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

[Purva Yeshi]

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@xxxxxxxxx>
> > ---
> >   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