Patch "rtc: interface: Validate alarm-time before handling rollover" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

rtc: interface: Validate alarm-time before handling rollover

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rtc-interface-validate-alarm-time-before-handling-rollover.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Vaibhav Jain <[email protected]>
Date: Fri, 19 May 2017 22:18:55 +0530
Subject: rtc: interface: Validate alarm-time before handling rollover

From: Vaibhav Jain <[email protected]>

[ Upstream commit da96aea0ed177105cb13ee83b328f6c61e061d3f ]

In function __rtc_read_alarm() its possible for an alarm time-stamp to be invalid even after replacing missing components with current time-stamp. The condition 'alarm->time.tm_year < 70' will trigger this case and will cause the call to 'rtc_tm_to_time64(&alarm->time)' return a negative value for variable t_alm.

While handling alarm rollover this negative t_alm (assumed to seconds offset from '1970-01-01 00:00:00') is converted back to rtc_time via rtc_time64_to_tm() which results in this error log with seemingly garbage values:

"rtc rtc0: invalid alarm value: -2-1--1041528741
2005511117:71582844:32"

This error was generated when the rtc driver (rtc-opal in this case) returned an alarm time-stamp of '00-00-00 00:00:00' to indicate that the alarm is disabled. Though I have submitted a separate fix for the rtc-opal driver, this issue may potentially impact other existing/future rtc drivers.

To fix this issue the patch validates the alarm time-stamp just after filling up the missing datetime components and if rtc_valid_tm() still reports it to be invalid then bails out of the function without handling the rollover.

---
 drivers/rtc/interface.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

@@ -227,6 +227,13 @@ int __rtc_read_alarm(struct rtc_device *
 			missing = year;
 	}
 
+	/* Can't proceed if alarm is still invalid after replacing
+	 * missing fields.
+	 */
+	err = rtc_valid_tm(&alarm->time);
+	if (err)
+		goto done;
+
 	/* with luck, no rollover is needed */
 	t_now = rtc_tm_to_time64(&now);
 	t_alm = rtc_tm_to_time64(&alarm->time);

@@ -278,9 +285,9 @@ int __rtc_read_alarm(struct rtc_device *
 		dev_warn(&rtc->dev, "alarm rollover not handled\n");
 	}
 
-done:
 	err = rtc_valid_tm(&alarm->time);
 
+done:
 	if (err) {
 		dev_warn(&rtc->dev, "invalid alarm value: %d-%d-%d %d:%d:%d\n",
 			alarm->time.tm_year + 1900, alarm->time.tm_mon + 1,

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/rtc-interface-validate-alarm-time-before-handling-rollover.patch queue-4.9/rtc-opal-handle-disabled-tpo-in-opal_get_tpo_time.patch