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MP2T: Detect stuffing bytes after SECTs when PUSI is 0 

When the payload_unit_start_indicator is 0, a continued section may be
followed by stuffing bytes. Detect the stuffing bytes based on the SECT
length and handle them in the MPEG2 TS dissector in that case, rather than
handing them to the SECT dissector (which assumes that the incoming tvb
contains only one section and no additional data), similar to how stuffing
bytes are already handled when the PUSI is 1.
This commit is contained in:
John Thacker 2021-03-07 15:06:15 -05:00 committed by Wireshark GitLab Utility
parent 31dc280d25
commit b3e55ba4b7
1 changed files with 41 additions and 1 deletions
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42
epan/dissectors/packet-mp2t.c
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@ -599,6 +599,34 @@ mp2t_fragment_handle(tvbuff_t *tvb, guint offset, packet_info *pinfo,
* For PES and PSI, see ISO/IEC 13818-1 / ITU-T Rec. H.222.0 (05/2006),
* section 2.4.3.3 "Semantic definition of fields in Transport Stream packet
* layer", which says much the same thing.
*
* When the payload is PES packet data, note that there is no pointer_field;
* if the PUSI is 1 then the TS payload "will commence with the first byte
* of a PES packet" and "one and only one PES packet starts in this Transport
* Stream packet". Furthermore, section 2.4.3.5 "Semantic definition of
* fields in adaptation field" mentions that stuffing in an adaptation field
* is "the only method of stuffing allowed for Transport Stream packets
* carrying PES packets." Thus stuff_bytes is not relevant for MPEG-TS payloads
* carrying PES. (It is possible to have stuffing *inside* the PES packet,
* as seen in section 2.4.3.6 "PES packet" and 2.4.3.7 "Semantic definition
* of fields in PES packet", which is handled in the MPEG PES dissector.)
*
* For MPEG-TS packets carrying PSI (which includes private data sections), an
* alternative stuffing method is allowed. This method involves stuff bytes
* at the end of a MPEG-TS packet after the last section contained within
* (similar to the stuff_bytes that may appear after a continued section
* before the byte referenced by pointer_field). According to Section 2.4.4
* "Program specific information", once a packet stuffing byte 0xFF appears,
* "all bytes until the end of the Transport Stream packet shall also be
* stuffing bytes of value 0xFF." In other words, as section C.3 "The Mapping
* of Sections into Transport Stream Packets" elaborates, while multiple
* entire sections are allowed within a TS packet, "no gaps between sections
* within a Transport Stream packet are allowed by the syntax".
*
* However, this function is permissive in what it accepts to the extent
* possible; it will allow multiple PES packets in the same TS packet and
* stuffing bytes to follow PES packets (at least those that indicate their
* length) and will allow stuffing bytes between complete PSI sections.
*/
static void
mp2t_process_fragmented_payload(tvbuff_t *tvb, gint offset, guint remaining_len, packet_info *pinfo,
@ -809,7 +837,19 @@ mp2t_process_fragmented_payload(tvbuff_t *tvb, gint offset, guint remaining_len,
/* There are remaining bytes. Add them to the fragment list */
if ((frag_tot_len && frag_cur_pos + remaining_len >= frag_tot_len) || (!frag_tot_len && pusi_flag)) {
if (frag_tot_len && frag_cur_pos + remaining_len > frag_tot_len) {
/* The case where PUSI was 0, a continuing SECT ended, and stuff
* bytes follow. */
stuff_len = frag_cur_pos + remaining_len - frag_tot_len;
mp2t_fragment_handle(tvb, offset, pinfo, tree, frag_id, frag_cur_pos, remaining_len - stuff_len, TRUE, pid_analysis->pload_type);
offset += remaining_len - stuff_len;
frag_id++;
fragmentation = FALSE;
frag_cur_pos = 0;
frag_tot_len = 0;
stuff_tree = proto_tree_add_subtree_format(tree, tvb, offset, stuff_len, ett_stuff, NULL, "Stuffing");
proto_tree_add_item(stuff_tree, hf_mp2t_stuff_bytes, tvb, offset, stuff_len, ENC_NA);
} else if ((frag_tot_len && frag_cur_pos + remaining_len == frag_tot_len) || (!frag_tot_len && pusi_flag)) {
mp2t_fragment_handle(tvb, offset, pinfo, tree, frag_id, frag_cur_pos, remaining_len, TRUE, pid_analysis->pload_type);
frag_id++;
fragmentation = FALSE;