Do a quick DNS probe to decide to stay in the forground and attempt

an (auto) settime or give up. 15s timeout is still in effect. ok florian@

src/usr.sbin/ntpd/client.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: client.c,v 1.108 2019/06/16 07:36:25 otto Exp $ */
+/*	$OpenBSD: client.c,v 1.109 2019/06/20 07:28:18 otto Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -240,7 +240,7 @@ handle_auto(double offset)
 
 	if (offset < AUTO_THRESHOLD) {
 		/* don't bother */
-		priv_settime(0);
+		priv_settime(0, "offset is negative or close enough");
 		return;
 	}
 	/* collect some more */
@@ -254,7 +254,7 @@ handle_auto(double offset)
 		offset = (v[AUTO_REPLIES / 2 - 1] + v[AUTO_REPLIES / 2]) / 2;
 	else
 		offset = v[AUTO_REPLIES / 2];
-	priv_settime(offset);
+	priv_settime(offset, "");
 }
 
 int
@@ -459,7 +459,7 @@ client_dispatch(struct ntp_peer *p, u_int8_t settime, u_int8_t automatic)
 		if (automatic)
 			handle_auto(p->reply[p->shift].offset);
 		else
-			priv_settime(p->reply[p->shift].offset);
+			priv_settime(p->reply[p->shift].offset, "");
 	}
 
 	if (++p->shift >= OFFSET_ARRAY_SIZE)

src/usr.sbin/ntpd/ntp.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp.c,v 1.155 2019/06/16 07:36:25 otto Exp $ */
+/*	$OpenBSD: ntp.c,v 1.156 2019/06/20 07:28:18 otto Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -302,7 +302,7 @@ ntp_main(struct ntpd_conf *nconf, struct passwd *pw, int argc, char **argv)
 			sensors_cnt = 0;
 			TAILQ_FOREACH(s, &conf->ntp_sensors, entry) {
 				if (conf->settime && s->offsets[0].offset)
-					priv_settime(s->offsets[0].offset);
+					priv_settime(s->offsets[0].offset, NULL);
 				sensors_cnt++;
 				if (s->next > 0 && s->next < nextaction)
 					nextaction = s->next;
@@ -312,7 +312,7 @@ ntp_main(struct ntpd_conf *nconf, struct passwd *pw, int argc, char **argv)
 		if (conf->settime &&
 		    ((trial_cnt > 0 && sent_cnt == 0) ||
 		    (peer_cnt == 0 && sensors_cnt == 0)))
-			priv_settime(0);	/* no good peers, don't wait */
+			priv_settime(0, "no valid peers configured");
 
 		TAILQ_FOREACH(cstr, &conf->constraints, entry) {
 			if (constraint_query(cstr) == -1)
@@ -521,7 +521,7 @@ ntp_dispatch_imsg_dns(void)
 				log_warnx("DNS lookup tempfail");
 				peer->state = STATE_DNS_TEMPFAIL;
 				if (++conf->tmpfail > TRIES_AUTO_DNSFAIL)
-					priv_settime(0);
+					priv_settime(0, "of dns failures");
 				break;
 			}
 
@@ -569,6 +569,14 @@ ntp_dispatch_imsg_dns(void)
 			constraint_msg_dns(imsg.hdr.peerid,
 			    imsg.data, imsg.hdr.len - IMSG_HEADER_SIZE);
 			break;
+		case IMSG_PROBE_ROOT:
+			dlen = imsg.hdr.len - IMSG_HEADER_SIZE;
+			if (dlen != sizeof(int))
+				fatalx("IMSG_PROBE_ROOT");
+			memcpy(&n, imsg.data, sizeof(int));
+			if (n < 0)
+				priv_settime(0, "dns probe failed");
+			break;
 		default:
 			break;
 		}
@@ -754,8 +762,10 @@ offset_compare(const void *aa, const void *bb)
 }
 
 void
-priv_settime(double offset)
+priv_settime(double offset, char *msg)
 {
+	if (offset == 0)
+		log_info("cancel settime because %s", msg);
 	imsg_compose(ibuf_main, IMSG_SETTIME, 0, 0, -1,
 	    &offset, sizeof(offset));
 	conf->settime = 0;

src/usr.sbin/ntpd/ntp_dns.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp_dns.c,v 1.22 2019/06/12 05:04:45 otto Exp $ */
+/*	$OpenBSD: ntp_dns.c,v 1.23 2019/06/20 07:28:18 otto Exp $ */
 
 /*
  * Copyright (c) 2003-2008 Henning Brauer <henning@openbsd.org>
@@ -19,6 +19,9 @@
 #include <sys/types.h>
 #include <sys/resource.h>
 #include <sys/time.h>
+#include <netinet/in.h>
+#include <arpa/nameser.h>
+#include <resolv.h>
 
 #include <netinet/in.h>
 
@@ -40,6 +43,8 @@ struct imsgbuf		*ibuf_dns;
 
 void	sighdlr_dns(int);
 int	dns_dispatch_imsg(struct ntpd_conf *);
+int	probe_root_ns(void);
+void	probe_root(void);
 
 void
 sighdlr_dns(int sig)
@@ -96,6 +101,8 @@ ntp_dns(struct ntpd_conf *nconf, struct passwd *pw)
 	if (pledge("stdio dns", NULL) == -1)
 		err(1, "pledge");
 
+	probe_root();
+
 	while (quit_dns == 0) {
 		pfd[0].fd = ibuf_dns->fd;
 		pfd[0].events = POLLIN;
@@ -202,3 +209,42 @@ dns_dispatch_imsg(struct ntpd_conf *nconf)
 	}
 	return (0);
 }
+
+int
+probe_root_ns(void)
+{
+	int ret;
+	int old_retrans, old_retry, old_options;
+	unsigned char buf[4096];
+
+	old_retrans = _res.retrans;
+	old_retry = _res.retry;
+	old_options = _res.options;
+	_res.retrans = 1;
+	_res.retry = 1;
+	_res.options |= RES_USE_CD;
+		
+	ret = res_query(".", C_IN, T_NS, buf, sizeof(buf));
+
+	_res.retrans = old_retrans;
+	_res.retry = old_retry;
+	_res.options = old_options;
+	
+	return ret;
+}
+
+void
+probe_root(void)
+{
+	int		n;
+
+	n = probe_root_ns();	
+	if (n < 0) {
+		/* give programs like unwind a second chance */
+		sleep(1);
+		n = probe_root_ns();
+	}
+	if (imsg_compose(ibuf_dns, IMSG_PROBE_ROOT, 0, 0, -1, &n,
+	    sizeof(int)) == -1)
+		fatalx("probe_root");
+}

src/usr.sbin/ntpd/ntpd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.h,v 1.143 2019/06/16 07:36:25 otto Exp $ */
+/*	$OpenBSD: ntpd.h,v 1.144 2019/06/20 07:28:18 otto Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -311,7 +311,8 @@ enum imsg_type {
 	IMSG_CTL_SHOW_ALL,
 	IMSG_CTL_SHOW_ALL_END,
 	IMSG_SYNCED,
-	IMSG_UNSYNCED
+	IMSG_UNSYNCED,
+	IMSG_PROBE_ROOT
 };
 
 enum ctl_actions {
@@ -327,7 +328,7 @@ enum ctl_actions {
 void	 ntp_main(struct ntpd_conf *, struct passwd *, int, char **);
 void	 peer_addr_head_clear(struct ntp_peer *);
 int	 priv_adjtime(void);
-void	 priv_settime(double);
+void	 priv_settime(double, char *);
 void	 priv_dns(int, char *, u_int32_t);
 int	 offset_compare(const void *, const void *);
 void	 update_scale(double);