Re: [PATCH v5] iio: adc: pac1934: validate ACPI _DSM return type and bounds

[Andy Shevchenko]

On Fri, Oct 30, 2026 at 12:35:28PM +0000, Tristan Madani wrote:

> pac1934_acpi_parse_channel_config() calls acpi_evaluate_dsm() four
> times to read channel configuration but does not validate the returned
> object type or array bounds:
> 
>   1. No check that the returned object is ACPI_TYPE_PACKAGE.  If
>      firmware returns a different type, accessing rez->package.count
>      and rez->package.elements on a non-package object produces
>      unpredictable values.
> 
>   2. The loop bounds use rez->package.count directly without capping
>      to PAC1934_MAX_NUM_CHANNELS (4).  A package with more elements
>      than expected causes writes past the fixed-size labels[],
>      shunts[], and active_channels[] arrays.
> 
>   3. The bipolar and sample rate DSM calls access elements[0] without
>      verifying package.count >= 1.
> 
> Use acpi_evaluate_dsm_typed() with ACPI_TYPE_PACKAGE to validate the
> return type at evaluation time.  Cap loop iterations to
> PAC1934_MAX_NUM_CHANNELS, and verify package count >= 1 before
> accessing elements[0].

...

> +	count = min_t(unsigned int, rez->package.count,
> +		      PAC1934_MAX_NUM_CHANNELS * 2);

We have already discussed that, that min_t() has not to be in use.
Ditto for the rest of the similar cases.

I would recommend you to slow down, drop AI assistance and check
the code (variable types, available macros and their usages) first.
Don't send a new version until you understand what AI is trying to
do and what we want to have at the end.

-- 
With Best Regards,
Andy Shevchenko