linux-kernel - Re: [PATCH 1/4] PM / devfreq: governor: Replace sscanf() with kstrtoul() in set_freq

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Message-ID: <215066b4-5f61-4a12-91f8-57b3c37ba3e8@huawei.com>
Date: Mon, 28 Apr 2025 16:07:02 +0800
From: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
To: David Laight <david.laight.linux@...il.com>
CC: <myungjoo.ham@...sung.com>, <kyungmin.park@...sung.com>,
	<cw00.choi@...sung.com>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
	<jonathan.cameron@...wei.com>, <zhanjie9@...ilicon.com>,
	<lihuisong@...wei.com>, <yubowen8@...wei.com>, <cenxinghai@...artners.com>
Subject: Re: [PATCH 1/4] PM / devfreq: governor: Replace sscanf() with
 kstrtoul() in set_freq_store()

On 2025/4/27 19:17, David Laight wrote:
> On Mon, 21 Apr 2025 11:00:17 +0800
> Lifeng Zheng <zhenglifeng1@...wei.com> wrote:
> 
>> Replace sscanf() with kstrtoul() in set_freq_store() and check the result
>> to avoid invalid input.
> 
> Isn't this a UAPI change?
> 
> The sscanf() version will ignore trailing characters.
> In this case it is actually likely that value might have a trailing "Hz".

I tried to still use sscanf() at first, but checkpatch warned: "Prefer
kstrto<type> to single variable sscanf".

I'm not sure if we should ignore this warning.

> 
> 	David
> 
>>
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
>> ---
>>  drivers/devfreq/governor_userspace.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
>> index d1aa6806b683..175de0c0b50e 100644
>> --- a/drivers/devfreq/governor_userspace.c
>> +++ b/drivers/devfreq/governor_userspace.c
>> @@ -9,6 +9,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/device.h>
>>  #include <linux/devfreq.h>
>> +#include <linux/kstrtox.h>
>>  #include <linux/pm.h>
>>  #include <linux/mutex.h>
>>  #include <linux/module.h>
>> @@ -39,10 +40,13 @@ static ssize_t set_freq_store(struct device *dev, struct device_attribute *attr,
>>  	unsigned long wanted;
>>  	int err = 0;
>>  
>> +	err = kstrtoul(buf, 0, &wanted);
>> +	if (err)
>> +		return err;
>> +
>>  	mutex_lock(&devfreq->lock);
>>  	data = devfreq->governor_data;
>>  
>> -	sscanf(buf, "%lu", &wanted);
>>  	data->user_frequency = wanted;
>>  	data->valid = true;
>>  	err = update_devfreq(devfreq);
> 
>