[Bug 2076023] Re: Failed to apply 'Match' directive in sshd_config with sshd-socket-generator

[Andreas Hasenack]

1:9.6p1-3ubuntu13.7 was moved back to noble-proposed due to a possible
regression[1] that is being investigated. Setting the bug tasks back to
fix committed.

1:9.6p1-3ubuntu13.5 was restored in noble-updates.

1. https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2087551

** Changed in: openssh (Ubuntu Noble)
       Status: Fix Released => Fix Committed

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https://bugs.launchpad.net/bugs/2076023

Title:
  Failed to apply 'Match' directive in sshd_config with sshd-socket-
  generator

Status in openssh package in Ubuntu:
  Fix Released
Status in openssh source package in Noble:
  Fix Committed
Status in openssh source package in Oracular:
  Fix Released

Bug description:
  [Impact]

  When users have a Match section in their sshd config, their
  configuration cannot be parsed by the sshd-socket-generator (because
  there is no connection, hence no connection spec to be matched), and
  the generator fails. This means no custom config is applied at all.

  [Test Plan]

  1. On a noble system with sshd installed, create a drop-in config with
  a Match directive, and run the generator locally:

  $ cat > /etc/ssh/sshd_config.d/custom.conf << EOF
  Port 1234
  Match LocalPort 22
      PasswordAuthentication no
  EOF
  $ /lib/systemd/system-generators/sshd-socket-generator .
  'Match LocalPort' in configuration but 'lport' not in connection test specification.

  On an affected system, the above error will be shown. On a patched
  system, the generator will succeed, and ./ssh.socket.d/addresses.conf
  will reflect the Port 1234 option.

  2. A new subtest was added to debian/tests/sshd-socket-generator,
  test_match_port. It does the same as the above, and should pass in
  autopkgtest.

  [Where problems could occur]

  This patch simply removes the code from sshd-socket-generator that
  tries to parse the match config. If problems did occur, it would be
  related to the generator again. Specifically, it would likely be
  related to missing/unparsed options.

  [Original Description]

  When using the Match statement in sshd_config or sshd_config.d/*.conf
  with socket activation(not classic method), sshd does not start as
  expected.

  Environment:

  Ubuntu: Ubuntu 24.04 LTS
  OpenSSH Server: 1:9.6p1-3ubuntu13.4

  Steps to Reproduce:

  /etc/ssh/sshd_config
  ```
  Include /etc/ssh/sshd_config.d/*.conf
  Port 22
  Port 22222
  KbdInteractiveAuthentication no
  UsePAM yes
  X11Forwarding yes
  PrintMotd no
  AcceptEnv LANG LC_*
  Subsystem	sftp	/usr/lib/openssh/sftp-server
  Match LocalPort 22222
      PasswordAuthentication no
      PubkeyAuthentication yes
  ```

  command:

  sudo systemctl daemon-reload && sudo systemctl restart ssh.socket

  Expected Behavior:

  sshd should listen on both ports 22 and 22222.
  When connecting via port 22222, password login should not be allowed and only public key authentication should be permitted.

  Actual Behavior:

  sshd only listens on port 22 and not on port 22222. The configuration
  is not correctly applied.

  After daemon-reload, the output from journalctl is as follows:

  $ sudo journalctl -t (sd-exec-
  Aug 04 12:47:36 ults (sd-exec-[479259]: /usr/lib/systemd/system-generators/sshd-socket-generator failed with exit status 255.

  Additional Information:

  1.Using sshd -T -C to test the configuration produces the following result:
  $ sudo sshd -T -C lport=22 | grep passwordauthentication
  passwordauthentication yes

  $ sudo sshd -T -C lport=22222 | grep passwordauthentication
  passwordauthentication no

  2.The output when manually running /usr/lib/systemd/system-generators/sshd-socket-generator is:
  $ sudo /usr/lib/systemd/system-generators/sshd-socket-generator ./
  'Match LocalPort' in configuration but 'lport' not in connection test specification.

  3.I have test some cases, if sshd-socket-generator can not handle
  config rightly, sshd seems to run with default config.

  And I also noticed that there is no test case about the Match
  directive in
  https://git.launchpad.net/ubuntu/+source/openssh/tree/debian/tests/sshd-
  socket-generator.

  I guess the root cause of the issue lies in the sshd-socket-generator
  not correctly handling the Match directive.

  And a detailed assessment of potential security issues which caused by
  this bug is needed.

  If socket activation is to be widely adopted, this issue will
  undoubtedly be a significant stumbling block.

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