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This script checks first whether it is running as root (the PAM stack does not necessarily run as root, but as the user as which the service that invoked it is running). If it is, it proceeds to encrypt the user's password (${PAM_AUTHTOK}) as an NT hash and update it in the 'value' column of the configured table in FreeRADIUS's MySQL database for the entry where the value of the 'username' column matches the user's username (${PAM_USER}). Due to the nature of the SQL query used, there needs to already be an entry in the table containing the matching username in the 'username' column (for functionality it should actually also already '@@@1' contain the appropriate values for the remaining columns, except the 'value' column). If it is not running as root, it uses a workaround to escalate its privileges. It uses the available credentials to SSH into localhost as the user in question, causing the SSH daemon to run a new instance of the PAM stack to verify the user's credentials (and sshd runs the PAM stack as root) and thus a new instance of the script, as root. Before doing so the script makes sure that the PAM stack has not already now been invoked by sshd, in order to avoid, in case sshd should ever decide to run the PAM stack as a non-root user, that an infinite loop occurs spawning endless processes of this script, sshd, PAM, etc.
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