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hwrng: remember rng chosen by user 

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: Harald Freudenberger <freude@linux.vnet.ibm.com>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Harald Freudenberger 2017-07-11 09:36:23 +02:00 committed by Herbert Xu
parent 2bbb698388
commit 10a515ddb5
1 changed files with 19 additions and 2 deletions
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21
drivers/char/hw_random/core.c
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@ -28,6 +28,8 @@
#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);
@ -304,6 +306,7 @@ 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;
@ -352,16 +355,27 @@ 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
};
@ -444,10 +458,12 @@ 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)
@ -479,6 +495,7 @@ 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;