linux-kernel - Re: [PATCH 00/23] Crypto keys and module signing

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Message-ID: <87obpfxdpr.fsf@rustcorp.com.au>
Date:	Wed, 23 May 2012 22:21:28 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	David Howells <dhowells@...hat.com>, kyle@...artin.ca
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, keyrings@...ux-nfs.org
Subject: Re: [PATCH 00/23] Crypto keys and module signing

On Wed, 23 May 2012 00:02:19 +0100, David Howells <dhowells@...hat.com> wrote:
> The extended module file format is as follows:
> 
>   The module signature is appended to the end of the module file, followed by
>   "@mod_size@\n@..._size@\nThis Is A Crypto Signed Module".
> 
>   The EOF must follow the magic string directly, so nothing further must be
>   appended to the file.
>
>   mod_size and sig_size are left-aligned decimal numbers, space-padded to 8
>   characters.  mod_size is the size of the module payload part of the file and
>   sig_size is the size of the signature blob.

Hi David,

        That's pretty weird.  Why not put the "@This Is A Crypto Signed
Module\n" before the signature?  Then module-size is implied: everything
before that signature.  The signature size is implied: everything after
that signature.

        In fact, I'd modify this slightly, to allow multiple signatures.
This would work nicely with a deterministic strip.  Find the signatures
backward, and truncate as they fail.

        If you want to be super-paranoid, scan for that signature before
signing the module.

Cheers,
Rusty.
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