2017-12-25 11:11:41

by Baolin Wang

Subject: [PATCH] rtc: Fix overflow when converting time64_t to rtc_time

If we convert one large time values to rtc_time, in the original formula
'days * 86400' can be overflowed in 'unsigned int' type to make the formula
get one incorrect remain seconds value. Thus we can use div_s64_rem()
function to avoid this situation.

Signed-off-by: Baolin Wang <[email protected]>
---
drivers/rtc/rtc-lib.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index 1ae7da5..ad5bb21 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -52,13 +52,11 @@ int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
*/
void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
{
- unsigned int month, year;
- unsigned long secs;
+ unsigned int month, year, secs;
int days;

/* time must be positive */
- days = div_s64(time, 86400);
- secs = time - (unsigned int) days * 86400;
+ days = div_s64_rem(time, 86400, &secs);

/* day of the week, 1970-01-01 was a Thursday */
tm->tm_wday = (days + 4) % 7;
--
1.7.9.5

2018-01-08 06:00:59

by Baolin Wang

Subject: Re: [PATCH] rtc: Fix overflow when converting time64_t to rtc_time

Hi Alexandre,

On 25 December 2017 at 19:10, Baolin Wang <[email protected]> wrote:
> If we convert one large time values to rtc_time, in the original formula
> 'days * 86400' can be overflowed in 'unsigned int' type to make the formula
> get one incorrect remain seconds value. Thus we can use div_s64_rem()
> function to avoid this situation.
>
> Signed-off-by: Baolin Wang <[email protected]>

Could you apply this patch if there are no other comments? Thanks.

> ---
> drivers/rtc/rtc-lib.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
> index 1ae7da5..ad5bb21 100644
> --- a/drivers/rtc/rtc-lib.c
> +++ b/drivers/rtc/rtc-lib.c
> @@ -52,13 +52,11 @@ int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
> */
> void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
> {
> - unsigned int month, year;
> - unsigned long secs;
> + unsigned int month, year, secs;
> int days;
>
> /* time must be positive */
> - days = div_s64(time, 86400);
> - secs = time - (unsigned int) days * 86400;
> + days = div_s64_rem(time, 86400, &secs);
>
> /* day of the week, 1970-01-01 was a Thursday */
> tm->tm_wday = (days + 4) % 7;
> --
> 1.7.9.5
>



--
Baolin.wang
Best Regards

2018-01-26 09:25:33

by Arnd Bergmann

Subject: Re: [RESEND PATCH] rtc: Fix overflow when converting time64_t to rtc_time

On Fri, Jan 26, 2018 at 6:06 AM, Baolin Wang <[email protected]> wrote:
> If we convert one large time values to rtc_time, in the original formula
> 'days * 86400' can be overflowed in 'unsigned int' type to make the formula
> get one incorrect remain seconds value. Thus we can use div_s64_rem()
> function to avoid this situation.
>
> Signed-off-by: Baolin Wang <[email protected]>

Acked-by: Arnd Bergmann <[email protected]>

2018-02-06 04:04:07

by Baolin Wang

Subject: Re: [RESEND PATCH] rtc: Fix overflow when converting time64_t to rtc_time

Hi Alexandre,

On 26 January 2018 at 17:24, Arnd Bergmann <[email protected]> wrote:
> On Fri, Jan 26, 2018 at 6:06 AM, Baolin Wang <[email protected]> wrote:
>> If we convert one large time values to rtc_time, in the original formula
>> 'days * 86400' can be overflowed in 'unsigned int' type to make the formula
>> get one incorrect remain seconds value. Thus we can use div_s64_rem()
>> function to avoid this situation.
>>
>> Signed-off-by: Baolin Wang <[email protected]>
>
> Acked-by: Arnd Bergmann <[email protected]>

Could you apply this patch? Since it was pending for a while and it is
a bug fix. Thanks.

--
Baolin.wang
Best Regards

2018-02-13 20:33:38

by Alexandre Belloni

Subject: Re: [RESEND PATCH] rtc: Fix overflow when converting time64_t to rtc_time

On 26/01/2018 at 13:06:01 +0800, Baolin Wang wrote:
> If we convert one large time values to rtc_time, in the original formula
> 'days * 86400' can be overflowed in 'unsigned int' type to make the formula
> get one incorrect remain seconds value. Thus we can use div_s64_rem()
> function to avoid this situation.
>
> Signed-off-by: Baolin Wang <[email protected]>
> ---
> drivers/rtc/rtc-lib.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
Applied, thanks.

--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com