Security Mechanisms
The extension API provides comprehensive options to influence the runtime system. As a result, the user has to pay attention to necessary security measures.
For CODESYS Control Extension Package 4.4.0.0 and higher, the codesysuser group is created when the package is installed. Some functions of the extension API require that the Linux user who uses them is a member of the codesysuser group. You can add a user to this group with administrator privileges the following command (as an example):
$ sudo adduser $USER codesysuser
The reason behind this procedure is that the mechanisms use the /var/run/codesysextension/ and /var/opt/codesysextension/ working directories. These have 770 permission and is assigned to the codesysuser group. This ensures that unauthorized users cannot interfere with the runtime system.
Important
All members of the codesysuser group can influence the runtime system.
Important
The following mechanisms are based on a Unix Domain Socket (UDS):
It is necessary for the IEC programmer to query error codes of the respective function block for these mechanisms and to react appropriately (example: establishing or aborting a connection).
Important
To prevent a workload attack, the Unix peers (Unix Domain Sockets) need to have at least the same priority or a higher priority than the IEC task itself. The UDS peers are the provided examples or the user-created programs which use the functions of the Extension API.
This priority is not the priority displayed in the task configuration of CODESYS. It can be determined on the Linux system by means of htop. This is a task which has the same name as the IEC task assigned in CODESYS.
Important
The PLC shell requires the "anonymous user". If this is enabled, then it is not possible to trace which Linux user has used the PLC shell.
Important
Due to the process separation, the new interfaces of the CODESYS Control Extension Package do not provide the capability of user authentication (from the point of view of the CODESYS Development System). It is not possible to assign a corresponding Linux user or user name to an IEC user.
As a result, not only the IEC users but also the Linux users have to be considered and administered accordingly when considering the security of the IEC application.
Only authorized users may have administrative access to the Linux system of the runtime system.
Important
In the case of interfaces which use process separation, it cannot be ruled out that data is passed unencrypted on the system. This means that an attacker with administrative permissions on the system could record them.