[tip:timers/core] time: Prevent 32 bit overflow with set_normalized_timespec()

tip-bot for Thomas Gleixner
2009-09-15T08:22:41Z

Commit-ID: 12e09337fe238981cb0c87543306e23775d1a143
Gitweb: http://git.kernel.org/tip/12e09337fe238981cb0c87543306e23775d1a143
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 14 Sep 2009 23:37:40 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 15 Sep 2009 10:17:30 +0200

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 <tglx@linutronix.de>
Tested-by: Carsten Emde <carsten.emde@osadl.org>
LKML-Reference: <new-submission>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: John Stultz <johnstul@us.ibm.com>

---
include/linux/time.h | 2 +-
kernel/time.c | 9 ++++++++-
2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index 256232f..56787c0 100644
--- 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
index 2951194..2e2e469 100644
--- 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;
}