On 2021-11-15 11:23:27, Daniel Thompson wrote:
On Fri, Nov 12, 2021 at 10:43:37PM +0100, Marijn Suijten wrote:
On 2021-11-12 13:35:03, Marijn Suijten wrote:
On 2021-11-12 12:08:39, Daniel Thompson wrote:
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");The warning should also be below the error message on the next if statement.
Agreed.
Thinking about this again while reworking the patches, I initially put this above the error to make DT writers aware. There's no point telling them that their values are out of sync (num-strings > len(enabled-strings)), when they "shouldn't even" (don't need to) set both in the first place. They might needlessly fix the discrepancy, see the driver finally probe (working backlight) and carry on without noticing this warning that now appears.
Sorry for bringing this back up, but I'm curious about your opinion.
With a more helpful warning about how to fix then I think it is OK to have both the warning and the error.
Thanks - I presume the message we settled upon last time is helpful enough:
Only one of qcom,num-strings or qcom,enabled-strings should be set
I'll respin this, together with this warning reordered into the next commit, and using __le16 for the cpu_to_le16 output.
- Marijn