To: Matti Linnanvuori <mattilinnanvuori@yahoo.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: /dev/urandom uses uninit bytes, leaks user data
In-Reply-To: Your message of "Fri, 14 Dec 2007 23:20:30 PST."
             <977119.41267.qm@web52005.mail.re2.yahoo.com>
From: Valdis.Kletnieks@vt.edu
References: <977119.41267.qm@web52005.mail.re2.yahoo.com>
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Date: Sat, 15 Dec 2007 02:54:01 -0500
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On Fri, 14 Dec 2007 23:20:30 PST, Matti Linnanvuori said:
> From: Matti Linnanvuori <mattilinnnvuori@yahoo.com>
> 
> /dev/urandom use no uninit bytes, leak no user data
> 
> Signed-off-by: Matti Linnanvuori <mattilinnnvuori@yahoo.com>
> 
> ---
> 
> --- a/drivers/char/random.c	2007-12-15 09:09:37.895414000 +0200
> +++ b/drivers/char/random.c	2007-12-15 09:12:02.607831500 +0200
> @@ -689,7 +689,7 @@ static ssize_t extract_entropy(struct en
>   */
>  static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
>  {
> -	__u32 tmp[OUTPUT_POOL_WORDS];
> +	static __u32 tmp[OUTPUT_POOL_WORDS];

This looks like a race waiting to happen - what lock is held so we don't have
'tmp' smashed by 2 instances on different CPUs (not a problem when each
instance lives on a hopefully separate stack)?

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