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 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@o2.pl>
Reviewed-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211210200131.153887-2-mat.jonczyk@o2.pl

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 4eb53412b8085e12d668c2aef3b215b939094143..dc3f8b0dde9891886e87b2e4e6a1735b1c10baad 100644 (file)
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -457,7 +457,10 @@ 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;