From: v.ondruch@...
Date: 2014-12-02T08:59:24+00:00
Subject: [ruby-core:66644] [ruby-trunk - Bug #10412] DNS Resolv broken when resolv.conf has option ndots > 1

Issue #10412 has been updated by Vit Ondruch.

Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN to 2.0.0: REQUIRED, 2.1: REQUIRED

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Bug #10412: DNS Resolv broken when resolv.conf has option ndots > 1
https://bugs.ruby-lang.org/issues/10412#change-50256

* Author: Vit Ondruch
* Status: Closed
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux]
* Backport: 2.0.0: REQUIRED, 2.1: REQUIRED
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This was originally reported by Frank Hirtz at Red Hat's Bugzilla:

https://bugzilla.redhat.com/show_bug.cgi?id=1132704


~~~
Description of problem:
Rubys resolver (/usr/lib/ruby/1.8/resolv.rb) attempts to implement name canonicalization similar to the system resolver.

It's implementation prevents simple lookups when ndots is set greater than 1 (the default).

For example, with this resolv.conf:

    nameserver 192.168.1.1
    nameserver 192.168.1.2
    options ndots:2
    search a.example.com b.example.com example.com

This script raises an Resolv::ResolvError exception:

    #!/usr/bin/ruby
    require 'resolv'
    p Resolv.getaddress('google.com')


Ruby's resolver parses /etc/resolv.conf extracting nameservers, search domains, and the ndots option.

When you attempt to resolv a name (which does not include a trailing "." indicating it is already fully qualified) it determines the number of dots in the name, and if there number of dots in the name is less than the ndots option, it attempts canonicalization.

This is correct behavior, but the canonicalization mechanism is where the problem lies. In the above example, it performs three lookups: google.com.a.example.com, google.com.b.example.com, and google.com.example.com. 

The linux resolver would do the same, and then fail back to google.com. if canonicalization fails. The issue is in /usr/lib/ruby/1.8/resolv.rb. The following patch makes ruby's resolver behave the same way as the system resolver:

    --- /usr/lib/ruby/1.8/resolv.rb 2010-12-22 22:22:57.000000000 -0500
    +++ resolv.rb   2014-08-20 18:50:05.653882000 -0400
    @@ -945,6 +945,10 @@
                 candidates = []
               end
               candidates.concat(@search.map {|domain| Name.new(name.to_a + domain)})
    +          fname = Name.create("#{name}.")
    +          if !candidates.include?(fname)
    +              candidates << fname
    +          end
             end
             return candidates
           end

It looks like the same bug exists in the upstream stable ruby 2.1.2.

This issue causes the client see failures in their configuration management system (puppet) and home-grown host provisioning system.

Version-Release number of selected component (if applicable):
All (RHEL versions as well as upstream). Tested on ruby and ruby200 in RHEL6 and Ruby 2.x in fedora.
~~~



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