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Subject[PATCH RFC 02/12] time: Add mktime() safe version(using time64_t)
Date
The kernel uses 32-bit signed value(time_t) for seconds since 1970-01-01:00:00:00, thus it
will overflow at 2038-01-19 03:14:08 on 32-bit systems. We call this "2038 safety" issue.

As part of addressing 2038 saftey for in-kernel uses, this patch adds the safe mktime() using
time64_t. After this patch, mktime_unsafe() should be replaced by mktime() one by one.

Eventually, mktime_unsafe() will be removed from the kernel when it has no users.

Signed-off-by: pang.xunlei <pang.xunlei@linaro.org>
---
include/linux/time.h | 8 ++++++--
kernel/time/time.c | 39 ++++++++++++++++++++++++++-------------
2 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index e49d421..08f413c 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -39,9 +39,13 @@ static inline int timeval_compare(const struct timeval *lhs, const struct timeva
return lhs->tv_usec - rhs->tv_usec;
}

+extern time64_t 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 unsigned long mktime_unsafe(const unsigned int year, const unsigned int mon,
- const unsigned int day, const unsigned int hour,
- const unsigned int min, const unsigned int sec);
+ 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, s64 nsec);

diff --git a/kernel/time/time.c b/kernel/time/time.c
index d6a4464..f9521fa 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -304,7 +304,8 @@ struct timespec timespec_trunc(struct timespec t, unsigned gran)
}
EXPORT_SYMBOL(timespec_trunc);

-/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
+/*
+ * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
* Assumes input in normal date format, i.e. 1980-12-31 23:59:59
* => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
*
@@ -314,16 +315,13 @@ EXPORT_SYMBOL(timespec_trunc);
* -year/100+year/400 terms, and add 10.]
*
* This algorithm was first published by Gauss (I think).
- *
- * WARNING: this function will overflow on 2106-02-07 06:28:16 on
- * machines where long is 32-bit! (However, as time_t is signed, we
- * will already get problems at other places on 2038-01-19 03:14:08)
*/
-unsigned long
-mktime_unsafe(const unsigned int year0, const unsigned int mon0,
+time64_t
+mktime(const unsigned int year0, const unsigned int mon0,
const unsigned int day, const unsigned int hour,
const unsigned int min, const unsigned int sec)
{
+ time64_t ret;
unsigned int mon = mon0, year = year0;

/* 1..12 -> 11,12,1..10 */
@@ -332,12 +330,27 @@ mktime_unsafe(const unsigned int year0, const unsigned int mon0,
year -= 1;
}

- return ((((unsigned long)
- (year/4 - year/100 + year/400 + 367*mon/12 + day) +
- year*365 - 719499
- )*24 + hour /* now have hours */
- )*60 + min /* now have minutes */
- )*60 + sec; /* finally seconds */
+ ret = (year/4 - year/100 + year/400 + 367*mon/12 + day) + year*365 - 719499;
+ ret = ret*24 + hour; /* now have hours */
+ ret = ret*60 + min; /* now have minutes */
+ ret = ret*60 + sec; /* finally seconds */
+
+ return ret;
+}
+
+EXPORT_SYMBOL(mktime);
+
+/*
+ * TODO: [2038 safety] 2038 unsafe for legacy, replace it by mktime().
+ * WARNING: mktime_unsafe() will overflow on 2106-02-07 06:28:16 on
+ * machines where long is 32-bit! (However, as time_t is signed, we
+ * will already get problems at other places on 2038-01-19 03:14:08)
+ */
+unsigned long mktime_unsafe(const unsigned int year0, const unsigned int mon0,
+ const unsigned int day, const unsigned int hour,
+ const unsigned int min, const unsigned int sec)
+{
+ return (unsigned long) mktime(year0, mon0, day, hour, min, sec);
}

EXPORT_SYMBOL(mktime_unsafe);
--
1.7.9.5


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