rtc: cmos: take rtc_lock while reading from CMOS

commit 454f47ff464325223129b9b5b8d0b61946ec704d upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index c633319cdb91319d8af218ec4eda30503e59ec4e..58c6382a2807caa293ed30da83ab0d4809c15463 100644 (file)
--- 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;