[pkg-ntp-maintainers] Bug#794054: ntpd inserts a leap second regardless of the step threshold

[Flos Lonicerae]

Package: ntp
Version: 1:4.2.6.p5+dfsg-7+deb8u2
Followup-For: Bug #794054

Hi all,

Kazuhiro's finding is true and this issue has been fixed in upstream:

** ntpd -x steps clock on leap second
http://bugs.ntp.org/show_bug.cgi?id=2745

I can confirm this bug with adding debugging code to ntp code and also monitor
the kernel's internal state with systemtap.

Below is the patch I ported from RH's source code:
~~~
$ cat ntp-4.2.6p5-xleap.patch
diff -uNr ntp-4.2.6.p5+dfsg.orig/html/miscopt.html
ntp-4.2.6.p5+dfsg/html/miscopt.html
--- ntp-4.2.6.p5+dfsg.orig/html/miscopt.html    2009-12-09 07:36:36.000000000
+0000
+++ ntp-4.2.6.p5+dfsg/html/miscopt.html 2016-10-23 13:44:44.822000703 +0000
@@ -88,7 +88,7 @@
                                                is 0.128 s. If set to zero,
step adjustments will never
                                                occur. Note: The kernel time
discipline is disabled if
                                                the step threshold is set to
zero or greater than 0.5
-                                               s.</dd>
+                                               s and the threshold is applied
also to leap second corrections.</dd>
                                        <dt><tt>stepout
<i>stepout</i></tt></dt>
                                        <dd>Specifies the stepout threshold in
seconds. The default without this
                                                command is 900 s.  If set to
zero, popcorn spikes will
diff -uNr ntp-4.2.6.p5+dfsg.orig/html/ntpd.html
ntp-4.2.6.p5+dfsg/html/ntpd.html
--- ntp-4.2.6.p5+dfsg.orig/html/ntpd.html       2011-07-11 02:18:26.000000000
+0000
+++ ntp-4.2.6.p5+dfsg/html/ntpd.html    2016-10-23 13:46:28.386001420 +0000
@@ -147,7 +147,7 @@
                        <dt><tt>-V <i>variable</i></tt></dt>
                        <dd>Add a system variable listed by default.</dd>
                        <dt><tt>-x</tt></dt>
-                       <dd>Normally, the time is slewed if the offset is less
than the step threshold, which is 128 ms by default, and stepped if above the
threshold. This option sets the threshold to 600 s, which is well within the
accuracy window to set the clock manually. Note: Since the slew rate of typical
Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an
amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take
almost 14 days to complete. This option can be used with the <tt>-g</tt> and
<tt>-q</tt> options. See the <tt>tinker</tt> command for other options. Note:
The kernel time discipline is disabled with this option.</dd>
+                       <dd>Normally, the time is slewed if the offset is less
than the step threshold, which is 128 ms by default, and stepped if above the
threshold. This option sets the threshold to 600 s, which is well within the
accuracy window to set the clock manually. Note: Since the slew rate of typical
Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an
amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take
almost 14 days to complete. This option can be used with the <tt>-g</tt> and
<tt>-q</tt> options. See the <tt>tinker</tt> command for other options. Note:
The kernel time discipline is disabled with this option and the step threshold
is applied also to leap second corrections.</dd>
                        <dt><tt>--pccfreq <i>frequency</i></tt></dt>
                        <dd>Substitute processor cycle counter for
QueryPerformanceCounter unconditionally
                                using the given frequency (in Hz).
<tt>--pccfreq</tt> can be used on systems
diff -uNr ntp-4.2.6.p5+dfsg.orig/ntpd/ntp_timer.c
ntp-4.2.6.p5+dfsg/ntpd/ntp_timer.c
--- ntp-4.2.6.p5+dfsg.orig/ntpd/ntp_timer.c     2011-12-01 02:55:17.000000000
+0000
+++ ntp-4.2.6.p5+dfsg/ntpd/ntp_timer.c  2016-10-23 13:48:15.578002161 +0000
@@ -338,7 +338,8 @@
                        sys_leap = LEAP_NOWARNING;
                        sys_tai = leap_tai;
 #ifdef KERNEL_PLL
-                       if (!(pll_control && kern_enable))
+                       if (clock_max < 1.0 && clock_max > 0.0 &&
+                                       !(pll_control && kern_enable))
                                step_systime(-1.0);
 #else /* KERNEL_PLL */
 #ifndef SYS_WINNT /* WinNT port has its own leap second handling */
~~~

This behaviour of this patch should be the same as Kazuhiro's except for the
log printing part.

If the ntp 4.2.6.p5 version will be used during jessie's lifecycle, this issue
should be escalated to IMPORTANT level as the leap second is coming.

Best Regards,
Flos



-- System Information:
Debian Release: 8.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.16.0-4-amd64 (SMP w/2 CPU cores)
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages ntp depends on:
ii  adduser      3.113+nmu3
ii  dpkg         1.17.27
ii  libc6        2.19-18+deb8u6
ii  libcap2      1:2.24-8
ii  libedit2     3.1-20140620-2
ii  libopts25    1:5.18.4-3
ii  libssl1.0.0  1.0.1t-1+deb8u5
ii  lsb-base     4.1+Debian13+nmu1
ii  netbase      5.3

Versions of packages ntp recommends:
ii  perl  5.20.2-3+deb8u6

Versions of packages ntp suggests:
pn  ntp-doc  <none>

-- Configuration Files:
/etc/ntp.conf changed [not included]

-- no debconf information