netdev - Re: [PATCH] random: seed random_int_secret at least poorly at core

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Date:	Wed, 13 Nov 2013 21:54:48 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Daniel Borkmann <dborkman@...hat.com>, davem@...emloft.net,
	shemminger@...workplumber.org, fweimer@...hat.com,
	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	linux-wireless@...r.kernel.org, keescook@...omium.org
Subject: Re: [PATCH] random: seed random_int_secret at least poorly at
 core_initcall time

On Tue, Nov 12, 2013 at 02:46:03PM +0100, Hannes Frederic Sowa wrote:
> > It is needed by fork to set up the stack canary. And this actually gets
> > called before the secret is initialized.
> 
> Maybe we could use this for the time being and use the seeding method
> of kaslr as soon as it hits the tree?

Hmm, from what I can tell even early_initcall() is going to be early
enough.  The stack canary is set up by boot_init_stack_canary(), which
is run very, very early in start_kerne() --- way before
early_initcalls, or even before interrupts are enabled.  So adding
random_int_secret_init_early() as a core_initcall is still too late.

I wonder if we need to do something in common with what Kees has been
considering for the kaslr code, since it's a similar issue --- we need
random number way earlier than we can really afford to initialize
/dev/random.

						- Ted

P.S.  Unless I'm missing something (and I hope I am), it would appear
that the stack canary is going to easily predictable by an attacker on
non-x86 platforms that don't have RDRAND.  Has someone tested whether
or not the stack canary isn't constant across ARM or pre-Sandy Bridge
x86 systems?

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