNREACHABLE 2
#define NONSTDTIME 3
#define HOSTDOWN 0x7fffffff
int interactive = 0;
uint16_t id;
int sock;
int sock_raw;
struct sockaddr_in server;
int ip_opt_len = 0;
#define BIASP 43199999
#define BIASN -43200000
#define MODULO 86400000
#define PROCESSING_TIME 0 /* ms. to reduce error in measurement */
#define PACKET_IN 1024
int measure_delta;
int measure_delta1;
static unsigned short seqno, seqno0, acked;
long rtt = 1000;
long min_rtt;
long rtt_sigma = 0;
/*
* Measures the differences between machines' clocks using
* ICMP timestamp messages.
*/
int
measure(struct sockaddr_in * addr)
{
socklen_t length;
int msgcount;
int cc, count;
fd_set ready;
long sendtime, recvtime, histime;
long min1, min2, diff;
long delta1, delta2;
struct timeval tv1, tout;
unsigned char packet[PACKET_IN], opacket[64];
struct icmphdr *icp;
struct icmphdr *oicp = (struct icmphdr *) opacket;
struct iphdr *ip = (struct iphdr *) packet;
min1 = min2 = 0x7fffffff;
min_rtt = 0x7fffffff;
measure_delta = HOSTDOWN;
measure_delta1 = HOSTDOWN;
/* empties the icmp input queue */
FD_ZERO(&ready);
empty:
tout.tv_sec = tout.tv_usec = 0;
FD_SET(sock_raw, &ready);
if (select(FD_SETSIZE, &ready, (fd_set *)0, (fd_set *)0, &tout)) {
length = sizeof(struct sockaddr_in);
cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0,
(struct sockaddr *)NULL, &length);
if (cc < 0)
return -1;
goto empty;
}
/*
* To measure the difference, select MSGS messages whose round-trip
* time is smaller than RANGE if ckrange is 1, otherwise simply
* select MSGS messages regardless of round-trip transmission time.
* Choose the smallest transmission time in each of the two directions.
* Use these two latter quantities to compute the delta between
* the two clocks.
*/
length = sizeof(struct sockaddr_in);
oicp->type = ICMP_TIMESTAMP;
oicp->code = 0;
oicp->checksum = 0;
oicp->un.echo.id = id;
((__u32*)(oicp+1))[0] = 0;
((__u32*)(oicp+1))[1] = 0;
((__u32*)(oicp+1))[2] = 0;
FD_ZERO(&ready);
acked = seqno = seqno0 = 0;
for (msgcount = 0; msgcount < MSGS; ) {
/*
* If no answer is received for TRIALS consecutive times,
* the machine is assumed to be down
*/
if (seqno - acked > TRIALS)
return HOSTDOWN;
oicp->un.echo.sequence = ++seqno;
oicp->checksum = 0;
(void)gettimeofday (&tv1, (struct timezone *)0);
*(__u32*)(oicp+1) = htonl((tv1.tv_sec % (24*60*60)) * 1000
+ tv1.tv_usec / 1000);
oicp->checksum = in_cksum((unsigned short *)oicp, sizeof(*oicp) + 12);
count = sendto(sock_raw, (char *)opacket, sizeof(*oicp)+12, 0,
(struct sockaddr *)addr, sizeof(struct sockaddr_in));
if (count < 0)
return UNREACHABLE;
for (;;) {
FD_ZERO(&ready);
FD_SET(sock_raw, &ready);
{
long tmo = rtt + rtt_sigma;
tout.tv_sec = tmo/1000;
tout.tv_usec = (tmo - (tmo/1000)*1000)*1000;
}
if ((count = select(FD_SETSIZE, &ready, (fd_set *)0,
(fd_set *)0, &tout)) <= 0)
break;
(void)gettimeofday(&tv1, (struct timezone *)0);
cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0,
(struct sockaddr *)NULL, &length);
if (cc < 0)
return(-1);
icp = (struct icmphdr *)(packet + (ip->ihl << 2));
if( icp->type == ICMP_TIMESTAMPREPLY &&
icp->un.echo.id == id && icp->un.echo.sequence >= seqno0 &&
icp->un.echo.sequence <= seqno) {
if (acked < icp->un.echo.sequence)
acked = icp->un.echo.sequence;
recvtime = (tv1.tv_sec % (24*60*60)) * 1000 +
tv1.tv_usec / 1000;
sendtime = ntohl(*(__u32*)(icp+1));
diff = recvtime - sendtime;
/*
* diff can be less than 0 aroud midnight
*/
if (diff < 0)
continue;
rtt = (rtt * 3 + diff)/4;
rtt_sigma = (rtt_sigma *3 + abs(diff-rtt))/4;
msgcount++;
histime = ntohl(((__u32*)(icp+1))[1]);
/*
* a hosts using a time format different from
* ms. since midnight UT (as per RFC792) should
* set the high order bit of the 32-bit time
* value it transmits.
*/
if ((histime & 0x80000000) != 0)
return NONSTDTIME;
if (interactive) {
printf(".");
fflush(stdout);
}
delta1 = histime - sendtime;
/*
* Handles wrap-around to avoid that around
* midnight small time differences appear
* enormous. However, the two machine's clocks
* must be within 12 hours from each other.
*/
if (delta1 < BIASN)
delta1 += MODULO;
else if (delta1 > BIASP)
delta1 -= MODULO;
delta2 = recvtime - histime;
if (delta2 < BIASN)
delta2 += MODULO;
else if (delta2 > BIASP)
delta2 -= MODULO;
if (delta1 < min1)
min1 = delta1;
if (delta2 < min2)
min2 = delta2;
if (delta1 + delta2 < min_rtt) {
min_rtt = delta1 + delta2;
measure_delta1 = (delta1 - delta2)/2 + PROCESSING_TIME;
}
if (diff < RANGE) {
min1 = delta1;
min2 = delta2;
goto good_exit;
}
}
}
}
good_exit:
measure_delta = (min1 - min2)/2 + PROCESSING_TIME;
return GOOD;
}
char *myname, *hisname;
int
measure_opt(struct sockaddr_in * addr)
{
socklen_t length;
int msgcount;
int cc, count;
fd_set ready;
long sendtime, recvtime, histime, histime1;
long min1, min2, diff;
long delta1, delta2;
struct timeval tv1, tout;
unsigned char packet[PACKET_IN], opacket[64];
struct icmphdr *icp;
struct icmphdr *oicp = (struct icmphdr *) opacket;
struct iphdr *ip = (struct iphdr *) packet;
min1 = min2 = 0x7fffffff;
min_rtt = 0x7fffffff;
measure_delta = HOSTDOWN;
measure_delta1 = HOSTDOWN;
/* empties the icmp input queue */
FD_ZERO(&ready);
empty:
tout.tv_sec = tout.tv_usec = 0;
FD_SET(sock_raw, &ready);
if (select(FD_SETSIZE, &ready, (fd_set *)0, (fd_set *)0, &tout)) {
length = sizeof(struct sockaddr_in);
cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0,
(struct sockaddr *)NULL, &length);
if (cc < 0)
return -1;
goto empty;
}
/*
* To measure the difference, select MSGS messages whose round-trip
* time is smaller than RANGE if ckrange is 1, otherwise simply
* select MSGS messages regardless of round-trip transmission time.
* Choose the smallest transmission time in each of the two directions.
* Use these two latter quantities to compute the delta between
* the two clocks.
*/
length = sizeof(struct sockaddr_in);
oicp->type = ICMP_ECHO;
oicp->code = 0;
oicp->checksum = 0;
oicp->un.echo.id = id;
((__u32*)(oicp+1))[0] = 0;
((__u32*)(oicp+1))[1] = 0;
((__u32*)(oicp+1))[2] = 0;
FD_ZERO(&ready);
acked = seqno = seqno0 = 0;
for (msgcount = 0; msgcount < MSGS; ) {
/*
* If no answer is received for TRIALS consecutive times,
* the machine is assumed to be down
*/
if ( seqno - acked > TRIALS) {
errno = EHOSTDOWN;
return HOSTDOWN;
}
oicp->un.echo.sequence = ++seqno;
oicp->checksum = 0;
gettimeofday (&tv1, NULL);
((__u32*)(oicp+1))[0] = htonl((tv1.tv_sec % (24*60*60)) * 1000
+ tv1.tv_usec / 1000);
oicp->checksum = in_cksum((unsigned short *)oicp, sizeof(*oicp)+12);
count = sendto(sock_raw, (char *)opacket, sizeof(*oicp)+12, 0,
(struct sockaddr *)addr, sizeof(struct sockaddr_in));
if (count < 0) {
errno = EHOSTUNREACH;
return UNREACHABLE;
}
for (;;) {
FD_ZERO(&ready);
FD_SET(sock_raw, &ready);
{
long tmo = rtt + rtt_sigma;
tout.tv_sec = tmo/1000;
tout.tv_usec = (tmo - (tmo/1000)*1000)*1000;
}
if ((count = select(FD_SETSIZE, &ready, (fd_set *)0,
(fd_set *)0, &tout)) <= 0)
break;
(void)gettimeofday(&tv1, (struct timezone *)0);
cc = recvfrom(sock_raw, (char *)packet, PACKET_IN, 0,
(struct sockaddr *)NULL, &length);
if (cc < 0)
return(-1);
icp = (struct icmphdr *)(packet + (ip->ihl << 2));
if (icp->type == ICMP_ECHOREPLY &&
packet[20] == IPOPT_TIMESTAMP &&
icp->un.echo.id == id &&
icp->un.echo.sequence >= seqno0 &&
icp->un.echo.sequence <= seqno) {
int i;
__u8 *opt = packet+20;
if (acked < icp->un.echo.sequence)
acked = icp->un.echo.sequence;
if ((opt[3]&0xF) != IPOPT_TS_PRESPEC) {
fprintf(stderr, "Wrong timestamp %d\n", opt[3]&0xF);
return NONSTDTIME;
}
if (opt[3]>>4) {
if ((opt[3]>>4) != 1 || ip_opt_len != 4+3*8)
fprintf(stderr, "Overflow %d hops\n", opt[3]>>4);
}
sendtime = recvtime = histime = histime1 = 0;
for (i=0; i < (opt[2]-5)/8; i++) {
__u32 *timep = (__u32*)(opt+4+i*8+4);
__u32 t = ntohl(*timep);
if (t & 0x80000000)
return NONSTDTIME;
if (i == 0)
sendtime = t;
if (i == 1)
histime = histime1 = t;
if (i == 2) {
if (ip_opt_len == 4+4*8)
histime1 = t;
else
recvtime = t;
}
if (i == 3)
recvtime = t;
}
if (!(sendtime&histime&histime1&recvtime)) {
fprintf(stderr, "wrong timestamps\n");
return -1;
}
diff = recvtime - sendtime;
/*
* diff can be less than 0 aroud midnight
*/
if (diff < 0)
continue;
rtt = (rtt * 3 + diff)/4;
rtt_sigma = (rtt_sigma *3 + abs(diff-rtt))/4;
msgcount++;
if (interactive) {
printf(".");
fflush(stdout);
}
delta1 = histime - sendtime;
/*
* Handles wrap-around to avoid that around
* midnight small time differences appear
* enormous. However, the two machine's clocks
* must be within 12 hours from each other.
*/
if (delta1 < BIASN)
delta1 += MODULO;
else if (delta1 > BIASP)
delta1 -= MODULO;
delta2 = recvtime - histime1;
if (delta2 < BIASN)
delta2 += MODULO;
else if (delta2 > BIASP)
delta2 -= MODULO;
if (delta1 < min1)
min1 = delta1;
if (delta2 < min2)
min2 = delta2;
if (delta1 + delta2 < min_rtt) {
min_rtt = delta1 + delta2;
measure_delta1 = (delta1 - delta2)/2 + PROCESSING_TIME;
}
if (diff < RANGE) {
min1 = delta1;
min2 = delta2;
goto good_exit;
}
}
}
}
good_exit:
measure_delta = (min1 - min2)/2 + PROCESSING_TIME;
return GOOD;
}
/*
* Clockdiff computes the difference between the time of the machine on
* which it is called and the time of the machines given as argument.
* The time differences measured by clockdiff are obtained using a sequence
* of ICMP TSTAMP messages which are returned to the sender by the IP module
* in the remote machine.
* In order to compare clocks of machines in different time zones, the time
* is transmitted (as a 32-bit value) in milliseconds since midnight UT.
* If a hosts uses a different time format, it should set the high order
* bit of the 32-bit quantity it transmits.
* However, VMS apparently transmits the time in milliseconds since midnight
* local time (rather than GMT) without setting the high order bit.
* Furthermore, it does not understand daylight-saving time. This makes
* clockdiff behaving inconsistently with hosts running VMS.
*
* In order to reduce the sensitivity to the variance of message transmission
* time, clockdiff sends a sequence of messages. Yet, measures between
* two `distant' hosts can be affected by a small error. The error can, however,
* be reduced by increasing the number of messages sent in each measurement.
*/
void
usage() {
fprintf(stderr, "Usage: clockdiff [-o] <host>\n");
exit(1);
}
void drop_rights(void) {
#ifdef CAPABILITIES
cap_t caps = cap_init();
if (cap_set_proc(caps)) {
perror("clockdiff: cap_set_proc");
exit(-1);
}
cap_free(caps);
#endif
if (setuid(getuid())) {
perror("clockdiff: setuid");
exit(-1);
}
}
int
main(int argc, char *argv[])
{
int measure_status;
struct addrinfo hints = { .ai_family = AF_INET, .ai_socktype = SOCK_RAW, .ai_flags = AI_CANONNAME };
struct addrinfo *result;
int status;
char hostname[MAX_HOSTNAMELEN];
int s_errno = 0;
int n_errno = 0;
if (argc < 2) {
drop_rights();
usage();
}
sock_raw = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
s_errno = errno;
errno = 0;
if (nice(-16) == -1)
n_errno = errno;
drop_rights();
if (argc == 3) {
if (strcmp(argv[1], "-o") == 0) {
ip_opt_len = 4 + 4*8;
argv++;
} else if (strcmp(argv[1], "-o1") == 0) {
ip_opt_len = 4 + 3*8;
argv++;
} else
usage();
} else if (argc != 2)
usage();
if (sock_raw < 0) {
errno = s_errno;
perror("clockdiff: socket");
exit(1);
}
if (n_errno < 0) {
errno = n_errno;
perror("clockdiff: nice");
exit(1);
}
if (isatty(fileno(stdin)) && isatty(fileno(stdout)))
interactive = 1;
id = getpid();
(void)gethostname(hostname,sizeof(hostname));
status = getaddrinfo(hostname, NULL, &hints, &result);
if (status) {
fprintf(stderr, "clockdiff: %s: %s\n", hostname, gai_strerror(status));
exit(2);
}
myname = strdup(result->ai_canonname);
freeaddrinfo(result);
status = getaddrinfo(argv[1], NULL, &hints, &result);
if (status) {
fprintf(stderr, "clockdiff: %s: %s\n", argv[1], gai_strerror(status));
exit(1);
}
hisname = strdup(result->ai_canonname);
memcpy(&server, result->ai_addr, sizeof server);
freeaddrinfo(result);
if (connect(sock_raw, (struct sockaddr*)&server, sizeof(server)) == -1) {
perror("connect");
exit(1);
}
if (ip_opt_len) {
struct sockaddr_in myaddr;
socklen_t addrlen = sizeof(myaddr);
unsigned char rspace[ip_opt_len];
memset(rspace, 0, sizeof(rspace));
rspace[0] = IPOPT_TIMESTAMP;
rspace[1] = ip_opt_len;
rspace[2] = 5;
rspace[3] = IPOPT_TS_PRESPEC;
if (getsockname(sock_raw, (struct sockaddr*)&myaddr, &addrlen) == -1) {
perror("getsockname");
exit(1);
}
((__u32*)(rspace+4))[0*2] = myaddr.sin_addr.s_addr;
((__u32*)(rspace+4))[1*2] = server.sin_addr.s_addr;
((__u32*)(rspace+4))[2*2] = myaddr.sin_addr.s_addr;
if (ip_opt_len == 4+4*8) {
((__u32*)(rspace+4))[2*2] = server.sin_addr.s_addr;
((__u32*)(rspace+4))[3*2] = myaddr.sin_addr.s_addr;
}
if (setsockopt(sock_raw, IPPROTO_IP, IP_OPTIONS, rspace, ip_opt_len) < 0) {
perror("ping: IP_OPTIONS (fallback to icmp tstamps)");
ip_opt_len = 0;
}
}
if ((measure_status = (ip_opt_len ? measure_opt : measure)(&server)) < 0) {
if (errno)
perror("measure");
else
fprintf(stderr, "measure: unknown failure\n");
exit(1);
}
switch (measure_status) {
case HOSTDOWN:
fprintf(stderr, "%s is down\n", hisname);
exit(1);
case NONSTDTIME:
fprintf(stderr, "%s time transmitted in a non-standard format\n", hisname);
exit(1);
case UNREACHABLE:
fprintf(stderr, "%s is unreachable\n", hisname);
exit(1);
default:
break;
}
{
time_t now = time(NULL);
if (interactive)
printf("\nhost=%s rtt=%ld(%ld)ms/%ldms delta=%dms/%dms %s", hisname,
rtt, rtt_sigma, min_rtt,
measure_delta, measure_delta1,
ctime(&now));
else
printf("%ld %d %d\n", now, measure_delta, measure_delta1);
}
exit(0);
}