[PATCH 5.16 0108/1017] rtc: mc146818-lib: fix locking in mc146818_set_time

Greg Kroah-Hartman
2022-04-05T11:07:53Z

From: Mateusz Jończyk <mat.jonczyk@o2.pl>

commit 811f5559270f25c34c338d6eaa2ece2544c3d3bd upstream.

In mc146818_set_time(), CMOS_READ(RTC_CONTROL) was performed without the
rtc_lock taken, which is required for CMOS accesses. Fix this.

Nothing in kernel modifies RTC_DM_BINARY, so a separate critical section
is allowed here.

Fixes: dcf257e92622 ("rtc: mc146818: Reduce spinlock section in mc146818_set_time()")
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220220090403.153928-1-mat.jonczyk@o2.pl
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/rtc/rtc-mc146818-lib.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -176,8 +176,10 @@ int mc146818_set_time(struct rtc_time *t
if (yrs >= 100)
yrs -= 100;

- if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY)
- || RTC_ALWAYS_BCD) {
+ spin_lock_irqsave(&rtc_lock, flags);
+ save_control = CMOS_READ(RTC_CONTROL);
+ spin_unlock_irqrestore(&rtc_lock, flags);
+ if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
sec = bin2bcd(sec);
min = bin2bcd(min);
hrs = bin2bcd(hrs);