Re: [PATCH v4] iio: adc: pac1934: validate ACPI _DSM return type and bounds

[Andy Shevchenko]

On Thu, Oct 29, 2026 at 04:56:02PM +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].

...

>  static int pac1934_acpi_parse_channel_config(struct i2c_client *client,
>  					     struct pac1934_chip_info *info)
>  {
> -	acpi_handle handle;
> -	union acpi_object *rez;
>  	struct device *dev = &client->dev;
>  	unsigned short bi_dir_mask;
> -	int idx, i;
> +	union acpi_object *rez;
> +	acpi_handle handle;
> +	unsigned int count;
>  	guid_t guid;
> +	int idx, i;

No need to touch lines that are unrelated to your change. Just make sure that
your change tries to keep reversed xmas tree order as much as possible.

...

> -	for (i = 0; i < rez->package.count; i += 2) {
> +	count = min(rez->package.count & ~1u, PAC1934_MAX_NUM_CHANNELS * 2);

What is the purpose of 'u' suffix? In case if you want to keep that 32-bit
value this might be even wrong (I haven't checked the promotion rules for the
values with suffix, though).

> +	for (i = 0; i < count; i += 2) {

-- 
With Best Regards,
Andy Shevchenko