[Bug 1567540] Re: ntpd crashed with SIGABRT (was: ntp crashes everytime the network goes up or down.)

Mon Aug 1 12:56:00 UTC 2016

Refined for SRU upload:
- clarified SRU template in this bug
- reduced number of patches by one to follow the "minimal change possible" guidance for SRU as hard 
  as possible
- fixed the reference in d/p/* files to the related upstream commits

** Patch removed: "debdiff for Xenial SRU - v2"
   https://bugs.launchpad.net/ubuntu/+source/ntp/+bug/1567540/+attachment/4711531/+files/SRU-fix-ntp-1567540-v2.debdiff

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Title:
  ntpd crashed with SIGABRT (was: ntp crashes everytime the network goes
  up or down.)

Status in NTP:
  Fix Released
Status in ntp package in Ubuntu:
  Fix Released
Status in ntp source package in Xenial:
  Fix Committed

Bug description:
  [Impact]

   * In NTP 4.2.8p4 there are several races that can cause a crash on
     startup or on a bit later but still on startup by DNS querying a
     peer.

   * The crash obviously affects users, especially as it seems - due to
     its racy nature - not appear on most, but severely hamstring some
     other users.

   * The details are a bit blurred, but overall there were four fixes
     upstream that address just this "kind of issue" that seemed to
     surface post 4.2.8p4.

  [Test Case]

   * Start NTP (service)

   * Expectation: work

   * Failure: Crash

   * Constraints: this is a race, it seems to appear at <0.1% chance to
     all systems I have (or lower - as I just can say it didn't trigger in
     1000 tests). But that matches other reports. OTOH for some systems it
     seems to trigger >50% which also matches the high amount of crash
     reports (close to 20k now) as referred in comment 43

  [Regression Potential]

   * Eventually the change is rather invasive as it changes the locking
     scheme of parts of the code - so there surely is some regression
     potential.

   * Fortunately all of this change is upstream and tested there
     quite heavily. Most of it for a few months already.

   * I tested as good as I could and could neither in code nor in test
     find an obvious weakness, and looking at all the crash reports it is
     about time.

  [Other Info]

   * While all study of bugs, upstream changes and tests suggest we
     haven't broken anything, still I have to admit that "on my own" I
     can't confirm that it fixed the bug. So we are really dependent on
     the reporters here that seem to have the kind of hardware where it
     "crashes reliably".

  --------

  ntp crashes every time the network goes up or down while the system is running and also crashes after booting up without network.
  ---
  ApportVersion: 2.20.1-0ubuntu1
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-03-12 (26 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160224)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu4
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-17-generic root=UUID=306314bc-efcb-4c2d-b0e9-e05ec92ed0f0 ro
  ProcVersionSignature: Ubuntu 4.4.0-17.33-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-17-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu1
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-03-12 (31 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160224)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-18-generic root=UUID=306314bc-efcb-4c2d-b0e9-e05ec92ed0f0 ro
  ProcVersionSignature: Ubuntu 4.4.0-18.34-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-18-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu1
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-04-13 (0 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160412)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-18-generic root=UUID=13f57794-2e19-4a56-836a-94185bba5ec5 ro quiet splash
  ProcVersionSignature: Ubuntu 4.4.0-18.34-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-18-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu1
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-04-13 (0 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160412)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-18-generic root=UUID=13f57794-2e19-4a56-836a-94185bba5ec5 ro quiet splash
  ProcVersionSignature: Ubuntu 4.4.0-18.34-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-18-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu2
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-04-14 (3 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160412)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-20-generic root=UUID=b9c0528f-e81f-4b08-9b31-032f14f72ccd ro quiet splash vt.handoff=7
  ProcVersionSignature: Ubuntu 4.4.0-20.36-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-20-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu2
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-04-14 (3 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160412)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-20-generic root=UUID=b9c0528f-e81f-4b08-9b31-032f14f72ccd ro quiet splash vt.handoff=7
  ProcVersionSignature: Ubuntu 4.4.0-20.36-generic 4.4.6
  Tags:  xenial
  Uname: Linux 4.4.0-20-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: True
  ---
  ApportVersion: 2.20.1-0ubuntu2.1
  Architecture: amd64
  CurrentDesktop: XFCE
  DistroRelease: Ubuntu 16.04
  InstallationDate: Installed on 2016-04-14 (63 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Beta amd64 (20160412)
  NtpStatus: ntpq: read: Connection refused
  Package: ntp 1:4.2.8p4+dfsg-3ubuntu5
  PackageArchitecture: amd64
  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.4.0-25-generic root=UUID=3aea4570-4011-4247-9636-68317385324d ro
  ProcVersionSignature: Ubuntu 4.4.0-25.44-generic 4.4.13
  Tags: xenial third-party-packages
  Uname: Linux 4.4.0-25-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dialout dip lpadmin mail netdev plugdev sambashare sudo
  _MarkForUpload: True

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