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 <stable@xxxxxxxxxxxxxxx> know about it.
>From f4781e76f90df7aec400635d73ea4c35ee1d4765 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Tue, 30 May 2017 23:15:34 +0200
Subject: alarmtimer: Prevent overflow of relative timers
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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 <andreyknvl@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Kostya Serebryany <kcc@xxxxxxxxxx>
Cc: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170530211655.802921648@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/alarmtimer.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -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 tglx@xxxxxxxxxxxxx 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