time: Prevent 32 bit overflow with set_normalized_timespec()

set_normalized_timespec() nsec argument is of type long. The recent timekeeping changes of ktime_get_ts() feed ts->tv_nsec + tomono.tv_nsec + nsecs to set_normalized_timespec(). On 32 bit machines that sum can be larger than (1 << 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 <[email protected]> Tested-by: Carsten Emde <[email protected]> LKML-Reference: <new-submission> Cc: Martin Schwidefsky <[email protected]> Cc: John Stultz <[email protected]>
CyanogenMod · Sep 15, 2009 · 12e0933 · 12e0933
1 parent 54a6bc0
commit 12e0933
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Showing 2 changed files with 9 additions and 2 deletions.
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;
 	}