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MSC: Intersect configured A5 algorithms with MS-supported ones 

There's no point of ever asking a MS to perform ciphering using an
algorithm it advertises no support for.  Let's hence use CLASSMARK
information to figure out the intersection between MSC policy (VTY
command) and MS-reported CLASSMARK.

Change-Id: Id124923ee52a357cb7d3e04d33f585214774f3a3
This commit is contained in:
Harald Welte 2017-12-23 19:59:02 +01:00
parent 7b222aa106
commit 71330720b6
1 changed files with 65 additions and 1 deletions
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66
src/libmsc/gsm_04_08.c
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@ -89,6 +89,62 @@ struct gsm_lai {
static uint32_t new_callref = 0x80000001;
/* Determine if the given CLASSMARK (1/2/3) value permits a given A5/n cipher */
static bool classmark_supports_a5(const struct gsm_classmark *cm, uint8_t a5)
{
switch (a5) {
case 0:
/* all phones must implement A5/0, see 3GPP TS 43.020 4.9 */
return true;
case 1:
/* 3GPP TS 43.020 4.9 requires A5/1 to be suppored by all phones and actually states:
* "The network shall not provide service to an MS which indicates that it does not
* support the ciphering algorithm A5/1.". However, let's be more tolerant based
* on policy here */
/* See 3GPP TS 24.008 10.5.1.7 */
if (!cm->classmark1_set) {
DEBUGP(DMSC, "CLASSMARK 1 unknown, assuming MS supports A5/1\n");
return true;
} else {
if (cm->classmark1.a5_1)
return false; /* Inverted logic for this bit! */
else
return true;
}
break;
case 2:
case 3:
/* See 3GPP TS 24.008 10.5.1.6 */
if (cm->classmark2_len < 3) {
DEBUGP(DMSC, "CLASSMARK 2 unknown, assuming MS doesn't support A5/%u\n", a5);
return false;
} else {
if (cm->classmark2[2] & (1 << (a5-2)))
return true;
else
return false;
}
break;
case 4:
case 5:
case 6:
case 7:
/* See 3GPP TS 24.008 10.5.1.7 */
if (cm->classmark3_len < 1) {
DEBUGP(DMSC, "CLASSMARK 3 unknown, assuming MS doesn't support A5/%u\n", a5);
return false;
} else {
if (cm->classmark3[0] & (1 << (a5-4)))
return true;
else
return false;
}
break;
default:
return false;
}
}
void cc_tx_to_mncc(struct gsm_network *net, struct msgb *msg)
{
net->mncc_recv(net, msg);
@ -3452,11 +3508,19 @@ static int msc_vlr_set_ciph_mode(void *msc_conn_ref,
int i, j = 0;
for (i = 0; i < 8; i++) {
if (net->a5_encryption_mask & (1 << i))
if (net->a5_encryption_mask & (1 << i) &&
classmark_supports_a5(&conn->classmark, i))
ei.perm_algo[j++] = vlr_ciph_to_gsm0808_alg_id(i);
}
ei.perm_algo_len = j;
if (ei.perm_algo_len == 0) {
LOGP(DMM, LOGL_ERROR, "%s: cannot start ciphering, no intersection "
"between MSC-configured and MS-supported A5 algorithms\n",
vlr_subscr_name(conn->vsub));
return -ENOTSUP;
}
/* In case of UMTS AKA, the Kc for ciphering must be derived from the 3G auth
* tokens. tuple->vec.kc was calculated from the GSM algorithm and is not
* necessarily a match for the UMTS AKA tokens. */