Public bug reported:
I am looking at the addition of 'Include /etc/ssh/sshd_config.d/*conf'
for use in Ubuntu cloud images. I wanted to add a config file and see
if I had done things correctly. I assumed that the files were sourced
lexographically (based on use of glob() in readconf.h) so that I could
document how users could override our tuning. But it appears from 'sshd
-T' output and observed behavior that the first file in
/etc/sshd_config.d/ to define a parameter wins. I see in 'sshd -ddd'
output that they are parsed lexographically but it seems that their
settings apply in reverse (or whichever comes first) if that makes
sense. I'd like to understand if this is correct behavior and get it
documented.
Steps to reproduce on focal with openssh-server 1:8.2p1-4:
1. Create the following files in /etc/ssh/sshd_config.d/ with the content shown
below:
40-cloudimg-settings.conf:
ClientAliveInterval 110
PasswordAuthentication yes
PermitRootLogin no
50-cloudimg-settings.conf:
ClientAliveInterval 120
PermitRootLogin yes
60-cloudimg-settings.conf:
ClientAliveInterval 180
2. Check what sshd thinks the values will be with 'sshd -T|grep -i
clientaliveinterval' and 'sshd -T|grep permitrootlogin'
clientaliveinterval 110
permitrootlogin no
(The tuning I cared about was ClientAliveInterval for my work but
PermitRootLogin is easier to demonstrate)
3. Run '/usr/sbin/sshd -ddd' to check debug output for config file parsing
behavior:
debug2: load_server_config: filename /etc/ssh/sshd_config
debug2: load_server_config: done config len = 296
debug2: parse_server_config_depth: config /etc/ssh/sshd_config len 296
debug2: /etc/ssh/sshd_config line 13: new include /etc/ssh/sshd_config.d/*.conf
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf
debug2: load_server_config: done config len = 71
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf len 71
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:1 setting
ClientAliveInterval 110
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:2 setting
PasswordAuthentication yes
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:3 setting
PermitRootLogin no
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf
debug2: load_server_config: done config len = 46
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf len 46
debug3: /etc/ssh/sshd_config.d/50-cloudimg-settings.conf:1 setting
ClientAliveInterval 120
debug3: /etc/ssh/sshd_config.d/50-cloudimg-settings.conf:2 setting
PermitRootLogin yes
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf
debug2: load_server_config: done config len = 25
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf len 25
debug3: /etc/ssh/sshd_config.d/60-cloudimg-settings.conf:1 setting
ClientAliveInterval 180
4. Set a root password and unlock the account.
5. Attempt to ssh as root to the instance with a password.
Observation:
* Root password login is denied if PermitRootLogin is 'no' in 40-foo.conf and
'yes' in 50-foo.conf
* Root password login is allowed if PermitRootLogin is 'yes' in 40-foo.conf
and 'no' in 50-foo.conf
It appears in 'sshd -ddd' output that files are parsed in lexographic
order (40-foo.conf before 50-foo.conf) but the behavior observed
indicates that the value set in 40-foo.conf overrides 50-foo.conf which
is counter to expectations.
** Affects: openssh (Ubuntu)
Importance: Undecided
Status: New
** Tags: champagne
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https://bugs.launchpad.net/bugs/1873528
Title:
sshd overrides from /etc/ssh/sshd_config.d/*conf apply in reverse
lexographic order
Status in openssh package in Ubuntu:
New
Bug description:
I am looking at the addition of 'Include /etc/ssh/sshd_config.d/*conf'
for use in Ubuntu cloud images. I wanted to add a config file and see
if I had done things correctly. I assumed that the files were sourced
lexographically (based on use of glob() in readconf.h) so that I could
document how users could override our tuning. But it appears from
'sshd -T' output and observed behavior that the first file in
/etc/sshd_config.d/ to define a parameter wins. I see in 'sshd -ddd'
output that they are parsed lexographically but it seems that their
settings apply in reverse (or whichever comes first) if that makes
sense. I'd like to understand if this is correct behavior and get it
documented.
Steps to reproduce on focal with openssh-server 1:8.2p1-4:
1. Create the following files in /etc/ssh/sshd_config.d/ with the content
shown below:
40-cloudimg-settings.conf:
ClientAliveInterval 110
PasswordAuthentication yes
PermitRootLogin no
50-cloudimg-settings.conf:
ClientAliveInterval 120
PermitRootLogin yes
60-cloudimg-settings.conf:
ClientAliveInterval 180
2. Check what sshd thinks the values will be with 'sshd -T|grep -i
clientaliveinterval' and 'sshd -T|grep permitrootlogin'
clientaliveinterval 110
permitrootlogin no
(The tuning I cared about was ClientAliveInterval for my work but
PermitRootLogin is easier to demonstrate)
3. Run '/usr/sbin/sshd -ddd' to check debug output for config file parsing
behavior:
debug2: load_server_config: filename /etc/ssh/sshd_config
debug2: load_server_config: done config len = 296
debug2: parse_server_config_depth: config /etc/ssh/sshd_config len 296
debug2: /etc/ssh/sshd_config line 13: new include
/etc/ssh/sshd_config.d/*.conf
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf
debug2: load_server_config: done config len = 71
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/40-cloudimg-settings.conf len 71
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:1 setting
ClientAliveInterval 110
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:2 setting
PasswordAuthentication yes
debug3: /etc/ssh/sshd_config.d/40-cloudimg-settings.conf:3 setting
PermitRootLogin no
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf
debug2: load_server_config: done config len = 46
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/50-cloudimg-settings.conf len 46
debug3: /etc/ssh/sshd_config.d/50-cloudimg-settings.conf:1 setting
ClientAliveInterval 120
debug3: /etc/ssh/sshd_config.d/50-cloudimg-settings.conf:2 setting
PermitRootLogin yes
debug2: /etc/ssh/sshd_config line 13: including
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf
debug2: load_server_config: filename
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf
debug2: load_server_config: done config len = 25
debug2: parse_server_config_depth: config
/etc/ssh/sshd_config.d/60-cloudimg-settings.conf len 25
debug3: /etc/ssh/sshd_config.d/60-cloudimg-settings.conf:1 setting
ClientAliveInterval 180
4. Set a root password and unlock the account.
5. Attempt to ssh as root to the instance with a password.
Observation:
* Root password login is denied if PermitRootLogin is 'no' in 40-foo.conf
and 'yes' in 50-foo.conf
* Root password login is allowed if PermitRootLogin is 'yes' in 40-foo.conf
and 'no' in 50-foo.conf
It appears in 'sshd -ddd' output that files are parsed in lexographic
order (40-foo.conf before 50-foo.conf) but the behavior observed
indicates that the value set in 40-foo.conf overrides 50-foo.conf
which is counter to expectations.
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