check_dhcp: Fix handling of "pad" options

Don't let "pad" options[*] terminate the parsing of DHCP options.  This
bug was triggered by using check_dhcp against Windows 2003 DHCP servers
(see #3503921).

[*] Cf. RFC 2132, 3.1.

NEWS

@@ -24,6 +24,7 @@ This file documents the major additions and syntax changes between releases.
 	Fix segfault in check_host when hostname returns multiple IP addresses (Sebastian Harl)
 	Fix check_smtp and check_tcp where duplicate messages were displayed for certificate errors
 	Fix check_ping's parsing of the output of Debian's ping6(1) implementation (#1894850 - Matej Vela)
+	Fix a check_dhcp bug which was triggered by using it to check Windows 2003 DHCP servers (#3503921)
 	Disable RFC4507 support, to work around SSL negotiation issues with (at least) some Tomcat versions
 
 1.4.15 27th July 2010

plugins-root/check_dhcp.c

@@ -839,8 +839,7 @@ int add_dhcp_offer(struct in_addr source,dhcp_packet *offer_packet){
 	/* process all DHCP options present in the packet */
 	for(x=4;x<MAX_DHCP_OPTIONS_LENGTH;){
 
-		/* end of options (0 is really just a pad, but bail out anyway) */
-		if((int)offer_packet->options[x]==-1 || (int)offer_packet->options[x]==0)
+		if((int)offer_packet->options[x]==-1)
 			break;
 
 		/* get option type */
@@ -872,7 +871,9 @@ int add_dhcp_offer(struct in_addr source,dhcp_packet *offer_packet){
 			}
 
 		/* skip option data we're ignoring */
-		if(option_type!=DHCP_OPTION_REBINDING_TIME)
+		if(option_type==0) /* "pad" option, see RFC 2132 (3.1) */
+			x+=1;
+		else
 			x+=option_length;
 		}