Bluetooth: Add enhanced security model for Simple Pairing

The current security model is based around the flags AUTH, ENCRYPT and
SECURE. Starting with support for the Bluetooth 2.1 specification this is
no longer sufficient. The different security levels are now defined as
SDP, LOW, MEDIUM and SECURE.

Previously it was possible to set each security independently, but this
actually doesn't make a lot of sense. For Bluetooth the encryption depends
on a previous successful authentication. Also you can only update your
existing link key if you successfully created at least one before. And of
course the update of link keys without having proper encryption in place
is a security issue.

The new security levels from the Bluetooth 2.1 specification are now
used internally. All old settings are mapped to the new values and this
way it ensures that old applications still work. The only limitation
is that it is no longer possible to set authentication without also
enabling encryption. No application should have done this anyway since
this is actually a security issue. Without encryption the integrity of
the authentication can't be guaranteed.

As default for a new L2CAP or RFCOMM connection, the LOW security level
is used. The only exception here are the service discovery sessions on
PSM 1 where SDP level is used. To have similar security strength as with
a Bluetooth 2.0 and before combination key, the MEDIUM level should be
used. This is according to the Bluetooth specification. The MEDIUM level
will not require any kind of man-in-the-middle (MITM) protection. Only
the HIGH security level will require this.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 30 insertions, 15 deletions

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index a4a789f24c8..98f97a1e9bb 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -325,7 +325,7 @@ EXPORT_SYMBOL(hci_get_route);
 
 /* Create SCO or ACL connection.
  * Device _must_ be locked */
-struct hci_conn *hci_connect(struct hci_dev *hdev, int type, bdaddr_t *dst, __u8 auth_type)
+struct hci_conn *hci_connect(struct hci_dev *hdev, int type, bdaddr_t *dst, __u8 sec_level, __u8 auth_type)
 {
 	struct hci_conn *acl;
 	struct hci_conn *sco;
@@ -340,6 +340,7 @@ struct hci_conn *hci_connect(struct hci_dev *hdev, int type, bdaddr_t *dst, __u8
 	hci_conn_hold(acl);
 
 	if (acl->state == BT_OPEN || acl->state == BT_CLOSED) {
+		acl->sec_level = sec_level;
 		acl->auth_type = auth_type;
 		hci_acl_connect(acl);
 	}
@@ -385,16 +386,17 @@ int hci_conn_check_link_mode(struct hci_conn *conn)
 EXPORT_SYMBOL(hci_conn_check_link_mode);
 
 /* Authenticate remote device */
-int hci_conn_auth(struct hci_conn *conn)
+static int hci_conn_auth(struct hci_conn *conn, __u8 sec_level)
 {
 	BT_DBG("conn %p", conn);
 
-	if (conn->ssp_mode > 0 && conn->hdev->ssp_mode > 0) {
-		if (!(conn->auth_type & 0x01)) {
-			conn->auth_type |= 0x01;
-			conn->link_mode &= ~HCI_LM_AUTH;
-		}
-	}
+	if (sec_level > conn->sec_level)
+		conn->link_mode &= ~HCI_LM_AUTH;
+
+	conn->sec_level = sec_level;
+
+	if (sec_level == BT_SECURITY_HIGH)
+		conn->auth_type |= 0x01;
 
 	if (conn->link_mode & HCI_LM_AUTH)
 		return 1;
@@ -405,31 +407,42 @@ int hci_conn_auth(struct hci_conn *conn)
 		hci_send_cmd(conn->hdev, HCI_OP_AUTH_REQUESTED,
 							sizeof(cp), &cp);
 	}
+
 	return 0;
 }
-EXPORT_SYMBOL(hci_conn_auth);
 
-/* Enable encryption */
-int hci_conn_encrypt(struct hci_conn *conn)
+/* Enable security */
+int hci_conn_security(struct hci_conn *conn, __u8 sec_level)
 {
 	BT_DBG("conn %p", conn);
 
+	if (sec_level == BT_SECURITY_SDP)
+		return 1;
+
+	if (sec_level == BT_SECURITY_LOW) {
+		if (conn->ssp_mode > 0 && conn->hdev->ssp_mode > 0)
+			return hci_conn_auth(conn, sec_level);
+		else
+			return 1;
+	}
+
 	if (conn->link_mode & HCI_LM_ENCRYPT)
-		return hci_conn_auth(conn);
+		return hci_conn_auth(conn, sec_level);
 
 	if (test_and_set_bit(HCI_CONN_ENCRYPT_PEND, &conn->pend))
 		return 0;
 
-	if (hci_conn_auth(conn)) {
+	if (hci_conn_auth(conn, sec_level)) {
 		struct hci_cp_set_conn_encrypt cp;
 		cp.handle  = cpu_to_le16(conn->handle);
 		cp.encrypt = 1;
 		hci_send_cmd(conn->hdev, HCI_OP_SET_CONN_ENCRYPT,
 							sizeof(cp), &cp);
 	}
+
 	return 0;
 }
-EXPORT_SYMBOL(hci_conn_encrypt);
+EXPORT_SYMBOL(hci_conn_security);
 
 /* Change link key */
 int hci_conn_change_link_key(struct hci_conn *conn)
@@ -442,12 +455,13 @@ int hci_conn_change_link_key(struct hci_conn *conn)
 		hci_send_cmd(conn->hdev, HCI_OP_CHANGE_CONN_LINK_KEY,
 							sizeof(cp), &cp);
 	}
+
 	return 0;
 }
 EXPORT_SYMBOL(hci_conn_change_link_key);
 
 /* Switch role */
-int hci_conn_switch_role(struct hci_conn *conn, uint8_t role)
+int hci_conn_switch_role(struct hci_conn *conn, __u8 role)
 {
 	BT_DBG("conn %p", conn);
 
@@ -460,6 +474,7 @@ int hci_conn_switch_role(struct hci_conn *conn, uint8_t role)
 		cp.role = role;
 		hci_send_cmd(conn->hdev, HCI_OP_SWITCH_ROLE, sizeof(cp), &cp);
 	}
+
 	return 0;
 }
 EXPORT_SYMBOL(hci_conn_switch_role);