[Bug 1966591] Please test proposed package

[Brian Murray]

Hello Evgeny, or anyone else affected,

Accepted openssh into bionic-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/openssh/1:7.6p1-4ubuntu0.7 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
bionic to verification-done-bionic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-bionic. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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https://bugs.launchpad.net/bugs/1966591

Title:
  ssh-keygen -R changes known_hosts file permissions (mode)

Status in portable OpenSSH:
  Unknown
Status in openssh package in Ubuntu:
  Fix Released
Status in openssh source package in Bionic:
  Fix Committed
Status in openssh source package in Focal:
  Fix Committed
Status in openssh source package in Impish:
  Fix Released
Status in openssh source package in Jammy:
  Fix Released

Bug description:
  [Impact]

  When using "ssh-keygen -R" to remove a host from "known_hosts" the
  command changes permissions on the file.  This can cause problems
  particularly when used on the global "known_hosts" file
  (/etc/ssh/ssh_known_hosts), because then only root can read it.
  Programs running non-interactively as non-root users suddenly fail to
  SSH and it's not immediately obvious why.

  [Test Plan]

  The problem happens on Bionic and Focal.

  $ lxc launch ubuntu-daily:focal openssh-bug1966591
  $ lxc shell openssh-bug1966591
  # ssh-keyscan github.com > test_known_hosts
  # chmod 644 test_known_hosts
  # ssh-keygen -R github.com -f test_known_hosts
  # stat test_known_hosts
  ...
  Access: (0600/-rw-------) ...
  ...

  [Where problems could occur]

  The upstream patch is very simple and it is unlikely that it will
  cause any regressions.  An indirect problem that could occur is that
  users might expect to see a more strict set of permissions on a
  "known_hosts" file after using "ssh-keygen -R", but arguably this is
  not defined behaviour and should not be relied upon.  Of course, there
  is always a (very) small risk of introducing problems when rebuilding
  packages using newer versions of its dependencies (especially on
  Bionic, because it's older).

  [Original Description]

  When I use ssh-keygen -R to remove a host from known_hosts it changes
  permissions on the file. This causes problems particularly when used
  on the global known hosts file (/etc/ssh/ssh_known_hosts), because
  then only root can read it. Programs running non-interactively as non-
  root users suddenly fail to SSH and it's not immediately obvious why.

  To reproduce:

  $ ssh-keyscan github.com >test_known_hosts
  $ chmod 741 test_known_hosts
  $ ssh-keygen -R github.com -f test_known_hosts
  $ stat test_known_hosts
  ...
  Access: (0600/-rw-------) ...

  Expected behavior: file permissions remain unchanged (mode 0741 in
  this example).

  $ lsb_release -rd
  Description:	Ubuntu 18.04.6 LTS
  Release:	18.04

  $ apt-cache policy openssh-client
  openssh-client:
    Installed: 1:7.6p1-4ubuntu0.6

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