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

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Date:	Sun, 25 Jan 2015 13:08:40 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Alexander Holler <holler@...oftware.de>
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

On Sun, Jan 25, 2015 at 12:42 PM, Alexander Holler <holler@...oftware.de> wrote:
> Now, after I ended up into flaming a lot (sorry again, but this topic made
> me angry for so long and I had to spent too much time to get rid of unwanted
> content and answering other peoples question in regard to that topic), I
> should offer something more useful.
>
> So I've written down in some short words, how I think it could be done:
>
> First offer a syscall named sunlink() (or whatever name) which fails if it
> can't overwrite or securely trim the contents of a file before deleting it.
>
> That could be done like this:
>
> (1) If it's a SSD or MMC without offering "Secure Trim" fail.
> (2) If it's a plain FLASH or conventional harddisk where writing a block
> means that block will be overwritten or if it's a SSD or MMC with "Secure
> Trim) go on with
> (3) Identify the blocks which contain the file contents (should be doable by
> using the same mechanisms used to read and write a file)
> (4) Mark the file as deleted
> (5) Overwrite or securely trim blocks which can be deleted completely
> (6) Build new blocks for blocks which can only partly deleted because they
> contain information still used by the FS or other files
> (7) Instruct the FS to us the new blocks instead of the old ones
> (8) Overwrite or securely trim the old blocks which previously contained
> partly information of other stuff.
>
> Afterwards use that new syscall in shred.
>
> Of course, this is just a totally simplified instruction in regard to how
> complicated filesystems have become, but I think there isn't any black magic
> involved in offering the user a simple way to really delete files.

Or add support for the "s" chattr to major filesystems.
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