From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 20 Oct 2014 11:07:50 +0000 (+0400)
Subject: clockevents: Prevent shift out of bounds
X-Git-Tag: v3.18-rc3~25^2~1
X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=10632008b9e18b76cbff0ffc69c15e948aa548e0;p=linux.git

clockevents: Prevent shift out of bounds

Andrey reported that on a kernel with UBSan enabled he found:

     UBSan: Undefined behaviour in ../kernel/time/clockevents.c:75:34

     I guess it should be 1ULL here instead of 1U:
            (!ismax || evt->mult <= (1U << evt->shift)))

That's indeed the correct solution because shift might be 32.

Reported-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 9c94c19f1305..55449909f114 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -72,7 +72,7 @@ static u64 cev_delta2ns(unsigned long latch, struct clock_event_device *evt,
 	 * Also omit the add if it would overflow the u64 boundary.
 	 */
 	if ((~0ULL - clc > rnd) &&
-	    (!ismax || evt->mult <= (1U << evt->shift)))
+	    (!ismax || evt->mult <= (1ULL << evt->shift)))
 		clc += rnd;
 
 	do_div(clc, evt->mult);