From 11942d45dcf0f4def7de6faa141ae1175c6a3a22 Mon Sep 17 00:00:00 2001
From: otto <>
Date: Thu, 30 May 2019 13:42:19 +0000
Subject: [PATCH] Use proper algorithm for median computation; use fabs() for
 computing an absolute value and fix poll loop to first generate messages and
 then compute poll flags the write cases. This makes the timeout workaround
 for constraints unneeded.  ok reyk@ tb@

---
 src/usr.sbin/ntpd/constraint.c | 28 +++++++++++++++-------------
 src/usr.sbin/ntpd/ntp.c        | 15 ++++++---------
 2 files changed, 21 insertions(+), 22 deletions(-)

diff --git a/src/usr.sbin/ntpd/constraint.c b/src/usr.sbin/ntpd/constraint.c
index 166e037f..13c05f92 100644
--- a/src/usr.sbin/ntpd/constraint.c
+++ b/src/usr.sbin/ntpd/constraint.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: constraint.c,v 1.43 2019/05/28 06:49:46 otto Exp $	*/
+/*	$OpenBSD: constraint.c,v 1.44 2019/05/30 13:42:19 otto Exp $	*/
 
 /*
  * Copyright (c) 2015 Reyk Floeter <reyk@openbsd.org>
@@ -41,6 +41,7 @@
 #include <ctype.h>
 #include <tls.h>
 #include <pwd.h>
+#include <math.h>
 
 #include "ntpd.h"
 
@@ -773,7 +774,7 @@ constraint_update(void)
 {
 	struct constraint *cstr;
 	int	 cnt, i;
-	time_t	*sum;
+	time_t	*values;
 	time_t	 now;
 
 	now = getmonotime();
@@ -784,29 +785,31 @@ constraint_update(void)
 			continue;
 		cnt++;
 	}
+	if (cnt == 0)
+		return;
 
-	if ((sum = calloc(cnt, sizeof(time_t))) == NULL)
+	if ((values = calloc(cnt, sizeof(time_t))) == NULL)
 		fatal("calloc");
 
 	i = 0;
 	TAILQ_FOREACH(cstr, &conf->constraints, entry) {
 		if (cstr->state != STATE_REPLY_RECEIVED)
 			continue;
-		sum[i++] = cstr->constraint + (now - cstr->last);
+		values[i++] = cstr->constraint + (now - cstr->last);
 	}
 
-	qsort(sum, cnt, sizeof(time_t), constraint_cmp);
+	qsort(values, cnt, sizeof(time_t), constraint_cmp);
 
 	/* calculate median */
 	i = cnt / 2;
 	if (cnt % 2 == 0)
-		if (sum[i - 1] < sum[i])
-			i -= 1;
+		conf->constraint_median = (values[i - 1] + values[i]) / 2;
+	else
+		conf->constraint_median = values[i];
 
 	conf->constraint_last = now;
-	conf->constraint_median = sum[i];
 
-	free(sum);
+	free(values);
 }
 
 void
@@ -826,7 +829,7 @@ int
 constraint_check(double val)
 {
 	struct timeval	tv;
-	double		constraint;
+	double		diff;
 	time_t		now;
 
 	if (conf->constraint_median == 0)
@@ -836,10 +839,9 @@ constraint_check(double val)
 	now = getmonotime();
 	tv.tv_sec = conf->constraint_median + (now - conf->constraint_last);
 	tv.tv_usec = 0;
-	constraint = gettime_from_timeval(&tv);
+	diff = fabs(val - gettime_from_timeval(&tv));
 
-	if (((val - constraint) > CONSTRAINT_MARGIN) ||
-	    ((constraint - val) > CONSTRAINT_MARGIN)) {
+	if (diff > CONSTRAINT_MARGIN) {
 		/* XXX get new constraint if too many errors happened */
 		if (conf->constraint_errors++ >
 		    (CONSTRAINT_ERROR_MARGIN * peer_cnt)) {
diff --git a/src/usr.sbin/ntpd/ntp.c b/src/usr.sbin/ntpd/ntp.c
index 7f7a42b7..25670f84 100644
--- a/src/usr.sbin/ntpd/ntp.c
+++ b/src/usr.sbin/ntpd/ntp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp.c,v 1.151 2019/05/29 18:48:33 otto Exp $ */
+/*	$OpenBSD: ntp.c,v 1.152 2019/05/30 13:42:19 otto Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -316,6 +316,11 @@ ntp_main(struct ntpd_conf *nconf, struct passwd *pw, int argc, char **argv)
 		    (peer_cnt == 0 && sensors_cnt == 0)))
 			priv_settime(0);	/* no good peers, don't wait */
 
+		TAILQ_FOREACH(cstr, &conf->constraints, entry) {
+			if (constraint_query(cstr) == -1)
+				continue;
+		}
+
 		if (ibuf_main->w.queued > 0)
 			pfd[PFD_PIPE_MAIN].events |= POLLOUT;
 		if (ibuf_dns->w.queued > 0)
@@ -330,15 +335,7 @@ ntp_main(struct ntpd_conf *nconf, struct passwd *pw, int argc, char **argv)
 		}
 		ctls = i;
 
-		TAILQ_FOREACH(cstr, &conf->constraints, entry) {
-			if (constraint_query(cstr) == -1)
-				continue;
-		}
-
 		now = getmonotime();
-		if (constraint_cnt)
-			nextaction = now + 1;
-
 		timeout = nextaction - now;
 		if (timeout < 0)
 			timeout = 0;