osmo_auth_gen_vec: UMTS auth: store last used SQN, not next

Prepare for the implementation of splitting SQN increments in SEQ and an IND
part; particularly to clearly show where the changes in auth/milenage_test's
expectations originate.

Rationale: the source of UMTS auth vectors, for us usually OsmoHLR, typically
stores the last used SQN, not the next one to be used. Particularly with the
upcoming fix of the SQN scheme, this change is important: the next SQN will
depend on which entity asks for it, because each auth consumer may have a
particular slot in the IND part of SQN. It does not make sense to store the
next SQN, because we will not know which consumer that will be for.

The milenage_test has always calculated a tuple for SQN == 34. To account for
the increment now happening before calculating a tuple, lower the test_aud->sqn
by one to 0x21 == 33, so that it is still calculating for SQN == 34.

Because we are no longer incrementing SQN after the tuple is generated,
milenage_test's expected output after doing an AUTS resync to 31 changes to the
next SQN = 32, the SQN used for the generated tuple.

(BTW, a subsequent patch will illustrate AUTS in detail.)

osmo-auc-gen now needs to pass the user requested SQN less one, because the SQN
will be incremented befor generating the auth vector. Also the SQN remains the
same after generating, so SQN output needs less decrementing. Note that the
expected output for osmo-auc-gen_test remains unchanged, hence the same input
arguments (particularly -s <sqn> and -A <auts>) still produce the same results.

Note: osmo-hlr regression tests will require adjustments when this patch is
merged, because it must now pass desired_sqn - 1 instead of just desired_sqn.
See osmo-hlr change-id I4ec5a578537acb1d9e1ebfe00a72417fc3ca5894 .

Related: OS#1968
Change-Id: Iadf43f21e0605e9e85f7e8026c40985f7ceff1a3

1 files changed, 9 insertions, 3 deletions

diff --git a/src/gsm/auth_milenage.c b/src/gsm/auth_milenage.c
index 1635ac6b..e1807621 100644
--- a/src/gsm/auth_milenage.c
+++ b/src/gsm/auth_milenage.c
@@ -30,10 +30,14 @@ static int milenage_gen_vec(struct osmo_auth_vector *vec,
 			    const uint8_t *_rand)
 {
 	size_t res_len = sizeof(vec->res);
+	uint64_t next_sqn;
 	uint8_t sqn[6];
 	int rc;
 
-	osmo_store64be_ext(aud->u.umts.sqn, sqn, 6);
+	/* keep the incremented SQN local until gsm_milenage() succeeded. */
+	next_sqn = aud->u.umts.sqn + 1;
+
+	osmo_store64be_ext(next_sqn, sqn, 6);
 	milenage_generate(aud->u.umts.opc, aud->u.umts.amf, aud->u.umts.k,
 			  sqn, _rand,
 			  vec->autn, vec->ik, vec->ck, vec->res, &res_len);
@@ -43,7 +47,9 @@ static int milenage_gen_vec(struct osmo_auth_vector *vec,
 		return rc;
 
 	vec->auth_types = OSMO_AUTH_TYPE_UMTS | OSMO_AUTH_TYPE_GSM;
-	aud->u.umts.sqn++;
+
+	/* for storage in the caller's AUC database */
+	aud->u.umts.sqn = next_sqn;
 
 	return 0;
 }
@@ -72,7 +78,7 @@ static int milenage_gen_vec_auts(struct osmo_auth_vector *vec,
 	if (rc < 0)
 		return rc;
 
-	aud->u.umts.sqn = 1 + (osmo_load64be_ext(sqn_out, 6) >> 16);
+	aud->u.umts.sqn = osmo_load64be_ext(sqn_out, 6) >> 16;
 
 	return milenage_gen_vec(vec, aud, _rand);
 }