sysmobts: Clean up transitions for lchan cipher state

There are three transitions:

1. LCHAN_CIPH_NONE -> LCHAN_CIPH_RX_REQ -> LCHAN_CIPH_RX_CONF

It is used to enable ciphering in RX (uplink) direction only.

2. LCHAN_CIPH_RX_CONF -> LCHAN_CIPH_RX_CONF_TX_REQ -> LCHAN_CIPH_RXTX_CONF

It is used to additionally enable ciphering in TX (downlink) direction.

3. LCHAN_CIPH_NONE -> LCHAN_CIPH_RXTX_REQ -> LCHAN_CIPH_RX_CONF_TX_REQ
   -> LCHAN_CIPH_RXTX_CONF

It is used to enable ciphering in both TX and RX directions. This is used
when the channel is activated with encryption already enabled. (assignment
or handover)

In order to follow the order of these transitions, the RX direction must
always be set before the TX direction.

If no cipher key is set (A5/0), ciphering is set to ALG 0, but lchan cipher
state remains at LCHAN_CIPH_NONE.

4 files changed, 22 insertions, 8 deletions

diff --git a/include/osmo-bts/gsm_data.h b/include/osmo-bts/gsm_data.h
index f2f7ee74..b5dc25fa 100644
--- a/include/osmo-bts/gsm_data.h
+++ b/include/osmo-bts/gsm_data.h
@@ -97,8 +97,9 @@ enum lchan_ciph_state {
 	LCHAN_CIPH_NONE,
 	LCHAN_CIPH_RX_REQ,
 	LCHAN_CIPH_RX_CONF,
-	LCHAN_CIPH_TXRX_REQ,
-	LCHAN_CIPH_TXRX_CONF,
+	LCHAN_CIPH_RXTX_REQ,
+	LCHAN_CIPH_RX_CONF_TX_REQ,
+	LCHAN_CIPH_RXTX_CONF,
 };
 
 #define bts_role_bts(x)	((struct gsm_bts_role_bts *)(x)->role)
diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index b9d5a2d0..d2534362 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -96,7 +96,6 @@ static int check_for_ciph_cmd(struct msgb *msg, struct gsm_lchan *lchan,
 	/* only do this if we are in the right state */
 	switch (lchan->ciph_state) {
 	case LCHAN_CIPH_NONE:
-	case LCHAN_CIPH_RX_REQ:
 		break;
 	default:
 		return 0;
diff --git a/src/osmo-bts-sysmo/l1_if.c b/src/osmo-bts-sysmo/l1_if.c
index 810ec6d4..83fe5049 100644
--- a/src/osmo-bts-sysmo/l1_if.c
+++ b/src/osmo-bts-sysmo/l1_if.c
@@ -616,8 +616,11 @@ static int mph_info_req(struct gsm_bts_trx *trx, struct msgb *msg,
 		}
 		if (l1sap->u.info.u.ciph_req.downlink) {
 			l1if_set_ciphering(fl1, lchan, 1);
-			lchan->ciph_state = LCHAN_CIPH_TXRX_REQ;
+			lchan->ciph_state = LCHAN_CIPH_RX_CONF_TX_REQ;
 		}
+		if (l1sap->u.info.u.ciph_req.downlink
+		 && l1sap->u.info.u.ciph_req.uplink)
+			lchan->ciph_state = LCHAN_CIPH_RXTX_REQ;
 		break;
 	case PRIM_INFO_ACTIVATE:
 	case PRIM_INFO_DEACTIVATE:
diff --git a/src/osmo-bts-sysmo/oml.c b/src/osmo-bts-sysmo/oml.c
index 8c701642..c5810898 100644
--- a/src/osmo-bts-sysmo/oml.c
+++ b/src/osmo-bts-sysmo/oml.c
@@ -1004,8 +1004,12 @@ static int sapi_activate_cb(struct gsm_lchan *lchan, int status)
 	mph_info_chan_confirm(lchan, PRIM_INFO_ACTIVATE, 0);
 
 	/* set the initial ciphering parameters for both directions */
-	l1if_set_ciphering(fl1h, lchan, 0);
 	l1if_set_ciphering(fl1h, lchan, 1);
+	l1if_set_ciphering(fl1h, lchan, 0);
+	if (lchan->encr.alg_id)
+		lchan->ciph_state = LCHAN_CIPH_RXTX_REQ;
+	else
+		lchan->ciph_state = LCHAN_CIPH_NONE;
 
 	return 0;
 }
@@ -1154,9 +1158,16 @@ static int chmod_modif_compl_cb(struct gsm_bts_trx *trx, struct msgb *l1_msg,
 			LOGPC(DL1C, LOGL_INFO, "RX_REQ -> RX_CONF\n");
 			lchan->ciph_state = LCHAN_CIPH_RX_CONF;
 			break;
-		case LCHAN_CIPH_TXRX_REQ:
-			LOGPC(DL1C, LOGL_INFO, "TX_REQ -> TX_CONF\n");
-			lchan->ciph_state = LCHAN_CIPH_TXRX_CONF;
+		case LCHAN_CIPH_RX_CONF_TX_REQ:
+			LOGPC(DL1C, LOGL_INFO, "RX_CONF_TX_REQ -> RXTX_CONF\n");
+			lchan->ciph_state = LCHAN_CIPH_RXTX_CONF;
+			break;
+		case LCHAN_CIPH_RXTX_REQ:
+			LOGPC(DL1C, LOGL_INFO, "RXTX_REQ -> RX_CONF_TX_REQ\n");
+			lchan->ciph_state = LCHAN_CIPH_RX_CONF_TX_REQ;
+			break;
+		case LCHAN_CIPH_NONE:
+			LOGPC(DL1C, LOGL_INFO, "\n");
 			break;
 		default:
 			LOGPC(DL1C, LOGL_INFO, "unhandled state %u\n", lchan->ciph_state);