Change in osmo-pcu[master]: tests/rlcmac: fix malformed MS RA capability in testRAcap()

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fixeria gerrit-no-reply at lists.osmocom.org
Tue Feb 18 17:08:27 UTC 2020


Hello pespin, laforge, Jenkins Builder, 

I'd like you to reexamine a change. Please visit

    https://gerrit.osmocom.org/c/osmo-pcu/+/17209

to look at the new patch set (#2).

Change subject: tests/rlcmac: fix malformed MS RA capability in testRAcap()
......................................................................

tests/rlcmac: fix malformed MS RA capability in testRAcap()

Long story short: as it turns out the test vector '12a5146200'O
has been generated by TITAN, and it's malformed. The length
indicator it contains must be at least 29 bits, not 21. This
field is calculated by TITAN automatically, so I guess there
is a bug somewhere in its RAW encoder implementation.

It's funny that Wireshark decodes the old malformed vector without
any problems if it's encapsulated into the BSSGP DL-UNITDATA. The
reason for that is because BSSGP dissector does not actually use
the CSN.1 codec and relies on its own hand-written parser [1],
which does not respect the length constraints.

Furthermore, table 10.5.146/3GPP TS 24.008, describing the format
of MS Radio Access Capability IE, has the following comment:

  < Multislot capability struct > ::=
    { 0 | 1 < HSCSD multislot class : bit (5) > }
    ...
  -- error: struct too short, assume features do not exist

so ideally our CSN.1 decoder should be more tolerant to the old
malformed vector, but unfortunately error handling is not implemented.

[1] See de_gmm_ms_radio_acc_cap() in epan/dissectors/packet-gsm_a_gm.c.

Change-Id: I5f810397b8d09c18e069168023429f6a4d899c86
---
M tests/rlcmac/RLCMACTest.cpp
M tests/rlcmac/RLCMACTest.err
M tests/rlcmac/RLCMACTest.ok
3 files changed, 22 insertions(+), 13 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/09/17209/2
-- 
To view, visit https://gerrit.osmocom.org/c/osmo-pcu/+/17209
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Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: I5f810397b8d09c18e069168023429f6a4d899c86
Gerrit-Change-Number: 17209
Gerrit-PatchSet: 2
Gerrit-Owner: fixeria <axilirator at gmail.com>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <axilirator at gmail.com>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: newpatchset
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