Bluetooth: Add support for returning the encryption key size

This will be useful when userspace wants to restrict some kinds of
operations based on the length of the key size used to encrypt the
link.
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

include/net/bluetooth/bluetooth.h

@@ -56,6 +56,7 @@
 #define BT_SECURITY	4
 struct bt_security {
 	__u8 level;
+	__u8 key_size;
 };
 #define BT_SECURITY_SDP		0
 #define BT_SECURITY_LOW		1

net/bluetooth/l2cap_sock.c

@@ -422,8 +422,12 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname, ch
 			break;
 		}
 
+		memset(&sec, 0, sizeof(sec));
 		sec.level = chan->sec_level;
 
+		if (sk->sk_state == BT_CONNECTED)
+			sec.key_size = chan->conn->hcon->enc_key_size;
+
 		len = min_t(unsigned int, len, sizeof(sec));
 		if (copy_to_user(optval, (char *) &sec, len))
 			err = -EFAULT;