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

From: Thomas Gleixner
Date: Tue Jun 20 2017 - 11:42:14 EST

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@xxxxxxxxxxxxx>
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_


- 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