Fix possible segfault in check_ntp_peer with deliberately invalid packets

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@2052 f882894a-f735-0410-b71e-b25c423dba1c

NEWS

@@ -11,7 +11,8 @@ This file documents the major additions and syntax changes between releases.
 	check_icmp now supports packet size modification
 	check_http -e now accepts a comma-delimited list of expected status codes
 	libtap now included with this distribution for easier testing. Run ./configure with --enable-libtap
-	check_ntp_peer/check_ntp_time used to show port in --help but ignored the argument - now implemented.
+	check_ntp_peer/check_ntp_time used to show port in --help but ignored the argument - now implemented
+	Fix possible segfault in check_ntp_peer with deliberately invalid packets
 
 1.4.12 27th May 2008
 	Added ./check_nt -v INSTANCES to count number of instances (Alessandro Ren)

plugins/check_ntp_peer.c

@@ -299,6 +299,9 @@ int ntp_request(const char *host, double *offset, int *offset_result, double *ji
 		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 paclet received from NTP server\n");
 		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.