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.suijten@somainline.org Reviewed-By: AngeloGioacchino Del Regno angelogioacchino.delregno@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.