[PATCH 05/10] backlight: qcom-wled: Fix off-by-one maximum with default num_strings

[Marijn Suijten]

When not specifying num-strings in the DT the default is used, but +1 is
added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
of 3 and 4 respectively, causing out of bounds reads and register
read/writes.  This +1 exists for a deficiency in the DT parsing code,
and is simply omitted entirely - solving this oob issue - by allowing
one extra iteration of the wled_var_cfg function parsing this particular
property.

Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxxx>
---
 drivers/video/backlight/qcom-wled.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index 27e8949c7922..66ce77ee3099 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c
@@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
 
 static u32 wled3_num_strings_values_fn(u32 idx)
 {
-	return idx + 1;
+	return idx;
 }
 
 static const struct wled_var_cfg wled3_num_strings_cfg = {
 	.fn = wled3_num_strings_values_fn,
-	.size = 3,
+	.size = 4, /* [0, 3] */
 };
 
 static const struct wled_var_cfg wled4_num_strings_cfg = {
 	.fn = wled3_num_strings_values_fn,
-	.size = 4,
+	.size = 5, /* [0, 4] */
 };
 
 static u32 wled3_switch_freq_values_fn(u32 idx)
@@ -1520,8 +1520,6 @@ static int wled_configure(struct wled *wled)
 			*bool_opts[i].val_ptr = true;
 	}
 
-	cfg->num_strings = cfg->num_strings + 1;
-
 	string_len = of_property_count_elems_of_size(dev->of_node,
 						     "qcom,enabled-strings",
 						     sizeof(u32));
-- 
2.33.0