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Date:   Sun, 17 Oct 2021 21:39:22 +0200
From:   Mateusz Jończyk <mat.jonczyk@...pl>
To:     linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org
Cc:     Mateusz Jończyk <mat.jonczyk@...pl>,
        Nobuhiro Iwamatsu <iwamatsu@...auri.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        stable@...r.kernel.org
Subject: [PATCH RESEND 1/6] rtc-cmos: take rtc_lock while reading from CMOS

Reading from the CMOS involves writing to the index register and then
reading from the data register. Therefore access to the CMOS has to be
serialized with the rtc_lock. This invocation of CMOS_READ was not
serialized, which could cause trouble when other code is accessing CMOS
at the same time.

Use spin_lock_irq() like the rest of the function.

Nothing in kernel modifies the RTC_DM_BINARY bit, so there could be a
separate pair of spin_lock_irq() / spin_unlock_irq() before doing the
math.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
Reviewed-by: Nobuhiro Iwamatsu <iwamatsu@...auri.org>
Cc: Alessandro Zummo <a.zummo@...ertech.it>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: stable@...r.kernel.org
---
 drivers/rtc/rtc-cmos.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 670fd8a2970e..2cd0fe728ab2 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -463,7 +463,10 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 	min = t->time.tm_min;
 	sec = t->time.tm_sec;
 
+	spin_lock_irq(&rtc_lock);
 	rtc_control = CMOS_READ(RTC_CONTROL);
+	spin_unlock_irq(&rtc_lock);
+
 	if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 		/* Writing 0xff means "don't care" or "match all".  */
 		mon = (mon <= 12) ? bin2bcd(mon) : 0xff;
-- 
2.25.1

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