In addition to checking that /etc/ssh/sshd_config is correct, you will want to check that the permissions on the user’s home directory and ~/.ssh are correct. I have gathered that:
- The home directory must only be owned by AND only be writable by the login user.
- The .ssh directory must only be accessible by the user.
- The authorized_keys file must be only writable by the user.
[foo@foo-nas ~/.ssh]$ ls -la -D "" total 14 drwx------ 2 foo foogrp 3 . drwxr-x--- 5 foo foogrp 15 .. -rw-r--r-- 1 foo foogrp 395 authorized_keys