From 6af7e471e5a7746b8024d70b4363d3dfe41d36b8 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Wed, 10 Aug 2011 10:26:09 -0700 Subject: [PATCH] alarmtimers: Avoid possible denial of service with high freq periodic timers Its possible to jam up the alarm timers by setting very small interval timers, which will cause the alarmtimer subsystem to spend all of its time firing and restarting timers. This can effectivly lock up a box. A deeper fix is needed, closely mimicking the hrtimer code, but for now just cap the interval to 100us to avoid userland hanging the system. CC: Thomas Gleixner CC: stable@kernel.org Signed-off-by: John Stultz --- kernel/time/alarmtimer.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c index 0e9263f6fd09..ea5e1a928d5b 100644 --- a/kernel/time/alarmtimer.c +++ b/kernel/time/alarmtimer.c @@ -481,6 +481,15 @@ static int alarm_timer_set(struct k_itimer *timr, int flags, if (!rtcdev) return -ENOTSUPP; + /* + * XXX HACK! Currently we can DOS a system if the interval + * period on alarmtimers is too small. Cap the interval here + * to 100us and solve this properly in a future patch! -jstultz + */ + if ((new_setting->it_interval.tv_sec == 0) && + (new_setting->it_interval.tv_nsec < 100000)) + new_setting->it_interval.tv_nsec = 100000; + if (old_setting) alarm_timer_get(timr, old_setting);