[pkg-ntp-maintainers] Bug#874540: ntpdate vs ntp service lock not safe with systemd service

[Christian Ehrhardt]

Package: ntp
Version: 1:4.2.8p10+dfsg-5

Hi,
this is a follow on to bug 806556
Back then you fixed it for sysv-init and I can confirm it worked great.
But since recent versions the sysv script is no more used as there is a
native systemd service.
I carried forward your change in bug 806556 to the systemd wrapper and it
works just fine - again locking the start of the service against
potentially racing ntpdate ifup hook executions.

If you agree, the following change should fix the issue:

diff --git a/debian/ntp-systemd-wrapper b/debian/ntp-systemd-wrapper
index 8d5d1f2..fead246 100755
--- a/debian/ntp-systemd-wrapper
+++ b/debian/ntp-systemd-wrapper
@@ -2,6 +2,7 @@

DAEMON=/usr/sbin/ntpd
PIDFILE=/var/run/ntpd.pid
+LOCKFILE=/run/lock/ntpdate

if [ -r /etc/default/ntp ]; then
        . /etc/default/ntp
@@ -17,5 +18,13 @@ if test "$(uname -s)" = "Linux"; then
        NTPD_OPTS="$NTPD_OPTS -u $UGID"
fi

-exec $DAEMON -p $PIDFILE $NTPD_OPTS
+# Protect the service startup against concurrent ntpdate ifup hooks
+(
+    if flock -w 180 9; then
+        exec $DAEMON -p $PIDFILE $NTPD_OPTS
+    else
+        echo "Timeout waiting for $LOCKFILE"
+        exit 1
+    fi
+) 9>$LOCKFILE

-- 
Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd
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