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Groups > linux.kernel > #1653581
| From | Thomas Gleixner <tglx@linutronix.de> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [patch 02/26] alarmtimer: Rate limit periodic intervals |
| Date | 2017-05-30 23:50 +0200 |
| Message-ID | <tMXbA-4e6-29@gated-at.bofh.it> (permalink) |
| References | <tMXbz-4e6-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
The alarmtimer code has another source of potentially rearming itself too
fast. Interval timers with a very samll interval have a similar CPU hog
effect as the previously fixed overflow issue.
The reason is that alarmtimers do not implement the normal protection
against this kind of problem which the other posix timer use:
timer expires -> queue signal -> deliver signal -> rearm timer
This scheme brings the rearming under scheduler control and prevents
permanently firing timers which hog the CPU.
Bringing this scheme to the alarm timer code is a major overhaul because it
lacks all the necessary mechanisms completely.
So for a quick fix limit the interval to one jiffie. This is not
problematic in practice as alarmtimers are usually backed by an RTC for
suspend which have 1 second resolution. It could be therefor argued that
the resolution of this clock should be set to 1 second in general, but
that's outside the scope of this fix.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: syzkaller <syzkaller@googlegroups.com>
---
kernel/time/alarmtimer.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -662,6 +662,14 @@ static int alarm_timer_set(struct k_itim
/* start the timer */
timr->it.alarm.interval = timespec64_to_ktime(new_setting->it_interval);
+
+ /*
+ * Rate limit to the tick as a hot fix to prevent DOS. Will be
+ * mopped up later.
+ */
+ if (timr->it.alarm.interval < TICK_NSEC)
+ timr->it.alarm.interval = TICK_NSEC;
+
exp = timespec64_to_ktime(new_setting->it_value);
/* Convert (if necessary) to absolute time */
if (flags != TIMER_ABSTIME) {
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[patch 00/26] alarmtimers/posixtimers: Bug fixes and spec conformity changes Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[patch 09/26] posix-timers: Unify overrun/requeue_pending handling Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Unify overrun/requeue_pending handling tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 19/26] posix-timers: Add cancel/arm callbacks Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Add cancel/arm callbacks tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 11/26] posix-timers: Store k_clock pointer in k_itimer Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Store k_clock pointer in k_itimer tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 24/26] alarmtimer: Implement try_to_cancel callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Implement try_to_cancel callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 08/26] posix-timers: Move posix-timer internals to core Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
Re: [patch 08/26] posix-timers: Move posix-timer internals to core Christoph Hellwig <hch@infradead.org> - 2017-05-31 17:40 +0200
[tip:timers/core] posix-timers: Move posix-timer internals to core tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:20 +0200
[patch 17/26] posix-timers: Make use of forward/remaining callbacks Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Make use of forward/remaining callbacks tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 07/26] posix-timers: Cleanup struct k_itimer Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Cleanup struct k_itimer tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:20 +0200
[patch 02/26] alarmtimer: Rate limit periodic intervals Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/urgent] alarmtimer: Rate limit periodic intervals tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-04 15:30 +0200
[tip:timers/urgent] alarmtimer: Rate limit periodic intervals tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-04 15:40 +0200
[patch 14/26] posix-timers: Use timer_rearm() callback in posixtimer_rearm() Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Use timer_rearm() callback in posixtimer_rearm() tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 04/26] posix-timers: Remove unused export of posix_timer_event() Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Remove unused export of posix_timer_event() tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:20 +0200
[patch 23/26] alarmtimer: Implement remaining callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Implement remaining callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 13/26] posix-timers: Rename do_schedule_next_timer Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
Re: [patch 13/26] posix-timers: Rename do_schedule_next_timer Christoph Hellwig <hch@infradead.org> - 2017-05-31 17:40 +0200
Re: [patch 13/26] posix-timers: Rename do_schedule_next_timer Thomas Gleixner <tglx@linutronix.de> - 2017-06-01 23:00 +0200
Re: [patch 13/26] posix-timers: Rename do_schedule_next_timer Christoph Hellwig <hch@infradead.org> - 2017-06-02 09:10 +0200
[tip:timers/core] posix-timers: Rename do_schedule_next_timer tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 22/26] alarmtimer: Implement forward callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Implement forward callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 03/26] alarmtimer: Remove pointless config conditional Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Remove pointless config conditional tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:20 +0200
[patch 26/26] alarmtimer: Switch over to generic set/get/rearm routine Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Switch over to generic set/get/rearm routine tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 06/26] posix-timers: Avoid gazillions of forward declarations Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Avoid gazillions of forward declarations tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:20 +0200
[patch 12/26] posix-timers: Add timer_rearm() callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Add timer_rearm() callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 01/26] alarmtimer: Prevent overflow of relative timers Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/urgent] alarmtimer: Prevent overflow of relative timers tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-04 15:30 +0200
[tip:timers/urgent] alarmtimer: Prevent overflow of relative timers tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-04 15:40 +0200
[patch 15/26] posix-timers: Add active flag to k_itimer Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Add active flag to k_itimer tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 16/26] posix-timers: Add forward/remaining callbacks Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Add forward/remaining callbacks tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 25/26] alarmtimer: Implement arm callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Implement arm callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 21/26] alarmtimer: Implement timer_rearm() callback Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] alarmtimer: Implement timer_rearm() callback tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 10/26] posix-timers: Move interval out of the union Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Move interval out of the union tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 20/26] posix-timers: Make use of cancel/arm callbacks Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Make use of cancel/arm callbacks tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
[patch 18/26] posix-timers: Zero settings value in common code Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 23:50 +0200
[tip:timers/core] posix-timers: Zero settings value in common code tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-05 10:30 +0200
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