Review at https://gerrit.osmocom.org/5560
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
---
M src/libmsc/gsm_04_08.c
1 file changed, 65 insertions(+), 1 deletion(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-msc refs/changes/60/5560/1
diff --git a/src/libmsc/gsm_04_08.c b/src/libmsc/gsm_04_08.c
index 5fd1607..95dfc14 100644
--- a/src/libmsc/gsm_04_08.c
+++ b/src/libmsc/gsm_04_08.c
@@ -98,6 +98,62 @@
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);
@@ -3421,11 +3477,19 @@
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. */
--
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Gerrit-MessageType: newchange
Gerrit-Change-Id: Id124923ee52a357cb7d3e04d33f585214774f3a3
Gerrit-PatchSet: 1
Gerrit-Project: osmo-msc
Gerrit-Branch: master
Gerrit-Owner: Harald Welte <[email protected]>
