linux-kernel - [PATCH] rtc-mc146818-lib: fix locking in mc146818_set

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Message-Id: <20220220090403.153928-1-mat.jonczyk@o2.pl>
Date:   Sun, 20 Feb 2022 10:04:03 +0100
From:   Mateusz Jończyk <mat.jonczyk@...pl>
To:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Mateusz Jończyk <mat.jonczyk@...pl>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org
Subject: [PATCH] rtc-mc146818-lib: fix locking in mc146818_set_time

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@...pl>
Cc: Alessandro Zummo <a.zummo@...ertech.it>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
---
 drivers/rtc/rtc-mc146818-lib.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index ae9f131b43c0..562f99b664a2 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -232,8 +232,10 @@ int mc146818_set_time(struct rtc_time *time)
 	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);

base-commit: 754e0b0e35608ed5206d6a67a791563c631cec07
-- 
2.25.1