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SubjectRe: time: hang due to timer_create/timer_settime
On Fri, 21 Apr 2017, Thomas Gleixner wrote:
> On Fri, 21 Apr 2017, Andrey Konovalov wrote:
> > Hi,
> >
> > I've got the following error report while fuzzing the kernel with syzkaller.
> >
> > On commit 4f7d029b9bf009fbee76bb10c0c4351a1870d2f3 (4.11-rc7).
> >
> > A reproducer and .config are attached.
> >
> > The program hangs the kernel.
> > lock_acquire+0x22d/0x560 kernel/locking/lockdep.c:3762
> > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> > _raw_spin_lock_irqsave+0xc4/0x110 kernel/locking/spinlock.c:159
> > alarmtimer_fired+0x169/0x7a0 kernel/time/alarmtimer.c:189
> > __run_hrtimer kernel/time/hrtimer.c:1212 [inline]
> > __hrtimer_run_queues+0x350/0xe50 kernel/time/hrtimer.c:1276
> > hrtimer_interrupt+0x1ab/0x5c0 kernel/time/hrtimer.c:1310
> > local_apic_timer_interrupt+0x6f/0xe0 arch/x86/kernel/apic/apic.c:937
> > smp_apic_timer_interrupt+0x71/0xa0 arch/x86/kernel/apic/apic.c:961
> > apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:487
>
> Right. That lacks the protection which we have in the other posix
> timers. I'll have a look.

But what's even more alarming is:

(*(uint64_t*)0x20aedfe0 = (uint64_t)0x0);
(*(uint64_t*)0x20aedfe8 = (uint64_t)0x989680);
(*(uint64_t*)0x20aedff0 = (uint64_t)0x800000077359400);
(*(uint64_t*)0x20aedff8 = (uint64_t)0x0);
r[11] = execute_syscall(__NR_timer_settime, r[6], 0x0ul, 0x20aedfe0ul,
0x20715fe0ul, 0, 0, 0, 0, 0);

0x20aedfe0 is the itimerspec handed to timer_create(). So

its->it_interval.tv_sec = 0;
its->it_interval.tv_nsec = 0x989680;

its->it_value.tv_sec = 0x800000077359400;
its->it_value.tv_nsec = 0;

it_value.tv_sec is 1.82795e+10 YEARS into the future.

How does that timer fire in the first place?

Thanks,

tglx

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