xfs: in _attrlist_by_handle, copy the cursor back to userspace

BugLink: http://bugs.launchpad.net/bugs/1697001

commit 0facef7f upstream.

When we're iterating inode xattrs by handle, we have to copy the
cursor back to userspace so that a subsequent invocation actually
retrieves subsequent contents.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Cc: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

fs/xfs/xfs_ioctl.c

@@ -403,6 +403,7 @@ xfs_attrlist_by_handle(
 {
 	int			error = -ENOMEM;
 	attrlist_cursor_kern_t	*cursor;
+	struct xfs_fsop_attrlist_handlereq __user	*p = arg;
 	xfs_fsop_attrlist_handlereq_t al_hreq;
 	struct dentry		*dentry;
 	char			*kbuf;
@@ -435,6 +436,11 @@ xfs_attrlist_by_handle(
 	if (error)
 		goto out_kfree;
 
+	if (copy_to_user(&p->pos, cursor, sizeof(attrlist_cursor_kern_t))) {
+		error = -EFAULT;
+		goto out_kfree;
+	}
+
 	if (copy_to_user(al_hreq.buffer, kbuf, al_hreq.buflen))
 		error = -EFAULT;