linux-kernel - Re: [kernel-hardening] Re: [PATCH v4 13/13] random: warn when kernel uses unseeded randomness

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Message-ID: <2812305.zGuAXT15AM@positron.chronox.de>
Date:   Sun, 18 Jun 2017 19:55:04 +0200
From:   Stephan Müller <smueller@...onox.de>
To:     Theodore Ts'o <tytso@....edu>
Cc:     kernel-hardening@...ts.openwall.com,
        Michael Ellerman <mpe@...erman.id.au>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Miller <davem@...emloft.net>,
        Eric Biggers <ebiggers3@...il.com>
Subject: Re: [kernel-hardening] Re: [PATCH v4 13/13] random: warn when kernel uses unseeded randomness

Am Sonntag, 18. Juni 2017, 17:46:25 CEST schrieb Theodore Ts'o:

Hi Theodore,

> > IMHO, users using the get_random_u64 or get_random_u32 are use cases that
> > do not require a fully seeded DRNG thus do not need a cryptographically
> > strong random number. Hence, I would think that the logging should be
> > removed from get_random_u32/u64.
> 
> You are effectively proposing that there ought to be a middle range of
> security between prandom_32, get_random_u32/get_random_u64 and
> get_random_bytes().  I think that's going to lead to all sorts of
> complexity and bugs from people not understanding when they should use
> get_random_u32 vs get_random_bytes versus prandom_u32.  And then we'll
> end up needing to audit all of the callsites for get_random_u32() so
> they don't violate this new usage rule that you are proposing.

I only proposed to get rid of the log messages indicating a non-seeded DRNG.

But you bring up an interesting point: if it is true you say that it is hard 
for people to use differnent types of APIs regarding entropy and random 
numbers right (which I would concur with), and considering that you imply that 
get_random_bytes, get_random_u32 and get_random_u64 have the same security 
strength, why do we have these three APIs to begin with? The get_random_bytes 
API would then be more than enough.

Ciao
Stephan