linux-kernel - [PATCH v4] rtc: wilco-ec: Handle reading invalid times

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Message-Id: <20191004142608.170159-1-ncrews@chromium.org>
Date:   Fri,  4 Oct 2019 08:26:08 -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, campello@...omium.org,
        Nick Crews <ncrews@...omium.org>
Subject: [PATCH v4] 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 | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/rtc/rtc-wilco-ec.c b/drivers/rtc/rtc-wilco-ec.c
index 8ad4c4e6d557..ff46066a68a4 100644
--- a/drivers/rtc/rtc-wilco-ec.c
+++ b/drivers/rtc/rtc-wilco-ec.c
@@ -110,10 +110,12 @@ 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);
+	/* Ignore other tm fields, man rtc says userspace shouldn't use them. */
 
-	/* Don't compute day of week, we don't need it. */
-	tm->tm_wday = -1;
+	if (rtc_valid_tm(tm)) {
+		dev_err(dev, "Time from RTC is invalid: %ptRr\n", tm);
+		return -EIO;
+	}
 
 	return 0;
 }
-- 
2.21.0