Wireshark · Wireshark-commits: [Wireshark-commits] master-2.4 5222e5f: rsl: Fix treatment of SACCH FILL / SACCH INFO MODIFY

[Wireshark code review <code-review-do-not-reply@xxxxxxxxxxxxx>]

URL: https://code.wireshark.org/review/gitweb?p=wireshark.git;a=commit;h=5222e5f95cbddd87b04a812b0cc1aece7941a5ca
Submitter: Pascal Quantin (pascal.quantin@xxxxxxxxx)
Changed: branch: master-2.4
Repository: wireshark

Commits:

5222e5f by Harald Welte (laforge@xxxxxxxxxxxx):

    rsl: Fix treatment of SACCH FILL / SACCH INFO MODIFY
    
    The RSL SACCH INFO MODIFY / RSL SACCH FILL messages contain a
    SI5 / SI6 / SI5bis / SI5ter message.  Those SI are (like the SI on CCCH)
    sent as UI frame in downlink direction.  Since Phase 2, the "L2
    pseudo-length field is part of the L3 message, and not stripped /
    interpreted at L2.
    
    3GPP TS 44.006 states that a special B4 frame format is used on the
    SACCH downlink for UI frames, which is basically a normal B frame, but
    with no length field at L2, shifting the length field into L3 where it
    becomes the L2 pseudo-length.
    
    From RSL, we need to call a variant of the RR dissector that is able to
    decode a L3 message that includes a L2 pseudo-length.  This is,
    paradoxically, not the "gsm_a_sacch" dissector, as that one is only used
    for B-frames, i.e. actual LAPDm ABM frames.  We must use the "gsm_a_ccch"
    dissector.
    
    See also the discussion in
    https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=14105
    as well as https://lists.osmocom.org/pipermail/openbsc/2017-December/011545.html
    and https://osmocom.org/issues/3059 for further background information.
    
    Ping-Bug: 14105
    Change-Id: Icdad2b7698d5d7d613cacceec6a3d848b946306c
    Reviewed-on: https://code.wireshark.org/review/26797
    Reviewed-by: Pascal Quantin <pascal.quantin@xxxxxxxxx>
    Petri-Dish: Pascal Quantin <pascal.quantin@xxxxxxxxx>
    Tested-by: Petri Dish Buildbot
    Reviewed-by: Anders Broman <a.broman58@xxxxxxxxx>
    (cherry picked from commit 91e0de19c921b91401421b06bd2b90cdbe1c7166)
    Reviewed-on: https://code.wireshark.org/review/26982
    

Actions performed:

    from  4feafbb   [Automatic update for 2018-04-15]
    adds  5222e5f   rsl: Fix treatment of SACCH FILL / SACCH INFO MODIFY


Summary of changes:
 epan/dissectors/packet-rsl.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)