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

From: Geert Uytterhoeven
Date: Wed Oct 05 2016 - 03:03:30 EST


On Tue, Oct 4, 2016 at 8:06 PM, Andrew Kim <andrew.kim@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxx

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