From e28dfada8c27f1306ba63f15ff96f8ac96042b5a Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Thu, 12 Jan 2017 13:43:41 +0100
Subject: [PATCH] rtc: check for backward RTC steps

When accumulating a new sample, check if the new RTC time is newer the
last sample time. If it is not, discard all previous samples, assuming
something has stepped the RTC, or it's a broken RTC/driver.
---
 rtc_linux.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/rtc_linux.c b/rtc_linux.c
index 8d73102..7394235 100644
--- a/rtc_linux.c
+++ b/rtc_linux.c
@@ -187,6 +187,11 @@ accumulate_sample(time_t rtc, struct timespec *sys)
     discard_samples(NEW_FIRST_WHEN_FULL);
   }
 
+  /* Discard all samples if the RTC was stepped back (not our trim) */
+  if (n_samples > 0 && rtc_sec[n_samples - 1] - rtc >= rtc_trim[n_samples - 1]) {
+    DEBUG_LOG(LOGF_RtcLinux, "RTC samples discarded");
+    n_samples = 0;
+  }
 
   /* Always use most recent sample as reference */
   /* use sample only if n_sample is not negative*/