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

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Date:   Tue, 08 Aug 2017 12:26:03 -0700
From:   Saravana Kannan <skannan@...eaurora.org>
To:     Pavan Kondeti <pkondeti@...eaurora.org>
CC:     Santosh Mardi <gsantosh@...eaurora.org>, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, rafael.j.wysocki@...el.com,
        cw00.choi@...sung.com, linux-pm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, gsantosh@....qualcomm.com,
        skannan@...cinc.com, rgottimu@....qualcomm.com
Subject: Re: [PATCH] devfreq: add error check for sscanf in userspace governor

On 08/07/2017 11:56 PM, Pavan Kondeti wrote:
> Hi Santosh,
>
> On Mon, Aug 7, 2017 at 6:36 PM, Santosh Mardi <gsantosh@...eaurora.org> 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@...eaurora.org>
>> ---
>>   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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