From: Harald Freudenberger <freude@linux.vnet.ibm.com>
Subject: Re: [PATCH] hw_random: core: Reset user selected rng by writing "" to
 rng_current
Date: Mon, 30 Oct 2017 09:10:43 +0100
Message-ID: <6442aa0b-6416-35fa-4f8b-e601403029fb@linux.vnet.ibm.com>
References: <20171027170404.21262-1-prasannatsmkumar@gmail.com>
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To: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>,
        mpm@selenic.com, herbert@gondor.apana.org.au,
        linux-crypto@vger.kernel.org
In-Reply-To: <20171027170404.21262-1-prasannatsmkumar@gmail.com>
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Sender: linux-crypto-owner@vger.kernel.org

On 10/27/2017 07:04 PM, PrasannaKumar Muralidharan wrote:
> User is able to select a chosen rng by writing its name to rng_current
> but there is no way to reset it without unbinding the rng. Let user
> write "" to rng_current and delesect the chosen rng.
>
> Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
> ---
>  drivers/char/hw_random/core.c | 51 +++++++++++++++++++++++++++----------------
>  1 file changed, 32 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 9701ac7..be03024 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -292,26 +292,48 @@ static struct miscdevice rng_miscdev = {
>  	.groups		= rng_dev_groups,
>  };
>
> +static int enable_best_rng(void)
> +{
> +	int ret = -ENODEV;
> +
> +	BUG_ON(!mutex_is_locked(&rng_mutex));
> +
> +	/* rng_list is sorted by quality, use the best (=first) one */
> +	if (!list_empty(&rng_list)) {
> +		struct hwrng *new_rng;
> +
> +		new_rng = list_entry(rng_list.next, struct hwrng, list);
> +		ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
> +		if (!ret)
> +			cur_rng_set_by_user = 0;
> +	}
> +
> +	return ret;
> +}
> +
>  static ssize_t hwrng_attr_current_store(struct device *dev,
>  					struct device_attribute *attr,
>  					const char *buf, size_t len)
>  {
> -	int err;
> +	int err = -ENODEV;
>  	struct hwrng *rng;
>
>  	err = mutex_lock_interruptible(&rng_mutex);
>  	if (err)
>  		return -ERESTARTSYS;
> -	err = -ENODEV;
> -	list_for_each_entry(rng, &rng_list, list) {
> -		if (sysfs_streq(rng->name, buf)) {
> -			err = 0;
> -			cur_rng_set_by_user = 1;
> -			if (rng != current_rng)
> +
> +	if (sysfs_streq(buf, "")) {
> +		err = enable_best_rng();
> +	} else {
> +		list_for_each_entry(rng, &rng_list, list) {
> +			if (sysfs_streq(rng->name, buf)) {
> +				cur_rng_set_by_user = 1;
>  				err = set_current_rng(rng);
> -			break;
> +				break;
> +			}
>  		}
>  	}
> +
>  	mutex_unlock(&rng_mutex);
>
>  	return err ? : len;
> @@ -493,17 +515,8 @@ void hwrng_unregister(struct hwrng *rng)
>  	mutex_lock(&rng_mutex);
>
>  	list_del(&rng->list);
> -	if (current_rng == rng) {
> -		drop_current_rng();
> -		cur_rng_set_by_user = 0;
> -		/* rng_list is sorted by quality, use the best (=first) one */
> -		if (!list_empty(&rng_list)) {
> -			struct hwrng *new_rng;
> -
> -			new_rng = list_entry(rng_list.next, struct hwrng, list);
> -			set_current_rng(new_rng);
> -		}
> -	}
> +	if (current_rng == rng)
> +		enable_best_rng();
>
>  	if (list_empty(&rng_list)) {
>  		mutex_unlock(&rng_mutex);
That's a really good idea. I also thought about something like that.
regards
Harald Freudenberger