lkml.org 
[lkml]   [2017]   [Sep]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[PATCH 3.16 115/233] alarmtimer: Prevent overflow of relative timers
    3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Thomas Gleixner <tglx@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 <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>
    Link: http://lkml.kernel.org/r/20170530211655.802921648@linutronix.de
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    kernel/time/alarmtimer.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    --- a/kernel/time/alarmtimer.c
    +++ b/kernel/time/alarmtimer.c
    @@ -342,7 +342,7 @@ int alarm_start_relative(struct alarm *a
    {
    struct alarm_base *base = &alarm_bases[alarm->type];

    - start = ktime_add(start, base->gettime());
    + start = ktime_add_safe(start, base->gettime());
    return alarm_start(alarm, start);
    }
    EXPORT_SYMBOL_GPL(alarm_start_relative);
    @@ -428,7 +428,7 @@ 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);
    @@ -620,7 +620,7 @@ 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);
    \
     
     \ /
      Last update: 2017-09-10 01:24    [W:4.388 / U:0.092 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site