linux-kernel - Re: [PATCH v2 2/3] iio: imu: st_lsm6dsx: Set buffer sampling frequency for accelerometer only

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Message-ID: <20260116194949.06b7b204@jic23-huawei>
Date: Fri, 16 Jan 2026 19:49:49 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Francesco Lavra <flavra@...libre.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>, David Lechner
 <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, Andy
 Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] iio: imu: st_lsm6dsx: Set buffer sampling
 frequency for accelerometer only

On Thu, 15 Jan 2026 13:24:30 +0100
Francesco Lavra <flavra@...libre.com> wrote:

> The st_lsm6dsx_hwfifo_odr_store() function, which is called when userspace
> writes the buffer sampling frequency sysfs attribute, calls
> st_lsm6dsx_check_odr(), which accesses the odr_table array at index
> `sensor->id`; since this array is only 2 entries long, an access for any
> sensor type other than accelerometer or gyroscope is an out-of-bounds
> access.
> 
> To prevent userspace from triggering an out-of-bounds array access, and to
> support the only use case for which FIFO sampling frequency values
> different from the sensor sampling frequency may be needed (which is for
> keeping FIFO data rate low while sampling acceleration data at high rates
> for accurate event detection), do not create the buffer sampling frequency
> attribute for sensor types other than the accelerometer.

If we are going to do this, I'd like a little more discussion of why this
matters for accelerometer events and not gyroscope ones.
(see follow up on v1 discussion I posted earlier today).

Thanks,

Jonathan

> 
> Fixes: 6b648a36c200 ("iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate")
> Signed-off-by: Francesco Lavra <flavra@...libre.com>
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> index 1ee2fc5f5f1f..cde29b2e6f34 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> @@ -862,12 +862,21 @@ int st_lsm6dsx_fifo_setup(struct st_lsm6dsx_hw *hw)
>  	int i, ret;
>  
>  	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
> +		const struct iio_dev_attr **attrs;
> +
>  		if (!hw->iio_devs[i])
>  			continue;
>  
> +		/*
> +		 * For the accelerometer, allow setting FIFO sampling frequency
> +		 * values different from the sensor sampling frequency, which
> +		 * may be needed to keep FIFO data rate low while sampling
> +		 * acceleration data at high rates for accurate event detection.
> +		 */
> +		attrs = (i == ST_LSM6DSX_ID_ACC) ? st_lsm6dsx_buffer_attrs : NULL;
>  		ret = devm_iio_kfifo_buffer_setup_ext(hw->dev, hw->iio_devs[i],
>  						      &st_lsm6dsx_buffer_ops,
> -						      st_lsm6dsx_buffer_attrs);
> +						      attrs);
>  		if (ret)
>  			return ret;
>  	}