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alarmtimer: Prevent overflow of relative timers

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Andrey reported a alartimer related RCU stall while fuzzing the kernel with
syzkaller.

The reason for this is an overflow in ktime_add() which brings the
resulting time into negative space and causes immediate expiry of the
timer. The following rearm with a small interval does not bring the timer
back into positive space due to the same issue.

This results in a permanent firing alarmtimer which hogs the CPU.

Use ktime_add_safe() instead which detects the overflow and clamps the
result to KTIME_SEC_MAX.

Reported-by: Andrey Konovalov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kostya Serebryany <[email protected]>
Cc: syzkaller <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
This commit is contained in:
Thomas Gleixner
2017-06-04 15:21:18 +02:00
parent 104c08ba8e
commit f4781e76f9
1 changed files with 3 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/time/alarmtimer.c
+3 -3
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@@ -387,7 +387,7 @@ void alarm_start_relative(struct alarm *alarm, ktime_t start)
{
struct alarm_base *base = &alarm_bases[alarm->type];
start = ktime_add(start, base->gettime());
start = ktime_add_safe(start, base->gettime());
alarm_start(alarm, start);
}
EXPORT_SYMBOL_GPL(alarm_start_relative);
@@ -475,7 +475,7 @@ u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval)
overrun++;
}
alarm->node.expires = ktime_add(alarm->node.expires, interval);
alarm->node.expires = ktime_add_safe(alarm->node.expires, interval);
return overrun;
}
EXPORT_SYMBOL_GPL(alarm_forward);
@@ -666,7 +666,7 @@ static int alarm_timer_set(struct k_itimer *timr, int flags,
ktime_t now;
now = alarm_bases[timr->it.alarm.alarmtimer.type].gettime();
exp = ktime_add(now, exp);
exp = ktime_add_safe(now, exp);
}
alarm_start(&timr->it.alarm.alarmtimer, exp);