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posix-cpu-timers: Make timespec to nsec conversion safe 

The expiry time of a posix cpu timer is supplied through sys_timer_set()
via a struct timespec. The timespec is validated for correctness.

In the actual set timer implementation the timespec is converted to a
scalar nanoseconds value. If the tv_sec part of the time spec is large
enough the conversion to nanoseconds (sec * NSEC_PER_SEC) overflows 64bit.

Mitigate that by using the timespec_to_ktime() conversion function, which
checks the tv_sec part for a potential mult overflow and clamps the result
to KTIME_MAX, which is about 292 years. 

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20170620154113.588276707@linutronix.de
This commit is contained in:
Thomas Gleixner 2017-06-20 17:37:36 +02:00
parent 35eb7258c0
commit 098b0e01a9
1 changed files with 5 additions and 1 deletions
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6
kernel/time/posix-cpu-timers.c
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@ -580,7 +580,11 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
WARN_ON_ONCE(p == NULL);
new_expires = timespec64_to_ns(&new->it_value);
/*
* Use the to_ktime conversion because that clamps the maximum
* value to KTIME_MAX and avoid multiplication overflows.
*/
new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
/*
* Protect against sighand release/switch in exit/exec and p->cpu_timers