linux-ext4 - Re: [PATCH 3/3] e2fsprogs: add a function computing old desc blocks without reserved ones

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Message-ID: <20120123164527.GA4439@thunk.org>
Date:	Mon, 23 Jan 2012 11:45:27 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/3] e2fsprogs: add a function computing old desc
 blocks without reserved ones

On Wed, Jan 04, 2012 at 07:02:12PM +0800, Yongqiang Yang wrote:
> If first_meta_bg > desc_blocks, ext2fs_open reads more decs_blocks,
> however desc buffer in memory is allocated based on desc_blocks.
> Maybe there are similar problems in other places, so this patch adds a
> function which computes right old_desc_blocks.
> 
> The problem can be reproduced by setting first_meta_bg.

s_first_meta_bg should never be greater than desc_blocks.  If it is,
the file system is corrupt.  This is something that we should check in
ext2fs_open() and in e2fsck as well.

A much better thing to do would be to have ext2fs_open simply fail the
open with an EXT2_ET_CORRUPT_SUPERBLOCK error.  Then e2fsck will
automatically try using the backup superblock, which will hopefully
allow the user to recover from the corrupted superblock.

      	       	  	       	   	     - Ted
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