Re: Ethereal comparison 1.265 vs 1.270 DHCP Discover

[Dan Williams <dcbw redhat com>]

Bill,

Can you apply this patch to current CVS copy of NM?  It changes 
dhcpcd/buildmsg.c only.  It now pads the  message to over 300 bytes and ensures 
that the message is always an even number of bytes long.

Thanks,
Dan

On Fri, 11 Feb 2005, Bill Moss wrote:

> I think older hardware may reject messages that are too short. The UDP 
> part of the message contains a BOOTP section of options and there was a 
> time when BOOTP messages had a minimize size of 300 bytes. If this is 
> what the SMC is doing, the a message with a UDP part of 297 bytes will 
> not pass muster. This is just a guess. I suppose you can pad the message 
> one byte at a time and see where the boundary is. I am betting on 300 or 
> 312.
> 
> -- 
> Bill Moss
> Professor, Mathematical Sciences
> Clemson University
> 
> _______________________________________________
> NetworkManager-list mailing list
> NetworkManager-list gnome org
> http://mail.gnome.org/mailman/listinfo/networkmanager-list
>

Index: dhcpcd/buildmsg.c
===================================================================
RCS file: /cvs/gnome/NetworkManager/dhcpcd/buildmsg.c,v
retrieving revision 1.5
diff -u -r1.5 buildmsg.c
--- dhcpcd/buildmsg.c	10 Feb 2005 20:54:04 -0000	1.5
+++ dhcpcd/buildmsg.c	12 Feb 2005 03:36:02 -0000
@@ -138,7 +138,8 @@
 /*****************************************************************************/
 unsigned char *fill_message_type (unsigned char request, unsigned char *p)
 {
-	const unsigned short dhcpMsgSize = htons (sizeof (dhcpMessage));
+#define MAX_DHCP_MSG_SIZE	576
+	const unsigned short dhcpMsgSize = htons (MAX_DHCP_MSG_SIZE);
 
 	*p++ = dhcpMessageType;
 	*p++ = 1;
@@ -150,6 +151,15 @@
 	return p;
 }
 /*****************************************************************************/
+unsigned char *fill_padding (dhcpMessage *start, unsigned char *p)
+{
+#define PAD_STOP	324		/* Completely arbitrary even number */
+
+	while ((char *)p - (char *)start < PAD_STOP)
+		*p++ = 0;
+	return p;
+}
+/*****************************************************************************/
 udpipMessage *build_dhcp_discover (dhcp_interface *iface, int *msg_len)
 {
 	udpipMessage			*udp_msg = calloc (1, sizeof (udpipMessage));
@@ -171,9 +181,9 @@
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
 	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), 0, INADDR_BROADCAST, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)p - (char *)udp_msg;
@@ -198,10 +208,10 @@
 		p = fill_lease_time (iface->dhcp_options.val[dhcpIPaddrLeaseTime], p);
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), 0, INADDR_BROADCAST, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -224,9 +234,10 @@
 #endif
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
-	p++;
+	/* build UDP/IP header */
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), iface->ciaddr, iface->siaddr, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -247,10 +258,10 @@
 		p = fill_lease_time (iface->dhcp_options.val[dhcpIPaddrLeaseTime], p);
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), iface->ciaddr, INADDR_BROADCAST, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -274,10 +285,10 @@
 	p = fill_lease_time (&lease_time, p);
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), 0, INADDR_BROADCAST, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -299,10 +310,10 @@
 	p = fill_server_id (iface->dhcp_options.val[dhcpServerIdentifier], p);
 	memcpy(p, iface->cli_id, iface->cli_id_len);
 	p += iface->cli_id_len;
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), iface->ciaddr, iface->siaddr, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -328,10 +339,10 @@
 		p = fill_requested_ipaddr (iface, p);
 	memcpy (p, iface->cli_id, iface->cli_id_len);
 	p += iface->cli_id_len;
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen ((udpiphdr *)(udp_msg->udpipmsg), 0, iface->siaddr, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;
@@ -351,10 +362,10 @@
 	p = fill_message_type (DHCP_INFORM, p);
 	p = fill_param_request (p);
 	p = fill_host_and_class_id (iface, p);
-	*p = endOption;
+	*p++ = endOption;
+	p = fill_padding (dhcp_msg, p);
 
 	/* build UDP/IP header */
-	p++;
 	dhcp_msg_len = (char *)p - (char *)dhcp_msg;
 	udpipgen((udpiphdr *)(udp_msg->udpipmsg), 0, INADDR_BROADCAST, &iface->ip_id, dhcp_msg_len);
 	*msg_len = (char *)(p++) - (char *)udp_msg;