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

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Date:   Sun, 18 Jun 2017 21:12:55 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Stephan Müller <smueller@...onox.de>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        kernel-hardening@...ts.openwall.com,
        Michael Ellerman <mpe@...erman.id.au>,
        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

On Sun, Jun 18, 2017 at 7:55 PM, Stephan Müller <smueller@...onox.de> wrote:
> 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.

Because there are efficiences we can benefit from for getting integer
sized outputs.

Use get_random_{u32,u64} when you want a secure random number.
Use get_random_bytes when you want a longer secure random bytestring.