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Commit 498c6cbd authored by Christopher Tate's avatar Christopher Tate
Browse files

Prevent some alarm pathologies 

* Sanity-check the recurrence interval.  Some buggy apps pass seconds
  where the API expects milliseconds, with the result that the device
  pins the CPU at 100% trying to deliver alarm broadcasts every 60 ms
  or what have you.  The minimum recurrence is now 1 minute.

* Sanity-check alarms being scheduled for the immediate future.  As
  with the above this will catch people trying to schedule alarms
  in a spammy way that keeps the device from entering low-power state.
  The minimum futurity of a new alarm is now 5 seconds.

Bug 17495168

Change-Id: If8ff7d88da48960532ac21a0ba20094af9912603
parent c9f1b3a0

services/core/java/com/android/server/AlarmManagerService.java

+20 −1
Original line number Original line Diff line number Diff line
@@ -75,6 +75,12 @@ class AlarmManagerService extends SystemService { 
    // warning message.  The time duration is in milliseconds.

    // warning message.  The time duration is in milliseconds.

    private static final long LATE_ALARM_THRESHOLD = 10 * 1000;

    private static final long LATE_ALARM_THRESHOLD = 10 * 1000;





    // Minimum futurity of a new alarm

    private static final long MIN_FUTURITY = 5 * 1000;  // 5 seconds, in millis



    // Minimum alarm recurrence interval

    private static final long MIN_INTERVAL = 60 * 1000;  // one minute, in millis



    private static final int RTC_WAKEUP_MASK = 1 << RTC_WAKEUP;

    private static final int RTC_WAKEUP_MASK = 1 << RTC_WAKEUP;

    private static final int RTC_MASK = 1 << RTC;

    private static final int RTC_MASK = 1 << RTC;

    private static final int ELAPSED_REALTIME_WAKEUP_MASK = 1 << ELAPSED_REALTIME_WAKEUP;

    private static final int ELAPSED_REALTIME_WAKEUP_MASK = 1 << ELAPSED_REALTIME_WAKEUP;
@@ -696,6 +702,15 @@ class AlarmManagerService extends SystemService { 
            windowLength = AlarmManager.INTERVAL_HOUR;

            windowLength = AlarmManager.INTERVAL_HOUR;

        }

        }





        // Sanity check the recurrence interval.  This will catch people who supply

        // seconds when the API expects milliseconds.

        if (interval > 0 && interval < MIN_INTERVAL) {

            Slog.w(TAG, "Suspiciously short interval " + interval

                    + " millis; expanding to " + (int)(MIN_INTERVAL/1000)

                    + " seconds");

            interval = MIN_INTERVAL;

        }



        if (type < RTC_WAKEUP || type > ELAPSED_REALTIME) {

        if (type < RTC_WAKEUP || type > ELAPSED_REALTIME) {

            throw new IllegalArgumentException("Invalid alarm type " + type);

            throw new IllegalArgumentException("Invalid alarm type " + type);

        }

        }
@@ -709,7 +724,11 @@ class AlarmManagerService extends SystemService { 
        }

        }





        final long nowElapsed = SystemClock.elapsedRealtime();

        final long nowElapsed = SystemClock.elapsedRealtime();

        final long triggerElapsed = convertToElapsed(triggerAtTime, type);

        final long nominalTrigger = convertToElapsed(triggerAtTime, type);

        // Try to prevent spamming by making sure we aren't firing alarms in the immediate future

        final long minTrigger = nowElapsed + MIN_FUTURITY;

        final long triggerElapsed = (nominalTrigger > minTrigger) ? nominalTrigger : minTrigger;



        final long maxElapsed;

        final long maxElapsed;

        if (windowLength == AlarmManager.WINDOW_EXACT) {

        if (windowLength == AlarmManager.WINDOW_EXACT) {

            maxElapsed = triggerElapsed;

            maxElapsed = triggerElapsed;