3 files changed, 72 insertions, 67 deletions

diff --git a/NEWS b/NEWS
index 8e5a494..628210d 100644
--- a/NEWS
+++ b/NEWS
@@ -4,10 +4,11 @@ This file documents the major additions and syntax changes between releases.
         Added ./check_nt -v INSTANCES to count number of instances (Alessandro Ren)
         New check_icmp -s option to specify the source IP address
         check_dns now sorts addresses for testing results for more than one returned IP (Matthias Urlichs)
-        Fix segfault in check_ntp_time and (deprecated) check_ntp. (Bug #1862300)
+        Fix segfault in check_ntp_time and (deprecated) check_ntp (Bug #1862300)
         check_disk should now work with large file systems (2TB+) on all archs that supports it
         Fixed check_disk disk usage calculation when using --group=NAME (related to bug #1348746)
         Fix help text of check_ntp_* (Bug #1880095)
+        Fix bugs and flaws in best offset server selection of check_ntp_time and (deprecated) check_ntp
 
 1.4.11 13th December 2007
         Fixed check_http regression in 1.4.10 where following redirects to
diff --git a/plugins/check_ntp.c b/plugins/check_ntp.c
index b474d9a..2b3cc91 100644
--- a/plugins/check_ntp.c
+++ b/plugins/check_ntp.c
@@ -302,50 +302,52 @@ void setup_request(ntp_message *p){
  * this is done by filtering servers based on stratum, dispersion, and
  * finally round-trip delay. */
 int best_offset_server(const ntp_server_results *slist, int nservers){
-        int i=0, j=0, cserver=0, candidates[5], csize=0;
+        int i=0, cserver=0, best_server=-1;
 
         /* for each server */
         for(cserver=0; cserver<nservers; cserver++){
-                /* sort out servers with error flags */
-                if ( LI(slist[cserver].flags) != LI_NOWARNING ){
-                        if (verbose) printf("discarding peer id %d: flags=%d\n", cserver, LI(slist[cserver].flags));
-                        break;
+                /* We don't want any servers that fails these tests */
+                /* Sort out servers that didn't respond or responede with a 0 stratum;
+                 * stratum 0 is for reference clocks so no NTP server should ever report
+                 * a stratum 0 */
+                if ( slist[cserver].stratum == 0){
+                        if (verbose) printf("discarding peer %d: stratum=%d\n", cserver, slist[cserver].stratum);
+                        continue;
+                }
+                /* Sort out servers with error flags */
+                if ( LI(slist[cserver].flags) == LI_ALARM ){
+                        if (verbose) printf("discarding peer %d: flags=%d\n", cserver, LI(slist[cserver].flags));
+                        continue;
                 }
 
-                /* compare it to each of the servers already in the candidate list */
-                for(i=0; i<csize; i++){
-                        /* does it have an equal or better stratum? */
-                        if(slist[cserver].stratum <= slist[i].stratum){
-                                /* does it have an equal or better dispersion? */
-                                if(slist[cserver].rtdisp <= slist[i].rtdisp){
-                                        /* does it have a better rtdelay? */
-                                        if(slist[cserver].rtdelay < slist[i].rtdelay){
-                                                break;
-                                        }
-                                }
-                        }
+                /* If we don't have a server yet, use the first one */
+                if (best_server == -1) {
+                        best_server = cserver;
+                        DBG(printf("using peer %d as our first candidate\n", best_server));
+                        continue;
                 }
 
-                /* if we haven't reached the current list's end, move everyone
-                 * over one to the right, and insert the new candidate */
-                if(i<csize){
-                        for(j=4; j>i; j--){
-                                candidates[j]=candidates[j-1];
+                /* compare the server to the best one we've seen so far */
+                /* does it have an equal or better stratum? */
+                DBG(printf("comparing peer %d with peer %d\n", cserver, best_server));
+                if(slist[cserver].stratum <= slist[best_server].stratum){
+                        DBG(printf("stratum for peer %d <= peer %d\n", cserver, best_server));
+                        /* does it have an equal or better dispersion? */
+                        if(slist[cserver].rtdisp <= slist[best_server].rtdisp){
+                                DBG(printf("dispersion for peer %d <= peer %d\n", cserver, best_server));
+                                /* does it have a better rtdelay? */
+                                if(slist[cserver].rtdelay < slist[best_server].rtdelay){
+                                        DBG(printf("rtdelay for peer %d < peer %d\n", cserver, best_server));
+                                        best_server = cserver;
+                                        DBG(printf("peer %d is now our best candidate\n", best_server));
+                                }
                         }
                 }
-                /* regardless, if they should be on the list... */
-                if(i<5) {
-                        candidates[i]=cserver;
-                        if(csize<5) csize++;
-                /* otherwise discard the server */
-                } else {
-                        DBG(printf("discarding peer id %d\n", cserver));
-                }
         }
 
-        if(csize>0) {
-                DBG(printf("best server selected: peer %d\n", candidates[0]));
-                return candidates[0];
+        if(best_server >= 0) {
+                DBG(printf("best server selected: peer %d\n", best_server));
+                return best_server;
         } else {
                 DBG(printf("no peers meeting synchronization criteria :(\n"));
                 return -1;
diff --git a/plugins/check_ntp_time.c b/plugins/check_ntp_time.c
index 16e4c3c..11a0ece 100644
--- a/plugins/check_ntp_time.c
+++ b/plugins/check_ntp_time.c
@@ -247,50 +247,52 @@ void setup_request(ntp_message *p){
  * this is done by filtering servers based on stratum, dispersion, and
  * finally round-trip delay. */
 int best_offset_server(const ntp_server_results *slist, int nservers){
-        int i=0, j=0, cserver=0, candidates[5], csize=0;
+        int i=0, cserver=0, best_server=-1;
 
         /* for each server */
         for(cserver=0; cserver<nservers; cserver++){
-                /* sort out servers with error flags */
-                if ( LI(slist[cserver].flags) != LI_NOWARNING ){
-                        if (verbose) printf("discarding peer id %d: flags=%d\n", cserver, LI(slist[cserver].flags));
-                        break;
+                /* We don't want any servers that fails these tests */
+                /* Sort out servers that didn't respond or responede with a 0 stratum;
+                 * stratum 0 is for reference clocks so no NTP server should ever report
+                 * a stratum 0 */
+                if ( slist[cserver].stratum == 0){
+                        if (verbose) printf("discarding peer %d: stratum=%d\n", cserver, slist[cserver].stratum);
+                        continue;
+                }
+                /* Sort out servers with error flags */
+                if ( LI(slist[cserver].flags) == LI_ALARM ){
+                        if (verbose) printf("discarding peer %d: flags=%d\n", cserver, LI(slist[cserver].flags));
+                        continue;
                 }
 
-                /* compare it to each of the servers already in the candidate list */
-                for(i=0; i<csize; i++){
-                        /* does it have an equal or better stratum? */
-                        if(slist[cserver].stratum <= slist[i].stratum){
-                                /* does it have an equal or better dispersion? */
-                                if(slist[cserver].rtdisp <= slist[i].rtdisp){
-                                        /* does it have a better rtdelay? */
-                                        if(slist[cserver].rtdelay < slist[i].rtdelay){
-                                                break;
-                                        }
-                                }
-                        }
+                /* If we don't have a server yet, use the first one */
+                if (best_server == -1) {
+                        best_server = cserver;
+                        DBG(printf("using peer %d as our first candidate\n", best_server));
+                        continue;
                 }
 
-                /* if we haven't reached the current list's end, move everyone
-                 * over one to the right, and insert the new candidate */
-                if(i<csize){
-                        for(j=4; j>i; j--){
-                                candidates[j]=candidates[j-1];
+                /* compare the server to the best one we've seen so far */
+                /* does it have an equal or better stratum? */
+                DBG(printf("comparing peer %d with peer %d\n", cserver, best_server));
+                if(slist[cserver].stratum <= slist[best_server].stratum){
+                        DBG(printf("stratum for peer %d <= peer %d\n", cserver, best_server));
+                        /* does it have an equal or better dispersion? */
+                        if(slist[cserver].rtdisp <= slist[best_server].rtdisp){
+                                DBG(printf("dispersion for peer %d <= peer %d\n", cserver, best_server));
+                                /* does it have a better rtdelay? */
+                                if(slist[cserver].rtdelay < slist[best_server].rtdelay){
+                                        DBG(printf("rtdelay for peer %d < peer %d\n", cserver, best_server));
+                                        best_server = cserver;
+                                        DBG(printf("peer %d is now our best candidate\n", best_server));
+                                }
                         }
                 }
-                /* regardless, if they should be on the list... */
-                if(i<5) {
-                        candidates[i]=cserver;
-                        if(csize<5) csize++;
-                /* otherwise discard the server */
-                } else {
-                        DBG(printf("discarding peer id %d\n", cserver));
-                }
         }
 
-        if(csize>0) {
-                DBG(printf("best server selected: peer %d\n", candidates[0]));
-                return candidates[0];
+        if(best_server >= 0) {
+                DBG(printf("best server selected: peer %d\n", best_server));
+                return best_server;
         } else {
                 DBG(printf("no peers meeting synchronization criteria :(\n"));
                 return -1;