linux-kernel - Re: [PATCH 1/2] random32: make prandom

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Message-ID: <CAKQ1sVM9SMYVTSZYaGuPDhQHfyEOFSxBL8PNixyaN4pR2PWMxQ@mail.gmail.com>
Date:   Tue, 1 Sep 2020 10:33:40 +0200
From:   Yann Ylavic <ylavic.dev@...il.com>
To:     Willy Tarreau <w@....eu>
Cc:     linux-kernel@...r.kernel.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        George Spelvin <lkml@....org>,
        Amit Klein <aksecurity@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>, tytso@....edu,
        Florian Westphal <fw@...len.de>,
        Marc Plumb <lkml.mplumb@...il.com>
Subject: Re: [PATCH 1/2] random32: make prandom_u32() output unpredictable

On Tue, Sep 1, 2020 at 8:45 AM Willy Tarreau <w@....eu> wrote:
>
> +/*
> + *     Generate some initially weak seeding values to allow
> + *     the prandom_u32() engine to be started.
> + */
> +static int __init prandom_init_early(void)
> +{
> +       int i;
> +       unsigned long v0, v1, v2, v3;
> +
> +       if (!arch_get_random_long(&v0))
> +               v0 = jiffies;
> +       if (!arch_get_random_long(&v1))
> +               v0 = random_get_entropy();

Shouldn't the above be:
                  v1 = random_get_entropy();
?

> +       v2 = v0 ^ PRND_K0;
> +       v3 = v1 ^ PRND_K1;
> +
> +       for_each_possible_cpu(i) {
> +               struct siprand_state *state;
> +
> +               v3 ^= i;
> +               PRND_SIPROUND(v0, v1, v2, v3);
> +               PRND_SIPROUND(v0, v1, v2, v3);
> +               v0 ^= i;
> +
> +               state = per_cpu_ptr(&net_rand_state, i);
> +               state->v0 = v0;  state->v1 = v1;
> +               state->v2 = v2;  state->v3 = v3;
> +       }
> +
> +       return 0;
> +}
> +core_initcall(prandom_init_early);


Regards;
Yann.