Re: "System error" when trying to logon via SSH to CentOS 8 joined to AD

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Do I understand correctly that this problem
- is too trivial
- isn't in fact CentOS-related
- never happened to anyone else ?

There are no good explanations as far as I see, to such PAM behavior. I 
would appreciate advice on where else to ask about this (the mentioned 
quick fix doesn't look too good).

Thanks.

Sincerely,
Konstantin

On 23.03.2021 13:09, Konstantin Boyandin via CentOS wrote:
> Hello,
> 
> I joined a CentOS 8 box to an AD, using the below document as general 
> guide:
> 
>
 https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/integrating_rhel_systems_directly_with_windows_active_directory/connecting-rhel-systems-directly-to-ad-using-sssd_integrating-rhel-systems-directly-with-active-directory
 
> (section 14.1)
> 
> A problem: after I tried to log on via SSH (as an AD user) to the box, 
> the journalctl gets the below records:
> 
> March 23 12:41:01 sandbox.lan sshd[2262]: pam_sss(sshd:auth): 
> authentication success; logname= uid=0 euid=0 tty=ssh ruser= 
> rhost=10.10.0.55 user=username
> March 23 12:41:01 sandbox.lan sshd[2262]: pam_sss(sshd:account): Access 
> denied for user username: 4 (System error)
> March 23 12:41:01 sandbox.lan sshd[2262]: Failed password for username 
> from 10.10.0.55 port 57610 ssh2
> March 23 12:41:01 sandbox.lan sshd[2262]: fatal: Access denied for user 
> username by PAM account configuration [preauth]
> 
> Quick and dirty fix:
> 
> When I comment a line in /etc/pam.d/password-auth (the one commented 
> below), error goes away:
> ======= /etc/pam.d/password-auth below
> auth       
 required                                     pam_env.so
> auth        required pam_faildelay.so delay=2000000
> auth        [default=1 ignore=ignore success=ok]        
 pam_usertype.so 
> isregular
> auth        [default=1 ignore=ignore success=ok] pam_localuser.so
> auth       
 sufficient                                   pam_unix.so 
> nullok try_first_pass
> auth        [default=1 ignore=ignore success=ok]        
 pam_usertype.so 
> isregular
> auth       
 sufficient                                   pam_sss.so 
> forward_pass
> auth       
 required                                     pam_deny.so
> 
> account    
 required                                     pam_unix.so
> account     sufficient pam_localuser.so
> account    
 sufficient                                   pam_usertype.so 
> issystem
> #account     [default=bad success=ok user_unknown=ignore] pam_sss.so
> account    
 required                                     pam_permit.so
> 
> password    requisite pam_pwquality.so try_first_pass local_users_only
> password   
 sufficient                                   pam_unix.so 
> sha512 shadow nullok try_first_pass use_authtok
> password   
 sufficient                                   pam_sss.so 
> use_authtok
> password   
 required                                     pam_deny.so
> 
> session    
 optional                                     pam_keyinit.so 
> revoke
> session    
 required                                     pam_limits.so
> -session   
 optional                                     pam_systemd.so
> session     optional pam_oddjob_mkhomedir.so umask=0077
> session     [success=1 default=ignore] pam_succeed_if.so service in 
> crond quiet use_uid
> session    
 required                                     pam_unix.so
> session    
 optional                                     pam_sss.so
> ======= /etc/pam.d/password-auth above
> 
> If I understand correctly, the commented line means "account is invalid 
> by default; if found in SSSD, it's good; if not found - ignore and 
> proceed". Commenting it is not a good idea, but I can't figure out 
> what's wrong (according to first line from jornalctl authentication *is* 
> passed normally).
> 
> Additional data (AD domain in this example is EXAMPLE.COM):
> 
> $ realm list
> realm list
> example.com
>   type: kerberos
>   realm-name: EXAMPLE.COM
>   domain-name: example.com
>   configured: kerberos-member
>   server-software: active-directory
>   client-software: sssd
>   required-package: oddjob
>   required-package: oddjob-mkhomedir
>   required-package: sssd
>   required-package: adcli
>   required-package: samba-common-tools
>   login-formats: %U
>   login-policy: allow-realm-logins
> 
> $ cat /etc/sssd/sssd.conf
> [sssd]
> domains = example.com
> config_file_version = 2
> services = nss, pam, ssh
> debug_level = 9
> 
> [domain/example.com]
> ad_domain = example.com
> krb5_realm = EXAMPLE.COM
> realmd_tags = manages-system joined-with-adcli
> cache_credentials = True
> id_provider = ad
> krb5_store_password_if_offline = True
> default_shell = /bin/bash
> ldap_sasl_authid = SANDBOX$
> ldap_id_mapping = True
> use_fully_qualified_names = False
> ad_gpo_ignore_unreadable = True
> fallback_homedir = /home/%u
> access_provider = ad
> debug_level = 9
> === end of /etc/sssd/sssd.conf
> 
> $ cat /etc/krb5.conf
> includedir /etc/krb5.conf.d/
> 
> [logging]
>     default = FILE:/var/log/krb5libs.log
>     kdc = FILE:/var/log/krb5kdc.log
>     admin_server = FILE:/var/log/kadmind.log
> 
> [libdefaults]
>     ticket_lifetime = 24h
>     renew_lifetime = 7d
>     forwardable = true
>     rdns = false
>     pkinit_anchors = FILE:/etc/pki/tls/certs/ca-bundle.crt
>     spake_preauth_groups = edwards25519
>     default_ccache_name = KEYRING:persistent:%{uid}
>     default_realm = EXAMPLE.COM
>     dns_lookup_realm = false
>     dns_lookup_kdc = true
> 
> 
> [realms]
>         EXAMPLE.COM = {
>                 kdc = dc.example.com
>                 kdc = bdc.example.com
>                 admin_server = dc.example.com
>         }
> 
> [domain_realm]
>         .example.com = EXAMPLE.COM
>         example.com = EXAMPLE.COM
> === end of /etc/krb5.conf
> 
> GPO cache exists and is properly owned:
> ls -al /var/lib/sss/gpo_cache/example.com/
> total 0
> drwx------. 3 sssd sssd 22 Mar 22 14:52 .
> drwxr-xr-x. 3 sssd sssd 24 Mar 22 14:52 ..
> drwx------. 3 sssd sssd 52 Mar 22 14:52 Policies
> 
> I would appreciate pieces of advice on how to fix authentication issue 
> without commenting out the pam.d configuration file line.
> 
> Thank you.
> 
> Sincerely,
> Konstantin
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