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

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Message-ID: <20250427121704.51e3af2a@pumpkin>
Date: Sun, 27 Apr 2025 12:17:04 +0100
From: David Laight <david.laight.linux@...il.com>
To: Lifeng Zheng <zhenglifeng1@...wei.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 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".

	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);