alarmtimer: Prevent overflow of relative timers
authorThomas Gleixner <tglx@linutronix.de>
Tue, 30 May 2017 21:15:34 +0000 (23:15 +0200)
committerThomas Gleixner <tglx@linutronix.de>
Sun, 4 Jun 2017 13:21:18 +0000 (15:21 +0200)
commitf4781e76f90df7aec400635d73ea4c35ee1d4765
tree040546b3abf04fce0471d15e7f8580b1e0e8a464
parent104c08ba8e921ef97abfdc10408d54921a6d9003
alarmtimer: Prevent overflow of relative timers

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 <andreyknvl@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kostya Serebryany <kcc@google.com>
Cc: syzkaller <syzkaller@googlegroups.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170530211655.802921648@linutronix.de
kernel/time/alarmtimer.c