md/raid10: fix two bugs affecting RAID10 reshape.

commit 78eaa0d4 upstream.

1/ If a RAID10 is being reshaped to a fewer number of devices
 and is stopped while this is ongoing, then when the array is
 reassembled the 'mirrors' array will be allocated too small.
 This will lead to an access error or memory corruption.

2/ A sanity test for a reshaping RAID10 array is restarted
 is slightly incorrect.

Due to the first bug, this is suitable for any -stable
kernel since 3.5 where this code was introduced.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/md/raid10.c

@@ -3531,7 +3531,7 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 
 	/* FIXME calc properly */
 	conf->mirrors = kzalloc(sizeof(struct raid10_info)*(mddev->raid_disks +
-							    max(0,mddev->delta_disks)),
+							    max(0,-mddev->delta_disks)),
 				GFP_KERNEL);
 	if (!conf->mirrors)
 		goto out;
@@ -3690,7 +3690,7 @@ static int run(struct mddev *mddev)
 		    conf->geo.far_offset == 0)
 			goto out_free_conf;
 		if (conf->prev.far_copies != 1 &&
-		    conf->geo.far_offset == 0)
+		    conf->prev.far_offset == 0)
 			goto out_free_conf;
 	}