From: AMEET M. PARANJAPE <aparanja@redhat.com>
Date: Thu, 26 Mar 2009 17:20:43 -0400
Subject: [misc] hrtimer: check relative timeouts for overflow
Message-id: 20090326211835.28676.70244.sendpatchset@squad5-lp1.lab.bos.redhat.com
O-Subject: [PATCH RHEL5.4 BZ492230] hrtimer: check relative timeouts for overflow
Bugzilla: 492230

RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=492230

Description:
===========
This patch backport the mainline operations on itimers to avoid the sec ->
nanosecs overflow when using 64-bit variables.

Instead of putting overflow checks into each place add a function
which does the sanity checking and convert all affected callers to use
it.

RHEL Version Found:
================
RHEL 5.3

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1739525

Upstream Status:
================
http://lkml.org/lkml/2008/2/22/534

Test Status:
============
There is a test script in the Bugzilla.  Without the patch the getitimer
function fails if the timer ITIMER_REAL is used.   With the patch applied
the test script does not fail.

==================================
=============================
Ameet Paranjape 978-392-3903 ext 23903
IBM on-site partner

Proposed Patch:
===============

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 8479e6f..6088238 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -295,6 +295,24 @@ static unsigned long ktime_divns(const ktime_t kt, s64 div)
 #endif /* BITS_PER_LONG >= 64 */
 
 /*
+ * Add two ktime values and do a safety check for overflow:
+ */
+ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs)
+{
+	ktime_t res = ktime_add(lhs, rhs);
+
+	/*    
+	* We use KTIME_SEC_MAX here, the maximum timeout which we can
+	* return to user space in a timespec:
+	*/  
+	if (res.tv64 < 0 || res.tv64 < lhs.tv64 || res.tv64 < rhs.tv64)
+		res = ktime_set(KTIME_SEC_MAX, 0);
+             
+	return res;
+}
+
+
+/*
  * Counterpart to lock_timer_base above:
  */
 static inline
@@ -447,7 +465,7 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
 	new_base = switch_hrtimer_base(timer, base);
 
 	if (mode == HRTIMER_REL) {
-		tim = ktime_add(tim, new_base->get_time());
+		tim = ktime_add_safe(tim, new_base->get_time());
 		/*
 		 * CONFIG_TIME_LOW_RES is a temporary way for architectures
 		 * to signal that they simply return xtime in
@@ -456,7 +474,7 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
 		 * timeouts. This will go away with the GTOD framework.
 		 */
 #ifdef CONFIG_TIME_LOW_RES
-		tim = ktime_add(tim, base->resolution);
+		tim = ktime_add_safe(tim, base->resolution);
 #endif
 	}
 	timer->expires = tim;