Re: [PATCH] devfreq: add error check for sscanf in userspace governor

[Saravana Kannan]

On 08/07/2017 11:56 PM, Pavan Kondeti wrote:
> Hi Santosh,
>
> On Mon, Aug 7, 2017 at 6:36 PM, Santosh Mardi <gsantosh@xxxxxxxxxxxxxx> wrote:
> > store_freq function of devfreq userspace governor
> > executes further, even if error is returned from sscanf,
> > this will result in setting up wrong frequency value.
> >
> > Add proper error check to bail out if any error is returned.
> >
> > Signed-off-by: Santosh Mardi <gsantosh@xxxxxxxxxxxxxx>
> > ---
> >   drivers/devfreq/governor_userspace.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
> > index 77028c2..1d0c9cc 100644
> > --- a/drivers/devfreq/governor_userspace.c
> > +++ b/drivers/devfreq/governor_userspace.c
> > @@ -53,12 +53,15 @@ static ssize_t store_freq(struct device *dev, struct device_attribute *attr,
> >          mutex_lock(&devfreq->lock);
> >          data = devfreq->data;
> >
> > -       sscanf(buf, "%lu", &wanted);
> > +       err = sscanf(buf, "%lu", &wanted);

Also, we could just use kstroul().

> > +       if (err != 1)
> > +               goto out;
>
> You can save this goto statement by moving this sscanf checking to
> before taking the mutex.
>
> >          data->user_frequency = wanted;
> >          data->valid = true;
> >          err = update_devfreq(devfreq);
> >          if (err == 0)
> >                  err = count;
> > +out:
> >          mutex_unlock(&devfreq->lock);
> >          return err;
> >   }
> > --
> > 1.9.1

-Saravana


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