linux-kernel - Re: Bug in random32.c: all-zero outputs with probability 1/2^32, other seeding bugs

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Message-ID: <alpine.LNX.1.10.0807020835200.20393@fbirervta.pbzchgretzou.qr>
Date:	Wed, 2 Jul 2008 08:38:16 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Benoit Boissinot <bboissin@...il.com>
cc:	linux-kernel@...r.kernel.org, Jack Lloyd <lloyd@...dombit.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Bug in random32.c: all-zero outputs with probability 1/2^32,
 other seeding bugs


On Wednesday 2008-07-02 01:19, Benoit Boissinot wrote:
>@@ -122,7 +122,7 @@
[ int i ]
>
> 	for_each_possible_cpu(i) {
> 		struct rnd_state *state = &per_cpu(net_rand_state,i);
>-		__set_random32(state, i + jiffies);
>+		__set_random32(state, (u32) i + jiffies);
> 	}
> 	return 0;
> }

This cast does not make sense since
 (int)i + jiffies ≡ i + jiffies ≡ (u32)i + jiffies          mod 2^32
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