[nagiosplug] check_ntp_peer: Verify type of response packets

[Nagios Plugin Development]

 Module: nagiosplug
 Branch: master
 Commit: 9dad98f33efe2519b67c76dbc4ce00e4201c8009
 Author: Holger Weiss <holger at zedat.fu-berlin.de>
   Date: Sun Jun 30 16:05:48 2013 +0200
    URL: http://nagiosplug.git.sf.net/git/gitweb.cgi?p=nagiosplug/nagiosplug;a=commit;h=9dad98f

check_ntp_peer: Verify type of response packets

The check_ntp_peer plugin now ignores response packets with an
unexpected "Operation Code" and/or "Sequence" number (cf. RFC 1305,
Appendix B).  This fixes an issue where the check_ntp_peer requests got
duplicated on their way to the server (due to some network switch bug),
and the server therefore sent multiple responses per request.

Thanks to Marc Haber for reporting the issue.

---

 plugins/check_ntp_peer.c |   32 +++++++++++++++++++-------------
 1 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/plugins/check_ntp_peer.c b/plugins/check_ntp_peer.c
index b59c056..76152e1 100644
--- a/plugins/check_ntp_peer.c
+++ b/plugins/check_ntp_peer.c
@@ -241,15 +241,19 @@ int ntp_request(const char *host, double *offset, int *offset_result, double *ji
 		DBG(printf("sending READSTAT request"));
 		write(conn, &req, SIZEOF_NTPCM(req));
 		DBG(print_ntp_control_message(&req));
-		/* Attempt to read the largest size packet possible */
-		req.count=htons(MAX_CM_SIZE);
-		DBG(printf("recieving READSTAT response"))
-		if(read(conn, &req, SIZEOF_NTPCM(req)) == -1)
-			die(STATE_CRITICAL, "NTP CRITICAL: No response from NTP server\n");
-		DBG(print_ntp_control_message(&req));
-		/* discard obviously invalid packets */
-		if (ntohs(req.count) > MAX_CM_SIZE)
-			die(STATE_CRITICAL, "NTP CRITICAL: Invalid packet received from NTP server\n");
+
+		do {
+			/* Attempt to read the largest size packet possible */
+			req.count=htons(MAX_CM_SIZE);
+			DBG(printf("recieving READSTAT response"))
+			if(read(conn, &req, SIZEOF_NTPCM(req)) == -1)
+				die(STATE_CRITICAL, "NTP CRITICAL: No response from NTP server\n");
+			DBG(print_ntp_control_message(&req));
+			/* discard obviously invalid packets */
+			if (ntohs(req.count) > MAX_CM_SIZE)
+				die(STATE_CRITICAL, "NTP CRITICAL: Invalid packet received from NTP server\n");
+		} while (!(req.op&OP_READSTAT && ntohs(req.seq) == 1));
+
 		if (LI(req.flags) == LI_ALARM) li_alarm = 1;
 		/* Each peer identifier is 4 bytes in the data section, which
 	 	 * we represent as a ntp_assoc_status_pair datatype.
@@ -312,10 +316,12 @@ int ntp_request(const char *host, double *offset, int *offset_result, double *ji
 				write(conn, &req, SIZEOF_NTPCM(req));
 				DBG(print_ntp_control_message(&req));
 
-				req.count = htons(MAX_CM_SIZE);
-				DBG(printf("receiving READVAR response...\n"));
-				read(conn, &req, SIZEOF_NTPCM(req));
-				DBG(print_ntp_control_message(&req));
+				do {
+					req.count = htons(MAX_CM_SIZE);
+					DBG(printf("receiving READVAR response...\n"));
+					read(conn, &req, SIZEOF_NTPCM(req));
+					DBG(print_ntp_control_message(&req));
+				} while (!(req.op&OP_READVAR && ntohs(req.seq) == 2));
 
 				if(!(req.op&REM_ERROR))
 					xasprintf(&data, "%s%s", data, req.data);