Bluetooth: Add debug setting for changing minimum encryption key size

For testing and qualification purposes it is useful to allow changing
the minimum encryption key size value that the host stack is going to
enforce. This adds a new debugfs setting min_encrypt_key_size to achieve
this functionality.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

include/net/bluetooth/hci_core.h

@@ -278,6 +278,7 @@ struct hci_dev {
 	__u16		conn_info_min_age;
 	__u16		conn_info_max_age;
 	__u16		auth_payload_timeout;
+	__u8		min_enc_key_size;
 	__u8		ssp_debug_mode;
 	__u8		hw_error_code;
 	__u32		clock;

net/bluetooth/hci_core.c

@@ -3202,6 +3202,7 @@ struct hci_dev *hci_alloc_dev(void)
 	hdev->conn_info_min_age = DEFAULT_CONN_INFO_MIN_AGE;
 	hdev->conn_info_max_age = DEFAULT_CONN_INFO_MAX_AGE;
 	hdev->auth_payload_timeout = DEFAULT_AUTH_PAYLOAD_TIMEOUT;
+	hdev->min_enc_key_size = HCI_MIN_ENC_KEY_SIZE;
 
 	mutex_init(&hdev->lock);
 	mutex_init(&hdev->req_lock);

net/bluetooth/hci_debugfs.c

@@ -433,6 +433,35 @@ static int auto_accept_delay_set(void *data, u64 val)
 	return 0;
 }
 
+static int min_encrypt_key_size_set(void *data, u64 val)
+{
+	struct hci_dev *hdev = data;
+
+	if (val < 1 || val > 16)
+		return -EINVAL;
+
+	hci_dev_lock(hdev);
+	hdev->min_enc_key_size = val;
+	hci_dev_unlock(hdev);
+
+	return 0;
+}
+
+static int min_encrypt_key_size_get(void *data, u64 *val)
+{
+	struct hci_dev *hdev = data;
+
+	hci_dev_lock(hdev);
+	*val = hdev->min_enc_key_size;
+	hci_dev_unlock(hdev);
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(min_encrypt_key_size_fops,
+			min_encrypt_key_size_get,
+			min_encrypt_key_size_set, "%llu\n");
+
 static int auto_accept_delay_get(void *data, u64 *val)
 {
 	struct hci_dev *hdev = data;
@@ -545,6 +574,8 @@ void hci_debugfs_create_bredr(struct hci_dev *hdev)
 	if (lmp_ssp_capable(hdev)) {
 		debugfs_create_file("ssp_debug_mode", 0444, hdev->debugfs,
 				    hdev, &ssp_debug_mode_fops);
+		debugfs_create_file("min_encrypt_key_size", 0644, hdev->debugfs,
+				    hdev, &min_encrypt_key_size_fops);
 		debugfs_create_file("auto_accept_delay", 0644, hdev->debugfs,
 				    hdev, &auto_accept_delay_fops);
 	}

net/bluetooth/l2cap_core.c

@@ -1361,7 +1361,7 @@ static bool l2cap_check_enc_key_size(struct hci_conn *hcon)
 	 * actually encrypted before enforcing a key size.
 	 */
 	return (!test_bit(HCI_CONN_ENCRYPT, &hcon->flags) ||
-		hcon->enc_key_size >= HCI_MIN_ENC_KEY_SIZE);
+		hcon->enc_key_size >= hcon->hdev->min_enc_key_size);
 }
 
 static void l2cap_do_start(struct l2cap_chan *chan)