linux-kernel - Re: [PATCH] hwmon: asus_atk0110: NULL buf.pointer after free

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Message-ID: <bba9ff87-90de-4eae-99d1-647ee413d480@roeck-us.net>
Date: Thu, 10 Apr 2025 13:04:08 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Purva Yeshi <purvayeshi550@...il.com>
Cc: Luca Tettamanti <kronos.it@...il.com>, Jean Delvare <jdelvare@...e.com>,
	linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: asus_atk0110: NULL buf.pointer after free

On Fri, Apr 11, 2025 at 12:04:50AM +0530, Purva Yeshi wrote:
> Fix Smatch-detected issue:
> drivers/hwmon/asus_atk0110.c:987 atk_enumerate_old_hwmon() error:
> double free of 'buf.pointer' (line 966)
> drivers/hwmon/asus_atk0110.c:1008 atk_enumerate_old_hwmon() error:
> double free of 'buf.pointer' (line 987)
> 
> Smatch warns about double free of 'buf.pointer'.
> This happens because the same buffer struct is reused multiple times
> without resetting the pointer after free. Set buf.pointer = NULL
> after each ACPI_FREE to prevent possible use-after-free bugs.
> 
> Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> ---
>  drivers/hwmon/asus_atk0110.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/hwmon/asus_atk0110.c b/drivers/hwmon/asus_atk0110.c
> index c80350e499e9..83ee7f25bb8e 100644
> --- a/drivers/hwmon/asus_atk0110.c
> +++ b/drivers/hwmon/asus_atk0110.c
> @@ -964,6 +964,7 @@ static int atk_enumerate_old_hwmon(struct atk_data *data)
>  			count++;
>  	}
>  	ACPI_FREE(buf.pointer);
> +	buf.pointer = NULL;
>  
>  	/* Temperatures */
>  	buf.length = ACPI_ALLOCATE_BUFFER;
> @@ -985,6 +986,7 @@ static int atk_enumerate_old_hwmon(struct atk_data *data)
>  			count++;
>  	}
>  	ACPI_FREE(buf.pointer);
> +	buf.pointer = NULL;
>  
>  	/* Fans */
>  	buf.length = ACPI_ALLOCATE_BUFFER;

buf.length is set to ACPI_ALLOCATE_BUFFER to trigger buffer
allocation in acpi_evaluate_object_typed(). The old content of
buf.pointer is irrelevant (and not initialized to start with
in the first call). The problem you describe does not exist.

Guenter

> @@ -1006,6 +1008,7 @@ static int atk_enumerate_old_hwmon(struct atk_data *data)
>  			count++;
>  	}
>  	ACPI_FREE(buf.pointer);
> +	buf.pointer = NULL;
>  
>  	return count;
>  }
> -- 
> 2.34.1
> 
>