linux-ext4 - Re: [PATCH 10/24] e2fsck: don't clobber critical metadata during check

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Message-ID: <20140725010322.GA1865@thunk.org>
Date:	Thu, 24 Jul 2014 21:03:22 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 10/24] e2fsck: don't clobber critical metadata during
 check_blocks

On Fri, Jul 18, 2014 at 03:53:28PM -0700, Darrick J. Wong wrote:
> If we encounter an inode with IND/DIND/TIND blocks or internal extent
> tree blocks that point into critical FS metadata such as the
> superblock, the group descriptors, the bitmaps, or the inode table,
> it's quite possible that the validation code for those blocks is not
> going to like what it finds, and it'll ask to try to fix the block.
> Unfortunately, this happens before duplicate block processing (pass
> 1b), which means that we can end up doing stupid things like writing
> extent blocks into the inode table, which multiplies e2fsck'
> destructive effect and can render a filesystem unfixable.
> 
> To solve this, create a bitmap of all the critical FS metadata.  If
> before pass1b runs (basically check_blocks) we find a metadata block
> that points into these critical regions, continue processing that
> block, but avoid making any modifications, because we could be
> misinterpreting inodes as block maps.  Pass 1b will find the
> multiply-owned blocks and fix that situation, which means that we can
> then restart e2fsck from the beginning and actually fix whatever
> problems we find.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>

Thanks, applied.

					- Ted
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