linux-ext4 - Re: [PATCH] ext4: Prevent massive fs corruption if verifying the block bitmap fails

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Message-ID: <20130717195503.GC26859@thunk.org>
Date:	Wed, 17 Jul 2013 15:55:03 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: Prevent massive fs corruption if verifying the
 block bitmap fails

On Wed, Jul 17, 2013 at 12:43:56PM -0700, Darrick J. Wong wrote:
> I also wrote a script that fills a fs, maliciously marks all the fs metadata
> blocks as free, and writes more files to the fs, with the result that you
> corrupt the metadata.  I wonder if it's feasible to modify mballoc to check
> that it's not handing out well known metadata locations to files?

We have that --- it's the block_validity mount option.  I use it
regularly for testing.  It's off by default because it does take a bit
more CPU time for every single block allocation and deallocation.  It
would be useful if someone who had access to fast PCIe-attached flash
tried to measure the CPU utilization of a metadata-intensive workload
(such as fs_mark) with and without block_validity.  If the overhead is
negligible, we could enable this by default, and remove the mount
option.

							- Ted
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