Re: [RESEND PATCH v2 04/13] backlight: qcom-wled: Fix off-by-one maximum with default num_strings
From: Daniel Thompson <hidden>
Date: 2021-11-12 12:08:46
Also in:
dri-devel, linux-arm-msm, linux-fbdev, lkml, phone-devel
On Fri, Nov 12, 2021 at 01:26:57AM +0100, Marijn Suijten wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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.