MFC r294807: MFV r294806:
6388 Failure of userland copy should return EFAULT

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Richard Yao <ryao@gentoo.org>

illumos/illumos-gate@c71c00bbe8a9cdc7e3f4048b751f48e80441d506