[PATCH] hrtimer: prevent overrun DoS in hrtimer_forward()

[Thomas Gleixner <tglx@linutronix.de>]

hrtimer_forward() does not check for the possible overflow of
timer->expires. This can happen on 64 bit machines with large interval
values and results currently in an endless loop in the softirq because
the expiry value becomes negative and therefor the timer is expired all
the time.

Check for this condition and set the expiry value to the max. expiry
time in the future.

The fix should be applied to stable kernel series as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix,de>

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index ec4cb9f..5e7122d 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -644,6 +644,12 @@ hrtimer_forward(struct hrtimer *timer, k
 		orun++;
 	}
 	timer->expires = ktime_add(timer->expires, interval);
+	/*
+	 * Make sure, that the result did not wrap with a very large
+	 * interval.
+	 */
+	if (timer->expires.tv64 < 0)
+		timer->expires = ktime_set(KTIME_SEC_MAX, 0);
 
 	return orun;
 }