[PATCH v2] bluetooth: Enforce classic key size verification.

[Alain Michaud <alainm@chromium.org>]

This change introduces a new configuration to strictly enforce key size
checks.  This ensures that systems are in a secured configuration by
default while allowing for a compatible posture via a Kconfig option to
support controllers who may not support the read encryption key size
command.

Signed-off-by: Alain Michaud <alainm@chromium.org>
---

 net/bluetooth/Kconfig     | 20 ++++++++++++++++++++
 net/bluetooth/hci_core.c  | 10 ++++++++++
 net/bluetooth/hci_event.c |  4 ++++
 3 files changed, 34 insertions(+)

diff --git a/net/bluetooth/Kconfig b/net/bluetooth/Kconfig
index 165148c7c4ce..8e177d4f3f02 100644
--- a/net/bluetooth/Kconfig
+++ b/net/bluetooth/Kconfig
@@ -128,4 +128,24 @@ config BT_DEBUGFS
 	  Provide extensive information about internal Bluetooth states
 	  in debugfs.
 
+config BT_EXPERT
+	bool "Expert Bluetooth options"
+	depends on BT
+	default n
+	help
+	  Provides a set of expert options and configurations that should
+	  only be used deliberately by BT experts.  This is considered a
+	  global switch to ensure these advanced features or options that
+	  depends on BT_EXPERT are only used in expert mode.
+
+config BT_ENFORCE_CLASSIC_KEY_SIZES
+	bool "Enforces security requirements for Bluetooth classic"
+	depends on BT && BT_EXPERT
+	default y
+	help
+	  Enforces Bluetooth classic security requirements by disallowing
+	  use of insecure Bluetooth controllers, i.e. that doesn't support
+	  Read Encryption Key Size command to prevent BT classic connection
+	  with very short encryption key.
+
 source "drivers/bluetooth/Kconfig"
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 4e6d61a95b20..142130d4b66b 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1540,6 +1540,16 @@ static int hci_dev_do_open(struct hci_dev *hdev)
 
 	clear_bit(HCI_INIT, &hdev->flags);
 
+#ifdef BT_ENFORCE_CLASSIC_KEY_SIZES
+	/* Don't allow usage of Bluetooth if the chip doesn't support */
+	/* Read Encryption Key Size command */
+	if (!ret && !(hdev->commands[20] & 0x10)) {
+		bt_dev_err(hdev,
+			   "Disabling BT, Read Encryption Key Size !supported");
+		ret = -EIO;
+	}
+#endif
+
 	if (!ret) {
 		hci_dev_hold(hdev);
 		hci_dev_set_flag(hdev, HCI_RPA_EXPIRED);
diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index a40ed31f6eb8..54f90799a088 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -2902,7 +2902,11 @@ static void read_enc_key_size_complete(struct hci_dev *hdev, u8 status,
 	if (rp->status) {
 		bt_dev_err(hdev, "failed to read key size for handle %u",
 			   handle);
+#ifdef BT_ENFORCE_CLASSIC_KEY_SIZES
+		conn->enc_key_size = 0;
+#else
 		conn->enc_key_size = HCI_LINK_KEY_SIZE;
+#endif
 	} else {
 		conn->enc_key_size = rp->key_size;
 	}
-- 
2.25.1.696.g5e7596f4ac-goog