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[Launchpad Bug Tracker <1479652@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package ntp - 1:4.2.6.p5+dfsg-3ubuntu2.14.04.8

---------------
ntp (1:4.2.6.p5+dfsg-3ubuntu2.14.04.8) trusty; urgency=medium

  * ntpd rejects source UDP ports less than 123 as bogus (closes: #691412)
    - d/p/reject-UDP-ports-less-than-123-as-bogus.patch (LP: #1479652)

 -- Eric Desrochers <slashd@xxxxxxxxxx>  Mon, 25 Jan 2016 11:39:44 -0500

** Changed in: ntp (Ubuntu Trusty)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1479652

Title:
  [patch] ntpd rejects source UDP ports less than 123 as bogus

Status in NTP:
  Fix Released
Status in ntp package in Ubuntu:
  Fix Committed
Status in ntp source package in Precise:
  Fix Committed
Status in ntp source package in Trusty:
  Fix Released
Status in ntp source package in Wily:
  Fix Released
Status in ntp source package in Xenial:
  Fix Committed
Status in ntp package in Debian:
  New

Bug description:
  [Impact]

  If an NTP client sends a request with a source port less than 123, the
  packet is silently ignored by ntpd. This is occurring in our
  environment due to NAT.

  [Development Fix]

  Fixed by merge of NTP of newer upstream release that includes the fix.
  Stuck in dep-wait in xenial-proposed due to an unrelated issue (pps-
  tools MIR or other resolution).

  [Test Case]

  The problem can easily be reproduced by having an iptable postrouting
  nat forcing the source port to be under 123 set on the client.

  Setup:
   ==> NTP server = y.y.y.y
   ntp.conf configured to be a server.

   ==> NTP client = x.x.x.x
   "ntpdate" used to submmit requests

   #iptable setup to force src port to be lower than 123
   iptables -t nat -A POSTROUTING -p UDP --dport 123  -j SNAT --to-source x.x.x.x:100-122

  ## On the client, set to force src port < 123 (without patch)

  $ ntpdate y.y.y.y
  ntpdate[<PID>]: no server suitable for synchronization found

  ## On the client, set to force src port < 123 (with patch)

  $ ntpdate y.y.y.y
  ntpdate[<PID>]: adjust time server y.y.y.y offset -0.028483 sec

  [Regression Potential]

  The patch comes from upstream:
  http://bugs.ntp.org/show_bug.cgi?id=2174

  A testfix[1] package has been provided to the community before the SRU
  process to bring more confidence for the patch. Positive feedbacks has
  been given by the community to confirm the patch addressed the bug
  [comment #7]

  [1]- https://launchpad.net/~slashd/+archive/ubuntu/bug1479652

  [Original description]

  [Title copied from Debian bug, which was not filed by me. Description
  below is mine.]

  If an NTP client sends a request with a source port less than 123, the
  packet is silently ignored by ntpd. This is occurring in our
  environment due to NAT.

  Attached is the patch already accepted upstream which fixes the issue.
  I've verified it fixes the problem. Debian has been ignoring this
  patch for almost 3 years. Can we get this in Ubuntu please?

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