Messages in this thread | | | From | Arnd Bergmann <> | Date | Wed, 6 Mar 2019 11:38:53 +0100 | Subject | Re: [PATCH v3] posix-cpu-timers: Avoid undefined behaviour in timespec64_to_ns() |
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On Wed, Mar 6, 2019 at 9:41 AM Xiongfeng Wang <wangxiongfeng2@huawei.com> wrote: > > > diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c > index 0e84bb7..4b57566 100644 > --- a/kernel/time/posix-timers.c > +++ b/kernel/time/posix-timers.c > @@ -856,6 +856,10 @@ static int do_timer_settime(timer_t timer_id, int flags, > if (!timespec64_valid(&new_spec64->it_interval) || > !timespec64_valid(&new_spec64->it_value)) > return -EINVAL; > + if (new_spec64->it_interval.tv_sec > KTIME_SEC_MAX) > + new_spec64->it_interval.tv_sec = KTIME_SEC_MAX; > + if (new_spec64->it_value.tv_sec > KTIME_SEC_MAX) > + new_spec64->it_value.tv_sec = KTIME_SEC_MAX; >
I looked at the calculation we do later, and I think this can still overflow if tv_nsec is too large. The largest timespec value we can support is
(struct timespec64) { .tv_sec = 9223372036, .tv_nsec = 854775807 }
Your patch caps the tv_sec value to 9223372036, but it does not cap the tv_nsec. The easiest fix would be to always set tv_nsec to 0 if tv_sec>=9223372036, or a more correct calculation would have to limit tv_nsec if tv_sec==9223372036. I don't know if that matters or not (it should not, unless we explicitly compare the ktime_t for equality with KTIME_MAX later).
Arnd
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