fix some conversion overflows

Fix page index to offset conversion overflows in buffer layer, ecryptfs,
and ocfs2.

It would be nice to convert the whole tree to page_offset, but for now
just fix the bugs.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/buffer.c b/fs/buffer.c
index 02ebb1f..0e5ec37 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2221,7 +2221,7 @@
 	lock_page(page);
 	size = i_size_read(inode);
 	if ((page->mapping != inode->i_mapping) ||
-	    ((page->index << PAGE_CACHE_SHIFT) > size)) {
+	    (page_offset(page) > size)) {
 		/* page got truncated out from underneath us */
 		goto out_unlock;
 	}