On Tue, Aug 13, 2013 at 4:17 AM, Manfred Schlaegl
<manfred.schlaegl@xxxxxx> wrote:
> 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.
>
Indeed, this is an issue. Thanks for this nice catch and fixing.
I merged this patch into my tree and it will hit 3.11 release.
Thanks,
-Bryan
> 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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