This is a speculative change for interrogateSS and by not answering
the request the radio connection would remain open long.
The SS/USSD code is from a time where none of knew much about GSM. We
do not support SS but should reject it. We have checked for an empty
string in the text field to guess if it is a result/release to not send
more information. The right way forward is to decode the ASN1 into the
fields REQUEST/RESULT(last).
Fix an issue and make the code worse. Assume ss_code > 0 to see if this
is a interrogate invoke. The issue is that code 0 is a well defined
value but unlikely to be used.
MAP ASN1 definition:
SS-Code ::= OCTET STRING (SIZE (1))
-- This type is used to represent the code identifying a single
-- supplementary service, a group of supplementary services, or
-- all supplementary services. The services and abbreviations
-- used are defined in TS 3GPP TS 22.004 [5]. The internal structure is
-- defined as follows:
--
-- bits 87654321: group (bits 8765), and specific service
-- (bits 4321)
allSS SS-Code ::= '00000000'B
Change-Id: Ib0dc4485388f030eb172fe21f5327b7ab94751f5
In case the unpack of a USSD request is failing the channel would
remain open and the phone would not receive a response. Simply
reject the interrogation.
Example interrogation:
0000 1b 7b 1c 0d a1 0b 02 01 01 02 01 0e 30 03 04 01
0010 11 7f 01 00
strstr() was used with wrong argument order, causing it to always match,
and causing an invalid response to a variety of different SS and USSD
requests.
This has apparently caused havoc among a number of HTC phones which
issue SS requests without user interaction upon boot, and then trip over
our inappropriate response.
Holger Hans Peter Freyther
Alexander Huemer
Harald Welte