Sometimes Ethernet captures include an FCS at the end of the packet.

An Ethernet trailer is only needed to pad the packet to 60 bytes of
Ethernet header plus payload; if the packet has what appears to be a
trailer, and it's 4 or more bytes (i.e., long enough to include an FCS),
and the Ethernet frame was claimed to have 64 or more bytes (i.e., it
has at least an FCS worth of data more than the minimum 60 bytes),
assume that the last 4 bytes of the frame were an FCS.

svn path=/trunk/; revision=8207

1 files changed, 24 insertions, 19 deletions

diff --git a/packet-ethertype.c b/packet-ethertype.c
index 87bc4faf7c..89642bbc1f 100644
--- a/packet-ethertype.c
+++ b/packet-ethertype.c
@@ -1,7 +1,7 @@
 /* ethertype.c
  * Routines for calling the right protocol for the ethertype.
  *
- * $Id: packet-ethertype.c,v 1.36 2003/06/11 09:17:00 guy Exp $
+ * $Id: packet-ethertype.c,v 1.37 2003/08/21 21:05:29 guy Exp $
  *
  * Gilbert Ramirez <gram@alumni.rice.edu>
  *
@@ -30,6 +30,7 @@
 
 #include <glib.h>
 #include <epan/packet.h>
+#include "packet-eth.h"
 #include "packet-ip.h"
 #include "packet-ipv6.h"
 #include "packet-ipx.h"
@@ -101,7 +102,7 @@ const value_string etype_vals[] = {
     {PPP_CCP,			"PPP Compression Control Protocol" },
     {0,				NULL				} };
 
-static void add_trailer(proto_tree *fh_tree, int trailer_id, tvbuff_t *tvb,
+static void add_dix_trailer(proto_tree *fh_tree, int trailer_id, tvbuff_t *tvb,
     tvbuff_t *next_tvb, int offset_after_etype, guint length_before);
 
 void
@@ -143,8 +144,9 @@ ethertype(guint16 etype, tvbuff_t *tvb, int offset_after_etype,
 	tvbuff_t		*next_tvb;
 	guint			length_before;
 	volatile gboolean	dissector_found;
+	const char		*saved_proto, *exception_proto;
 
-	/* Add to proto_tree */
+	/* Add the Ethernet type to the protocol tree */
 	if (tree) {
 		proto_tree_add_uint(fh_tree, etype_id, tvb,
 		    offset_after_etype - 2, 2, etype);
@@ -163,6 +165,7 @@ ethertype(guint16 etype, tvbuff_t *tvb, int offset_after_etype,
 	   reported length of "next_tvb" was reduced by some dissector
 	   before an exception was thrown, we can still put in an item
 	   for the trailer. */
+	saved_proto = pinfo->current_proto;
 	TRY {
 		dissector_found = dissector_try_port(ethertype_dissector_table,
 		    etype, next_tvb, pinfo, tree);
@@ -174,12 +177,24 @@ ethertype(guint16 etype, tvbuff_t *tvb, int offset_after_etype,
 		   columns. */
 		dissector_found = TRUE;
 
+		/* Save the protocol for which the exception was
+		   thrown, and restore pinfo->current_proto to the
+		   one for us, so if we throw an exception adding
+		   the trailer (e.g., if we get an FCS when capturing,
+		   but the snapshot length cut off the FCS), the
+		   exception will reflect the appropriate protocol. */
+		exception_proto = pinfo->current_proto;
+		pinfo->current_proto = saved_proto;
+
 		/* Add the trailer, if appropriate. */
-		add_trailer(fh_tree, trailer_id, tvb, next_tvb,
+		add_dix_trailer(fh_tree, trailer_id, tvb, next_tvb,
 		    offset_after_etype, length_before);
 
-		/* Rrethrow the exception, so the "Short Frame" or "Mangled
-		   Frame" indication can be put into the tree. */
+		/* Put back the protocol for which the exception is
+		   thrown, and rethrow the exception, so the
+		   appropriate indication for the exception can be
+		   put into the tree. */
+		pinfo->current_proto = exception_proto;
 		RETHROW;
 
 		/* XXX - RETHROW shouldn't return. */
@@ -217,12 +232,12 @@ ethertype(guint16 etype, tvbuff_t *tvb, int offset_after_etype,
 		}
 	}
 
-	add_trailer(fh_tree, trailer_id, tvb, next_tvb, offset_after_etype,
+	add_dix_trailer(fh_tree, trailer_id, tvb, next_tvb, offset_after_etype,
 	    length_before);
 }
 
 static void
-add_trailer(proto_tree *fh_tree, int trailer_id, tvbuff_t *tvb,
+add_dix_trailer(proto_tree *fh_tree, int trailer_id, tvbuff_t *tvb,
     tvbuff_t *next_tvb, int offset_after_etype, guint length_before)
 {
 	guint		length;
@@ -256,17 +271,7 @@ add_trailer(proto_tree *fh_tree, int trailer_id, tvbuff_t *tvb,
 	} else
 		trailer_tvb = NULL;	/* no trailer */
 
-	/* If there's some bytes left over, and we were given an item ID
-	   for a trailer, mark those bytes as a trailer. */
-	if (trailer_tvb) {
-		guint	trailer_length;
-
-		trailer_length = tvb_length(trailer_tvb);
-		if (trailer_length != 0) {
-			proto_tree_add_item(fh_tree, trailer_id, trailer_tvb, 0,
-			    trailer_length, FALSE);
-		}
-	}
+	add_ethernet_trailer(fh_tree, trailer_id, tvb, trailer_tvb);
 }