openssh bugs - Apr 2025 - [Bug 3816] New: regression: valid_hostname() refuses hostname with comma

https://bugzilla.mindrot.org/show_bug.cgi?id=3816

            Bug ID: 3816
           Summary: regression: valid_hostname() refuses hostname with
                    comma
           Product: Portable OpenSSH
           Version: 10.0p1
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: scp
          Assignee: unassigned-bugs at mindrot.org
          Reporter: watanabe.yu at gmail.com

Since 487cf4c18c123b66c1f3f733398cd37e6b2ab6ab, hostname with comma is
refused.
Hostname with comma may be used by scp, e.g.
scp -v vsock,1:/etc/machine-id /tmp

The commit breaks a test case in systemd:
https://github.com/systemd/systemd/blob/defd5060d69ba31c1815e7d5427bde93a3db88c0/test/units/TEST-74-AUX-UTILS.ssh.sh#L65-L71
With openssh 10.0p1, the test case failed with the following:
```
[   78.014567] TEST-74-AUX-UTILS.sh[2634]: + command -v scp
[   78.016996] TEST-74-AUX-UTILS.sh[2694]: ++ mktemp -u
[   78.019724] TEST-74-AUX-UTILS.sh[2634]: +
OUT_FILE=/tmp/tmp.e3WBq62ziC
[   78.021470] TEST-74-AUX-UTILS.sh[2634]: + scp -o
StrictHostKeyChecking=no -v -i /tmp/tmp.L5BYceUUfs
vsock,1:/etc/machine-id /tmp/tmp.e3WBq62ziC
[   78.023570] TEST-74-AUX-UTILS.sh[2695]: Executing: program
/usr/bin/ssh host vsock,1, user (unspecified), command sftp
[   78.031887] TEST-74-AUX-UTILS.sh[2697]: hostname contains invalid
characters
[FAILED] Failed to start TEST-74-AUX-UTILS.service.
[   78.035067] TEST-74-AUX-UTILS.sh[2695]: scp: Connection closed
[   78.037831] TEST-74-AUX-UTILS.sh[307]: + echo 'Subtest
/usr/lib/systemd/tests/testdata/units/TEST-74-AUX-UTILS.ssh.sh failed'
[   78.038431] TEST-74-AUX-UTILS.sh[307]: Subtest
/usr/lib/systemd/tests/testdata/units/TEST-74-AUX-UTILS.ssh.sh failed
[   78.039110] TEST-74-AUX-UTILS.sh[307]: + return 1
```

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
Comma characters are not valid in hostnames. Why is systemd using them?

BTW, the strictness in hostnames is only applied to ones specified on
the command-line, you can override them via the configuration file if
you want to use arbitrary characters.

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Matthieu Baerts <matttbe at kernel.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|NEW                         |RESOLVED
                 CC|                            |matttbe at kernel.org

--- Comment #2 from Matthieu Baerts <matttbe at kernel.org> ---
Hello,
> Comma characters are not valid in hostnames. Why is systemd using them?
The comma was used as a separator in systemd (and virtme-ng) to be able
to easily connect to a VM by only giving the VSOCK CID number, e.g.

  scp vsock,42:/FILE .


This works thanks to this config:

    Host unix/* unix,% vsock/* vsock,* machine/* machine,*
        ProxyCommand /usr/lib/systemd/systemd-ssh-proxy %h %p
        (...)


With 'scp' and 'rsync', the slash separator cannot be used, and
that's
why the comma was added, see:

  https://github.com/systemd/systemd/pull/37035/


Note that systemd (and soon virtme-ng) has recently switched to '%' for
the separator, see:

  https://github.com/systemd/systemd/pull/37191


Then I guess this ticket can be marked as "wontfix".

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Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|10.0p1                      |10.0p2

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