Re: [PATCH 2/3] crypto: hwrng remember rng chosen by user

[PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>]

Hi Harald,

On 3 July 2017 at 15:33, Harald Freudenberger <freude@linux.vnet.ibm.com> wrote:
> 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 choise.
>
> Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
> ---
>  drivers/char/hw_random/core.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index e9dda16..ffd4e36 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -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;
> @@ -444,10 +447,12 @@ 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 +484,7 @@ 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;
> --
> 2.7.4
>

Looks good to me. Reviewed-by: PrasannaKumar Muralidharan
<prasannatsmkumar@gmail.com>.

Regards,
PrasannaKumar