LinuxLists.cc - [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to

2015-12-04 00:12:48

Subject: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

At some point after humans go extinct and robots cotrol the world, dividing
he time64_t by 86400 to extract the days will overflow a 32bit integer,
leading to incorrect conversion into rtc_time in rtc_time64_to_tm().

Signed-off-by: Sasha Levin <[email protected]>
---
drivers/rtc/rtc-lib.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index e6bfb9c..459cd4d 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -54,11 +54,11 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
{
unsigned int month, year;
unsigned long secs;
- int days;
+ time64_t days;

/* time must be positive */
days = div_s64(time, 86400);
- secs = time - (unsigned int) days * 86400;
+ secs = time - days * 86400;

/* day of the week, 1970-01-01 was a Thursday */
tm->tm_wday = (days + 4) % 7;
--
1.7.10.4

2015-12-04 00:22:40

by kernel test robot

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Subject: Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

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2015-12-04 01:40:39

by kernel test robot

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Subject: Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

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2015-12-04 01:42:35

by kernel test robot

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Subject: Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
Hi Sasha,

[auto build test ERROR on abelloni/rtc-next]
[also build test ERROR on v4.4-rc3 next-20151202]

url: https://github.com/0day-ci/linux/commits/Sasha-Levin/rtc-fix-overflow-and-incorrect-calculation-in-rtc_time64_to_tm/20151204-081508
base: https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git rtc-next
config: arm-prima2_defconfig (attached as .config)
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=arm

All errors (new ones prefixed by >>):

drivers/built-in.o: In function `rtc_time64_to_tm':
>> drivers/rtc/rtc-lib.c:64: undefined reference to `__aeabi_ldivmod'
drivers/rtc/rtc-lib.c:66: undefined reference to `__aeabi_ldivmod'

vim +64 drivers/rtc/rtc-lib.c

c58411e9 Alessandro Zummo 2006-03-27 58
c2c11ae4 pang.xunlei 2014-11-18 59 /* time must be positive */
c2c11ae4 pang.xunlei 2014-11-18 60 days = div_s64(time, 86400);
ee9fd0e8 Sasha Levin 2015-12-03 61 secs = time - days * 86400;
c58411e9 Alessandro Zummo 2006-03-27 62
c58411e9 Alessandro Zummo 2006-03-27 63 /* day of the week, 1970-01-01 was a Thursday */
c58411e9 Alessandro Zummo 2006-03-27 @64 tm->tm_wday = (days + 4) % 7;
c58411e9 Alessandro Zummo 2006-03-27 65
c58411e9 Alessandro Zummo 2006-03-27 66 year = 1970 + days / 365;
c58411e9 Alessandro Zummo 2006-03-27 67 days -= (year - 1970) * 365

:::::: The code at line 64 was first introduced by commit
:::::: c58411e95d7f5062dedd1a3064af4d359da1e633 [PATCH] RTC Subsystem: library functions

:::::: TO: Alessandro Zummo <[email protected]>
:::::: CC: Linus Torvalds <[email protected]>

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation

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2015-12-04 01:55:57

by Alexandre Belloni

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Subject: Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

On 03/12/2015 at 19:12:24 -0500, Sasha Levin wrote :
> At some point after humans go extinct and robots cotrol the world, dividing
> he time64_t by 86400 to extract the days will overflow a 32bit integer,
> leading to incorrect conversion into rtc_time in rtc_time64_to_tm().
>

And at that time, the robots won't care about 32bit platforms :)

> Signed-off-by: Sasha Levin <[email protected]>
> ---
> drivers/rtc/rtc-lib.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
> index e6bfb9c..459cd4d 100644
> --- a/drivers/rtc/rtc-lib.c
> +++ b/drivers/rtc/rtc-lib.c
> @@ -54,11 +54,11 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
> {
> unsigned int month, year;
> unsigned long secs;
> - int days;
> + time64_t days;
>
> /* time must be positive */
> days = div_s64(time, 86400);
> - secs = time - (unsigned int) days * 86400;
> + secs = time - days * 86400;
>
> /* day of the week, 1970-01-01 was a Thursday */
> tm->tm_wday = (days + 4) % 7;
> --
> 1.7.10.4
>

--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

2015-12-04 02:07:05

by Sasha Levin

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Subject: Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

On 12/03/2015 08:55 PM, Alexandre Belloni wrote:
> On 03/12/2015 at 19:12:24 -0500, Sasha Levin wrote :
>> > At some point after humans go extinct and robots cotrol the world, dividing
>> > he time64_t by 86400 to extract the days will overflow a 32bit integer,
>> > leading to incorrect conversion into rtc_time in rtc_time64_to_tm().
>> >
> And at that time, the robots won't care about 32bit platforms :)

One can only hope... :)

I'll resend.

Thanks,
Sasha