[PATCH v2] iio: gts-helper: add __counted_by_ptr to struct iio_gts

[Bill Wendling <morbo@google.com>]

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.

Cc: codemender-patching+linux@google.com
Assisted-by: LLM
Signed-off-by: Bill Wendling <morbo@google.com>
Acked-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
v2: Remove reordering of assignments. It's not necessary as an assignment of
    the pointer isn't an access that's checked by KASAN.
---
 include/linux/iio/iio-gts-helper.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/iio/iio-gts-helper.h b/include/linux/iio/iio-gts-helper.h
index 66f830ab9b49..7e7d3396ff1a 100644
--- a/include/linux/iio/iio-gts-helper.h
+++ b/include/linux/iio/iio-gts-helper.h
@@ -58,14 +58,14 @@ struct iio_itime_sel_mul {
 
 struct iio_gts {
 	u64 max_scale;
-	const struct iio_gain_sel_pair *hwgain_table;
+	const struct iio_gain_sel_pair *hwgain_table __counted_by_ptr(num_hwgain);
 	int num_hwgain;
-	const struct iio_itime_sel_mul *itime_table;
+	const struct iio_itime_sel_mul *itime_table __counted_by_ptr(num_itime);
 	int num_itime;
-	int **per_time_avail_scale_tables;
-	int *avail_all_scales_table;
+	int **per_time_avail_scale_tables __counted_by_ptr(num_itime);
+	int *avail_all_scales_table __counted_by_ptr(num_avail_all_scales);
 	int num_avail_all_scales;
-	int *avail_time_tables;
+	int *avail_time_tables __counted_by_ptr(num_avail_time_tables);
 	int num_avail_time_tables;
 };
 
-- 
2.56.0.rc1.310.g51773c2048-goog