linux-kernel - Re: [PATCH 6/7] lib/random32.c: Randomize timeout to the millisecond, not the second

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Message-ID: <53943E34.7030502@redhat.com>
Date:	Sun, 08 Jun 2014 12:43:00 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	George Spelvin <linux@...izon.com>
CC:	davem@...emloft.net, shemminger@...l.org, tytso@....edu,
	linux-kernel@...r.kernel.org, hannes@...essinduktion.org
Subject: Re: [PATCH 6/7] lib/random32.c: Randomize timeout to the millisecond,
 not the second

On 06/07/2014 10:28 AM, George Spelvin wrote:
> If you're going to bother randomizing it, do it right.
> And use prandom_u32_max(), which is designed for the job, rather
> than "% 40".
>
> Signed-off-by: George Spelvin <linux@...izon.com>

Fine by me this cleanup, although not strictly needed.

> ---
>   lib/random32.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/lib/random32.c b/lib/random32.c
> index eee60100..9cc410dd 100644
> --- a/lib/random32.c
> +++ b/lib/random32.c
> @@ -208,14 +208,14 @@ static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
>   static void __prandom_timer(unsigned long dontcare)
>   {
>   	u32 entropy;
> -	unsigned long expires;
> +	unsigned int expires;
>
>   	get_random_bytes(&entropy, sizeof(entropy));
>   	prandom_seed(entropy);
>
>   	/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
> -	expires = 40 + (prandom_u32() % 40);
> -	seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
> +	expires = 40000 + prandom_u32_max(40000);
> +	seed_timer.expires = jiffies + msecs_to_jiffies(expires);
>
>   	add_timer(&seed_timer);
>   }
>
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