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>
int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
{
	struct sctp_association *asoc = sctp_id2assoc(sk, id);
	struct socket *sock;
	struct sctp_af *af;
	int err = 0;

	if (!asoc)
		return -EINVAL;

	/* An association cannot be branched off from an already peeled-off
	 * socket, nor is this supported for tcp style sockets.
	 */
	if (!sctp_style(sk, UDP))
		return -EINVAL;

	/* Create a new socket.  */
	err = sock_create(sk->sk_family, SOCK_SEQPACKET, IPPROTO_SCTP, &sock);
	if (err < 0)
		return err;

	sctp_copy_sock(sock->sk, sk, asoc);

	/* Make peeled-off sockets more like 1-1 accepted sockets.
	 * Set the daddr and initialize id to something more random
	 */
	af = sctp_get_af_specific(asoc->peer.primary_addr.sa.sa_family);
	af->to_sk_daddr(&asoc->peer.primary_addr, sk);

	/* Populate the fields of the newsk from the oldsk and migrate the
	 * asoc to the newsk.
	 */
	sctp_sock_migrate(sk, sock->sk, asoc, SCTP_SOCKET_UDP_HIGH_BANDWIDTH);

	*sockp = sock;

	return err;
}

int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
{
	struct sctp_association *asoc = sctp_id2assoc(sk, id);
	struct socket *sock;
	struct sctp_af *af;
	int err = 0;

	if (!asoc)
		return -EINVAL;

	/* An association cannot be branched off from an already peeled-off
	 * socket, nor is this supported for tcp style sockets.
	 */
	if (!sctp_style(sk, UDP))
		return -EINVAL;

	/* Create a new socket.  */
	err = sock_create(sk->sk_family, SOCK_SEQPACKET, IPPROTO_SCTP, &sock);
	if (err < 0)
		return err;

	sctp_copy_sock(sock->sk, sk, asoc);

	/* Make peeled-off sockets more like 1-1 accepted sockets.
	 * Set the daddr and initialize id to something more random
	 */
	af = sctp_get_af_specific(asoc->peer.primary_addr.sa.sa_family);
	af->to_sk_daddr(&asoc->peer.primary_addr, sk);

	/* Populate the fields of the newsk from the oldsk and migrate the
	 * asoc to the newsk.
	 */
	sctp_sock_migrate(sk, sock->sk, asoc, SCTP_SOCKET_UDP_HIGH_BANDWIDTH);

	*sockp = sock;

	return err;
}
