linux-kernel - [PATCH v3] rtc: wilco-ec: Handle reading invalid times

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Message-Id: <20190925203209.79941-1-ncrews@chromium.org>
Date:   Wed, 25 Sep 2019 14:32:09 -0600
From:   Nick Crews <ncrews@...omium.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alessandro Zummo <a.zummo@...ertech.it>
Cc:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pavel Machek <pavel@....cz>, enric.balletbo@...labora.com,
        bleung@...omium.org, dlaurie@...omium.org, djkurtz@...omium.org,
        dtor@...gle.com, Nick Crews <ncrews@...omium.org>
Subject: [PATCH v3] rtc: wilco-ec: Handle reading invalid times

If the RTC HW returns an invalid time, the rtc_year_days()
call would crash. This patch adds error logging in this
situation, and removes the tm_yday and tm_wday calculations.
These fields should not be relied upon by userspace
according to man rtc, and thus we don't need to calculate
them.

Signed-off-by: Nick Crews <ncrews@...omium.org>
---
 drivers/rtc/rtc-wilco-ec.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-wilco-ec.c b/drivers/rtc/rtc-wilco-ec.c
index 8ad4c4e6d557..53da355d996a 100644
--- a/drivers/rtc/rtc-wilco-ec.c
+++ b/drivers/rtc/rtc-wilco-ec.c
@@ -110,10 +110,15 @@ static int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
 	tm->tm_mday	= rtc.day;
 	tm->tm_mon	= rtc.month - 1;
 	tm->tm_year	= rtc.year + (rtc.century * 100) - 1900;
-	tm->tm_yday	= rtc_year_days(tm->tm_mday, tm->tm_mon, tm->tm_year);
-
-	/* Don't compute day of week, we don't need it. */
-	tm->tm_wday = -1;
+	/* Ignore other tm fields, man rtc says userspace shouldn't use them. */
+
+	if (rtc_valid_tm(tm)) {
+		dev_err(dev,
+			 "Time from RTC is invalid: second=%u, minute=%u, hour=%u, day=%u, month=%u, year=%u, century=%u",
+			 rtc.second, rtc.minute, rtc.hour, rtc.day, rtc.month,
+			 rtc.year, rtc.century);
+		return -EIO;
+	}
 
 	return 0;
 }
-- 
2.21.0