linux-ext4 - Re: [PATCH 1/2 v3] EXT4: Secure Delete: Zero out file data

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Message-ID: <4E120FD0.70003@linux.vnet.ibm.com>
Date:	Mon, 04 Jul 2011 12:09:04 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	Andreas Dilger <adilger@...ger.ca>
CC:	Amir Goldstein <amir73il@...il.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 1/2 v3] EXT4: Secure Delete: Zero out file data

On 07/04/2011 11:19 AM, Andreas Dilger wrote:
> On 2011-07-04, at 11:44 AM, Amir Goldstein wrote:
>> On Mon, Jul 4, 2011 at 8:19 PM, Allison Henderson
>> <achender@...ux.vnet.ibm.com>  wrote:
>>>
>>> Thx all for the reviews!  It sounds like the zero out code is in the right
>>> spot then.  We are thinking about adding an optimization too, where we use
>>> use secure discard instead of the sb_issue_zeroout, but only if the device
>>> supports it.  I was thinking about putting that code some where in the
>>> commit call back because that is where the existing discard code is, but
>>> maybe that's not such a good place to put it then?  What does everyone
>>> think?  Thx!
>>
>> I already stated my opinion about the need for 2-phase secure delete.
>> If you have to choose between security (zeroout pre commit) and the
>> atomicity of the unlink() command (zeroout post commit), then it's
>> a question of policy.
>> Is there any other FS (or OS) that implements secure delete?
>> Perhaps we could follow its semantics.
>
> One thing we did ages ago, before extent-mapped files made unlink so
> fast, was to move the blocks from unlinked files and truncated-to-zero
> files to a delete queue in the main transaction, and then do the unlink
> via a separate thread.
>
> This facility could be resurrected (a version of the patch was posted to
> linux-ext4 at http://www.spinics.net/lists/linux-ext4/msg06178.html) to
> do the block zeroing/discard in the context of the unlink thread.  It
> could be structured so that sync/fsync on the file waits for background
> zeroing to complete, so that apps doing secure delete + fsync will be
> sure that the file is safely erased.  The fsync would be needed for this
> in any case, otherwise even an inline async zero-fill could fail if the
> system crashes before the blocks are actually flushed to disk.
>
> Cheers, Andreas
>
>
Oh alrighty, I will look into that then.  Thx all for your input!  :)

Allison
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