linux-kernel - Re: [PATCH] rtc: Fix overflow when converting time64_t to rtc

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Message-ID: <CAMz4kuL5TLMS7cKWcbmJ_0qNgiijNTxzuG4vzk=4DqyEvFKPYw@mail.gmail.com>
Date:   Mon, 8 Jan 2018 14:00:56 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        linux-rtc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Baolin Wang <baolin.wang@...aro.org>
Subject: Re: [PATCH] rtc: Fix overflow when converting time64_t to rtc_time

Hi Alexandre,

On 25 December 2017 at 19:10, Baolin Wang <baolin.wang@...aro.org> 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 <baolin.wang@...aro.org>

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