Bug#998834: Multiple subsystem options in sshd_config prevent sshd from starting

[Marcus Frings]

Package: openssh-server
Version: 1:8.7p1-1
Severity: important

Dear maintainers,

In /etc/ssh/sshd_config the option

"Subsystem sftp /usr/lib/openssh/sftp-server"

is active by default.

"man 5 sshd_config" states:

"/etc/ssh/sshd_config.d/*.conf files are included at the start of the
configuration file, so options set there will override those in
/etc/ssh/sshd_config."

However, after adding

"Subsystem sftp /usr/lib/openssh/sftp-server -f AUTHPRIV -l INFO"

to /etc/ssh/sshd_config.d/10-marcus-sshd-config.conf, the ssh server fails
to start.

Hence, my attempt to leave the original sshd_config untouched and move
all my manually modified settings to a file parsed via the include
directive results in a broken ssh server.

Running "sshd -T" tells:

/etc/ssh/sshd_config line 116: Subsystem 'sftp' already defined.

This undocumented behaviour contradicts the statement of the man page cited
above. I could not find any Debian bug report in the openssh-* packages
regarding this issue (please forgive me if I missed it).

In the end I dropped my new approach of using
/etc/ssh/sshd_config.d/*.conf and went back to a manually modified
/etc/ssh/sshd_config, until this issue is solved.

By the way, after a brief search on the error message I found the same
problem reported there as well:

https://bugzilla.mindrot.org/show_bug.cgi?id=3236

(Thus, I used the same subject line as in the cited bug report.)

Best regards,
Marcus

-- System Information:
Debian Release: bookworm/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.14.0-3-amd64 (SMP w/8 CPU threads)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages openssh-server depends on:
ii adduser 3.118
ii debconf [debconf-2.0] 1.5.79
ii dpkg 1.20.9
ii libaudit1 1:3.0.6-1
ii libc6 2.32-4
ii libcom-err2 1.46.4-1
ii libcrypt1 1:4.4.25-2
ii libgssapi-krb5-2 1.18.3-7
ii libkrb5-3 1.18.3-7
ii libpam-modules 1.4.0-10
ii libpam-runtime 1.4.0-10
ii libpam0g 1.4.0-10
ii libselinux1 3.1-3+b1
ii libssl1.1 1.1.1l-1
ii libsystemd0 249.5-2
ii libwrap0 7.6.q-31
ii lsb-base 11.1.0
ii openssh-client 1:8.7p1-1
ii openssh-sftp-server 1:8.7p1-1
ii procps 2:3.3.17-5
ii runit-helper 2.10.3
ii ucf 3.0043
ii zlib1g 1:1.2.11.dfsg-2

Versions of packages openssh-server recommends:
ii libpam-systemd [logind] 249.5-2
pn ncurses-term <none>
ii xauth 1:1.1-1

Versions of packages openssh-server suggests:
pn molly-guard <none>
pn monkeysphere <none>
pn ssh-askpass <none>
pn ufw <none>

-- debconf information excluded

[Jan Wagner]

tags 998834 + patch
thanks

https://bugzilla.mindrot.org/attachment.cgi?id=3591&action=diff&collapsed=&headers=1&format=raw
has a patch for this

[Jan Wagner]

Hi,

Am 09.05.23 um 09:43 schrieb Jan Wagner:

> https://bugzilla.mindrot.org/attachment.cgi?id=3591&action=diff&collapsed=&headers=1&format=raw has a patch for this

what needs to happen to raise the chance to get that integrated? It's
super annoying to work around this and (re)integrate this back after
every dist upgrade. If Debian wants to be user friedly this is a feature
which might underline it.
If there is anything I can help to move things forward, please let me
know and I will try my best to do so.

Many thanks, Jan