[chrony-dev] [PATCH v2 5/6] leapdb: support leap-seconds.list as second source

[patrick.oppenlander@xxxxxxxxx]

From: Patrick Oppenlander <patrick.oppenlander@xxxxxxxxx>

The existing implementation of getting leap second information from a
timezone in get_tz_leap() relies on non-portable C library behaviour.

Specifically, mktime is not required to return '60' in the tm_sec field
when a leap second is inserted leading to "Timezone right/UTC failed
leap second check, ignoring" errors on musl based systems.

This patch adds support for getting leap second information from the
leap-seconds.list file included with tzdata and adds a new configuration
directive leapseclist to switch on the feature.
---
 conf.c               |  14 +++++
 conf.h               |   1 +
 doc/chrony.conf.adoc |  19 +++++-
 leapdb.c             | 135 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 166 insertions(+), 3 deletions(-)

diff --git a/conf.c b/conf.c
index fa74459..06857a8 100644
--- a/conf.c
+++ b/conf.c
@@ -249,6 +249,9 @@ static REF_LeapMode leapsec_mode = REF_LeapModeSystem;
 /* Name of a system timezone containing leap seconds occuring at midnight */
 static char *leapsec_tz = NULL;
 
+/* File name of leap seconds list, usually /usr/share/zoneinfo/leap-seconds.list */
+static char *leapsec_list = NULL;
+
 /* Name of the user to which will be dropped root privileges. */
 static char *user;
 
@@ -471,6 +474,7 @@ CNF_Finalise(void)
   Free(hwclock_file);
   Free(keys_file);
   Free(leapsec_tz);
+  Free(leapsec_list);
   Free(logdir);
   Free(bind_ntp_iface);
   Free(bind_acq_iface);
@@ -620,6 +624,8 @@ CNF_ParseLine(const char *filename, int number, char *line)
     parse_leapsecmode(p);
   } else if (!strcasecmp(command, "leapsectz")) {
     parse_string(p, &leapsec_tz);
+  } else if (!strcasecmp(command, "leapseclist")) {
+    parse_string(p, &leapsec_list);
   } else if (!strcasecmp(command, "local")) {
     parse_local(p);
   } else if (!strcasecmp(command, "lock_all")) {
@@ -2386,6 +2392,14 @@ CNF_GetLeapSecTimezone(void)
 
 /* ================================================== */
 
+char *
+CNF_GetLeapSecList(void)
+{
+  return leapsec_list;
+}
+
+/* ================================================== */
+
 int
 CNF_GetSchedPriority(void)
 {
diff --git a/conf.h b/conf.h
index 58ebdeb..4c0a787 100644
--- a/conf.h
+++ b/conf.h
@@ -91,6 +91,7 @@ extern char *CNF_GetNtpSigndSocket(void);
 extern char *CNF_GetPidFile(void);
 extern REF_LeapMode CNF_GetLeapSecMode(void);
 extern char *CNF_GetLeapSecTimezone(void);
+extern char *CNF_GetLeapSecList(void);
 
 /* Value returned in ppm, as read from file */
 extern double CNF_GetMaxUpdateSkew(void);
diff --git a/doc/chrony.conf.adoc b/doc/chrony.conf.adoc
index abb8403..41646c4 100644
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -672,9 +672,10 @@ trusted and required source.
 *tai*:::
 This option indicates that the reference clock keeps time in TAI instead of UTC
 and that *chronyd* should correct its offset by the current TAI-UTC offset. The
-<<leapsectz,*leapsectz*>> directive must be used with this option and the
-database must be kept up to date in order for this correction to work as
-expected. This option does not make sense with PPS refclocks.
+<<leapsectz,*leapsectz*>> or <<leapseclist,*leapseclist*>> directive must be
+used with this option and the database must be kept up to date in order for
+this correction to work as expected. This option does not make sense with PPS
+refclocks.
 *local*:::
 This option specifies that the reference clock is an unsynchronised clock which
 is more stable than the system clock (e.g. TCXO, OCXO, or atomic clock) and
@@ -1261,6 +1262,18 @@ $ TZ=right/UTC date -d 'Dec 31 2008 23:59:60'
 Wed Dec 31 23:59:60 UTC 2008
 ----
 
+[[leapseclist]]*leapseclist* _file_::
+This directive specifies the path to a file containing a list of leap seconds.
+It is recommended to use the file _leap-seconds.list_ usually included with the
+system timezone database. The behaviour of this directive is otherwise equivalent
+to <<leapsectz,*leapsectz*>>.
++
+An example of this directive is:
++
+----
+leapseclist /usr/share/zoneinfo/leap-seconds.list
+----
+
 [[makestep]]*makestep* _threshold_ _limit_::
 Normally *chronyd* will cause the system to gradually correct any time offset,
 by slowing down or speeding up the clock as required. In certain situations,
diff --git a/leapdb.c b/leapdb.c
index 98bb2f5..c790c20 100644
--- a/leapdb.c
+++ b/leapdb.c
@@ -35,9 +35,24 @@
 
 typedef NTP_Leap (*GetLeapFn)(time_t when, int *tai_offset);
 
+/* Offset between leap-seconds.list epoch timestamps and Unix epoch.
+   leap-seconds.list epoch is 1 Jan 1900, 00:00:00 */
+static const long long LEAP_SECONDS_LIST_OFFSET = 2208988800;
+
 /* Current leap second data source */
 GetLeapFn get_leap;
 
+/* Leap second database */
+struct leapdb {
+  long long updated;
+  long long expiry;
+  size_t len;
+  struct leap {
+    long long when;
+    int tai_offset;
+  } leap[];
+};
+
 /* ================================================== */
 
 static NTP_Leap
@@ -95,6 +110,110 @@ get_tz_leap(time_t when, int *tai_offset)
 
 /* ================================================== */
 
+static struct leapdb *
+read_leap_seconds_list(const char *file)
+{
+  size_t ll = 0;
+  size_t len = 32; /* 28 entries to 1 Jan 2017 */
+  struct leapdb *db = calloc(1, sizeof *db + sizeof *db->leap * len);
+  FILE *f = fopen(file, "r");
+  char *l = NULL;
+
+  if (!db || !f)
+    goto error;
+
+  while (getline(&l, &ll, f) > 0) {
+    if (*l == '#') {
+      /* update time */
+      if (l[1] == '$' && sscanf(l + 2, "%lld", &db->updated) != 1)
+        goto error;
+      /* expiration time */
+      if (l[1] == '@' && sscanf(l + 2, "%lld", &db->expiry) != 1)
+        goto error;
+      /* comment or a special comment we don't care about */
+      continue;
+    }
+
+    if (db->len >= len) {
+      len += len / 2;
+      void *p = realloc(db, sizeof *db + sizeof *db->leap * len);
+      if (!p)
+        goto error;
+      db = p;
+    }
+
+    /* leap entry */
+    struct leap *lp = db->leap + db->len;
+    if (sscanf(l, "%lld %d", &lp->when, &lp->tai_offset) != 2)
+      goto error;
+    ++db->len;
+  }
+
+  /* make sure the database looks sensible */
+  if (!feof(f) || !db->updated || !db->expiry || !db->len)
+    goto error;
+
+  goto out;
+
+error:
+  free(db);
+  db = 0;
+out:
+  free(l);
+  if (f)
+    fclose(f);
+  return db;
+}
+
+/* ================================================== */
+
+static NTP_Leap
+get_db_leap(time_t when, int *tai_offset)
+{
+  NTP_Leap db_leap = LEAP_Normal;
+  struct leapdb *db = read_leap_seconds_list(CNF_GetLeapSecList());
+
+  if (!db) {
+    LOG(LOGS_ERR, "Failed to read leap second list %s", CNF_GetLeapSecList());
+    return db_leap;
+  }
+
+  /* leap second happens at midnight */
+  when = (when / (24 * 3600) + 1) * (24 * 3600);
+
+  /* leap-seconds.list timestamps are relative to 1 Jan 1900, 00:00:00 */
+  long long leap_when = when + LEAP_SECONDS_LIST_OFFSET;
+  db_leap = LEAP_Normal;
+
+  if (leap_when >= db->expiry)
+    LOG(LOGS_WARN, "Leap second list %s needs update", CNF_GetLeapSecList());
+
+  /* find leap entry */
+  struct leap *lp = db->leap;
+  for (int i = db->len - 1; i >= 0; --i) {
+    lp = db->leap + i;
+    if (leap_when >= lp->when)
+      break;
+  }
+
+  if (leap_when == lp->when) {
+    struct leap *lp_prev = lp > db->leap ? lp - 1 : db->leap;
+    if (lp->tai_offset > lp_prev->tai_offset) {
+      db_leap = LEAP_InsertSecond;
+    } else if (lp->tai_offset < lp_prev->tai_offset)
+      db_leap = LEAP_DeleteSecond;
+    /* tai offset hasn't changed yet! */
+    *tai_offset = lp_prev->tai_offset;
+  } else
+    *tai_offset = lp->tai_offset;
+
+  free(db);
+
+  return db_leap;
+}
+
+/* ================================================== */
+
 static int
 check_leap_source(GetLeapFn fn)
 {
@@ -119,6 +238,22 @@ LDB_Initialise(void)
     leap_tzname = NULL;
   }
 
+  const char *leap_list = CNF_GetLeapSecList();
+  if (leap_list && !check_leap_source(get_db_leap)) {
+    LOG(LOGS_WARN, "Leap second list %s failed check, ignoring", leap_list);
+    leap_list = NULL;
+  }
+
+  if (leap_list && leap_tzname) {
+    LOG(LOGS_WARN, "Multiple leap second sources, ignoring leapsectz");
+    leap_tzname = NULL;
+  }
+
+  if (leap_list) {
+    LOG(LOGS_INFO, "Using leap second list %s", leap_list);
+    get_leap = get_db_leap;
+  }
+
   if (leap_tzname) {
     LOG(LOGS_INFO, "Using %s timezone to obtain leap second data", leap_tzname);
     get_leap = get_tz_leap;
-- 
2.43.0


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