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_peer_auth_chunks(struct sock *sk, int len,
				    char __user *optval, int __user *optlen)
{
	struct net *net = sock_net(sk);
	struct sctp_authchunks __user *p = (void __user *)optval;
	struct sctp_authchunks val;
	struct sctp_association *asoc;
	struct sctp_chunks_param *ch;
	u32    num_chunks = 0;
	char __user *to;

	if (!net->sctp.auth_enable)
		return -EACCES;

	if (len < sizeof(struct sctp_authchunks))
		return -EINVAL;

	if (copy_from_user(&val, optval, sizeof(struct sctp_authchunks)))
		return -EFAULT;

	to = p->gauth_chunks;
	asoc = sctp_id2assoc(sk, val.gauth_assoc_id);
	if (!asoc)
		return -EINVAL;

	ch = asoc->peer.peer_chunks;
	if (!ch)
		goto num;

	/* See if the user provided enough room for all the data */
	num_chunks = ntohs(ch->param_hdr.length) - sizeof(sctp_paramhdr_t);
	if (len < num_chunks)
		return -EINVAL;

	if (copy_to_user(to, ch->chunks, num_chunks))
		return -EFAULT;
num:
	len = sizeof(struct sctp_authchunks) + num_chunks;
	if (put_user(len, optlen)) return -EFAULT;
	if (put_user(num_chunks, &p->gauth_number_of_chunks))
		return -EFAULT;
	return 0;
}

static int sctp_getsockopt_peer_auth_chunks(struct sock *sk, int len,
				    char __user *optval, int __user *optlen)
{
	struct net *net = sock_net(sk);
	struct sctp_authchunks __user *p = (void __user *)optval;
	struct sctp_authchunks val;
	struct sctp_association *asoc;
	struct sctp_chunks_param *ch;
	u32    num_chunks = 0;
	char __user *to;

	if (!net->sctp.auth_enable)
		return -EACCES;

	if (len < sizeof(struct sctp_authchunks))
		return -EINVAL;

	if (copy_from_user(&val, optval, sizeof(struct sctp_authchunks)))
		return -EFAULT;

	to = p->gauth_chunks;
	asoc = sctp_id2assoc(sk, val.gauth_assoc_id);
	if (!asoc)
		return -EINVAL;

	ch = asoc->peer.peer_chunks;
	if (!ch)
		goto num;

	/* See if the user provided enough room for all the data */
	num_chunks = ntohs(ch->param_hdr.length) - sizeof(sctp_paramhdr_t);
	if (len < num_chunks)
		return -EINVAL;

	if (copy_to_user(to, ch->chunks, num_chunks))
		return -EFAULT;
num:
	len = sizeof(struct sctp_authchunks) + num_chunks;
	if (put_user(len, optlen)) return -EFAULT;
	if (put_user(num_chunks, &p->gauth_number_of_chunks))
		return -EFAULT;
	return 0;
}
