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

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Message-ID: <0a1ea318-20e3-44b8-9d5e-f603c5341087@gmail.com>
Date: Fri, 11 Apr 2025 12:29:14 +0530
From: Purva Yeshi <purvayeshi550@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
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 11/04/25 01:34, Guenter Roeck wrote:
> 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

Thank you for the clarification, Guenter. I appreciate your review.

> 
>> @@ -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
>>
>>

Best regards,
Purva