static void
add_dix_trailer(packet_info *pinfo, proto_tree *tree, proto_tree *fh_tree, int trailer_id,
tvbuff_t *tvb, tvbuff_t *next_tvb, int offset_after_etype,
guint length_before, gint fcs_len)
{
guint length;
tvbuff_t *trailer_tvb;
/* OK, how much is there in that tvbuff now? */
length = tvb_reported_length(next_tvb);
/* If there's less than there was before, what's left is
a trailer. */
if (length < length_before) {
/*
* Is any of the padding present in the tvbuff?
*/
if (tvb_offset_exists(tvb, offset_after_etype + length)) {
/*
* Yes - create a tvbuff for the padding.
*/
trailer_tvb = tvb_new_subset_remaining(tvb,
offset_after_etype + length);
} else {
/*
* No - don't bother showing the trailer.
* XXX - show a Short Frame indication?
*/
trailer_tvb = NULL;
}
} else
trailer_tvb = NULL; /* no trailer */
add_ethernet_trailer(pinfo, tree, fh_tree, trailer_id, tvb, trailer_tvb, fcs_len);
}
/* Called for the Ethernet Wiretap encapsulation type; pass the FCS length
reported to us, or, if the "assume_fcs" preference is set, pass 4. */
static void
dissect_eth_maybefcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
proto_tree *fh_tree;
/* Some devices slice the packet and add their own trailer before
putting the frame on the network. Make sure these packets get
a proper trailer (even though the sliced frame might not
properly dissect. */
if ( (eth_trailer_length > 0) && (eth_trailer_length < tvb_length(tvb)) ) {
tvbuff_t *next_tvb;
guint total_trailer_length;
total_trailer_length = eth_trailer_length + (eth_assume_fcs ? 4 : 0);
/* Dissect the tvb up to, but not including the trailer */
next_tvb = tvb_new_subset(tvb, 0,
tvb_length(tvb) - total_trailer_length,
tvb_reported_length(tvb) - total_trailer_length);
fh_tree = dissect_eth_common(next_tvb, pinfo, tree, 0);
/* Now handle the ethernet trailer and optional FCS */
next_tvb = tvb_new_subset_remaining(tvb, tvb_length(tvb) - total_trailer_length);
add_ethernet_trailer(pinfo, tree, fh_tree, hf_eth_trailer, tvb, next_tvb,
eth_assume_fcs ? 4 : pinfo->pseudo_header->eth.fcs_len);
} else {
dissect_eth_common(tvb, pinfo, tree, eth_assume_fcs ? 4 : pinfo->pseudo_header->eth.fcs_len);
}
}
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;
void *pd_save;
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(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;
pd_save = pinfo->private_data;
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. */
pinfo->private_data = pd_save;
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, and restore the private_data structure in
case one of the called dissectors modified it. */
pinfo->private_data = pd_save;
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
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,
int fcs_len)
{
proto_item *length_it;
tvbuff_t *volatile next_tvb = NULL;
tvbuff_t *volatile 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_format(pinfo, length_it, PI_MALFORMED, PI_ERROR,
"Length field value goes past the end of the payload");
}
/* Give the next dissector only 'length' number of bytes. */
captured_length = tvb_length_remaining(tvb, offset_after_length);
if (captured_length > length)
captured_length = length;
next_tvb = tvb_new_subset(tvb, offset_after_length, captured_length, length);
TRY {
trailer_tvb = tvb_new_subset_remaining(tvb, offset_after_length + length);
}
CATCH2(BoundsError, ReportedBoundsError) {
/* The packet has exactly "length" bytes worth of captured data
left in it, so the "tvb_new_subset()" creating "trailer_tvb"
threw an exception.
This means that all the data in the frame is within the length
value (assuming our offset isn't past the end of the tvb), so
we give all the data to the next protocol and have no trailer. */
trailer_tvb = NULL;
}
ENDTRY;
/* Dissect the payload either as IPX or as an LLC frame.
Catch BoundsError and ReportedBoundsError, 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(BoundsError) {
/* Somebody threw BoundsError, which means that dissecting the payload
found that the packet was cut off by a snapshot length before the
end of the payload. The trailer comes after the payload, so *all*
of the trailer is cut off - don't bother adding the trailer, just
rethrow the exception so it gets reported. */
RETHROW;
}
CATCH_ALL {
/* Well, somebody threw an exception other than BoundsError.
Show the exception, and then drive on to show the trailer,
restoring the protocol value that was in effect before we
called the subdissector. */
show_exception(next_tvb, pinfo, tree, EXCEPT_CODE, GET_MESSAGE);
pinfo->current_proto = saved_proto;
}
ENDTRY;
add_ethernet_trailer(pinfo, fh_tree, trailer_id, tvb, trailer_tvb, fcs_len);
}