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USSD: fix handling of ussd-DataCodingScheme != 0x0f 

The usual Data Coding Scheme value in the mobile-originated USSD
request (processUnstructuredSS-Request) is 0x0f, which means:

  0000 .... = Coding Group: Coding Group 0 (Language using the GSM 7 bit default alphabet)
  .... 1111 = Language: unspecified

However some modems are known to use a different default value, if
not specified explicitly (AT+CUSD has optional DCS parameter):

  0000 .... = Coding Group: Coding Group 0 (Language using the GSM 7 bit default alphabet)
  .... 0000 = Language: German (0)

In function rx_proc_ss_req(), we should not be using req.ussd_text,
because this field has been deprecated and may contain unexpected
data.  For example, in the abovementioned case it would contain the
7 bit encoded ussd-String 'aa510c061b01'O and osmo-hlr would indeed
fail to find a matching route for a non-ASCII string.

Instead of relaying on gsm0480_parse_facility_ie(), let's check the
Data Coding Scheme value and decode the request string ourselves.
Expect the Coding Group 0, but be more tolerant to the indicated
language: print a warning and treat it as '1111'B (unspecified).

Change-Id: Ib7bac660b1a7942adcfbe7b14f162c95061a25db
Related: OS#6075
This commit is contained in:
Vadim Yanitskiy 2023-06-28 19:07:49 +07:00 committed by fixeria
parent f8b73f0682
commit 5800f3add5
1 changed files with 33 additions and 2 deletions
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35
src/hlr_ussd.c
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@ -122,9 +122,40 @@ void ussd_route_del(struct hlr_ussd_route *rt)
talloc_free(rt);
}
static struct hlr_ussd_route *ussd_route_lookup_7bit(struct hlr *hlr, const char *ussd_code)
static struct hlr_ussd_route *ussd_route_lookup_for_req(struct hlr *hlr, const struct ss_request *req)
{
const uint8_t cgroup = req->ussd_data_dcs >> 4;
const uint8_t lang = req->ussd_data_dcs & 0x0f;
char ussd_code[GSM0480_USSD_7BIT_STRING_LEN];
struct hlr_ussd_route *rt;
ussd_code[0] = '\0';
/* We support only the Coding Group 0 (GSM 7-bit default alphabeet). In fact,
* the USSD request is usually limited to [*#0-9], so we don't really need to
* support other coding groups and languages. */
switch (cgroup) {
case 0:
/* The Language is usually set to '1111'B (unspecified), but some UEs
* are known to indicate '0000'B (German). */
if (lang != 0x0f) {
LOGP(DSS, LOGL_NOTICE, "USSD DataCodingScheme (0x%02x): "
"the Language is usually set to 15 (unspecified), "
"but the request indicates %u - ignoring this\n",
req->ussd_data_dcs, lang);
/* do not abort, attempt to decode as if it was '1111'B */
}
gsm_7bit_decode_n_ussd(&ussd_code[0], sizeof(ussd_code),
req->ussd_data, (req->ussd_data_len * 8) / 7);
break;
default:
LOGP(DSS, LOGL_ERROR, "USSD DataCodingScheme (0x%02x): "
"Coding Group %u is not supported, expecting Coding Group 0\n",
req->ussd_data_dcs, cgroup);
return NULL;
}
llist_for_each_entry(rt, &hlr->ussd_routes, list) {
if (!strncmp(ussd_code, rt->prefix, strlen(rt->prefix))) {
LOGP(DSS, LOGL_DEBUG, "Found %s '%s' (prefix '%s') for USSD "
@ -603,7 +634,7 @@ void rx_proc_ss_req(struct osmo_gsup_req *gsup_req)
} else {
/* VLR->EUSE: MO USSD. VLR is known ('conn'), EUSE is to be resolved */
struct hlr_ussd_route *rt;
rt = ussd_route_lookup_7bit(hlr, (const char *) req.ussd_text);
rt = ussd_route_lookup_for_req(hlr, &req);
if (rt) {
if (rt->is_external) {
ss->is_external = true;