linux-kernel - Re: [PATCH v4 12/13] bluetooth/smp: ensure RNG is properly seeded before ECDH use

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Message-Id: <707C1A6E-D79A-45BC-A868-A78289A327EC@holtmann.org>
Date:   Thu, 8 Jun 2017 19:05:25 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Biggers <ebiggers3@...il.com>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>
Subject: Re: [PATCH v4 12/13] bluetooth/smp: ensure RNG is properly seeded
 before ECDH use

Hi Jason,

>> yes, there are plenty of commands needed before a controller becomes usable.
> 
> That doesn't clearly address with precision what Ted was wondering.
> Specifically, the inquiry is: can you confirm with certainty whether
> or not all calls to get_random_bytes() in the bluetooth directory are
> *necessarily* going to come after a call to hci_power_on()?

on a powered down controller, you can not do any crypto. SMP is only during a connection and the RPAs are only generated when needed. So yes, doing this once in hci_power_on is plenty. However we might want to limit this to LE capable controllers since for BR/EDR only controllers this is not needed. For A2MP I need to check that we need the random numbers seeded there. However this hidden behind the high speed feature.

Regards

Marcel