From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751231AbdE3Vl5 (ORCPT ); Tue, 30 May 2017 17:41:57 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:55700 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751022AbdE3Vly (ORCPT ); Tue, 30 May 2017 17:41:54 -0400 Message-Id: <20170530211655.802921648@linutronix.de> User-Agent: quilt/0.63-1 Date: Tue, 30 May 2017 23:15:34 +0200 From: Thomas Gleixner To: LKML Cc: John Stultz , Peter Zijlstra , Ingo Molnar , Andrey Konovalov , Dmitry Vyukov , Kostya Serebryany , syzkaller Subject: [patch 01/26] alarmtimer: Prevent overflow of relative timers References: <20170530211533.216608851@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=alarmtimer--Prevent-overflow-of-relative-timers.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Signed-off-by: Thomas Gleixner Cc: Dmitry Vyukov Cc: Kostya Serebryany Cc: syzkaller --- kernel/time/alarmtimer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/time/alarmtimer.c +++ b/kernel/time/alarmtimer.c @@ -357,7 +357,7 @@ 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); @@ -445,7 +445,7 @@ 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); @@ -668,7 +668,7 @@ 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);