ocfs2: Fix memory overflow in cow_by_page.

In ocfs2_duplicate_clusters_by_page, we calculate map_end
by shifting page_index. But actually in case we meet with
a large offset(say in a i686 box, poff_t is only 32 bits
and page_index=2056240), we will overflow. So change the
type of page_index to loff_t.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

fs/ocfs2/refcounttree.c

@@ -2945,7 +2945,7 @@ static int ocfs2_duplicate_clusters_by_page(handle_t *handle,
 
 	while (offset < end) {
 		page_index = offset >> PAGE_CACHE_SHIFT;
-		map_end = (page_index + 1) << PAGE_CACHE_SHIFT;
+		map_end = ((loff_t)page_index + 1) << PAGE_CACHE_SHIFT;
 		if (map_end > end)
 			map_end = end;
 
@@ -3170,7 +3170,7 @@ static int ocfs2_cow_sync_writeback(struct super_block *sb,
 
 	while (offset < end) {
 		page_index = offset >> PAGE_CACHE_SHIFT;
-		map_end = (page_index + 1) << PAGE_CACHE_SHIFT;
+		map_end = ((loff_t)page_index + 1) << PAGE_CACHE_SHIFT;
 		if (map_end > end)
 			map_end = end;