Re: [PATCH] iio: gts-helper: add __counted_by_ptr to struct iio_gts

[Kees Cook <kees@kernel.org>]

On Wed, Sep 23, 2026 at 04:16:30AM +0000, Bill Wendling wrote:
> The compiler attribute __counted_by_ptr can be used by KASAN and UBSAN
> to detect out-of-bounds accesses to pointer fields in structs where a
> corresponding element count field is available.
> 
> In "struct iio_gts", there are multiple pointer fields associated with
> an element count. This patch annotates these pointer fields with
> "__counted_by_ptr" to improve runtime safety:
> 
> - 'hwgain_table': counted by 'num_hwgain'
> - 'itime_table': counted by 'num_itime'
> - 'per_time_avail_scale_tables': counted by 'num_itime'
> - 'avail_all_scales_table': counted by 'num_avail_all_scales'
> - 'avail_time_tables': counted by 'num_avail_time_tables'
> 
> To ensure that the count is set correctly before any pointer is
> accessed or assigned, we update "iio_init_iio_gts()" to set the counts
> prior to assigning the pointers.

"Accessed" yes, "assigned" no. :) Let's not churn on assignment ordering
unless there is some problem I'm not seeing. The only time this should
ever matter is if there is multithread visibility on the object already,
but that would require both counter and pointer be set, so that'd be a
general locking issue, but ordering during initialization doesn't
matter.

-- 
Kees Cook