ax25: fix info leak via msg_name in ax25_recvmsg()

When msg_namelen is non-zero the sockaddr info gets filled out, as
requested, but the code fails to initialize the padding bytes of struct
sockaddr_ax25 inserted by the compiler for alignment. Additionally the
msg_namelen value is updated to sizeof(struct full_sockaddr_ax25) but is
not always filled up to this size.

Both issues lead to the fact that the code will leak uninitialized
kernel stack bytes in net/socket.c.

Fix both issues by initializing the memory with memset(0).

Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
static void ax25_fillin_cb_from_dev(ax25_cb *ax25, ax25_dev *ax25_dev)
{
	ax25->rtt     = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]) / 2;
	ax25->t1      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]);
	ax25->t2      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T2]);
	ax25->t3      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T3]);
	ax25->n2      = ax25_dev->values[AX25_VALUES_N2];
	ax25->paclen  = ax25_dev->values[AX25_VALUES_PACLEN];
	ax25->idle    = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_IDLE]);
	ax25->backoff = ax25_dev->values[AX25_VALUES_BACKOFF];

	if (ax25_dev->values[AX25_VALUES_AXDEFMODE]) {
		ax25->modulus = AX25_EMODULUS;
		ax25->window  = ax25_dev->values[AX25_VALUES_EWINDOW];
	} else {
		ax25->modulus = AX25_MODULUS;
		ax25->window  = ax25_dev->values[AX25_VALUES_WINDOW];
	}
}

static void ax25_fillin_cb_from_dev(ax25_cb *ax25, ax25_dev *ax25_dev)
{
	ax25->rtt     = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]) / 2;
	ax25->t1      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]);
	ax25->t2      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T2]);
	ax25->t3      = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T3]);
	ax25->n2      = ax25_dev->values[AX25_VALUES_N2];
	ax25->paclen  = ax25_dev->values[AX25_VALUES_PACLEN];
	ax25->idle    = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_IDLE]);
	ax25->backoff = ax25_dev->values[AX25_VALUES_BACKOFF];

	if (ax25_dev->values[AX25_VALUES_AXDEFMODE]) {
		ax25->modulus = AX25_EMODULUS;
		ax25->window  = ax25_dev->values[AX25_VALUES_EWINDOW];
	} else {
		ax25->modulus = AX25_MODULUS;
		ax25->window  = ax25_dev->values[AX25_VALUES_WINDOW];
	}
}
