Patch "alarmtimer: Prevent overflow of relative timers" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

alarmtimer: Prevent overflow of relative timers

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alarmtimer-prevent-overflow-of-relative-timers.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Tue, 30 May 2017 23:15:34 +0200
Subject: alarmtimer: Prevent overflow of relative timers

From: Thomas Gleixner <[email protected]>

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.

---
 kernel/time/alarmtimer.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -339,7 +339,7 @@ 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);

@@ -425,7 +425,7 @@ 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);

@@ -617,7 +617,7 @@ 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/genirq-release-resources-in-__setup_irq-error-path.patch queue-4.4/x86-mm-32-set-the-__vmalloc_start_set-flag-in-initmem_init.patch queue-4.4/alarmtimer-prevent-overflow-of-relative-timers.patch