Chapter 18. Granting sudo access to an IdM user on an IdM client

18.1. Sudo access on an IdM client

System administrators can grant sudo access to allow non-root users to execute administrative commands that are normally reserved for the root user. Consequently, when users need to perform an administrative command normally reserved for the root user, they precede that command with sudo. After entering their password, the command is executed as if they were the root user. To execute a sudo command as another user or group, such as a database service account, you can configure a RunAs alias for a sudo rule.

If a Red Hat Enterprise Linux (RHEL) 8 host is enrolled as an Identity Management (IdM) client, you can specify sudo rules defining which IdM users can perform which commands on the host in the following ways:

  • Locally in the /etc/sudoers file
  • Centrally in IdM

This section describes creating a central sudo rule for an IdM client using the command line interface (CLI) and the IdM Web UI.

In RHEL 8.4 and later, you can also configure password-less authentication for sudo using the Generic Security Service Application Programming Interface (GSSAPI), the native way for UNIX-based operating systems to access and authenticate Kerberos services. You can use the pam_sss_gss.so Pluggable Authentication Module (PAM) to invoke GSSAPI authentication via the SSSD service, allowing users to authenticate to the sudo command with a valid Kerberos ticket.

Additional resources

18.2. Granting sudo access to an IdM user on an IdM client using the CLI

In Identity Management (IdM), you can grant sudo access for a specific command to an IdM user account on a specific IdM host. First, add a sudo command and then create a sudo rule for one or more commands.

For example, complete this procedure to create the idm_user_reboot sudo rule to grant the idm_user account the permission to run the /usr/sbin/reboot command on the idmclient machine.

Prerequisites

  • You are logged in as IdM administrator.
  • You have created a user account for idm_user in IdM and unlocked the account by creating a password for the user. For details on adding a new IdM user using the CLI, see Adding users using the command line.
  • No local idm_user account is present on the idmclient host. The idm_user user is not listed in the local /etc/passwd file.

Procedure

  1. Retrieve a Kerberos ticket as the IdM admin.

    [root@idmclient ~]# kinit admin
  2. Add the /usr/sbin/reboot command to the IdM database of sudo commands:

    [root@idmclient ~]# ipa sudocmd-add /usr/sbin/reboot
    -------------------------------------
    Added Sudo Command "/usr/sbin/reboot"
    -------------------------------------
      Sudo Command: /usr/sbin/reboot
  3. Create a sudo rule named idm_user_reboot:

    [root@idmclient ~]# ipa sudorule-add idm_user_reboot
    ---------------------------------
    Added Sudo Rule "idm_user_reboot"
    ---------------------------------
      Rule name: idm_user_reboot
      Enabled: TRUE
  4. Add the /usr/sbin/reboot command to the idm_user_reboot rule:

    [root@idmclient ~]# ipa sudorule-add-allow-command idm_user_reboot --sudocmds '/usr/sbin/reboot'
      Rule name: idm_user_reboot
      Enabled: TRUE
      Sudo Allow Commands: /usr/sbin/reboot
    -------------------------
    Number of members added 1
    -------------------------
  5. Apply the idm_user_reboot rule to the IdM idmclient host:

    [root@idmclient ~]# ipa sudorule-add-host idm_user_reboot --hosts idmclient.idm.example.com
    Rule name: idm_user_reboot
    Enabled: TRUE
    Hosts: idmclient.idm.example.com
    Sudo Allow Commands: /usr/sbin/reboot
    -------------------------
    Number of members added 1
    -------------------------
  6. Add the idm_user account to the idm_user_reboot rule:

    [root@idmclient ~]# ipa sudorule-add-user idm_user_reboot --users idm_user
    Rule name: idm_user_reboot
    Enabled: TRUE
    Users: idm_user
    Hosts: idmclient.idm.example.com
    Sudo Allow Commands: /usr/sbin/reboot
    -------------------------
    Number of members added 1
    -------------------------
Note

Propagating the changes from the server to the client can take a few minutes.

Verification steps

  1. Log in to the idmclient host as the idm_user account.
  2. Display which sudo rules the idm_user account is allowed to perform.

    [idm_user@idmclient ~]$ sudo -l
    Matching Defaults entries for idm_user on idmclient:
        !visiblepw, always_set_home, match_group_by_gid, always_query_group_plugin,
        env_reset, env_keep="COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS",
        env_keep+="MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE",
        env_keep+="LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES",
        env_keep+="LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE",
        env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY KRB5CCNAME",
        secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin
    
    User idm_user may run the following commands on idmclient:
        (root) /usr/sbin/reboot
  3. Reboot the machine using sudo. Enter the password for idm_user when prompted:

    [idm_user@idmclient ~]$ sudo /usr/sbin/reboot
    [sudo] password for idm_user:

18.3. Granting sudo access to an IdM user on an IdM client using the IdM Web UI

In Identity Management (IdM), you can grant sudo access for a specific command to an IdM user account on a specific IdM host. First, add a sudo command and then create a sudo rule for one or more commands.

Complete this procedure to create the idm_user_reboot sudo rule to grant the idm_user account the permission to run the /usr/sbin/reboot command on the idmclient machine.

Prerequisites

  • You are logged in as IdM administrator.
  • You have created a user account for idm_user in IdM and unlocked the account by creating a password for the user. For details on adding a new IdM user using the command-line interface, see Adding users using the command line.
  • No local idm_user account is present on the idmclient host. The idm_user user is not listed in the local /etc/passwd file.

Procedure

  1. Add the /usr/sbin/reboot command to the IdM database of sudo commands:

    1. Navigate to PolicySudoSudo Commands.
    2. Click Add in the upper right corner to open the Add sudo command dialog box.
    3. Enter the command you want the user to be able to perform using sudo: /usr/sbin/reboot.

      Figure 18.1. Adding IdM sudo command

      A screenshot of a pop-up window labeled "Add sudo command." There is a required field labeled "Sudo command" with contents "/usr/sbin/reboot". A "Description" field is empty. The bottom-right of the window has four buttons: "Add" - "Add and Add Another" - "Add and Edit" - "Cancel".
    4. Click Add.
  2. Use the new sudo command entry to create a sudo rule to allow idm_user to reboot the idmclient machine:

    1. Navigate to PolicySudoSudo rules.
    2. Click Add in the upper right corner to open the Add sudo rule dialog box.
    3. Enter the name of the sudo rule: idm_user_reboot.
    4. Click Add and Edit.
    5. Specify the user:

      1. In the Who section, check the Specified Users and Groups radio button.
      2. In the User category the rule applies to subsection, click Add to open the Add users into sudo rule "idm_user_reboot" dialog box.
      3. In the Add users into sudo rule "idm_user_reboot" dialog box in the Available column, check the idm_user checkbox, and move it to the Prospective column.
      4. Click Add.
    6. Specify the host:

      1. In the Access this host section, check the Specified Hosts and Groups radio button.
      2. In the Host category this rule applies to subsection, click Add to open the Add hosts into sudo rule "idm_user_reboot" dialog box.
      3. In the Add hosts into sudo rule "idm_user_reboot" dialog box in the Available column, check the idmclient.idm.example.com checkbox, and move it to the Prospective column.
      4. Click Add.
    7. Specify the commands:

      1. In the Command category the rule applies to subsection of the Run Commands section, check the Specified Commands and Groups radio button.
      2. In the Sudo Allow Commands subsection, click Add to open the Add allow sudo commands into sudo rule "idm_user_reboot" dialog box.
      3. In the Add allow sudo commands into sudo rule "idm_user_reboot" dialog box in the Available column, check the /usr/sbin/reboot checkbox, and move it to the Prospective column.
      4. Click Add to return to the idm_sudo_reboot page.

    Adding IdM sudo rule

    + image::IdM-sudo-rule-WebUI.png[A screenshot of an overview of the sudo rule that was added. There is a "Who" section with a table of users the rule applies to. There is an "Access this host" section with a table of hosts that the rule applies to. There is a "Run Commands" section with a table of commands that pertain to the rule.]

    1. Click Save in the top left corner.

The new rule is enabled by default.

Note

Propagating the changes from the server to the client can take a few minutes.

Verification steps

  1. Log in to idmclient as idm_user.
  2. Reboot the machine using sudo. Enter the password for idm_user when prompted:

    $ sudo /usr/sbin/reboot
    [sudo] password for idm_user:

If the sudo rule is configured correctly, the machine reboots.

18.4. Creating a sudo rule on the CLI that runs a command as a service account on an IdM client

In IdM, you can configure a sudo rule with a RunAs alias to run a sudo command as another user or group. For example, you might have an IdM client that hosts a database application, and you need to run commands as the local service account that corresponds to that application.

Use this example to create a sudo rule on the command line called run_third-party-app_report to allow the idm_user account to run the /opt/third-party-app/bin/report command as the thirdpartyapp service account on the idmclient host.

Prerequisites

  • You are logged in as IdM administrator.
  • You have created a user account for idm_user in IdM and unlocked the account by creating a password for the user. For details on adding a new IdM user using the CLI, see Adding users using the command line.
  • No local idm_user account is present on the idmclient host. The idm_user user is not listed in the local /etc/passwd file.
  • You have a custom application named third-party-app installed on the idmclient host.
  • The report command for the third-party-app application is installed in the /opt/third-party-app/bin/report directory.
  • You have created a local service account named thirdpartyapp to execute commands for the third-party-app application.

Procedure

  1. Retrieve a Kerberos ticket as the IdM admin.

    [root@idmclient ~]# kinit admin
  2. Add the /opt/third-party-app/bin/report command to the IdM database of sudo commands:

    [root@idmclient ~]# ipa sudocmd-add /opt/third-party-app/bin/report
    ----------------------------------------------------
    Added Sudo Command "/opt/third-party-app/bin/report"
    ----------------------------------------------------
      Sudo Command: /opt/third-party-app/bin/report
  3. Create a sudo rule named run_third-party-app_report:

    [root@idmclient ~]# ipa sudorule-add run_third-party-app_report
    --------------------------------------------
    Added Sudo Rule "run_third-party-app_report"
    --------------------------------------------
      Rule name: run_third-party-app_report
      Enabled: TRUE
  4. Use the --users=<user> option to specify the RunAs user for the sudorule-add-runasuser command:

    [root@idmclient ~]# ipa sudorule-add-runasuser run_third-party-app_report --users=thirdpartyapp
      Rule name: run_third-party-app_report
      Enabled: TRUE
      RunAs External User: thirdpartyapp
    -------------------------
    Number of members added 1
    -------------------------

    The user (or group specified with the --groups=* option) can be external to IdM, such as a local service account or an Active Directory user. Do not add a % prefix for group names.

  5. Add the /opt/third-party-app/bin/report command to the idm_user_reboot rule:

    [root@idmclient ~]# ipa sudorule-add-allow-command run_third-party-app_report --sudocmds '/opt/third-party-app/bin/report'
    Rule name: run_third-party-app_report
    Enabled: TRUE
    Sudo Allow Commands: /opt/third-party-app/bin/report
    RunAs External User: thirdpartyapp
    -------------------------
    Number of members added 1
    -------------------------
  6. Apply the run_third-party-app_report rule to the IdM idmclient host:

    [root@idmclient ~]# ipa sudorule-add-host run_third-party-app_report --hosts idmclient.idm.example.com
    Rule name: run_third-party-app_report
    Enabled: TRUE
    Hosts: idmclient.idm.example.com
    Sudo Allow Commands: /opt/third-party-app/bin/report
    RunAs External User: thirdpartyapp
    -------------------------
    Number of members added 1
    -------------------------
  7. Add the idm_user account to the run_third-party-app_report rule:

    [root@idmclient ~]# ipa sudorule-add-user run_third-party-app_report --users idm_user
    Rule name: run_third-party-app_report
    Enabled: TRUE
    Users: idm_user
    Hosts: idmclient.idm.example.com
    Sudo Allow Commands: /opt/third-party-app/bin/report
    RunAs External User: thirdpartyapp
    -------------------------
    Number of members added 1
Note

Propagating the changes from the server to the client can take a few minutes.

Verification steps

  1. Log in to the idmclient host as the idm_user account.
  2. Test the new sudo rule:

    1. Display which sudo rules the idm_user account is allowed to perform.

      [idm_user@idmclient ~]$ sudo -l
      Matching Defaults entries for idm_user@idm.example.com on idmclient:
          !visiblepw, always_set_home, match_group_by_gid, always_query_group_plugin,
          env_reset, env_keep="COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS",
          env_keep+="MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE",
          env_keep+="LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES",
          env_keep+="LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE",
          env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY KRB5CCNAME",
          secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin
      
      User idm_user@idm.example.com may run the following commands on idmclient:
          (thirdpartyapp) /opt/third-party-app/bin/report
    2. Run the report command as the thirdpartyapp service account.

      [idm_user@idmclient ~]$ sudo -u thirdpartyapp /opt/third-party-app/bin/report
      [sudo] password for idm_user@idm.example.com:
      Executing report...
      Report successful.

18.5. Creating a sudo rule in the IdM WebUI that runs a command as a service account on an IdM client

In IdM, you can configure a sudo rule with a RunAs alias to run a sudo command as another user or group. For example, you might have an IdM client that hosts a database application, and you need to run commands as the local service account that corresponds to that application.

Use this example to create a sudo rule in the IdM WebUI called run_third-party-app_report to allow the idm_user account to run the /opt/third-party-app/bin/report command as the thirdpartyapp service account on the idmclient host.

Prerequisites

  • You are logged in as IdM administrator.
  • You have created a user account for idm_user in IdM and unlocked the account by creating a password for the user. For details on adding a new IdM user using the CLI, see Adding users using the command line.
  • No local idm_user account is present on the idmclient host. The idm_user user is not listed in the local /etc/passwd file.
  • You have a custom application named third-party-app installed on the idmclient host.
  • The report command for the third-party-app application is installed in the /opt/third-party-app/bin/report directory.
  • You have created a local service account named thirdpartyapp to execute commands for the third-party-app application.

Procedure

  1. Add the /opt/third-party-app/bin/report command to the IdM database of sudo commands:

    1. Navigate to PolicySudoSudo Commands.
    2. Click Add in the upper right corner to open the Add sudo command dialog box.
    3. Enter the command: /opt/third-party-app/bin/report.

      A screenshot of a pop-up window labeled "Add sudo command." There is a required field labeled "Sudo command" with contents "/opt/third-party-app/bin/report". A "Description" field is empty. The bottom-right of the window has four buttons: "Add" - "Add and Add Another" - "Add and Edit" - "Cancel".
    4. Click Add.
  2. Use the new sudo command entry to create the new sudo rule:

    1. Navigate to PolicySudoSudo rules.
    2. Click Add in the upper right corner to open the Add sudo rule dialog box.
    3. Enter the name of the sudo rule: run_third-party-app_report.

      A screenshot of a pop-up window labeled "Add sudo rule." There is a required field labeled "Rule name" with contents "run_third-party-app_report". The bottom-right of the window has four buttons: "Add" - "Add and Add Another" - "Add and Edit" - "Cancel".
    4. Click Add and Edit.
    5. Specify the user:

      1. In the Who section, check the Specified Users and Groups radio button.
      2. In the User category the rule applies to subsection, click Add to open the Add users into sudo rule "run_third-party-app_report" dialog box.
      3. In the Add users into sudo rule "run_third-party-app_report" dialog box in the Available column, check the idm_user checkbox, and move it to the Prospective column.

        A screenshot of a pop-up window labeled "Add users into sudo rule." You can select users from an Available list on the left and move them to a Prospective column on the right. The bottom-right of the window has two buttons: "Add" - "Cancel".
      4. Click Add.
    6. Specify the host:

      1. In the Access this host section, check the Specified Hosts and Groups radio button.
      2. In the Host category this rule applies to subsection, click Add to open the Add hosts into sudo rule "run_third-party-app_report" dialog box.
      3. In the Add hosts into sudo rule "run_third-party-app_report" dialog box in the Available column, check the idmclient.idm.example.com checkbox, and move it to the Prospective column.

        A screenshot of a pop-up window labeled "Add hosts into sudo rule." You can select hosts from an Available list on the left and move them to a Prospective column on the right. The bottom-right of the window has two buttons: "Add" - "Cancel".
      4. Click Add.
    7. Specify the commands:

      1. In the Command category the rule applies to subsection of the Run Commands section, check the Specified Commands and Groups radio button.
      2. In the Sudo Allow Commands subsection, click Add to open the Add allow sudo commands into sudo rule "run_third-party-app_report" dialog box.
      3. In the Add allow sudo commands into sudo rule "run_third-party-app_report" dialog box in the Available column, check the /opt/third-party-app/bin/report checkbox, and move it to the Prospective column.

        A screenshot of a pop-up window labeled "Add allow sudo commands into sudo rule." You can select sudo commands from an Available list on the left and move them to a Prospective column on the right. The bottom-right of the window has two buttons: "Add" - "Cancel".
      4. Click Add to return to the run_third-party-app_report page.
    8. Specify the RunAs user:

      1. In the As Whom section, check the Specified Users and Groups radio button.
      2. In the RunAs Users subsection, click Add to open the Add RunAs users into sudo rule "run_third-party-app_report" dialog box.
      3. In the Add RunAs users into sudo rule "run_third-party-app_report" dialog box, enter the thirdpartyapp service account in the External box and move it to the Prospective column.

        A screenshot of a dialog box where you can specify the "thirdpartyapp" service account as an external user.
      4. Click Add to return to the run_third-party-app_report page.
    9. Click Save in the top left corner.

The new rule is enabled by default.

Figure 18.2. Details of the sudo rule

A screenshot of an overview of the sudo rule that was added. The "Who" section has an entry for "idm_user." The "Access this host" section has "idmclient.idm.example.com." The "Run Commands" section has the "/opt/third-party-app/bin/report" command. The "As Whom" section lists the "thirdpartyapp" account.
Note

Propagating the changes from the server to the client can take a few minutes.

Verification steps

  1. Log in to the idmclient host as the idm_user account.
  2. Test the new sudo rule:

    1. Display which sudo rules the idm_user account is allowed to perform.

      [idm_user@idmclient ~]$ sudo -l
      Matching Defaults entries for idm_user@idm.example.com on idmclient:
          !visiblepw, always_set_home, match_group_by_gid, always_query_group_plugin,
          env_reset, env_keep="COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS",
          env_keep+="MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE",
          env_keep+="LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES",
          env_keep+="LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE",
          env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY KRB5CCNAME",
          secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin
      
      User idm_user@idm.example.com may run the following commands on idmclient:
          (thirdpartyapp) /opt/third-party-app/bin/report
    2. Run the report command as the thirdpartyapp service account.

      [idm_user@idmclient ~]$ sudo -u thirdpartyapp /opt/third-party-app/bin/report
      [sudo] password for idm_user@idm.example.com:
      Executing report...
      Report successful.

18.6. Enabling GSSAPI authentication for sudo on an IdM client

The following procedure describes enabling GSSAPI authentication on an IdM client for the sudo and sudo -i commands via the pam_sss_gss.so PAM module. This configuration allows IdM users to authenticate to the sudo command with their Kerberos ticket.

Prerequisites

  • You have created a sudo rule for an IdM user that applies to an IdM host. For this example, you have created the idm_user_reboot sudo rule to grant the idm_user account the permission to run the /usr/sbin/reboot command on the idmclient host.
  • The idmclient host is running RHEL 8.4 or later.
  • You need root privileges to modify the /etc/sssd/sssd.conf file and PAM files in the /etc/pam.d/ directory.

Procedure

  1. Open the /etc/sssd/sssd.conf configuration file.
  2. Add the following entry to the [domain/<domain_name>] section.

    [domain/<domain_name>]
    pam_gssapi_services = sudo, sudo-i
  3. Save and close the /etc/sssd/sssd.conf file.
  4. Restart the SSSD service to load the configuration changes.

    [root@idmclient ~]# systemctl restart sssd
  5. Open the /etc/pam.d/sudo PAM configuration file.
  6. Add the following entry as the first line of the auth section in the /etc/pam.d/sudo file.

    #%PAM-1.0
    auth sufficient pam_sss_gss.so
    auth       include      system-auth
    account    include      system-auth
    password   include      system-auth
    session    include      system-auth
  7. Save and close the /etc/pam.d/sudo file.
  8. Open the /etc/pam.d/sudo-i PAM configuration file.
  9. Add the following entry as the first line of the auth section in the /etc/pam.d/sudo-i file.

    #%PAM-1.0
    auth sufficient pam_sss_gss.so
    auth       include      sudo
    account    include      sudo
    password   include      sudo
    session    optional     pam_keyinit.so force revoke
    session    include      sudo
  10. Save and close the /etc/pam.d/sudo-i file.

Verification steps

  1. Log into the host as the idm_user account.

    [root@idm-client ~]# ssh -l idm_user@idm.example.com localhost
    idm_user@idm.example.com's password:
  2. Verify that you have a ticket-granting ticket as the idm_user account.

    [idmuser@idmclient ~]$ klist
    Ticket cache: KCM:1366201107
    Default principal: idm_user@IDM.EXAMPLE.COM
    
    Valid starting       Expires              Service principal
    01/08/2021 09:11:48  01/08/2021 19:11:48  krbtgt/IDM.EXAMPLE.COM@IDM.EXAMPLE.COM
    	renew until 01/15/2021 09:11:44
  3. (Optional) If you do not have Kerberos credentials for the idm_user account, destroy your current Kerberos credentials and request the correct ones.

    [idm_user@idmclient ~]$ kdestroy -A
    
    [idm_user@idmclient ~]$ kinit idm_user@IDM.EXAMPLE.COM
    Password for idm_user@idm.example.com:
  4. Reboot the machine using sudo, without specifying a password.

    [idm_user@idmclient ~]$ sudo /usr/sbin/reboot

18.7. Enabling GSSAPI authentication and enforcing Kerberos authentication indicators for sudo on an IdM client

The following procedure describes enabling GSSAPI authentication on an IdM client for the sudo and sudo -i commands via the pam_sss_gss.so PAM module. Additionally, only users who have logged in with a smart card will authenticate to those commands with their Kerberos ticket.

Note

You can use this procedure as a template to configure GSSAPI authentication with SSSD for other PAM-aware services, and further restrict access to only those users that have a specific authentication indicator attached to their Kerberos ticket.

Prerequisites

  • You have created a sudo rule for an IdM user that applies to an IdM host. For this example, you have created the idm_user_reboot sudo rule to grant the idm_user account the permission to run the /usr/sbin/reboot command on the idmclient host.
  • You have configured smart card authentication for the idmclient host.
  • The idmclient host is running RHEL 8.4 or later.
  • You need root privileges to modify the /etc/sssd/sssd.conf file and PAM files in the /etc/pam.d/ directory.

Procedure

  1. Open the /etc/sssd/sssd.conf configuration file.
  2. Add the following entries to the [domain/<domain_name>] section.

    [domain/<domain_name>]
    pam_gssapi_services = sudo, sudo-i
    pam_gssapi_indicators_map = sudo:pkinit, sudo-i:pkinit
  3. Save and close the /etc/sssd/sssd.conf file.
  4. Restart the SSSD service to load the configuration changes.

    [root@idmclient ~]# systemctl restart sssd
  5. Open the /etc/pam.d/sudo PAM configuration file.
  6. Add the following entry as the first line of the auth section in the /etc/pam.d/sudo file.

    #%PAM-1.0
    auth sufficient pam_sss_gss.so
    auth       include      system-auth
    account    include      system-auth
    password   include      system-auth
    session    include      system-auth
  7. Save and close the /etc/pam.d/sudo file.
  8. Open the /etc/pam.d/sudo-i PAM configuration file.
  9. Add the following entry as the first line of the auth section in the /etc/pam.d/sudo-i file.

    #%PAM-1.0
    auth sufficient pam_sss_gss.so
    auth       include      sudo
    account    include      sudo
    password   include      sudo
    session    optional     pam_keyinit.so force revoke
    session    include      sudo
  10. Save and close the /etc/pam.d/sudo-i file.

Verification steps

  1. Log into the host as the idm_user account and authenticate with a smart card.

    [root@idmclient ~]# ssh -l idm_user@idm.example.com localhost
    PIN for smart_card
  2. Verify that you have a ticket-granting ticket as the smart card user.

    [idm_user@idmclient ~]$ klist
    Ticket cache: KEYRING:persistent:1358900015:krb_cache_TObtNMd
    Default principal: idm_user@IDM.EXAMPLE.COM
    
    Valid starting       Expires              Service principal
    02/15/2021 16:29:48  02/16/2021 02:29:48  krbtgt/IDM.EXAMPLE.COM@IDM.EXAMPLE.COM
    	renew until 02/22/2021 16:29:44
  3. Display which sudo rules the idm_user account is allowed to perform.

    [idm_user@idmclient ~]$ sudo -l
    Matching Defaults entries for idmuser on idmclient:
        !visiblepw, always_set_home, match_group_by_gid, always_query_group_plugin,
        env_reset, env_keep="COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS",
        env_keep+="MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE",
        env_keep+="LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES",
        env_keep+="LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE",
        env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY KRB5CCNAME",
        secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin
    
    User idm_user may run the following commands on idmclient:
        (root) /usr/sbin/reboot
  4. Reboot the machine using sudo, without specifying a password.

    [idm_user@idmclient ~]$ sudo /usr/sbin/reboot

18.8. SSSD options controlling GSSAPI authentication for PAM services

You can use the following options for the /etc/sssd/sssd.conf configuration file to adjust the GSSAPI configuration within the SSSD service.

pam_gssapi_services
GSSAPI authentication with SSSD is disabled by default. You can use this option to specify a comma-separated list of PAM services that are allowed to try GSSAPI authentication using the pam_sss_gss.so PAM module. To explicitly disable GSSAPI authentication, set this option to -.
pam_gssapi_indicators_map

This option only applies to Identity Management (IdM) domains. Use this option to list Kerberos authentication indicators that are required to grant PAM access to a service. Pairs must be in the format <PAM_service>:_<required_authentication_indicator>_.

Valid authentication indicators are:

  • otp for two-factor authentication
  • radius for RADIUS authentication
  • pkinit for PKINIT, smart card, or certificate authentication
  • hardened for hardened passwords
pam_gssapi_check_upn
This option is enabled and set to true by default. If this option is enabled, the SSSD service requires that the user name matches the Kerberos credentials. If false, the pam_sss_gss.so PAM module authenticates every user that is able to obtain the required service ticket.

Examples

The following options enable Kerberos authentication for the sudo and sudo-i services, requires that sudo users authenticated with a one-time password, and user names must match the Kerberos principal. Because these settings are in the [pam] section, they apply to all domains:

[pam]
pam_gssapi_services = sudo, sudo-i
pam_gssapi_indicators_map = sudo:otp
pam_gssapi_check_upn = true

You can also set these options in individual [domain] sections to overwrite any global values in the [pam] section. The following options apply different GSSAPI settings to each domain:

For the idm.example.com domain
  • Enable GSSAPI authentication for the sudo and sudo -i services.
  • Require certificate or smart card authentication authenticators for the sudo command.
  • Require one-time password authentication authenticators for the sudo -i command.
  • Enforce matching user names and Kerberos principals.
For the ad.example.com domain
  • Enable GSSAPI authentication only for the sudo service.
  • Do not enforce matching user names and principals.
[domain/idm.example.com]
pam_gssapi_services = sudo, sudo-i
pam_gssapi_indicators_map = sudo:pkinit, sudo-i:otp
pam_gssapi_check_upn = true
...

[domain/ad.example.com]
pam_gssapi_services = sudo
pam_gssapi_check_upn = false
...

18.9. Troubleshooting GSSAPI authentication for sudo

If you are unable to authenticate to the sudo service with a Kerberos ticket from IdM, use the following scenarios to troubleshoot your configuration.

Prerequisites

Procedure

  • If you see the following error, the Kerberos service might not able to resolve the correct realm for the service ticket based on the host name:

    Server not found in Kerberos database

    In this situation, add the hostname directly to [domain_realm] section in the /etc/krb5.conf Kerberos configuration file:

    [idm-user@idm-client ~]$ cat /etc/krb5.conf
    ...
    
    [domain_realm]
     .example.com = EXAMPLE.COM
     example.com = EXAMPLE.COM
     server.example.com = EXAMPLE.COM
  • If you see the following error, you do not have any Kerberos credentials:

    No Kerberos credentials available

    In this situation, retrieve Kerberos credentials with the kinit utility or authenticate with SSSD:

    [idm-user@idm-client ~]$ kinit idm-user@IDM.EXAMPLE.COM
    Password for idm-user@idm.example.com:
  • If you see either of the following errors in the /var/log/sssd/sssd_pam.log log file, the Kerberos credentials do not match the username of the user currently logged in:

    User with UPN [<UPN>] was not found.
    
    UPN [<UPN>] does not match target user [<username>].

    In this situation, verify that you authenticated with SSSD, or consider disabling the pam_gssapi_check_upn option in the /etc/sssd/sssd.conf file:

    [idm-user@idm-client ~]$ cat /etc/sssd/sssd.conf
    ...
    
    pam_gssapi_check_upn = false
  • For additional troubleshooting, you can enable debugging output for the pam_sss_gss.so PAM module.

    • Add the debug option at the end of all pam_sss_gss.so entries in PAM files, such as /etc/pam.d/sudo and /etc/pam.d/sudo-i:

      [root@idm-client ~]# cat /etc/pam.d/sudo
      #%PAM-1.0
      auth       sufficient   pam_sss_gss.so   debug
      auth       include      system-auth
      account    include      system-auth
      password   include      system-auth
      session    include      system-auth
      [root@idm-client ~]# cat /etc/pam.d/sudo-i
      #%PAM-1.0
      auth       sufficient   pam_sss_gss.so   debug
      auth       include      sudo
      account    include      sudo
      password   include      sudo
      session    optional     pam_keyinit.so force revoke
      session    include      sudo
    • Try to authenticate with the pam_sss_gss.so module and review the console output. In this example, the user did not have any Kerberos credentials.

      [idm-user@idm-client ~]$ sudo ls -l /etc/sssd/sssd.conf
      pam_sss_gss: Initializing GSSAPI authentication with SSSD
      pam_sss_gss: Switching euid from 0 to 1366201107
      pam_sss_gss: Trying to establish security context
      pam_sss_gss: SSSD User name: idm-user@idm.example.com
      pam_sss_gss: User domain: idm.example.com
      pam_sss_gss: User principal:
      pam_sss_gss: Target name: host@idm.example.com
      pam_sss_gss: Using ccache: KCM:
      pam_sss_gss: Acquiring credentials, principal name will be derived
      pam_sss_gss: Unable to read credentials from [KCM:] [maj:0xd0000, min:0x96c73ac3]
      pam_sss_gss: GSSAPI: Unspecified GSS failure.  Minor code may provide more information
      pam_sss_gss: GSSAPI: No credentials cache found
      pam_sss_gss: Switching euid from 1366200907 to 0
      pam_sss_gss: System error [5]: Input/output error

18.10. Using an Ansible playbook to ensure sudo access for an IdM user on an IdM client

In Identity Management (IdM), you can ensure sudo access to a specific command is granted to an IdM user account on a specific IdM host.

Complete this procedure to ensure a sudo rule named idm_user_reboot exists. The rule grants idm_user the permission to run the /usr/sbin/reboot command on the idmclient machine.

Prerequisites

Procedure

  1. Create an inventory file, for example inventory.file, and define ipaservers in it:

    [ipaservers]
    server.idm.example.com
  2. Add one or more sudo commands:

    1. Create an ensure-reboot-sudocmd-is-present.yml Ansible playbook that ensures the presence of the /usr/sbin/reboot command in the IdM database of sudo commands. To simplify this step, you can copy and modify the example in the /usr/share/doc/ansible-freeipa/playbooks/sudocmd/ensure-sudocmd-is-present.yml file:

      ---
      - name: Playbook to manage sudo command
        hosts: ipaserver
        become: true
      
        tasks:
        # Ensure sudo command is present
        - ipasudocmd:
            ipaadmin_password: MySecret123
            name: /usr/sbin/reboot
            state: present
    2. Run the playbook:

      $ ansible-playbook -v -i path_to_inventory_directory/inventory.file path_to_playbooks_directory/ensure-reboot-sudocmd-is-present.yml
  3. Create a sudo rule that references the commands:

    1. Create an ensure-sudorule-for-idmuser-on-idmclient-is-present.yml Ansible playbook that uses the sudo command entry to ensure the presence of a sudo rule. The sudo rule allows idm_user to reboot the idmclient machine. To simplify this step, you can copy and modify the example in the /usr/share/doc/ansible-freeipa/playbooks/sudorule/ensure-sudorule-is-present.yml file:

      ---
      - name: Tests
        hosts: ipaserver
        become: true
      
        tasks:
        # Ensure a sudorule is present granting idm_user the permission to run /usr/sbin/reboot on idmclient
        - ipasudorule:
            ipaadmin_password: MySecret123
            name: idm_user_reboot
            description: A test sudo rule.
            allow_sudocmd: /usr/sbin/reboot
            host: idmclient.idm.example.com
            user: idm_user
            state: present
    2. Run the playbook:

      $ ansible-playbook -v -i path_to_inventory_directory/inventory.file path_to_playbooks_directory/ensure-sudorule-for-idmuser-on-idmclient-is-present.yml

Verification steps

Test that the sudo rule whose presence you have ensured on the IdM server works on idmclient by verifying that idm_user can reboot idmclient using sudo. Note that it can take a few minutes for the changes made on the server to take effect on the client.

  1. Log in to idmclient as idm_user.
  2. Reboot the machine using sudo. Enter the password for idm_user when prompted:

    $ sudo /usr/sbin/reboot
    [sudo] password for idm_user:

If sudo is configured correctly, the machine reboots.

Additional materials

  • For more details on how to apply sudo commands, command groups, and rules in IdM using an Ansible playbook including the descriptions of playbook variables, see the README-sudocmd.md, README-sudocmdgroup.md, and README-sudorule.md Markdown files available in the /usr/share/doc/ansible-freeipa/ directory.