Rationale behind ipa_ccm_idtag_parse_off() ?

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Harald Welte laforge at gnumonks.org
Mon Jul 30 20:03:23 UTC 2018


Hi Holger,

On Sun, Jul 29, 2018 at 12:51:47PM +0200, Harald Welte wrote:
> On Sun, Jul 29, 2018 at 11:11:13AM +0100, Holger Freyther wrote:
>
> > It seemed it was disobeying a reasonable TLV structure and the closest I found
> > back then seemed to have been this patch? Could you check if the testcase matches
> > an ipaccess-find result?
> 
> Yes, I will check for that.  The test case definitely does not match the IPA CCM
> seen inside OML/RSL from a nanoBTS, not even from the first traces I have from 2010.

I think the solution to the problem is that your test case parses the
IDENTITY REQUESET format, which has 8bit length fields, while the function
is normally (without the offset) used for the IDENTITY RESPONSE packets, where
there are 16bit length fields.

See attached pcap file that I just created.

I'll look into this once I find time and make sure we have test cases for both,
as well as fix the bug about the extraneous byte that my patch
https://gerrit.osmocom.org/#/c/libosmocore/+/10216/ attempts to fix - and which
is required to make external USSD entities in osmo-hlr work.

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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