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[patch 2/2] posix-cpu-timers: Make timespec to nsec conversion safe

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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>
---
 kernel/time/posix-cpu-timers.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -572,7 +572,11 @@ static int posix_cpu_timer_set(struct k_
 
 	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

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[patch 0/2] timers: Prevent multiplication overflow in timespec/val  conversions Thomas Gleixner <tglx@linutronix.de> - 2017-06-20 17:50 +0200
  [patch 1/2] itimer: Make timeval to nsec conversion range limited Thomas Gleixner <tglx@linutronix.de> - 2017-06-20 17:50 +0200
    [tip:timers/core] itimer: Make timeval to nsec conversion range  limited tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-20 21:50 +0200
  [patch 2/2] posix-cpu-timers: Make timespec to nsec conversion safe Thomas Gleixner <tglx@linutronix.de> - 2017-06-20 17:50 +0200
    [tip:timers/core] posix-cpu-timers: Make timespec to nsec  conversion safe tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-06-20 21:50 +0200

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