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[Scott Moser <smoser@xxxxxxxxxx>]

With some other work that I was doing, I found bug 1272414
it seems that getifaddrs() is somewhat slow when lots of interfaces are used.  so this could have a bit of a performance impact in some places.  that said, dhclient is not likely a heavy use path.

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https://bugs.launchpad.net/bugs/1446767

Title:
  dhclient can fail if other nics are renamed

Status in isc-dhcp package in Ubuntu:
  Fix Released
Status in isc-dhcp source package in Trusty:
  Fix Committed
Status in isc-dhcp source package in Vivid:
  Fix Committed
Status in isc-dhcp source package in Wily:
  Fix Released
Status in isc-dhcp package in Fedora:
  Unknown

Bug description:
  === Begin SRU Information ===
  [Impact] 
  Systems that use dhcp for network config combined with network device re-naming can hit a race condition in dhclient which causes dhcp to fail.  Any network device renaming could cause this, but the most likely scenario is boot with udev persistent naming in /etc/udev/rules.d/70-persistent-net.rules.

  This can be a fatal error when network devices that are required for
  proper function.

  [Test Case]
  To recreate the failure:
   * boot an ubuntu system with an interface that can dhcp
   * configure /etc/network/interfaces for dhcp on that interface
     $ grep eth0 /etc/network/interfaces
     auto eth0
     iface eth0 inet dhcp
   * run attached 'nic-go-crazy' as root in one window/shell
     this will create by default 10 tuntap devices and repeatedly rename them.
   * run attached 'ifup-loop eth0'

  ifup-loop will exit failure if dhclient failed to bring the network
  up.

  With the fix provided, this will/should run indefinitely.

  [Regression Potential]
  Chance for regression here should be reasonably small.  However, a very significant number of systems run dhclient, so any change has to be considered risky.

  One thing to note, is that Fedora has carried this patch for > 3
  years.

  Per getifaddrs(3):
   | The getifaddrs() function first appeared in glibc 2.3, but before glibc
   | 2.3.3, the implementation supported only IPv4 addresses; IPv6 support
   | was added in glibc 2.3.3. Support of address families other than IPv4
   | is available only on kernels that support netlink.

  These versions are older than any supported Ubuntu release, so that should not be a problem.
  === End SRU Information ===

  
  given 3 nics eth0, eth1, eth2

  dhclient -1 -v -pf /run/dhclient.eth0.pid -lf
  /var/lib/dhcp/dhclient.eth0.leases eth0

  while that in its early phases, if eth1 is renamed a race condition
  can cause dhclient to exit failure.

  This can happen in real life when udev and persistent rules are used.
  Ie, in a system where eth0 is configured for 'auto' and dhcp  and
  persistent rules cause renaming of devices during boot.

  I have set up recreate of that more complex system
  lp:~smoser/+junk/lp1444428 , but this recreate is simpler to catch.

  example, while running attached 'nic-go-crazy' on other nics, I try
  ifup eth1

  $ sudo ifup eth1
  sudo: unable to resolve host ubuntu
  Internet Systems Consortium DHCP Client 4.3.1
  Copyright 2004-2014 Internet Systems Consortium.
  All rights reserved.
  For info, please visit https://www.isc.org/software/dhcp/

  Error getting interface address for 'nic0317610'; No such device
  Error getting interface information.

  If you think you have received this message due to a bug rather
  than a configuration issue please read the section on submitting
  bugs on either our web page at www.isc.org or in the README file
  before submitting a bug.  These pages explain the proper
  process and the information we find helpful for debugging..

  exiting.
  Failed to bring up eth1.

  ProblemType: Bug
  DistroRelease: Ubuntu 15.04
  Package: isc-dhcp-client 4.3.1-5ubuntu2
  ProcVersionSignature: User Name 3.19.0-15.15-generic 3.19.3
  Uname: Linux 3.19.0-15-generic x86_64
  ApportVersion: 2.17.2-0ubuntu1
  Architecture: amd64
  Date: Tue Apr 21 16:35:10 2015
  DhclientLeases:

  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: isc-dhcp
  UpgradeStatus: No upgrade log present (probably fresh install)

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