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[Launchpad Bug Tracker <1088611@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package cloud-init -
0.7.9-233-ge586fe35-0ubuntu1~16.04.1

---------------
cloud-init (0.7.9-233-ge586fe35-0ubuntu1~16.04.1) xenial-proposed; urgency=medium

  * debian/cloud-init.templates: enable Scaleway cloud.
  * debian/cloud-init.templates: enable Aliyun cloud.
  * drop the following cherry picks, now incorporated in snapshot.
    + debian/patches/cpick-5fb49bac-azure-identify-platform...
    + debian/patches/cpick-003c6678-net-remove-systemd-link...
    + debian/patches/cpick-1cd4323b-azure-remove-accidental...
    + debian/patches/cpick-ebc9ecbc-Azure-Add-network-config...
    + debian/patches/cpick-11121fe4-systemd-make-cloud-final...
  * debian/patches/stable-release-no-jsonschema-dep.patch:
    add patch to remove optional dependency on jsonschema.
  * New upstream snapshot.
    - cloudinit.net: add initialize_network_device function and tests
      [Chad Smith]
    - makefile: fix ci-deps-ubuntu target [Chad Smith]
    - tests: adjust locale integration test to parse default locale.
    - tests: remove 'yakkety' from releases as it is EOL.
    - centos: do not package systemd-fsck drop-in.
    - systemd: make systemd-fsck run after cloud-init.service (LP: #1691489)
    - tests: Add initial tests for EC2 and improve a docstring.
    - locale: Do not re-run locale-gen if provided locale is system default.
    - archlinux: fix set hostname usage of write_file. [Joshua Powers]
    - sysconfig: support subnet type of 'manual'.
    - tools/run-centos: make running with no argument show help.
    - Drop rand_str() usage in DNS redirection detection
      [Bob Aman] (LP: #1088611)
    - sysconfig: use MACADDR on bonds/bridges to configure mac_address
      [Ryan Harper]
    - net: eni route rendering missed ipv6 default route config
      [Ryan Harper] (LP: #1701097)
    - sysconfig: enable mtu set per subnet, including ipv6 mtu
      [Ryan Harper]
    - sysconfig: handle manual type subnets [Ryan Harper]
    - sysconfig: fix ipv6 gateway routes [Ryan Harper]
    - sysconfig: fix rendering of bond, bridge and vlan types.
      [Ryan Harper]
    - Templatize systemd unit files for cross distro deltas. [Ryan Harper]
    - sysconfig: ipv6 and default gateway fixes. [Ryan Harper]
    - net: fix renaming of nics to support mac addresses written in upper
      case. (LP: #1705147)
    - tests: fixes for issues uncovered when moving to python 3.6.
    - sysconfig: include GATEWAY value if set in subnet
      [Ryan Harper]
    - Scaleway: add datasource with user and vendor data for Scaleway.
      [Julien Castets]
    - Support comments in content read by load_shell_content.
    - cloudinitlocal fail to run during boot [Hongjiang Zhang]
    - doc: fix disk setup example table_type options [Sandor Zeestraten]
    - tools: Fix exception handling. [Joonas Kylmälä]
    - tests: fix usage of mock in GCE test.
    - test_gce: Fix invalid mock of platform_reports_gce to return False
      [Chad Smith]
    - test: fix incorrect keyid for apt repository.  [Joshua Powers]
    - tests: Update version of pylxd [Joshua Powers]
    - write_files: Remove log from helper function signatures.
      [Andrew Jorgensen]
    - doc: document the cmdline options to NoCloud [Brian Candler]
    - read_dmi_data: always return None when inside a container. (LP: #1701325)
    - requirements.txt: remove trailing white space.
    - Tests: Simplify the check on ssh-import-id [Joshua Powers]
    - tests: update ntp tests after sntp added [Joshua Powers]
    - FreeBSD: Make freebsd a variant, fix unittests and
      tools/build-on-freebsd.
    - FreeBSD: fix test failure
    - FreeBSD: replace ifdown/ifup with "ifconfig down" and "ifconfig up".
      [Hongjiang Zhang]
    - FreeBSD: fix cdrom mounting failure if /mnt/cdrom/secure did not exist.
      [Hongjiang Zhang]
    - main: Don't use templater to format the welcome message
      [Andrew Jorgensen]
    - docs: Automatically generate module docs form schema if present.
      [Chad Smith]
    - debian: fix path comment in /etc/hosts template. [Jens Sandmann]
    - suse: add hostname and fully qualified domain to template.
      [Jens Sandmann]
    - write_file(s): Print permissions as octal, not decimal [Andrew Jorgensen]
    - ci deps: Add --test-distro to read-dependencies to install all deps
      [Chad Smith]
    - tools/run-centos: cleanups and move to using read-dependencies
    - pkg build ci: Add make ci-deps-<distro> target to install pkgs
      [Chad Smith]
    - selinux: Allow restorecon to be non-fatal. [Ryan Harper]
    - net: Allow netinfo subprocesses to return 0 or 1 due to selinux.
      [Ryan Harper]
    - net: Allow for NetworkManager configuration [Ryan McCabe]
    - Use distro release version to determine if we use systemd in redhat spec
      [Ryan Harper]
    - net: normalize data in network_state object
    - Integration Testing: tox env, pyxld 2.2.3, and revamp framework
      [Wesley Wiedenmeier]
    - Chef: Update omnibus url to chef.io, minor doc changes. [JJ Asghar]
    - tools: add centos scripts to build and test [Joshua Powers]
    - Drop cheetah python module as it is not needed by trunk [Ryan Harper]
    - rhel/centos spec cleanups.
    - cloud.cfg: move to a template.  setup.py changes along the way.
    - Makefile: add deb-src and srpm targets. use PYVER more places.
    - makefile: fix python 2/3 detection in the Makefile [Chad Smith]
    - snap: Removing snapcraft plug line [Joshua Powers]
    - RHEL/CentOS: Fix default routes for IPv4/IPv6 configuration.
      [Andreas Karis]
    - test: Fix pyflakes complaint of unused import. [Joshua Powers]
    - NoCloud: support seed of nocloud from smbios information
      [Vladimir Pouzanov] (LP: #1691772)
    - net: when selecting a network device, use natural sort order
      [Marc-Aurèle Brothier]
    - fix typos and remove whitespace in various docs [Stephan Telling]
    - systemd: Fix typo in comment in cloud-init.target. [Chen-Han Hsiao]
    - Tests: Skip jsonschema related unit tests when dependency is absent.
      [Chad Smith]
    - tools/net-convert.py: support old cloudinit versions by using kwargs.
    - ntp: Add schema definition and passive schema validation.
      [Chad Smith] (LP: #1692916)
    - Fix eni rendering for bridge params that require repeated key for
      values. [Ryan Harper] (LP: #1706752)
    - AliYun: Enable platform identification and enable by default.
      [Junjie Wang] (LP: #1638931)

 -- Scott Moser <smoser@xxxxxxxxxx>  Mon, 31 Jul 2017 16:36:16 -0400

** Changed in: cloud-init (Ubuntu Xenial)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1088611

Title:
  using random hostnames to detect dns proxies allows for false
  positives

Status in cloud-init:
  Fix Committed
Status in cloud-init package in Ubuntu:
  Fix Released
Status in cloud-init source package in Xenial:
  Fix Released
Status in cloud-init source package in Zesty:
  Fix Released

Bug description:
  === Begin SRU Template ===
  [Impact]
  Prior to this fix, cloud-init attempts to detect dns redirection by doing
  dns queries for a random hostname and two invalid hostnames.  Then, if
  the result returned for the input value was the same as the response for
  the invalid query cloud-init would assume that result was also invalid.

  The change was to replace the random string with
    __cloud_init_expected_not_found__
  This is a valid hostname and resolution will use the 'search' path in
  resolv.conf where the other invalid domain names would not.

  [Test Case]
  The test case for this consists of excercising the the 'is_resolvable_url'
  method in cloudinit.util and watching dns queries.  To do this, see the
  following steps:
  a.) start an lxc container
     $ release=xenial
     $ name=$release-1088611
     $ lxc launch ubuntu-daily:$release $name
  b.) start a dnsmasq server
     $ ./run-dnsmasq lxdbr0
     ... 
     === listening on 10.75.205.2/24 ===

     # run-dnsmasq is attached and at
     #  https://git.launchpad.net/~smoser/cloud-init/+git/sru-info/tree/bugs/lp-1088611/run-dnsmasq

  c.) point /etc/resolv.conf at your server ip
     $ lxc exec $name -- sh -c 'exec >/etc/resolv.conf;
         echo nameserver 10.75.205.2; echo search foo;'

  d.) perform query via is_resolvable_url watch dnsmasq output, expect
      to see the random query.
     $ lxc exec $name -- python3 -c 'import sys;
  from cloudinit.util import is_resolvable_url; 
  print(is_resolvable_url(sys.argv[1]))' http://ubuntu.com

  e.) upgrade to -proposed version
  f.) perform query via is_resolvable_url, expect to *not* see random query.

  [Regression Potential]
  Immediate regression seems unlikely.  Effectively the change in cloud-init
  code path was simply to change a dns lookup attempt from rand() to a defined
  string.

  We chose a random string initially to make it difficult for a dns server to
  circumvent cloud-init's attempt to identify dns redirection.  The regression
  path really then seems to involve a dns redirection service specifically
  provding a response for '__cloud_init_expected_not_found__' that differs
  from does-not-exist.example.com.  Cloud-init could then be tricked into
  believing that a apt mirror was valid where it previously would have
  identified the dns redirection.  The failure would be seen as errors
  in package installation or 'apt-get update'.

  [Other Info]
  Upstream commit at
    https://git.launchpad.net/cloud-init/commit/?id=42a7b34a12

  Original upstream commit at
    https://git.launchpad.net/cloud-init/commit/?id=1bb67be5bd

  === End SRU Template ===

  The fix that's been applied for bug #974509 checks for the presence of
  a redirector by looking of three hostnames, and treating as invalid
  any results pointing to a matching address:

   - does-not-exist.example.com.
   - example.invalid.
   - a random, unqualified 32-character alphanumeric hostname.

  The last of these carries a small but non-zero risk of colliding with
  a real hostname, and there's a small but non-zero risk that this host
  points to the same address as something we care about.  If possible,
  it would be better to not include this random-host lookup in the
  algorithm, as somewhere, some day, chances are there will eventually
  be a collision, causing an incomprehensible and unreproducible failure
  for a user.

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