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MP2T: Fix packet length for short packets 

Small payload packets that fit into a single TSP without
fragmentation are dissected without ever being placed in
the reassembly table, so fragment_get_reassembled_id returns
NULL even on the second pass and later. Handle them (and
distinguish that case from packets not reassembled because they
were at the end of a capture.)

Add a few comments to clarify what's going on.
This commit is contained in:
John Thacker 2021-08-18 21:35:53 -04:00 committed by Wireshark GitLab Utility
parent e490f93072
commit 7bd16e0dd9
1 changed files with 36 additions and 9 deletions
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45
epan/dissectors/packet-mp2t.c
View File

@ -546,6 +546,12 @@ mp2t_dissect_packet(tvbuff_t *tvb, enum pid_payload_type pload_type,
call_data_dissector(tvb, pinfo, tree);
}
/* Determine the length of a payload packet. If there aren't enough
* bytes to determine the length, returns -1. This will usually be
* called on the first fragment of a packet, but will be called
* on the second fragment if it returned -1 previously. (Returning
* -1 a second time indicates issues with dropped packets, etc.)
*/
static guint
mp2t_get_packet_length(tvbuff_t *tvb, guint offset, packet_info *pinfo,
guint32 frag_id, enum pid_payload_type pload_type)
@ -556,18 +562,30 @@ mp2t_get_packet_length(tvbuff_t *tvb, guint offset, packet_info *pinfo,
gint pkt_len = 0;
guint remaining_len;
stream = (mp2t_stream_key *)p_get_proto_data(pinfo->pool, pinfo, proto_mp2t, MP2T_PROTO_DATA_STREAM);
if (pinfo->fd->visited) {
frag = fragment_get_reassembled_id(&mp2t_reassembly_table, pinfo, frag_id);
if (!frag) {
/* Not reassembled on the first pass, i.e. at the end of the
* capture. We're not going to reassemble it, so just return -1.
if (frag) {
len_tvb = frag->tvb_data;
offset = 0;
} else {
/* Not reassembled on the first pass. There are two possibilities:
* 1) An entire packet contained within a TSP, so it never was
* put in the table.
* 2) Dangling fragments at the end of the capture.
*/
return -1;
frag = fragment_get(&mp2t_reassembly_table, pinfo, frag_id, stream);
if (!frag) {
/* This is the entire packet */
len_tvb = tvb;
} else {
/* Dangling packets at the end that failed to reassemble the
* first time around, so don't bother this time
*/
return -1;
}
}
len_tvb = frag->tvb_data;
offset = 0;
} else {
stream = (mp2t_stream_key *)p_get_proto_data(pinfo->pool, pinfo, proto_mp2t, MP2T_PROTO_DATA_STREAM);
frag = fragment_get(&mp2t_reassembly_table, pinfo, frag_id, stream);
if (frag)
frag = frag->next;
@ -852,14 +870,23 @@ mp2t_process_fragmented_payload(tvbuff_t *tvb, gint offset, guint remaining_len,
}
if (frag_tot_len == (guint)-1) {
/* We couldn't determine the total length of the reassembly from
* the first fragment (too short), so get it now that we have the
* second fragment.
*/
frag_tot_len = mp2t_get_packet_length(tvb, offset, pinfo, frag_id, pid_analysis->pload_type);
if (frag_tot_len == (guint)-1) {
/* We still don't have enough to determine the length; this can
* only happen with dropped or out of order packets. Bail out.
* XXX: This just skips the packet and tries the next one, but
* there are probably better ways to handle it, especially if
* the PUSI flag is set in this packet.
*/
return;
}
}
/* The beginning of a new packet is present */
if (pusi_flag) {
if (pointer > remaining_len) {
@ -909,7 +936,7 @@ mp2t_process_fragmented_payload(tvbuff_t *tvb, gint offset, guint remaining_len,
}
while (remaining_len > 0) {
/* Don't like subsequent packets overwrite the Info column */
/* Don't let subsequent packets overwrite the Info column */
col_append_str(pinfo->cinfo, COL_INFO, " ");
col_set_fence(pinfo->cinfo, COL_INFO);