Commit 7e7c005b authored Oct 21, 2019 by Alexandre Belloni

rtc: disable uie before setting time and enable after

When setting the time in the future with the uie timer enabled,
rtc_timer_do_work will loop for a while because the expiration of the uie
timer was way before the current RTC time and a new timer will be enqueued
until the current rtc time is reached.

If the uie timer is enabled, disable it before setting the time and enable
it after expiring current timers (which may actually be an alarm).

This is the safest thing to do to ensure the uie timer is still
synchronized with the RTC, especially in the UIE emulation case.

Reported-by: <syzbot+08116743f8ad6f9a6de7@syzkaller.appspotmail.com>
Fixes: 6610e089 ("RTC: Rework RTC code to use timerqueue for events")
Link: https://lore.kernel.org/r/20191020231320.8191-1-alexandre.belloni@bootlin.com

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

parent bb451661

drivers/rtc/interface.c

+18 −1

Original line number	Diff line number	Diff line
		@@ -125,7 +125,7 @@ EXPORT_SYMBOL_GPL(rtc_read_time);

		int rtc_set_time(struct rtc_device rtc, struct rtc_time tm)
		{
		int err;
		int err, uie;

		err = rtc_valid_tm(tm);
		if (err != 0)
		@@ -137,6 +137,17 @@ int rtc_set_time(struct rtc_device rtc, struct rtc_time tm)

		rtc_subtract_offset(rtc, tm);

		#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
		uie = rtc->uie_rtctimer.enabled \|\| rtc->uie_irq_active;
		#else
		uie = rtc->uie_rtctimer.enabled;
		#endif
		if (uie) {
		err = rtc_update_irq_enable(rtc, 0);
		if (err)
		return err;
		}

		err = mutex_lock_interruptible(&rtc->ops_lock);
		if (err)
		return err;
		@@ -153,6 +164,12 @@ int rtc_set_time(struct rtc_device rtc, struct rtc_time tm)
		/* A timer might have just expired */
		schedule_work(&rtc->irqwork);

		if (uie) {
		err = rtc_update_irq_enable(rtc, 1);
		if (err)
		return err;
		}

		trace_rtc_set_time(rtc_tm_to_time64(tm), err);
		return err;
		}

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