Bluetooth: Use unresolvable private address for active scanning

When running active scanning during LE discovery, do not reveal the own
identity to the peer devices. In case LE privacy has been enabled, then
a resolvable private address is used. If the LE privacy option is off,
then use an unresolvable private address.

The public address or static random address is never used in active
scanning anymore. This ensures that scan request are send using a
random address.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

include/net/bluetooth/hci_core.h

@@ -1256,7 +1256,8 @@ void hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max,
 void hci_le_start_enc(struct hci_conn *conn, __le16 ediv, __u8 rand[8],
 							__u8 ltk[16]);
 
-int hci_update_random_address(struct hci_request *req, u8 *own_addr_type);
+int hci_update_random_address(struct hci_request *req, bool require_privacy,
+			      u8 *own_addr_type);
 
 #define SCO_AIRMODE_MASK       0x0003
 #define SCO_AIRMODE_CVSD       0x0000

net/bluetooth/hci_conn.c

@@ -563,7 +563,10 @@ static int hci_create_le_conn(struct hci_conn *conn)
 
 	memset(&cp, 0, sizeof(cp));
 
-	err = hci_update_random_address(&req, &own_addr_type);
+	/* Update random address, but set require_privacy to false so
+	 * that we never connect with an unresolvable address.
+	 */
+	err = hci_update_random_address(&req, false, &own_addr_type);
 	if (err < 0)
 		return err;
 

net/bluetooth/hci_core.c

@@ -3332,7 +3332,8 @@ static void le_scan_disable_work(struct work_struct *work)
 		BT_ERR("Disable LE scanning request failed: err %d", err);
 }
 
-int hci_update_random_address(struct hci_request *req, u8 *own_addr_type)
+int hci_update_random_address(struct hci_request *req, bool require_privacy,
+			      u8 *own_addr_type)
 {
 	struct hci_dev *hdev = req->hdev;
 	int err;
@@ -3365,6 +3366,21 @@ int hci_update_random_address(struct hci_request *req, u8 *own_addr_type)
 		return 0;
 	}
 
+	/* In case of required privacy without resolvable private address,
+	 * use an unresolvable private address. This is useful for active
+	 * scanning and non-connectable advertising.
+	 */
+	if (require_privacy) {
+		bdaddr_t urpa;
+
+		get_random_bytes(&urpa, 6);
+		urpa.b[5] &= 0x3f;	/* Clear two most significant bits */
+
+		*own_addr_type = ADDR_LE_DEV_RANDOM;
+		hci_req_add(req, HCI_OP_LE_SET_RANDOM_ADDR, 6, &urpa);
+		return 0;
+	}
+
 	/* If forcing static address is in use or there is no public
 	 * address use the static address as random address (but skip
 	 * the HCI command if the current random address is already the

net/bluetooth/mgmt.c

@@ -844,7 +844,7 @@ static void enable_advertising(struct hci_request *req)
 
 	memset(&cp, 0, sizeof(cp));
 
-	if (hci_update_random_address(req, &own_addr_type) < 0)
+	if (hci_update_random_address(req, false, &own_addr_type) < 0)
 		return;
 
 	cp.min_interval = __constant_cpu_to_le16(0x0800);
@@ -3389,7 +3389,11 @@ static int start_discovery(struct sock *sk, struct hci_dev *hdev,
 
 		memset(&param_cp, 0, sizeof(param_cp));
 
-		err = hci_update_random_address(&req, &own_addr_type);
+		/* All active scans will be done with either a resolvable
+		 * private address (when privacy feature has been enabled)
+		 * or unresolvable private address.
+		 */
+		err = hci_update_random_address(&req, true, &own_addr_type);
 		if (err < 0) {
 			err = cmd_status(sk, hdev->id, MGMT_OP_START_DISCOVERY,
 					 MGMT_STATUS_FAILED);