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

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Message-ID: <17249.1338473462@redhat.com>
Date:	Thu, 31 May 2012 15:11:02 +0100
From:	David Howells <dhowells@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	dhowells@...hat.com, kyle@...artin.ca,
	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

Rusty Russell <rusty@...tcorp.com.au> wrote:

> > That then adds 5 bytes to the magic string.  Is that really so bad?
> 
> Yes, because it's unnecessary.

I'm sorry Rusty, but this argument is disingenuous.

Yes, a length field in the file is unnecessary - BUT SO TOO is scanning!  By
this argument, your idea is really so bad too.  It's all about the trade off
one chooses to make.  I do not accept your chosen trade off[*] as being the
best one.

David

[*] And, yes, it *is* a trade off: you are trading CPU time and permanently
    resident kernel code space in order to save a tiny amount of disk
    space[**].

[**] Assuming 512 byte blocks and a 5 byte size field, probably fewer than 1%
     of modules will expand sufficiently to consume an extra block.  Further,
     making it a 2-byte binary field would make it even less intrusive, both
     in the file and in the module verifier.
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