From: Juergen Perlinger <perlinger@ntp.org>
Date: Sun, 5 Apr 2020 08:10:12 +0000 (+0200)
Subject: [Bug 3646] Avoid sync with unsync orphan
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=650919e3c588d6653af3b06a0347787484b5fc5f;p=thirdparty%2Fntp.git

[Bug 3646] Avoid sync with unsync orphan

bk: 5e899264Q-E6lY8_HHNxues2Ptu6Kg
---

diff --git a/ChangeLog b/ChangeLog
index 35d5d36c2..a90ba834a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+---
+* [Bug 3646] Avoid sync with unsync orphan <perlinger@ntp.org>
+  - patch by Gerry Garvey
+
 ---
 (4.2.8p14) 2020/03/03 Released by Harlan Stenn <stenn@ntp.org>
 
diff --git a/ntpd/ntp_proto.c b/ntpd/ntp_proto.c
index 33e97ef9d..b95670577 100644
--- a/ntpd/ntp_proto.c
+++ b/ntpd/ntp_proto.c
@@ -3455,11 +3455,13 @@ clock_select(void)
 	double	d, e, f, g;
 	double	high, low;
 	double	speermet;
+	double	lastresort_dist = MAXDISPERSE;
 	double	orphmet = 2.0 * U_INT32_MAX; /* 2x is greater than */
 	struct endpoint endp;
 	struct peer *osys_peer;
 	struct peer *sys_prefer = NULL;	/* prefer peer */
 	struct peer *typesystem = NULL;
+	struct peer *typelastresort = NULL;
 	struct peer *typeorphan = NULL;
 #ifdef REFCLOCK
 	struct peer *typeacts = NULL;
@@ -3523,6 +3525,22 @@ clock_select(void)
 			continue;
 		}
 
+		/*
+		 * If we have never been synchronised, look for any peer 
+		 * which has ever been synchronised and pick the one which 
+		 * has the lowest root distance. This can be used as a last 
+		 * resort if all else fails. Once we get an initial sync 
+		 * with this peer, sys_reftime gets set and so this 
+		 * function becomes disabled.
+		 */
+		if (L_ISZERO(&sys_reftime)) {
+			d = root_distance(peer);
+			if (!L_ISZERO(&peer->reftime) && d < lastresort_dist) {
+				typelastresort = peer;
+				lastresort_dist = d;
+			}
+		}
+
 		/*
 		 * If this peer is an orphan parent, elect the
 		 * one with the lowest metric defined as the
@@ -3756,6 +3774,9 @@ clock_select(void)
 		if (typeorphan != NULL) {
 			peers[0].peer = typeorphan;
 			nlist = 1;
+		} else if (typelastresort != NULL) {
+			peers[0].peer = typelastresort;
+			nlist = 1;
 		}
 	}