itimer: Make timeval to nsec conversion range limited

The expiry time of a itimer is supplied through sys_setitimer() via a
struct timeval. The timeval is validated for correctness.

In the actual set timer implementation the timeval 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 timeval_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.

Reported-by: Xishi Qiu <qiuxishi@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20170620154113.505981643@linutronix.de

diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index 9dd7ff5e445a6c5e4b2522fb50b8126caa6b3cff..2ef98a02376af2a4ecdd26da46c8d91c9913cc1b 100644 (file)
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -152,8 +152,12 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
        u64 oval, nval, ointerval, ninterval;
        struct cpu_itimer *it = &tsk->signal->it[clock_id];
 
-       nval = timeval_to_ns(&value->it_value);
-       ninterval = timeval_to_ns(&value->it_interval);
+       /*
+        * Use the to_ktime conversion because that clamps the maximum
+        * value to KTIME_MAX and avoid multiplication overflows.
+        */
+       nval = ktime_to_ns(timeval_to_ktime(value->it_value));
+       ninterval = ktime_to_ns(timeval_to_ktime(value->it_interval));
 
        spin_lock_irq(&tsk->sighand->siglock);