Re: [PATCH 2/2] iio: proximity: sx9360: reject unsupported hardware gain values

[Jonathan Cameron]

On Sat,  7 Nov 2026 16:47:04 +0530
Arnav Kapoor <kapoorarnav43@xxxxxxxxx> wrote:

> sx9360_write_gain() passes any value from userspace to ilog2() and then
> FIELD_PREP() into the 3-bit PROX_CTRL0 gain field without checking it.
> Only gains of 1, 2, 4 and 8 are supported (and listed in
> hardwaregain_available), but other values are not rejected:
> 
>   - 3, 5, 6, 7 are rounded down to the next power of two;
>   - 16 to 128 write gain codes 4 to 7, which the driver does not
>     advertise, and the next read reports gains of 16 to 128;
>   - 256 and larger wrap around in the field, e.g. 256 sets a gain of 1;
>   - 0 and negative values write code 7 (read back as 128), because
>     ilog2(0) is -1 and a negative int becomes a large unsigned value.
> 
> The write returns success in every case.
> 
> Return -EINVAL for anything other than 1, 2, 4 or 8.
> 
> Fixes: 1cdb4c47f7f5 ("iio:proximity:sx9360: Add sx9360 support")
> Signed-off-by: Arnav Kapoor <kapoorarnav43@xxxxxxxxx>
Same comments as for the previous.  Fine to reject stuff that will
get unexpected results. The rounding down is more reasonable so
don't reject that.

J
> ---
>  drivers/iio/proximity/sx9360.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iio/proximity/sx9360.c b/drivers/iio/proximity/sx9360.c
> index 2a9b37df8f62..c6e5b3e557bb 100644
> --- a/drivers/iio/proximity/sx9360.c
> +++ b/drivers/iio/proximity/sx9360.c
> @@ -625,6 +625,9 @@ static int sx9360_write_gain(struct sx_common_data *data,
>  {
>  	unsigned int gain, reg;
>  
> +	if (val <= 0 || val > 8 || !is_power_of_2(val))
> +		return -EINVAL;
> +
>  	gain = ilog2(val);
>  	reg = SX9360_REG_PROX_CTRL0_PHR + chan->channel;
>  	gain = FIELD_PREP(SX9360_REG_PROX_CTRL0_GAIN_MASK, gain);