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[Bug 1543185] Re: Malformed query causing timeouts due to ignored upstream queries

 

Ah, it looks like Colin did just cherry pick the fix for this bug; from
the backport .deb's changelog:

+dnsmasq (2.68-1ubuntu0.1ppa1) trusty; urgency=medium
+
+  * Cherry-pick from 2.73:
+    - Correctly sanitise DNS header bits in answer when recreating query for
+      retry.
+
+ -- Colin Watson <cjwatson@xxxxxxxxxx>  Mon, 08 Feb 2016 15:46:48 +0000

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https://bugs.launchpad.net/bugs/1543185

Title:
  Malformed query causing timeouts due to ignored upstream queries

Status in dnsmasq package in Ubuntu:
  New

Bug description:
  In some situations dnsmasq makes malformed upstream queries resulting
  in servfail being returned after the 5s timeout built in to dnsmask.

  For example asking for

  foo

  with athing.bar.com and bar.com in the search path and two servers
  dns1.bar.com and dns1.bar.com results in

  System asks both dns1 and dns2 about: 
                 foo.athing.bar.com => immediate NXDomain from both;
  asks  dns1 about:
                foo.  => Servfail;
  asks both about:
               foo. with what tcpdump transcribes as '[b2&3=0x182] A?  => no response from either [5 sec timeout];
  retries:
               simple "A? foo." query to both, immediate Servfail from both

  The query giving the time out appear to be malformed and the upstream
  servers are completely ignoring it leading to the time out.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: dnsmasq-base 2.68-1ubuntu0.1
  ProcVersionSignature: Ubuntu 3.13.0-77.121-generic 3.13.11-ckt32
  Uname: Linux 3.13.0-77-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.19
  Architecture: amd64
  CurrentDesktop: XFCE
  Date: Mon Feb  8 15:38:26 2016
  InstallationDate: Installed on 2014-05-07 (642 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
  SourcePackage: dnsmasq
  UpgradeStatus: No upgrade log present (probably fresh install)

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References