linux-kernel - Re: [PATCH v2] modsign: use shred to overwrite the private key before deleting it

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Message-ID: <54C4E351.6010601@ahsoftware.de>
Date:	Sun, 25 Jan 2015 13:36:33 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Richard Weinberger <richard.weinberger@...il.com>
CC:	Pádraig Brady <P@...igbrady.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Michal Marek <mmarek@...e.cz>,
	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] modsign: use shred to overwrite the private key before
 deleting it

Am 25.01.2015 um 13:24 schrieb Alexander Holler:
> Am 25.01.2015 um 13:08 schrieb Richard Weinberger:
>>
>> Or add support for the "s" chattr to major filesystems.
>>
> And change the manpage for the 's' attribute to change the "overwriting
> with zero" with some other wording.
>
> But thanks for the hint. I wasn't aware of that bit (maybe because it's
> still useless on most filesystems).
>
> But the above silly instruction might still help in implementing support
> for the 's' attribute.
>
> Also I wonder what happens if you delete a file with such an attribute
> on e.g. an SSD. I assume the user just gets a false positive that the
> file is deleted, which isn't much different to what nowadays happens and
> doesn't therefor really help.
>
> So maybe shred should first set the 's' attribute before calling unlink
> on that file (if it doesn't already do it). I will look at it and send a
> patch if necessary. It's at least a small bit where I can help. ;)

And the manpage for chattr doesn't explain what should happen if a file 
with the 's' attrribute is changed. A reasonable answer to that is that 
the old contents, if not changed by overwriting them, should be 
deleted/zeroed too.

Regards,

Alexander Holler
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