[Bug 1906970] Please test proposed package

[Brian Murray]

Hello Klaus, or anyone else affected,

Accepted postfix into bionic-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/postfix/3.3.0-1ubuntu0.4 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
bionic to verification-done-bionic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-bionic. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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https://bugs.launchpad.net/bugs/1906970

Title:
  [SRU] dpkg hook hostname error

Status in postfix package in Ubuntu:
  Fix Released
Status in sbuild package in Ubuntu:
  Fix Released
Status in postfix source package in Bionic:
  Fix Committed
Status in postfix source package in Focal:
  Fix Committed
Status in postfix source package in Hirsute:
  Fix Committed
Status in postfix package in Debian:
  Unknown

Bug description:
  [Impact]

  /etc/resolv.conf search domain with a leading dot cause
  postfix.postinst to fail because it constructs a 'myhostname' with a
  duplicate dot.

  The glibc resolver tolerates such domains and strips the leading dot
  from the search domain [1]. This change makes postfix.postinst do the
  same.

  This same fix has been proposed for inclusion in Debian [2].

  [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=resolv/res_query.c;h=ebbe5a6a4ed86abe3fccd4a134bfcf6f613c9bbb;hb=HEAD#l411
  [2] https://salsa.debian.org/postfix-team/postfix-dev/-/merge_requests/12

  [Test Plan]

  1. Start an LXD container
  2. Edit /etc/resolv.conf and add search line like one of these:

       search .
       search .foo.bar
       domain .foo.bar

  3. Install postfix from the archive, accept all the debconf defaults,
     and verify that postinst fails with a broken domain name.
  4. Purge postfix and install the version to test (e.g. from -proposed).
  5. Verify that the installation succeeds.
  6. Verify that `myhostname` in /etc/postfix/main.cf is sane.

  Test PPA: https://launchpad.net/~paride/+archive/ubuntu/postfix-
  lp1906970

  [Where problems could occur]

  There is no reasonable case where a user could rely on a "broken"
  setup, as its result is a postinst failure (= install failure) and an
  invalid "myhostname" in main.cf.

  The regression potential is in my opinion very low and, given the
  scope and nature of the change, mostly due to the newer Build-Deps the
  package will be built with.

  The postfix service is restarted on upgrades of the postfix package,
  so problems may also occur on systems with issues (misconfiguration,
  filled partitions, ...) but where Postfix has not been restarted and
  it's still working, but won't resume its operations on upgrade. While
  this is technically a "not a bug in Ubuntu" case it is also something
  we don't want to expose users to for no good reason.

  [Development Fix]

  This is fixed already in the current devel release (Impish). This SRU
  backports the very same fix to the stable releases.

  Once [2] or equivalent gets accepted in Debian we'll be able to drop
  the delta and make postfix.

  [Original Description]

  I tried to install postfix (3.4.13-0ubuntu1) within a Dockerfile
  (Ubuntu 20.04.01 LTS) and it failed because there is an error in the
  dpkg info file.

  I'm attaching the log of the 2nd time "apt install -y postfix" is
  executed, as it is way shorter and still shows the error message.

  ```
  root at cc1a572af0dc:/etc# apt install -y postfix
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  postfix is already the newest version (3.4.13-0ubuntu1).
  0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
  1 not fully installed or removed.
  After this operation, 0 B of additional disk space will be used.
  Setting up postfix (3.4.13-0ubuntu1) ...

  Postfix (main.cf) configuration was untouched.  If you need to make changes,
  edit /etc/postfix/main.cf (and others) as needed.  To view Postfix
  configuration values, see postconf(1).

  After modifying main.cf, be sure to run 'systemctl reload postfix'.

  Running newaliases
  newaliases: warning: valid_hostname: misplaced delimiter: cc1a572af0dc..
  newaliases: fatal: file /etc/postfix/main.cf: parameter myhostname: bad parameter value: cc1a572af0dc..
  dpkg: error processing package postfix (--configure):
   installed postfix package post-installation script subprocess returned error exit status 75
  Processing triggers for libc-bin (2.31-0ubuntu9.1) ...
  Errors were encountered while processing:
   postfix
  E: Sub-process /usr/bin/dpkg returned an error code (1)
  ```

  I then looked into the /etc/postfix/main.cf file and tried to manually
  change the hostname, but it automatically gets overwritten by dpkg
  when apt install is ran.

  After that I was able to track the issue into the script
  "/var/lib/dpkg/info/postfix.postinst" more exactly the sed command in
  line 52. It reads the content of the search parameter from
  /etc/resolv.conf, and concatenates it with a "." as delimiter with the
  hostname, but it doesn't honor the special case of "search ." and
  therefore constructs an incorrect myhostname parameter for postfix of
  "cc1a572af0dc..".

  I'd propose to remove this resolve.conf lookup entirely so that the package installation doesn't fail within docker containers...
  It is a bad practice in my opinion to overwrite existing config files upon package installation.
  Also I'd suggest not executing postfix after the configuration is written, so that in case of unforeseen circumstances (like this one) a user can just simply run a sed against the config file after installing the package.

  And the Dockerfile for reference:
  ```
  FROM ubuntu:latest

  ENV DEBIAN_FRONTEND=noninteractive
  #ENV DEBIAN_PRIORITY=low

  RUN apt update \
      && echo "postfix postfix/main_mailer_type select Internet Site" | debconf-set-selections \
      && echo "postfix postfix/mailname string mysubdomain.mydomain.com" | debconf-set-selections \
      && apt install -y postfix
  ```

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