From c99c5bb88c8b02f24a2b0b15ea8bc9fe2a8dc6c4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pavel=20B=C5=99ezina?= <pbrezina@redhat.com>
Date: Mon, 22 Aug 2016 13:15:04 +0200
Subject: [PATCH 116/117] watchdog: cope with time shift
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When a time is changed into the past during sssd runtime
(e.g. on boot during time correction), it is possible that
we never hit watchdog tevent timer since it is based on
system time.

This patch adds a past-time shift detection mechanism. If a time
shift is detected we restart watchdog.

Resolves:
https://fedorahosted.org/sssd/ticket/3154

Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
---
 src/util/util_watchdog.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/src/util/util_watchdog.c b/src/util/util_watchdog.c
index 5032fddba1b94b3fc7e560162c392dfa57d699cf..1c27d73f13b3042ecb549a2184e1368e8339d199 100644
--- a/src/util/util_watchdog.c
+++ b/src/util/util_watchdog.c
@@ -29,8 +29,39 @@ struct watchdog_ctx {
     struct timeval interval;
     struct tevent_timer *te;
     volatile int ticks;
+
+    /* To detect time shift. */
+    struct tevent_context *ev;
+    int input_interval;
+    time_t timestamp;
 } watchdog_ctx;
 
+static bool watchdog_detect_timeshift(void)
+{
+    time_t prev_time;
+    time_t cur_time;
+    errno_t ret;
+
+    prev_time = watchdog_ctx.timestamp;
+    cur_time = watchdog_ctx.timestamp = time(NULL);
+    if (cur_time < prev_time) {
+        /* Time shift detected. We need to restart watchdog. */
+        DEBUG(SSSDBG_IMPORTANT_INFO, "Time shift detected, "
+              "restarting watchdog!\n");
+        teardown_watchdog();
+        ret = setup_watchdog(watchdog_ctx.ev, watchdog_ctx.input_interval);
+        if (ret != EOK) {
+            DEBUG(SSSDBG_FATAL_FAILURE, "Unable to restart watchdog "
+                  "[%d]: %s\n", ret, sss_strerror(ret));
+            orderly_shutdown(1);
+        }
+
+        return true;
+    }
+
+    return false;
+}
+
 /* the watchdog is purposefully *not* handled by the tevent
  * signal handler as it is meant to check if the daemon is
  * still processing the event queue itself. A stuck process
@@ -38,6 +69,12 @@ struct watchdog_ctx {
  * signals either */
 static void watchdog_handler(int sig)
 {
+    /* Do not count ticks if time shift was detected
+     * since watchdog was restarted. */
+    if (watchdog_detect_timeshift()) {
+        return;
+    }
+
     /* if 3 ticks passed by kills itself */
 
     if (__sync_add_and_fetch(&watchdog_ctx.ticks, 1) > 3) {
@@ -101,6 +138,10 @@ int setup_watchdog(struct tevent_context *ev, int interval)
     watchdog_ctx.interval.tv_sec = interval;
     watchdog_ctx.interval.tv_usec = 0;
 
+    watchdog_ctx.ev = ev;
+    watchdog_ctx.input_interval = interval;
+    watchdog_ctx.timestamp = time(NULL);
+
     /* Start the timer */
     /* we give 1 second head start to the watchdog event */
     its.it_value.tv_sec = interval + 1;
-- 
2.4.11