Changing AuthorizedKeysFile in `sshd_config` not solving public key auth failure with encrypted home

Question

The case sounds simple. I have my home folder encrypted using eCryptFS on the "server", it looks like:

/home/<user_name>/.Private on /home/<user_name> type ecryptfs (ecryptfs_check_dev_ruid,
ecryptfs_cipher=aes,ecryptfs_key_bytes=16,ecryptfs_unlink_sigs,ecryptfs_sig=<...>,
ecryptfs_fnek_sig=<...>)

Because the "authorized_keys" file is in ~/.ssh by default, which is not decrypted before I actually login, I moved that file to /home/ssh/<user_name>/authorized_keys. The permissions of /home/ssh/<user_name> is 755, and that of the authorized_keys file is 644. The file contains the public key of the machine that I would like to login from.

Then I changed the "AuthorizedKeysFile" option in /etc/ssh/sshd_config, to /home/ssh/%u/authorized_keys. As is suggested by this manual: https://help.ubuntu.com/community/SSH/OpenSSH/Keys and this post: https://stephen.rees-carter.net/thought/encrypted-home-directories-ssh-key-authentication. I searched for this problem here but mostly got the same instructions. However, still I cannot log-in without a password.

Then I did some tests, I generated a pair of SSH keys on the server (which I would like to SSH into), and copied the public key to /home/ssh/<user_name>/authorized_keys. Then I found that I cannot even login to localhost without using my password, on that server machine. Therefore, I assume that for some reason SSH daemon didn't load the authorized_keys file at all. I also tried to put the file in the original location which is ~/.ssh, still cannot do public key auth.

Attached is my sshd_config:

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin without-password
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile  /home/ssh/%u/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

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

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes

The authorized_keys file is located here:

$ ll
total 24K
drwx------  2 root        root         16K Feb 26 19:23 lost+found
drwxrwxr-x  3 root        root        4.0K Mar  1 13:12 ssh
drwx------ 22 <user_name> <user_name> 4.0K Mar  1 13:42 <user_name>
$ cd ssh
$ ll
total 4.0K
drwxr-xr-x 2 <user_name> <user_name> 4.0K Mar  1 13:12 <user_name>
$ cd <user_name>
$ ll
total 4.0K
-rw-r--r-- 1 <user_name> <user_name> 790 Mar  1 13:32 authorized_keys
$

I also tried to change permissions (of the directory and the file) to 700 and 600, didn't work either...

Solution

You question is missing information from log produced by sshd:

/var/log/auth.log

Error message says something about wrong permissions on /home.

Manual page for sshd adds this condition:

~/.ssh/authorized_keys

If this file, the ~/.ssh directory, or the user's home directory are writable by other users, then the file could be modified or replaced by unauthorized users. In this case, sshd will not allow it to be used unless the StrictModes option has been set to “no”.

So option is to fix permissions or if you need to have the /home group writable, use StrictModes no in your sshd_config.

Comments

[Jakuje]

did you restart your ssh server? Did you check for errors in the server log? Did you try to run server in more verbose mode?

[bfrguci]

Restarted. Where is the server log? @Jakuje

[Jakuje]

probably in /var/log/auth.log. If it will not help, set LogLevel DEBUG3 and try again.

[bfrguci]

@Jakuje It says bad ownership or modes for /home... Now it is 775... Probably I need to move it somewhere else...

[Jakuje]

No. It is wrong to have 775 on /home. /home should be root owned with 755 if I am right.

[bfrguci]

I thought sshd only required modes for the authorized_keys file and the folder containing it... Now it seems that it also requires that of all the upstream folders. @Jakuje I will try and will let you know if it works.

[Jakuje]

Yes. All the path to the authorized_keys file needs to satisfy this requirements. Also to the home folders. Does it work for you now or can I fill the answer?

[bfrguci]

@Jakuje Actually I moved the <user_name> folder to /etc/ssh and changed sshd_config accordingly. Now it works. You can surely fill in the answer :-) The weird part is, on another machine I also have /home 775, but my home folder is not encrypted. SSH worked pretty fine with public key auth on that machine, though ~/.ssh is also under a 775 /home...