4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Thomas Gleixner <t...@linutronix.de> commit f4781e76f90df7aec400635d73ea4c35ee1d4765 upstream. 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 <andreyk...@google.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Kostya Serebryany <k...@google.com> Cc: syzkaller <syzkal...@googlegroups.com> Cc: John Stultz <john.stu...@linaro.org> Cc: Dmitry Vyukov <dvyu...@google.com> Link: http://lkml.kernel.org/r/20170530211655.802921...@linutronix.de Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- kernel/time/alarmtimer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/time/alarmtimer.c +++ b/kernel/time/alarmtimer.c @@ -354,7 +354,7 @@ void alarm_start_relative(struct alarm * { 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); @@ -440,7 +440,7 @@ u64 alarm_forward(struct alarm *alarm, k 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); @@ -630,7 +630,7 @@ static int alarm_timer_set(struct k_itim 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);
