linux-kernel - [PATCH] prevent timespec/timeval to ktime

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Date:	Wed, 30 Aug 2006 10:44:28 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Frank v Waveren <fvw@....cx>
Subject: [PATCH] prevent timespec/timeval to ktime_t overflow

Frank v. Waveren pointed out that on 64bit machines the timespec to
ktime_t conversion might overflow. This is also true for timeval to
ktime_t conversions. This breaks a "sleep inf" on 64bit machines.

While a timespec/timeval with tx.sec = MAX_LONG is valid by
specification the internal representation of ktime_t is based on
nanoseconds. The conversion of seconds to nanoseconds overflows for
seconds values >= (MAX_LONG / NSEC_PER_SEC).

Check the seconds argument to the conversion and limit it to the maximum
time which can be represented by ktime_t.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index ed3396d..1beafb3 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -57,6 +57,7 @@ typedef union {
 } ktime_t;

 #define KTIME_MAX			(~((u64)1 << 63))
+#define KTIME_SEC_MAX			(KTIME_MAX / NSEC_PER_SEC)

 /*
  * ktime_t definitions when using the 64-bit scalar representation:
@@ -73,6 +74,10 @@ typedef union {
  */
 static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)
 {
+#if (BITS_PER_LONG == 64)
+	if (unlikely(secs >= KTIME_SEC_MAX))
+		return (ktime_t){ .tv64 = KTIME_MAX };
+#endif
 	return (ktime_t) { .tv64 = (s64)secs * NSEC_PER_SEC + (s64)nsecs };
 }

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