On Fri, Nov 12, 2021 at 01:26:57AM +0100, Marijn Suijten wrote:
> 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 parsing the
> property separately much like qcom,enabled-strings.
>
> This also allows more stringent checks on the maximum value when
> qcom,enabled-strings is provided in the DT. Note that num-strings is
> parsed after enabled-strings to give it final sign-off over the length,
> which DT currently utilizes to get around an incorrect fixed read of
> four elements from that array (has been addressed in a prior patch).
>
> Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> Signed-off-by: Marijn Suijten <marijn.suij...@somainline.org>
> Reviewed-By: AngeloGioacchino Del Regno
> <angelogioacchino.delre...@somainline.org>
> ---
> drivers/video/backlight/qcom-wled.c | 51 +++++++++++------------------
> 1 file changed, 19 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/video/backlight/qcom-wled.c
> b/drivers/video/backlight/qcom-wled.c
> index 977cd75827d7..c5232478a343 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -1552,6 +1520,25 @@ static int wled_configure(struct wled *wled)
> }
> }
>
> + rc = of_property_read_u32(dev->of_node, "qcom,num-strings", &val);
> + if (!rc) {
> + if (val < 1 || val > wled->max_string_count) {
> + dev_err(dev, "qcom,num-strings must be between 1 and
> %d\n",
> + wled->max_string_count);
> + return -EINVAL;
> + }
> +
> + if (string_len > 0) {
> + dev_warn(dev, "qcom,num-strings and
> qcom,enabled-strings are ambiguous\n");
This warning occurs even when there is no ambiguity.
This could be:
if (string_len > 0 && val != string_len)
The warning should also be below the error message on the next if statement.
Combined these changes allows us to give a much more helpful and assertive
warning message:
qcom,num-strings mis-matches and will partially override
qcom,enabled-strings (remove qcom,num-strings?)
> + if (val > string_len) {
> + dev_err(dev, "qcom,num-strings exceeds
> qcom,enabled-strings\n");
> + return -EINVAL;
> + }
> + }
Daniel.
