linux-kernel - Re: [PATCH 1/1] rtc: add century field data boundary

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Message-ID: <CAMuHMdUiahSOq3HsBG157tZp0KJArfRV-OE790PL6o4nnpiDOA@mail.gmail.com>
Date:   Wed, 5 Oct 2016 09:03:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andrew Kim <andrew.kim@...el.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] rtc: add century field data boundary

On Tue, Oct 4, 2016 at 8:06 PM, Andrew Kim <andrew.kim@...el.com> wrote:
> According to ACPI specification, the century field data
> should be ranged 0-63. so if it's over this range, it could
> cause system RTC settings error including alarmwakeup settings.
> So it's required to have this boundary for safe RTC init settings.
>
> Signed-off-by: Andrew Kim <andrew.kim@...el.com>
> ---
>  arch/x86/kernel/rtc.c          | 7 +++++--
>  drivers/rtc/rtc-mc146818-lib.c | 7 +++++--
>  include/linux/mc146818rtc.h    | 2 ++
>  3 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
> index 79c6311c..feac180 100644
> --- a/arch/x86/kernel/rtc.c
> +++ b/arch/x86/kernel/rtc.c
> @@ -84,8 +84,11 @@ void mach_get_cmos_time(struct timespec *now)
>
>  #ifdef CONFIG_ACPI
>         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
> -           acpi_gbl_FADT.century)
> -               century = CMOS_READ(acpi_gbl_FADT.century);
> +           acpi_gbl_FADT.century) {
> +               if ((century = CMOS_READ(acpi_gbl_FADT.century)) >
> +                       RTC_CENTURY_LIMIT)

Please don't combine assignments and comparisons into a single statement
(especially for non-NULL comparisons), i.e. use

        century = CMOS_READ(acpi_gbl_FADT.century);
        if (century > RTC_CENTURY_LIMIT) {
                ...

> +                       century = 0;
> +       }
>  #endif
>
>         status = CMOS_READ(RTC_CONTROL);
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index 2f1772a..1d83c2c 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -61,8 +61,11 @@ unsigned int mc146818_get_time(struct rtc_time *time)
>  #endif
>  #ifdef CONFIG_ACPI
>         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
> -           acpi_gbl_FADT.century)
> -               century = CMOS_READ(acpi_gbl_FADT.century);
> +           acpi_gbl_FADT.century) {
> +               if ((century = CMOS_READ(acpi_gbl_FADT.century)) >
> +                       RTC_CENTURY_LIMIT)

Likewise

> +                       century = 0;
> +       }
>  #endif

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds