Bluetooth: RFCOMM - Fix info leak via getsockname()

The RFCOMM code fails to initialize the trailing padding byte of struct
sockaddr_rc added for alignment. It that for leaks one byte kernel stack
via the getsockname() syscall. Add an explicit memset(0) before filling
the structure to avoid the info leak.

Signed-off-by: Mathias 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: David S. Miller <davem@davemloft.net>
static int rfcomm_sock_debugfs_show(struct seq_file *f, void *p)
{
	struct sock *sk;
	struct hlist_node *node;

	read_lock(&rfcomm_sk_list.lock);

	sk_for_each(sk, node, &rfcomm_sk_list.head) {
		seq_printf(f, "%s %s %d %d\n",
				batostr(&bt_sk(sk)->src),
				batostr(&bt_sk(sk)->dst),
				sk->sk_state, rfcomm_pi(sk)->channel);
	}

	read_unlock(&rfcomm_sk_list.lock);

	return 0;
}

static int rfcomm_sock_debugfs_show(struct seq_file *f, void *p)
{
	struct sock *sk;
	struct hlist_node *node;

	read_lock(&rfcomm_sk_list.lock);

	sk_for_each(sk, node, &rfcomm_sk_list.head) {
		seq_printf(f, "%s %s %d %d\n",
				batostr(&bt_sk(sk)->src),
				batostr(&bt_sk(sk)->dst),
				sk->sk_state, rfcomm_pi(sk)->channel);
	}

	read_unlock(&rfcomm_sk_list.lock);

	return 0;
}
