From dc0056f6e88582c0b8725e108fd86e52fc88ba08 Mon Sep 17 00:00:00 2001
From: Mathias Lang <mlang@symmetryinvestments.com>
Date: Sun, 24 Mar 2024 16:01:00 +0100
Subject: [PATCH] networking: Workaround 2693 by ignoring resolv.conf entries
 starting with dot

Currently, systems without a FQDN can be mishandled by facter for certain `/etc/resolv.conf` content.
This was initially noticed when systemd-resolved was installed on a host without domain.

systemd-resolved stub resolver sets 'search .' as a search domain, which results in the
following hostname/domain/fqdn triplet: foo, ., foo...
See: https://github.com/systemd/systemd/blob/v255/src/resolve/resolv.conf#L19

This is wrong on multiple levels: first, facter does not seem to handle '.' (the root level)
well, and there have been PRs to remove the trailing dot in FQDN as far back as 2012 (PR 200),
leaving user with a convenient, but sometimes ambiguous string that is not fully qualified.

This commit implements a a middle ground solution to support top-level/domainless servers
without making a breaking change. Additionally, it adds more coverage for various search
cases.
---
 lib/facter/resolvers/hostname.rb             |  4 ++--
 lib/facter/resolvers/linux/hostname.rb       |  4 ++--
 spec/facter/resolvers/linux/hostname_spec.rb | 24 ++++++++++++++++++++
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/lib/facter/resolvers/hostname.rb b/lib/facter/resolvers/hostname.rb
index eba8782db1..53c7f9ac3c 100644
--- a/lib/facter/resolvers/hostname.rb
+++ b/lib/facter/resolvers/hostname.rb
@@ -68,9 +68,9 @@ def hostname_and_no_domain?(hostname, domain)
 
         def read_domain
           file_content = Facter::Util::FileHelper.safe_read('/etc/resolv.conf')
-          if file_content =~ /^domain\s+(\S+)/
+          if file_content =~ /^domain\s+([^.]\S+)/
             Regexp.last_match(1)
-          elsif file_content =~ /^search\s+(\S+)/
+          elsif file_content =~ /^search\s+([^.]\S+)/
             Regexp.last_match(1)
           end
         end
diff --git a/lib/facter/resolvers/linux/hostname.rb b/lib/facter/resolvers/linux/hostname.rb
index e2dba54eb6..32e0688559 100644
--- a/lib/facter/resolvers/linux/hostname.rb
+++ b/lib/facter/resolvers/linux/hostname.rb
@@ -96,9 +96,9 @@ def hostname_and_no_domain?(hostname, domain)
 
           def read_domain
             file_content = Facter::Util::FileHelper.safe_read('/etc/resolv.conf')
-            if file_content =~ /^domain\s+(\S+)/
+            if file_content =~ /^domain\s+([^.]\S+)/
               Regexp.last_match(1)
-            elsif file_content =~ /^search\s+(\S+)/
+            elsif file_content =~ /^search\s+([^.]\S+)/
               Regexp.last_match(1)
             end
           end
diff --git a/spec/facter/resolvers/linux/hostname_spec.rb b/spec/facter/resolvers/linux/hostname_spec.rb
index a69bdebf8e..f3ee0e77fc 100644
--- a/spec/facter/resolvers/linux/hostname_spec.rb
+++ b/spec/facter/resolvers/linux/hostname_spec.rb
@@ -79,6 +79,30 @@
 
             it_behaves_like 'detects values'
           end
+
+          context 'when /etc/resolv.conf has "search ."' do
+            let(:resolv_conf) { "search .\n" }
+            let(:domain) { nil }
+            let(:fqdn) { hostname }
+
+            it_behaves_like 'detects values'
+          end
+
+          context 'when /etc/resolv.conf has "search ." with multiple entires' do
+            let(:resolv_conf) { 'search . foo.bar' }
+            let(:domain) { nil }
+            let(:fqdn) { hostname }
+
+            it_behaves_like 'detects values'
+          end
+
+          context 'when /etc/resolv.conf has "search" with multiple entires' do
+            let(:resolv_conf) { 'search foo.bar example.com' }
+            let(:domain) { 'foo.bar' }
+            let(:fqdn) { "#{hostname}.#{domain}" }
+
+            it_behaves_like 'detects values'
+          end
         end
 
         context 'when FFI is not installed' do