3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexandre Belloni <alexandre.bell...@bootlin.com>

[ Upstream commit abfdff44bc38e9e2ef7929f633fb8462632299d4 ]

When using RTC_ALM_SET or RTC_WKALM_SET with rtc_wkalrm.enabled not set,
rtc_timer_enqueue() is not called and rtc_set_alarm() may succeed but the
subsequent RTC_AIE_ON ioctl will fail. RTC_ALM_READ would also fail in that
case.

Ensure rtc_set_alarm() fails when alarms are not supported to avoid letting
programs think the alarms are working for a particular RTC when they are
not.

Signed-off-by: Alexandre Belloni <alexandre.bell...@bootlin.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/rtc/interface.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -381,6 +381,11 @@ int rtc_set_alarm(struct rtc_device *rtc
 {
        int err;
 
+       if (!rtc->ops)
+               return -ENODEV;
+       else if (!rtc->ops->set_alarm)
+               return -EINVAL;
+
        err = rtc_valid_tm(&alarm->time);
        if (err != 0)
                return err;


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