linux-kernel - Re: [GIT PULL] MODSIGN: Use PKCS#7 for module signatures

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Message-ID: <1438074741.26913.96.camel@infradead.org>
Date:	Tue, 28 Jul 2015 10:12:21 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	David Howells <dhowells@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Cc:	jmorris@...ei.org, mcgrof@...il.com, keyrings@...ux-nfs.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [GIT PULL] MODSIGN: Use PKCS#7 for module signatures

On Mon, 2015-07-27 at 23:43 +0100, David Howells wrote:
> 
>     PKCS#7: Require authenticated attributes
>     
>     Require there to be authenticated attributes in the PKCS#7/CMS message so
>     that an attacker can't drop them to provide greater opportunity for
>     manipulating the message.

There doesn't seem to be a lot of point in this part. If the
authenticated attribute isn't being *checked*, then the attacker
doesn't need to drop it at all. There's no point in merely requiring
its *existence*.

As part of the firmware signatures, if we are asked to check the
filename then yes we should require it to be present *and* match. But
if we aren't checking (which we can't for modules since we don't know
what's being loaded), why require it to be present at all?

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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