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Commit f6b013ee authored by Harald Freudenberger's avatar Harald Freudenberger Committed by Greg Kroah-Hartman
Browse files

hwrng: remember rng chosen by user 



commit 10a515ddb5f19a1ff0b9882c430b4427843169f3 upstream.

When a user chooses a rng source via sysfs attribute
this rng should be sticky, even when other sources
with better quality to register. This patch introduces
a simple way to remember the user's choice. This is
reflected by a new sysfs attribute file 'rng_selected'
which shows if the current rng has been chosen by
userspace. The new attribute file shows '1' for user
selected rng and '0' otherwise.

Signed-off-by: default avatarHarald Freudenberger <freude@linux.vnet.ibm.com>
Reviewed-by: default avatarPrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 42802952

drivers/char/hw_random/core.c

+19 −2
Original line number Diff line number Diff line
@@ -27,6 +27,8 @@ 
#define RNG_MODULE_NAME		"hw_random"



static struct hwrng *current_rng;

/* the current rng has been explicitly chosen by user via sysfs */

static int cur_rng_set_by_user;

static struct task_struct *hwrng_fill;

/* list of registered rngs, sorted decending by quality */

static LIST_HEAD(rng_list);
@@ -303,6 +305,7 @@ static ssize_t hwrng_attr_current_store(struct device *dev, 
	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)

				err = set_current_rng(rng);

			break;
@@ -351,16 +354,27 @@ static ssize_t hwrng_attr_available_show(struct device *dev, 
	return strlen(buf);

}



static ssize_t hwrng_attr_selected_show(struct device *dev,

					struct device_attribute *attr,

					char *buf)

{

	return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);

}



static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,

		   hwrng_attr_current_show,

		   hwrng_attr_current_store);

static DEVICE_ATTR(rng_available, S_IRUGO,

		   hwrng_attr_available_show,

		   NULL);

static DEVICE_ATTR(rng_selected, S_IRUGO,

		   hwrng_attr_selected_show,

		   NULL);



static struct attribute *rng_dev_attrs[] = {

	&dev_attr_rng_current.attr,

	&dev_attr_rng_available.attr,

	&dev_attr_rng_selected.attr,

	NULL

};
@@ -443,10 +457,12 @@ int hwrng_register(struct hwrng *rng) 


	old_rng = current_rng;

	err = 0;

	if (!old_rng || (rng->quality > old_rng->quality)) {

	if (!old_rng ||

	    (!cur_rng_set_by_user && rng->quality > old_rng->quality)) {

		/*

		 * Set new rng as current as the new rng source

		 * provides better entropy quality.

		 * provides better entropy quality and was not

		 * chosen by userspace.

		 */

		err = set_current_rng(rng);

		if (err)
@@ -478,6 +494,7 @@ void hwrng_unregister(struct hwrng *rng) 
	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;