[Bug 1748147] [NEW] [SRU] debhelper support override from /etc/tmpfiles.d for systemd

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[Impact]

/var/log's Permission is going back to 755
after upgrading systemd
if there are rsyslog's configuration on /var/lib/tmpfiles.d/

Affected X, A, B, C

This is because rsyslog's pkg has 00rsyslog.conf and copied it on /var/lib/tmpfiles.d/ when it is installing.
after upgrading systemd, systemd only refresh it's own tmpfiles so disappear conf for 00rsyslog.conf ( it doesn't remove file itself )
so, systemd-tmpfiles --create /var/lib/tmpfiles.d/00rsyslog.conf back permission to 775

[Test Case]

1. deploy 16.04 vm
2. check ll /var (775)
3. apt install --reinstall systemd
4. check ll /var (755)

[Regression Potential]
This fix changes debhelper's override process by using absolute path to filename. so if the other pkgs using debhelper e.g systemd are there, It should be re-build with new debhelper after patching. also, pkg like rsyslog which is using systemd's tmpfile system need to be changed to use /etc/tmpfiles.d/[SAME_FILENAME_IN_VAR_LIB_TMPFILES.D_FOR_OVERRIDING] instead of 00rsyslog.conf.

[Others]

For this issue, need to fix below pkgs

debhelper
systemd ( rebuilding with new debhelper is needed )
rsyslog ( 00rsyslog.conf to var.conf and location should be /etc/tmpfiles.d, to support override supported by debhelper )

[Original description]

Upgrading or reinstalling the systemd package when using rsyslogd
results in bad permissions (0755 instead of 0775) being set on
/var/log/. As a consequence of this, rsyslogd can no longer create new
files within this directory, resulting in lost log messages.

The default configuration of rsyslogd provided by Ubuntu runs the daemon
as syslog:syslog and sets ownership of /var/log to syslog:adm with mode
0775.

Systemd's default tmpfiles configuration sets /var/log to 0755 in
/usr/lib/tmpfiles.d/var.conf, however this is overridden in
/usr/lib/tmpfiles.d/00rsyslog.conf which is provided by package rsyslog.

It looks as though an upgrade of the systemd package fails to take
/usr/lib/tmpfiles.d/00rsyslog.conf into account, as demonstrated below.
This results in /var/log receiving mode 0755 instead of the expected
0775:

nick @ log2.be1.ams1:~ $ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.3 LTS
Release:	16.04
Codename:	xenial

nick @ log2.be1.ams1:~ $ apt policy systemd
systemd:
  Installed: 229-4ubuntu21.1
  Candidate: 229-4ubuntu21.1
  Version table:
 *** 229-4ubuntu21.1 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        100 /var/lib/dpkg/status
     229-4ubuntu4 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages

nick @ log2.be1.ams1:~ $ apt policy rsyslog
rsyslog:
  Installed: 8.16.0-1ubuntu3
  Candidate: 8.16.0-1ubuntu3
  Version table:
 *** 8.16.0-1ubuntu3 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

nick @ log2.be1.ams1:~ $ grep -F /var/log /usr/lib/tmpfiles.d/var.conf
d /var/log 0755 - - -
f /var/log/wtmp 0664 root utmp -
f /var/log/btmp 0600 root utmp -

nick @ log2.be1.ams1:~ $ cat /usr/lib/tmpfiles.d/00rsyslog.conf
# Override systemd's default tmpfiles.d/var.conf to make /var/log writable by
# the syslog group, so that rsyslog can run as user.
# See tmpfiles.d(5) for details.

# Type Path    Mode UID  GID  Age Argument
d /var/log 0775 root syslog -

nick @ log2.be1.ams1:~ $ ls -ld /var/log
drwxrwxr-x 8 root syslog 4096 Feb  7 13:45 /var/log

nick @ log2.be1.ams1:~ $ sudo apt install --reinstall systemd
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 7 not upgraded.
Need to get 3,634 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 systemd amd64 229-4ubuntu21.1 [3,634 kB]
Fetched 3,634 kB in 0s (24.3 MB/s)
(Reading database ... 86614 files and directories currently installed.)
Preparing to unpack .../systemd_229-4ubuntu21.1_amd64.deb ...
Unpacking systemd (229-4ubuntu21.1) over (229-4ubuntu21.1) ...
Processing triggers for dbus (1.10.6-1ubuntu3.3) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up systemd (229-4ubuntu21.1) ...
addgroup: The group `systemd-journal' already exists as a system group. Exiting.

nick @ log2.be1.ams1:~ $ ls -ld /var/log
drwxr-xr-x 8 root syslog 4096 Feb  7 13:45 /var/log

** Affects: debhelper
     Importance: Unknown
         Status: Fix Released

** Affects: debhelper (Ubuntu)
     Importance: High
     Assignee: Seyeong Kim (xtrusia)
         Status: New


** Tags: patch sts sts-sru-needed xenial
-- 
[SRU] debhelper support override from /etc/tmpfiles.d for systemd
https://bugs.launchpad.net/bugs/1748147
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