Configuring PAM Authentication and User Mapping with Unix Authentication
This guide shows how to authenticate database users using local Unix accounts and map Unix groups to MariaDB users with the PAM plugin.
We walk through the configuration of PAM authentication using the pam authentication plugin and user and group mapping with the pam_user_map PAM module. The primary authentication will be handled by the pam_unix PAM module, which performs standard Unix password authentication.
Hypothetical Requirements
In this walkthrough, we are going to assume the following hypothetical requirements:
The Unix user
fooshould be mapped to the MariaDB userbar. (foo: bar)Any Unix user in the Unix group
dbashould be mapped to the MariaDB userdba. (@dba: dba)
Creating Our Unix Users and Groups
Let's go ahead and create the Unix users and groups that we are using for this hypothetical scenario.
First, let's create the foo user and a couple users to go into the dba group. Note that each of these users needs a password.
sudo useradd foo
sudo passwd foo
sudo useradd alice
sudo passwd alice
sudo useradd bob
sudo passwd bobNext, let's create the dba group and add our two users to it:
sudo groupadd dba
sudo usermod -a -G dba alice
sudo usermod -a -G dba bobWe also need to create Unix users with the same name as the bar and dba MariaDB users. See here to read more about why. No one will be logging in as these users, so they do not need passwords.
Installing the pam_user_map PAM Module
Next, let's install the pam_user_map PAM module.
Before the module can be compiled from source, we may need to install some dependencies.
On RHEL, CentOS, and other similar Linux distributions that use RPM packages, we need to install gcc and pam-devel:
On Debian, Ubuntu, and other similar Linux distributions that use DEB packages, we need to install gcc and libpam0g-dev:
And then we can build and install the library with the following:
Configuring the pam_user_map PAM Module
Next, let's configure the pam_user_map PAM module based on our hypothetical requirements.
The configuration file for the pam_user_map PAM module is /etc/security/user_map.conf. Based on our hypothetical requirements, ours would look like:
Installing the PAM Authentication Plugin
Next, let's install the pam authentication plugin.
Log into the MariaDB Server and execute the following:
Configuring the PAM Service
Next, let's configure the PAM service. We will call our service mariadb, so our PAM service configuration file will be located at /etc/pam.d/mariadb on most systems.
Since we are only doing Unix authentication with the pam_unix PAM module and group mapping with the pam_user_map PAM module, our configuration file would look like this:
Configuring the pam_unix PAM Module
The pam_unix PAM module adds some additional configuration steps on a lot of systems. We basically have to give the user that runs mysqld access to /etc/shadow.
If the mysql user is running mysqld, then we can do that by executing the following:
The server needs to be restarted for this change to take affect.
Creating MariaDB Users
Next, let's create the MariaDB users. Remember that our PAM service is called mariadb.
First, let's create the MariaDB user for the user mapping: foo: bar . This means we need to create a bar user:
Next, let's create the MariaDB user for the group mapping: @dba: dba . This means that we need to create a dba user:
Next, to allow for the user and group mapping, we need to create an anonymous user that authenticates with the pam authentication plugin that is also able to PROXY as the bar and dba users. Before we can create the proxy user, we might need to clean up some defaults:
Finally, let's create the anonymous proxy user:
Testing our Configuration
Next, let's test out our configuration by verifying that mapping is occurring. We can verify this by logging in as each of our users and comparing the return value of USER(), which is the original user name and the return value of CURRENT_USER(), which is the authenticated user name.
First, let's test our foo user:
We can verify that our foo Unix user was properly mapped to the bar MariaDB user by looking at the return value of CURRENT_USER().
Next, let's test our alice user in the dba group:
Finally, let's test our bob user in the dba group:
We can verify that our alice and bob Unix users in the dba Unix group were properly mapped to the dba MariaDB user by looking at the return values of CURRENT_USER().
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