[Bug 1674330] Re: Please consider dropping /etc/network/if-up.d/openssh-server

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https://bugs.launchpad.net/bugs/1674330

Title:
  Please consider dropping /etc/network/if-up.d/openssh-server

Status in openssh package in Ubuntu:
  In Progress

Bug description:
  The /etc/network/if-up.d/openssh-server hack was introduced ten years ago [1] as a response to bug 
  103436. At least from today's perspective this isn't justified:

  I can't seem to be able to actually reproduce that issue: I can start
  a VM with no network interfaces, remove the above hack, then start
  sshd, then bring up an ethernet interface, and I can connect to ssh
  via ethernet just fine. Also, e. g. Fedora has no counterpart of this
  hack, and these days a lot of people would complain if that would
  cause problems, as hotpluggable/roaming network devices are
  everywhere.

  The hack introduces a race: you run into connection errors after
  bringing up a new interface as sshd stops listening briefly while
  being reloaded. That's the reason why I looked at it, as this
  regularly happens in upstream's cockpit integration tests.

  Also, /etc/network/if-up.d/ isn't being run when using
  networkd/netplan, i. e. in more recent Ubuntnu cloud instances. So far
  this doesn't seem to have caused any issues.

  I asked the original reporter of bug 103436 for some details, and to
  check whether that hack is still necessary. There is actually a
  proposed patch upstream [2] to use IP_FREEBIND, which is the modern
  solution to listening to all "future" interfaces as well. But at least
  for the majority of cases it seems to work fine without that even.

  So I wonder if it's time to bury that hack?

  [1] https://anonscm.debian.org/cgit/pkg-ssh/openssh.git/commit/?id=ba6b55ed6
  [2] https://bugzilla.mindrot.org/show_bug.cgi?id=2512

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