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