linux-kernel - Re: [PATCH 1/2] hwrng: don't fetch rng from sources without init

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Date:	Wed, 2 Jul 2014 07:58:23 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	herbert@...dor.apana.org.au, keescook@...omium.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/2] hwrng: don't fetch rng from sources without init

On Wed, Jul 02, 2014 at 03:58:15PM +0530, Amit Shah wrote:
> Commit d9e7972619334 "hwrng: add randomness to system from rng sources"
> added a call to rng_get_data() from the hwrng_register() function.
> However, some rng devices need initialization before data can be read
> from them.
> 
> Also, the virtio-rng device does not behave properly when this call is
> made in its probe() routine - the virtio core sets the DRIVER_OK status
> bit only on a successful probe, which means the host ignores all
> communication from the guest, and the guest insmod or boot process just
> sits there doing nothing.
> 
> This commit makes the call to rng_get_data() depend on no init fn
> pointer being registered by the device.  If an init function is
> registered, this call isn't made.
> 
> CC: Kees Cook <keescook@...omium.org>
> CC: Jason Cooper <jason@...edaemon.net>
> CC: Herbert Xu <herbert@...dor.apana.org.au>
> CC: <stable@...r.kernel.org> # For 3.15 only

# v3.15+ should be fine here.

> Signed-off-by: Amit Shah <amit.shah@...hat.com>
> ---
>  drivers/char/hw_random/core.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 334601c..3f3941d 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -347,9 +347,11 @@ int hwrng_register(struct hwrng *rng)
>  	INIT_LIST_HEAD(&rng->list);
>  	list_add_tail(&rng->list, &rng_list);
>  
> -	bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> -	if (bytes_read > 0)
> -		add_device_randomness(bytes, bytes_read);
> +	if (!rng->init) {
> +		bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> +		if (bytes_read > 0)
> +			add_device_randomness(bytes, bytes_read);
> +	}

afaict, this is redundant at initialization time.  current_rng shouldn't
be set yet, so hwrng_init(rng) will get called at line 333.  Or, am I
missing something?

thx,

Jason.
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