Re: [PATCH RESEND v2] iio: accel: fxls8962af: clamp FIFO sample count

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 09 Aug 2026 05:04:41 +0800
"Shengzhuo Wei" <me@cherr.cc> wrote:

> fxls8962af_fifo_flush() copies the number of samples the device reports
> in its FIFO status register into an on-stack buffer
> 
> 	u16 buffer[FXLS8962AF_FIFO_LENGTH * 3];
> 
> which is sized for at most FXLS8962AF_FIFO_LENGTH (32) samples. The
> sample count is read from the BUF_STATUS register and only masked to its
> 6 valid bits (0..63), with no clamp to the buffer size. The watermark
> path caps the count on the write side (fxls8962af_set_watermark) but
> the read path does not, so a malfunctioning or malicious device
> reporting BUF_CNT > 32 overflows the buffer.
> 
> Clamp count to FXLS8962AF_FIFO_LENGTH, mirroring the watermark clamp.
> 
> Fixes: 79e3a5bdd9ef ("iio: accel: fxls8962af: add hw buffered sampling")

Same comments as similar patches.
- Not a fix, but rather hardening against buggy hardware.
- Don't hide the problem by clamping.  If this happens in the wild
  we want to know about it!


> Cc: stable@vger.kernel.org
> Assisted-by: GLM:5.2
> Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
> Signed-off-by: Shengzhuo Wei <me@cherr.cc>
> ---
> The transfer reads count * 6 bytes through regmap, so a device reporting
> up to 63 samples writes up to 378 bytes into the 192-byte buffer,
> clobbering the stack canary, saved registers and the return address.
> This mirrors the bmc150 fix (ce0e1cae2609). A well-formed flush reports
> at most FXLS8962AF_FIFO_LENGTH samples, so legitimate devices are
> unaffected.
> ---
> Changes in v2:
> - Use min() instead of min_t() as suggested by Andy Shevchenko.
> - Link to v1: https://lore.kernel.org/r/20260806-fxls8962af-fifo-v1-1-bd9d27047fee@cherr.cc
> ---
>  drivers/iio/accel/fxls8962af-core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/accel/fxls8962af-core.c b/drivers/iio/accel/fxls8962af-core.c
> index d0c2a8daef0db964134ad10b25782b9f5752613d..18d7b09bddd2b4f506c3348bf4e8cf94ce1c554a 100644
> --- a/drivers/iio/accel/fxls8962af-core.c
> +++ b/drivers/iio/accel/fxls8962af-core.c
> @@ -969,6 +969,8 @@ static int fxls8962af_fifo_flush(struct iio_dev *indio_dev)
>  	if (!count)
>  		return 0;
>  
> +	count = min(count, FXLS8962AF_FIFO_LENGTH);
> +
>  	data->old_timestamp = data->timestamp;
>  	data->timestamp = iio_get_time_ns(indio_dev);
>  
> 
> ---
> base-commit: 848acc8ffe1b7cd5f1bf427b93069becfebc2c9d
> change-id: 20260806-fxls8962af-fifo-c3812fd02eeb
> 
> Best regards,