[Bug 1717015] Re: libc resolver stops searching domain search list after getting back NSEC record

[Steve Langasek]

On Tue, Apr 03, 2018 at 08:59:19AM -0000, Dimitri John Ledkov wrote:
> 1) one should not manually adjust search domains in /etc/resolv.conf
> 2) systemd-resolved should learn about search domains
>  - for example, set search domains in /etc/systemd/resolved.conf if
> nothing sets them on per link basis vai resolved dbus api or
> networkd.network files.
> 
> 3) /etc/resolv.conf should be a symlink to
> ../run/systemd/resolve/stub-resolv.conf

> 4) ../run/systemd/resolve/stub-resolv.conf should be dynamically updated
> by resolved to contain the correct search domains

If systemd-resolved is going to publish search domain instructions to
../run/systemd/resolve/stub-resolv.conf anyway for use by the libc client, I
don't see any reason to say "one should not manually adjust search domains".

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https://bugs.launchpad.net/bugs/1717015

Title:
  libc resolver stops searching domain search list after getting back
  NSEC record

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  Suppose that:

  1. you have a "search" line in your /etc/resolv.conf file;
  2. it has two domains in it; and
  3. the first of the two domains does DNSSEC, including returning NSEC records for nonexisting hosts.

  In this situation, when you try to look up a host name in the second
  domain without specifying the domain part of the host name, the libc
  resolver will stop after it gets back the NSEC record and report that
  the host name doesn't exist, rather than moving on to the second
  domain in the search list and searching for the host in that domain.

  See also https://bugs.launchpad.net/ubuntu/+source/bind9/+bug/1717014
  .

  ProblemType: Bug
  DistroRelease: Ubuntu 17.04
  Package: libc6 2.24-9ubuntu2.2
  ProcVersionSignature: Ubuntu 4.10.0-33.37-generic 4.10.17
  Uname: Linux 4.10.0-33-generic x86_64
  ApportVersion: 2.20.4-0ubuntu4.5
  Architecture: amd64
  CurrentDesktop: Unity:Unity7
  Date: Wed Sep 13 16:00:45 2017
  Dependencies:
   gcc-6-base 6.3.0-12ubuntu2
   libc6 2.24-9ubuntu2.2
   libgcc1 1:6.3.0-12ubuntu2
  InstallationDate: Installed on 2016-08-09 (400 days ago)
  InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
  SourcePackage: glibc
  UpgradeStatus: Upgraded to zesty on 2017-04-19 (147 days ago)

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