We always have to make one pass over the BOOTP options to see if the

packet is BOOTP or DHCP; have "bootp_option()" take a flag indicating
whether it's the first pass or the second and, in the first pass, don't
put anything in the protocol tree - just return, through pointers, the
DHCP packet type and the vendor class ID.  On the second pass, don't
modify what those pointers point to, just use them as appropriate.

Make the vendor class ID pointer local to "dissect_bootp()", and have
"dissect_bootp()" do the first pass, set the Protocol and Info columns
appropriately if the packet is DHCP, and then, if a protocol tree is to
be built, make a second pass, handing "bootp_option()" the DHCP packet
type and vendor class ID we found.

If the vendor class ID is null, don't try to compare it with Intel's PXE
client indicator.

svn path=/trunk/; revision=3449

1 files changed, 96 insertions, 50 deletions

diff --git a/packet-bootp.c b/packet-bootp.c
index 4eb6243a80..21ab5f2c7e 100644
--- a/packet-bootp.c
+++ b/packet-bootp.c
@@ -2,7 +2,7 @@
  * Routines for BOOTP/DHCP packet disassembly
  * Gilbert Ramirez <gram@xiexie.org>
  *
- * $Id: packet-bootp.c,v 1.52 2001/05/24 19:21:15 guy Exp $
+ * $Id: packet-bootp.c,v 1.53 2001/05/25 06:56:53 guy Exp $
  *
  * The information used comes from:
  * RFC  951: Bootstrap Protocol
@@ -68,8 +68,6 @@ static int hf_bootp_dhcp = -1;
 static guint ett_bootp = -1;
 static guint ett_bootp_option = -1;
 
-static const guint8 *vendor_class_id = NULL;
-
 #define UDP_PORT_BOOTPS  67
 
 enum field_type { none, ipv4, string, toggle, yes_no, special, opaque,
@@ -117,7 +115,9 @@ get_dhcp_type(guint8 byte)
 
 /* Returns the number of bytes consumed by this option. */
 static int
-bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff)
+bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff,
+    gboolean first_pass, const char **dhcp_type_p,
+    const guint8 **vendor_class_id_p)
 {
 	char			*text;
 	enum field_type		ftype;
@@ -363,15 +363,23 @@ bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff)
 			}
 		}
 		i = i - voff;
-		if (bp_tree != NULL)
-			proto_tree_add_text(bp_tree, tvb, voff, i, "Padding");
+		if (!first_pass) {
+			if (bp_tree != NULL) {
+				proto_tree_add_text(bp_tree, tvb, voff, i,
+				    "Padding");
+			}
+		}
 		consumed = i;
 		return consumed;
 		break;
 
 	case 255:	/* End Option */
-		if (bp_tree != NULL)
-			proto_tree_add_text(bp_tree, tvb, voff, 1, "End Option");
+		if (!first_pass) {
+			if (bp_tree != NULL) {
+				proto_tree_add_text(bp_tree, tvb, voff, 1,
+				    "End Option");
+			}
+		}
 		consumed = 1;
 		return consumed;
 	}
@@ -383,14 +391,41 @@ bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff)
 	 */
 	vlen = tvb_get_guint8(tvb, voff+1);
 	consumed = vlen + 2;
-	/* Handling of options we need to scan for first:
-	 * 60 (Vendor class identifier)
-	 * This is ugly but I don't have any better ideas
-	 * -- Joerg Mayer
+
+	/*
+	 * In the first pass, we don't put anything into the protocol
+	 * tree; we just check for some options we have to look at
+	 * in order to properly process the packet:
+	 *
+	 *	53 (DHCP message type) - if this is present, this is DHCP
+	 *
+	 *	60 (Vendor class identifier) - we need this in order to
+	 *	   interpret the vendor-specific info
 	 */
-	if ( (code == 60) && (bp_tree == NULL) ) {
-		vendor_class_id = tvb_get_ptr(tvb, voff+2, consumed-2);
+	if (first_pass) {
+		switch (code) {
+
+		case 53:
+			*dhcp_type_p =
+			    get_dhcp_type(tvb_get_guint8(tvb, voff+2));
+			break;
+
+		case 60:
+			*vendor_class_id_p =
+			    tvb_get_ptr(tvb, voff+2, consumed-2);
+			break;
+		}
+
+		/*
+		 * We don't do anything else here.
+		 */
+		return consumed;
 	}
+
+	/*
+	 * This is the second pass - if there's a protocol tree to be
+	 * built, we put stuff into it, otherwise we just return.
+	 */
 	if (bp_tree == NULL) {
 		/* Don't put anything in the protocol tree. */
 		return consumed;
@@ -443,7 +478,8 @@ bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff)
 
 	case 43:	/* Vendor-Specific Info */
 		/* PXE protocol 2.1 as described in the intel specs */
-		if (strncmp(vendor_class_id, "PXEClient", strlen("PXEClient")) == 0) {
+		if (*vendor_class_id_p != NULL &&
+		    strncmp(*vendor_class_id_p, "PXEClient", strlen("PXEClient")) == 0) {
 			vti = proto_tree_add_text(bp_tree, tvb, voff,
 				consumed, "Option %d: %s (PXEClient)", code, text);
 			v_tree = proto_item_add_subtree(vti, ett_bootp_option);
@@ -489,11 +525,10 @@ bootp_option(tvbuff_t *tvb, proto_tree *bp_tree, int voff, int eoff)
 		break;
 
 	case 60:	/* Vendor class identifier */
-                        proto_tree_add_text(bp_tree, tvb, voff, consumed,
-                                        "Option %d: %s = \"%.*s\"", code, text,
-vlen,
-                                        tvb_get_ptr(tvb, voff+2, consumed-2));
-                        break;
+		proto_tree_add_text(bp_tree, tvb, voff, consumed,
+			"Option %d: %s = \"%.*s\"", code, text, vlen,
+			tvb_get_ptr(tvb, voff+2, consumed-2));
+		break;
 
 	case 61:	/* Client Identifier */
 		/* We *MAY* use hwtype/hwaddr. If we have 7 bytes, I'll
@@ -966,10 +1001,10 @@ dissect_bootp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 	guint8		op;
 	guint8		htype, hlen;
 	const guint8	*haddr;
-	int		voff, eoff, tmpvoff; /* vender offset, end offset */
+	int		voff, eoff, tmpvoff; /* vendor offset, end offset */
 	guint32		ip_addr;
-	gboolean	is_dhcp = FALSE;
-	const char	*dhcp_type;
+	const char	*dhcp_type = NULL;
+	const guint8	*vendor_class_id = NULL;
 
 	if (check_col(pinfo->fd, COL_PROTOCOL))
 		col_set_str(pinfo->fd, COL_PROTOCOL, "BOOTP");
@@ -1090,38 +1125,49 @@ dissect_bootp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 
 	voff = 240;
 	eoff = tvb_reported_length(tvb);
+
 	/*
-	 * If we are displaying the details, we need two passes:
-	 * the first to find out about vendor specific options,
-	 * the second to do the actual decoding (option 60 is needed
-	 * to decode option 43 )
+	 * In the first pass, we just look for the DHCP message type
+	 * and Vendor class identifier options.
 	 */
 	tmpvoff = voff;
-	if (bp_tree) {
-		while (tmpvoff < eoff )
-			tmpvoff += bootp_option(tvb, 0, tmpvoff, eoff);
+	while (tmpvoff < eoff) {
+		tmpvoff += bootp_option(tvb, 0, tmpvoff, eoff, TRUE,
+		    &dhcp_type, &vendor_class_id);
+	}
+
+	/*
+	 * If there was a DHCP message type option, flag this packet
+	 * as DHCP.
+	 */
+	if (dhcp_type != NULL) {
+		/*
+		 * Yes, this is a DHCP packet, and "dhcp_type" is the
+		 * packet type.
+		 */
+		if (check_col(pinfo->fd, COL_PROTOCOL))
+			col_set_str(pinfo->fd, COL_PROTOCOL, "DHCP");
+		if (check_col(pinfo->fd, COL_INFO))
+			col_add_fstr(pinfo->fd, COL_INFO, "DHCP %-8s - Transaction ID 0x%x",
+			    dhcp_type, tvb_get_ntohl(tvb, 4));
+		if (tree)
+			proto_tree_add_boolean_hidden(bp_tree, hf_bootp_dhcp,
+			    tvb, 0, 0, 1);
 	}
+
+	/*
+	 * If we're not building the protocol tree, we don't need to
+	 * make a second pass.
+	 */
+	if (tree == NULL)
+		return;
+
+	/*
+	 * OK, now build the protocol tree.
+	 */
 	while (voff < eoff) {
-		/* Handle the DHCP option specially here, so that we
-		   can flag DHCP packets as such. */
-		if (!is_dhcp && tvb_get_guint8(tvb, voff) == 53) {
-			/*
-			 * We haven't already seen a DHCP Type option, and
-			 * this is a DHCP Type option, so flag this packet
-			 * as DHCP.
-			 */
-			dhcp_type = get_dhcp_type(tvb_get_guint8(tvb, voff+2));
-			if (check_col(pinfo->fd, COL_PROTOCOL))
-				col_set_str(pinfo->fd, COL_PROTOCOL, "DHCP");
-			if (check_col(pinfo->fd, COL_INFO))
-				col_add_fstr(pinfo->fd, COL_INFO, "DHCP %-8s - Transaction ID 0x%x",
-				    dhcp_type, tvb_get_ntohl(tvb, 4));
-			if (tree)
-				proto_tree_add_boolean_hidden(bp_tree, hf_bootp_dhcp,
-				    tvb, 0, 0, 1);
-			is_dhcp = TRUE;
-		}
-		voff += bootp_option(tvb, bp_tree, voff, eoff);
+		voff += bootp_option(tvb, bp_tree, voff, eoff, FALSE,
+		    &dhcp_type, &vendor_class_id);
 	}
 }