linux-kernel - Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early

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Date:   Mon, 17 Oct 2016 19:17:31 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Jens Axboe <axboe@...com>, Matt Mullins <mmullins@...x.us>
Subject: Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness()

Am Montag, 17. Oktober 2016, 10:06:27 CEST schrieb Andy Lutomirski:

Hi Andy,

> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 9203f2d130c0..340f96e44642 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -84,14 +84,14 @@ static size_t rng_buffer_size(void)
> 
>  static void add_early_randomness(struct hwrng *rng)
>  {
> -	unsigned char bytes[16];
>  	int bytes_read;
> +	size_t size = min_t(size_t, 16, rng_buffer_size());
> 
>  	mutex_lock(&reading_mutex);
> -	bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> +	bytes_read = rng_get_data(rng, rng_buffer, size, 1);
>  	mutex_unlock(&reading_mutex);
>  	if (bytes_read > 0)
> -		add_device_randomness(bytes, bytes_read);
> +		add_device_randomness(rng_buffer, bytes_read);

Shouldn't there be a memset(0) of the rng_buffer at this point to avoid having 
such data lingering in memory?


Ciao
Stephan