linux-kernel - Re: [PATCH] rtc: fix overflow and incorrect calculation in rtc_time64_to

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Message-ID: <20151204015554.GB3515@piout.net>
Date:	Fri, 4 Dec 2015 02:55:54 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	a.zummo@...ertech.it, rtc-linux@...glegroups.com,
	linux-kernel@...r.kernel.org
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 <sasha.levin@...cle.com>
> ---
>  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
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