Bluetooth: RFCOMM - Fix info leak in getsockopt(BT_SECURITY)

The RFCOMM code fails to initialize the key_size member of struct
bt_security before copying it to userland -- that for leaking one
byte kernel stack. Initialize key_size with 0 to avoid the info
leak.
Signed-off-by: NMathias Krause <minipli@googlemail.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bluetooth/rfcomm/sock.c

@@ -822,6 +822,7 @@ static int rfcomm_sock_getsockopt(struct socket *sock, int level, int optname, c
 		}
 
 		sec.level = rfcomm_pi(sk)->sec_level;
+		sec.key_size = 0;
 
 		len = min_t(unsigned int, len, sizeof(sec));
 		if (copy_to_user(optval, (char *) &sec, len))