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Message-ID: <20131114025448.GB31602@thunk.org>
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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