Re: [PATCH v2 1/3] rtc: ds1685: arm the wake-up alarm at power-off only if an alarm is set

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] rtc: ds1685: NULL pointer deref in poweroff handler if unbound
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commit e81b71e9197dea1b3b5991740fdeeb891e509522
Author: Imre Kaloz <kaloz@kernel.org>

rtc: ds1685: arm the wake-up alarm at power-off only if an alarm is set

This commit modifies the DS1685 RTC driver to only arm the wake-up alarm
during power-off if an alarm is actually set. It prevents stale alarm
registers from inadvertently powering the machine back on.

> diff --git a/drivers/rtc/rtc-ds1685.c b/drivers/rtc/rtc-ds1685.c
> index 5fc8e36b1abf8..94c89333c5d5c 100644
> --- a/drivers/rtc/rtc-ds1685.c
> +++ b/drivers/rtc/rtc-ds1685.c
> @@ -1367,7 +1367,7 @@ module_platform_driver(ds1685_rtc_driver);
>  void __noreturn
>  ds1685_rtc_poweroff(struct platform_device *pdev)
>  {
> -	u8 ctrla, ctrl4a, ctrl4b;
> +	u8 ctrla, ctrlb, ctrl4a, ctrl4b;
>  	struct ds1685_priv *rtc;
>  
>  	/* Check for valid RTC data, else, spin forever. */

[ ... ]

> @@ -1394,6 +1394,8 @@ ds1685_rtc_poweroff(struct platform_device *pdev)
>  		ctrla &= ~(RTC_CTRL_A_DV2);
>  		rtc->write(rtc, RTC_CTRL_A, ctrla);
>  
> +		ctrlb = rtc->read(rtc, RTC_CTRL_B);

[Severity: High]
Can this lead to a NULL pointer dereference during the system poweroff
sequence?

If the driver failed to probe or was explicitly unbound via sysfs,
platform_get_drvdata(pdev) will return NULL. When the global shutdown handler
calls ds1685_rtc_poweroff(), we fetch the driver data and dereference it
without checking:

        /* Get the rtc data. */
        rtc = platform_get_drvdata(pdev);

        /* ... */
        if (rtc->irq_num)
                disable_irq_nosync(rtc->irq_num);

        ctrla = rtc->read(rtc, RTC_CTRL_A);

Could this hang the system instead of powering off by causing a panic when rtc
is NULL?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261013120208.11268-1-kaloz@kernel.org?part=1