Bluetooth: Align minimum encryption key size for LE and BR/EDR connections

BugLink: https://bugs.launchpad.net/bugs/1836668

commit d5bb334a upstream.

The minimum encryption key size for LE connections is 56 bits and to
align LE with BR/EDR, enforce 56 bits of minimum encryption key size for
BR/EDR connections as well.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

include/net/bluetooth/hci_core.h

@@ -174,6 +174,9 @@ struct adv_info {
 
 #define HCI_MAX_SHORT_NAME_LENGTH	10
 
+/* Min encryption key size to match with SMP */
+#define HCI_MIN_ENC_KEY_SIZE		7
+
 /* Default LE RPA expiry time, 15 minutes */
 #define HCI_DEFAULT_RPA_TIMEOUT		(15 * 60)
 

net/bluetooth/hci_conn.c

@@ -1177,6 +1177,14 @@ int hci_conn_check_link_mode(struct hci_conn *conn)
 	    !test_bit(HCI_CONN_ENCRYPT, &conn->flags))
 		return 0;
 
+	/* The minimum encryption key size needs to be enforced by the
+	 * host stack before establishing any L2CAP connections. The
+	 * specification in theory allows a minimum of 1, but to align
+	 * BR/EDR and LE transports, a minimum of 7 is chosen.
+	 */
+	if (conn->enc_key_size < HCI_MIN_ENC_KEY_SIZE)
+		return 0;
+
 	return 1;
 }