1 files changed, 138 insertions, 0 deletions
diff --git a/epan/dissectors/packet-ieee8023.c b/epan/dissectors/packet-ieee8023.c
new file mode 100644
index 00000000..626df268
--- /dev/null
+++ b/epan/dissectors/packet-ieee8023.c
@@ -0,0 +1,138 @@
+/* packet-ieee8023.c
+ * Routine for dissecting Ethernet packets with a length field (as opposed
+ * to a type field).
+ *
+ * The name "ieee8023" is historical, dating back to when IEEE Std 802.3
+ * had only a length field and expected all packets to have an 802.2
+ * header following the MAC header.  Since IEEE 802.3y-1997, 802.3
+ * supports either a type field or a length field, so it's no longer
+ * correct to refer to "802.3" vs. "D/I/X" or vs. "Ethernet II" frames.
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "config.h"
+
+#include <epan/packet.h>
+#include <epan/exceptions.h>
+#include <epan/expert.h>
+#include <epan/show_exception.h>
+#include "packet-ieee8023.h"
+#include "packet-eth.h"
+
+void proto_reg_handoff_ieee802_3(void);
+
+static dissector_handle_t ipx_handle;
+static dissector_handle_t llc_handle;
+static dissector_handle_t ccsds_handle;
+
+void
+dissect_802_3(volatile int length, gboolean is_802_2, tvbuff_t *tvb,
+              int offset_after_length, packet_info *pinfo, proto_tree *tree,
+              proto_tree *fh_tree, int length_id, int trailer_id, expert_field* ei_len,
+              int fcs_len)
+{
+  proto_item *length_it;
+  tvbuff_t   *volatile next_tvb = NULL;
+  tvbuff_t   *trailer_tvb = NULL;
+  const char *saved_proto;
+  gint        captured_length, reported_length;
+
+  length_it = proto_tree_add_uint(fh_tree, length_id, tvb,
+                                  offset_after_length - 2, 2, length);
+
+  /* Get the length of the payload.
+     If the FCS length is positive, remove the FCS.
+     (If it's zero, there's no FCS; if it's negative, we don't know whether
+     there's an FCS, so we'll guess based on the length of the trailer.) */
+  reported_length = tvb_reported_length_remaining(tvb, offset_after_length);
+  if (fcs_len > 0) {
+    if (reported_length >= fcs_len)
+      reported_length -= fcs_len;
+  }
+
+  /* Make sure the length in the 802.3 header doesn't go past the end of
+     the payload. */
+  if (length > reported_length) {
+    length = reported_length;
+    expert_add_info(pinfo, length_it, ei_len);
+  }
+
+  /* Give the next dissector only 'length' number of bytes. */
+  captured_length = tvb_captured_length_remaining(tvb, offset_after_length);
+  if (captured_length > length)
+    captured_length = length;
+  next_tvb = tvb_new_subset_length_caplen(tvb, offset_after_length, captured_length, length);
+
+  /* Dissect the payload either as IPX or as an LLC frame.
+     Catch non-fatal exceptions, so that if the 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 {
+    if (is_802_2)
+      call_dissector(llc_handle, next_tvb, pinfo, tree);
+    else {
+      /* Check if first three bits of payload are 0x7.
+         If so, then payload is IPX.  If not, then it's CCSDS.
+         Refer to packet-eth.c for setting of is_802_2 variable. */
+      if (tvb_get_bits8(next_tvb, 0, 3) == 7)
+        call_dissector(ipx_handle, next_tvb, pinfo, tree);
+      else
+        call_dissector(ccsds_handle, next_tvb, pinfo, tree);
+    }
+  }
+  CATCH_NONFATAL_ERRORS {
+    /* Somebody threw an exception that means that there was a problem
+       dissecting the payload; that means that a dissector was found,
+       so we don't need to dissect the payload as data or update the
+       protocol or info columns.
+
+       Just show the exception and then drive on to show the trailer,
+       after noting that a dissector was found and restoring the
+       protocol value that was in effect before we called the subdissector. */
+    show_exception(next_tvb, pinfo, tree, EXCEPT_CODE, GET_MESSAGE);
+  }
+  ENDTRY;
+
+  /* Restore the protocol value, so that any exception thrown by
+     tvb_new_subset_remaining() refers to the protocol for which
+     this is a trailer. */
+  pinfo->current_proto = saved_proto;
+
+  /* Construct a tvbuff for the trailer; if the trailer is past the
+     end of the captured data, this will throw a BoundsError, which
+     is what we want, as it'll report that the packet was cut short. */
+  trailer_tvb = tvb_new_subset_remaining(tvb, offset_after_length + length);
+
+  add_ethernet_trailer(pinfo, tree, fh_tree, trailer_id, tvb, trailer_tvb, fcs_len);
+}
+
+void
+proto_reg_handoff_ieee802_3(void)
+{
+  /*
+   * Get handles for the subdissectors.
+   */
+  ipx_handle = find_dissector("ipx");
+  llc_handle = find_dissector("llc");
+  ccsds_handle = find_dissector("ccsds");
+}
+
+/*
+ * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
+ *
+ * Local Variables:
+ * c-basic-offset: 2
+ * tab-width: 8
+ * indent-tabs-mode: nil
+ * End:
+ *
+ * ex: set shiftwidth=2 tabstop=8 expandtab:
+ * :indentSize=2:tabSize=8:noTabs=true:
+ */