1 files changed, 28 insertions, 10 deletions

diff --git a/plugins-root/check_dhcp.c b/plugins-root/check_dhcp.c
index 245946b..993531c 100644
--- a/plugins-root/check_dhcp.c
+++ b/plugins-root/check_dhcp.c
@@ -182,6 +182,7 @@ typedef struct requested_server_struct{
 #define DHCP_OPTION_BROADCAST_ADDRESS   28
 #define DHCP_OPTION_REQUESTED_ADDRESS   50
 #define DHCP_OPTION_LEASE_TIME          51
+#define DHCP_OPTION_SERVER_IDENTIFIER   54
 #define DHCP_OPTION_RENEWAL_TIME        58
 #define DHCP_OPTION_REBINDING_TIME      59
 
@@ -765,9 +766,9 @@ int add_requested_server(struct in_addr server_address){
 int add_dhcp_offer(struct in_addr source,dhcp_packet *offer_packet){
         dhcp_offer *new_offer;
         int x;
-        int y;
         unsigned option_type;
         unsigned option_length;
+        struct in_addr serv_ident = {0};
 
         if(offer_packet==NULL)
                 return ERROR;
@@ -789,23 +790,28 @@ int add_dhcp_offer(struct in_addr source,dhcp_packet *offer_packet){
                         printf("Option: %d (0x%02X)\n",option_type,option_length);
 
                 /* get option data */
-                if(option_type==DHCP_OPTION_LEASE_TIME){
+                switch(option_type){
+                case DHCP_OPTION_LEASE_TIME:
                         memcpy(&dhcp_lease_time, &offer_packet->options[x],sizeof(dhcp_lease_time));
                         dhcp_lease_time = ntohl(dhcp_lease_time);
-                        }
-                if(option_type==DHCP_OPTION_RENEWAL_TIME){
+                        break;
+                case DHCP_OPTION_RENEWAL_TIME:
                         memcpy(&dhcp_renewal_time, &offer_packet->options[x],sizeof(dhcp_renewal_time));
                         dhcp_renewal_time = ntohl(dhcp_renewal_time);
-                        }
-                if(option_type==DHCP_OPTION_REBINDING_TIME){
+                        break;
+                case DHCP_OPTION_REBINDING_TIME:
                         memcpy(&dhcp_rebinding_time, &offer_packet->options[x],sizeof(dhcp_rebinding_time));
                         dhcp_rebinding_time = ntohl(dhcp_rebinding_time);
+                        break;
+                case DHCP_OPTION_SERVER_IDENTIFIER:
+                        memcpy(&serv_ident.s_addr, &offer_packet->options[x],sizeof(serv_ident.s_addr));
+                        break;
                         }
 
                 /* skip option data we're ignoring */
-                else
-                        for(y=0;y<option_length;y++,x++);
-                }
+                if(option_type!=DHCP_OPTION_REBINDING_TIME)
+                        x+=option_length;
+                }
 
         if(verbose){
                 if(dhcp_lease_time==DHCP_INFINITE_TIME)
@@ -826,7 +832,19 @@ int add_dhcp_offer(struct in_addr source,dhcp_packet *offer_packet){
         if(new_offer==NULL)
                 return ERROR;
 
-        new_offer->server_address=source;
+        /*
+         * RFC 2131 (2.) says: "DHCP clarifies the interpretation of the
+         * 'siaddr' field as the address of the server to use in the next step
+         * of the client's bootstrap process.  A DHCP server may return its own
+         * address in the 'siaddr' field, if the server is prepared to supply
+         * the next bootstrap service (e.g., delivery of an operating system
+         * executable image).  A DHCP server always returns its own address in
+         * the 'server identifier' option."  'serv_ident' is the 'server
+         * identifier' option, 'source' is the 'siaddr' field or (if 'siaddr'
+         * wasn't available) the IP address we received the DHCPOFFER from.  If
+         * 'serv_ident' isn't available for some reason, we use 'source'.
+         */
+        new_offer->server_address=serv_ident.s_addr?serv_ident:source;
         new_offer->offered_address=offer_packet->yiaddr;
         new_offer->lease_time=dhcp_lease_time;
         new_offer->renewal_time=dhcp_renewal_time;