fb_notifier_callback is called on any event fired by fb_notifier_call_chain. Events may, or may not contain some data (fb_event.data).
In case of FB_EVENT_BLANK fb_event.data contains a pointer to an integer holding the blank state. The Problem is, that in ledtrig-backlight.c - fb_notifier_callback the pointer to blank state is
dereferenced BEFORE the event-type is checked.
Obviously this leads to problems with other events than FB_EVENT_BLANK, where fb_event.data is undefined or NULL.
It seems, that this problem existed ever since the driver was added.
Like in drivers/video/backlight/backlight.c line 43 I would suggest to return immediately on events other than FB_EVENT_BLANK.
Signed-off-by: Manfred Schlaegl <manfred.schlaegl@xxxxxx>
---
Background information:
I'm currently working on a IMX53(ARM) based hardware and Linux 3.11-rc5 and detected a problem in drivers/leds/trigger/ledtrig-backlight.c
ledtrig is used on our hardware (besides pwm-backlight) to switch off a gpio-line connected to display-supply enable-line, when the display is blanked.
On first boot after configuring ledtrig I detected an invalid memory access in ledtrig-backlight.c - fb_notifier_callback. In my special case the segfault was caused by an FB_EVENT_FB_REGISTERED,
fired with undefined fb_event.data in drivers/video/fbmem.c line 1653.
diff --git a/drivers/leds/trigger/ledtrig-backlight.c b/drivers/leds/trigger/ledtrig-backlight.c
index 3c9c88a..2538dbe 100644
--- a/drivers/leds/trigger/ledtrig-backlight.c
+++ b/drivers/leds/trigger/ledtrig-backlight.c
@@ -36,26 +36,28 @@ static int fb_notifier_callback(struct notifier_block *p,
struct bl_trig_notifier, notifier);
struct led_classdev *led = n->led;
struct fb_event *fb_event = data;
- int *blank = fb_event->data;
- int new_status = *blank ? BLANK : UNBLANK;
+ int *blank;
+ int new_status;
+
+ /* If we aren't interested in this event, skip it immediately ... */
+ if (event != FB_EVENT_BLANK)
+ return 0;
- switch (event) {
- case FB_EVENT_BLANK:
- if (new_status == n->old_status)
- break;
+ blank = fb_event->data;
+ new_status = *blank ? BLANK : UNBLANK;
- if ((n->old_status == UNBLANK) ^ n->invert) {
- n->brightness = led->brightness;
- __led_set_brightness(led, LED_OFF);
- } else {
- __led_set_brightness(led, n->brightness);
- }
+ if (new_status == n->old_status)
+ return 0;
- n->old_status = new_status;
-
- break;
+ if ((n->old_status == UNBLANK) ^ n->invert) {
+ n->brightness = led->brightness;
+ __led_set_brightness(led, LED_OFF);
+ } else {
+ __led_set_brightness(led, n->brightness);
}
+ n->old_status = new_status;
+
return 0;
}
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