time: Prevent 32 bit overflow with set_normalized_timespec()

KAGA-KOKO · KAGA-KOKO · commit 12e09337fe23 · 2009-09-15T10:17:30.000+02:00
set_normalized_timespec() nsec argument is of type long. The recent
timekeeping changes of ktime_get_ts() feed 

	ts-&gt;tv_nsec + tomono.tv_nsec + nsecs

to set_normalized_timespec(). On 32 bit machines that sum can be
larger than (1 &lt;&lt; 31) and therefor result in a negative value which
screws up the result completely.

Make the nsec argument of set_normalized_timespec() s64 to fix the
problem at hand. This also prevents similar problems for future users
of set_normalized_timespec().

Signed-off-by: Thomas Gleixner &lt;tglx@linutronix.de&gt;
Tested-by: Carsten Emde &lt;carsten.emde@osadl.org&gt;
LKML-Reference: &lt;new-submission&gt;
Cc: Martin Schwidefsky &lt;schwidefsky@de.ibm.com&gt;
Cc: John Stultz &lt;johnstul@us.ibm.com&gt;
diff --git a/include/linux/time.h b/include/linux/time.h
@@ -75,7 +75,7 @@ extern unsigned long mktime(const unsigned int year, const unsigned int mon,
 			    const unsigned int day, const unsigned int hour,
 			    const unsigned int min, const unsigned int sec);
 
-extern void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec);
+extern void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec);
 extern struct timespec timespec_add_safe(const struct timespec lhs,
 					 const struct timespec rhs);
 
diff --git a/kernel/time.c b/kernel/time.c
@@ -370,13 +370,20 @@ EXPORT_SYMBOL(mktime);
  *	0 <= tv_nsec < NSEC_PER_SEC
  * For negative values only the tv_sec field is negative !
  */
-void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
+void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
 {
 	while (nsec >= NSEC_PER_SEC) {
+		/*
+		 * The following asm() prevents the compiler from
+		 * optimising this loop into a modulo operation. See
+		 * also __iter_div_u64_rem() in include/linux/time.h
+		 */
+		asm("" : "+rm"(nsec));
 		nsec -= NSEC_PER_SEC;
 		++sec;
 	}
 	while (nsec < 0) {
+		asm("" : "+rm"(nsec));
 		nsec += NSEC_PER_SEC;
 		--sec;
 	}
