net/sctp: Validate parameter size for SCTP_GET_ASSOC_STATS

Building sctp may fail with:

In function ‘copy_from_user’,
    inlined from ‘sctp_getsockopt_assoc_stats’ at
    net/sctp/socket.c:5656:20:
arch/x86/include/asm/uaccess_32.h:211:26: error: call to
    ‘copy_from_user_overflow’ declared with attribute error: copy_from_user()
    buffer size is not provably correct

if built with W=1 due to a missing parameter size validation
before the call to copy_from_user.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int sctp_getsockopt_partial_delivery_point(struct sock *sk, int len,
						  char __user *optval,
						  int __user *optlen)
{
	u32 val;

	if (len < sizeof(u32))
		return -EINVAL;

	len = sizeof(u32);

	val = sctp_sk(sk)->pd_point;
	if (put_user(len, optlen))
		return -EFAULT;
	if (copy_to_user(optval, &val, len))
		return -EFAULT;

	return 0;
}

static int sctp_getsockopt_partial_delivery_point(struct sock *sk, int len,
						  char __user *optval,
						  int __user *optlen)
{
	u32 val;

	if (len < sizeof(u32))
		return -EINVAL;

	len = sizeof(u32);

	val = sctp_sk(sk)->pd_point;
	if (put_user(len, optlen))
		return -EFAULT;
	if (copy_to_user(optval, &val, len))
		return -EFAULT;

	return 0;
}
