linux-kernel - Re: Should we automatically generate a module signing key at all?

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Message-ID: <20150519155532.GB2871@thunk.org>
Date:	Tue, 19 May 2015 11:55:32 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	David Howells <dhowells@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michal Marek <mmarek@...e.cz>,
	David Woodhouse <dwmw2@...radead.org>,
	Abelardo Ricart III <aricart@...nix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Sedat Dilek <sedat.dilek@...il.com>, keyrings@...ux-nfs.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	LSM List <linux-security-module@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>
Subject: Re: Should we automatically generate a module signing key at all?

On Tue, May 19, 2015 at 04:30:17PM +0100, David Howells wrote:
> We do have to allow people to load external modules.  Yes, you could argue
> that you should just disable all your security systems if you want to do
> that...

Is module signing really meant for distro kernels, or would anyone
besides people creating distro kernels care about this?  I thought I
saw some messages (including from Linus) that the "common case" is the
average kernel developer who creates a throw-away key, uses it to sign
all of the modules in the kernel build, and then throws it away.

I wouldn't know, because I don't use module signing at all, and I
don't really see the point.  I build my own kernels for my own use,
which means either modules for my own developer convenience, or if I'm
building it for a server where I really care about security, I'll
build in exactly the drivers I need and disable modules entirely.  So
I'm clearly not the intended use case, either as a distro kernel
release engineer, or as a "build a kernel with modules and then throw
away the key use case".

So I'm really curious --- are there significant numbers of people
doing kernel builds, besides distro kernel engineers, who would use
module signing?  If so, them sure, let's spend time optimizing so that
it's really easy for those folks.  If not, maybe it's simpler just
make things easy for people who will be storing the key in some
external hardware device, and just be done with it.

Cheers,

						- Ted
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