Messages in this thread | | | Subject | Re: [PATCH v3] posix-cpu-timers: Avoid undefined behaviour in timespec64_to_ns() | From | Xiongfeng Wang <> | Date | Fri, 8 Mar 2019 14:47:11 +0800 |
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On 2019/3/6 18:38, Arnd Bergmann wrote: > 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).
Thanks for your advice. I will send another one to set tv_nsec to 0 if tv_sec>=9223372036. Do need to add a helper to clamp timespec64, such as 'saturate_timespec64_valid()' to limit it between 0 and KTIME_MAX(or KTIME_SEC_MAX, it's easier.)
Thanks, Xiongfeng
> > Arnd > > . >
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