SELinux policy module for Springboot (Spring Boot) applications

Maintained and provided as a community contribution by LHQG.

Table of Contents

1. Introduction
2. How to use this SELinux module
   • Filesystem labelling
   • Networking
     • Listen port
     • Monitoring port
     • Services consumed bu the Springboot application
   • SELinux booleans
   • Interfaces for deployment tools
   • Starting the Springboot application
3. Running multiple Springboot applications on the same host
4. Related projects
5. Disclaimer

Introduction

This SELinux policy module aims to prevent a Java Spring Boot (daemon/background) application to perform unexpected actions on a Linux host.

It should be used when the Springboot application is possibly exposed to a world full of bad guys.

The module should prevent the application from going rogue, and should the application be compromised by an attacker this SELinux policy module should help limit the damage on the system on which the Springboot application is running.

When used correctly, this SELinux policy module will make the Springboot application(s) run on the host in the dedicated springboot_t SELinux domain.

How to use this SELinux module

Once the SELinux policy module is compiled and installed in the running Kernel SELinux policy, a few actions must be taken for the new policy to apply to the Springboot application(s).

The policy can be adjusted with a handfull of SELinux booleans.

Filesystem labelling

This SELinux policy module SELinux file context definitions are based on the Filesystem Hierarchy Standards [https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard].

The root for the Springboot installation is expected to be /opt/springboot. The root for log files of the Springboot application(s) is expected to be /var/log/springboot.

A typical directory layout for the Springboot application my_app would be:

/opt/springboot/my_app
                      \ conf
                      \ lib
                      \ keys
                      
/var/log/springboot/my_app

/var/run/springboot/my_app

/srv/springboot/my_app
                      \ cache
                      \ work
                      \ dynlib
                      

Files with .so and .jar extensions under the /opt/springboot and /srv/springboot trees will be assigned the Springboot library SELinux type.

Files with .jks, .jceks, .p12 or .pkcs12 extensions placed in a conf or properties directory under /opt/springboot will be assigned the Springboot authentication/credentials SELinux type springboot_auth_t. All files located in a keys directory under /opt/springboot will be assigned this SELinux type. You may want to assign this type, using fcontext customizations, to your sensitive files containing authentication data for your Springboot application (passwords, private keys, tokens, ...). Such files can only be read by the Springboot application, deployment tools (Ansible, Puppet, ...) will need specific permissions to create/modify them. (See also boolean allow_sysadm_manage_springboot_auth_files below).

Should you prefer to use a different directory structure, you should consider using SELinux fcontext equivalence rules to map your specifics to the filesystem layout expected in the policy module, using the semanage fcontext -a -e ORIGINAL CUSTOMISATION command.

Networking

Listen port

The TCP port the Springboot application binds and listens to MUST be assigned the springboot_port_t SELinux type.

Monitoring port

If the Springboot application needs to bind and listen to a specific port to offer monitoring metrics and information, then this TCP port should be assigned the springboot_monitoring_port_t SELinux type.

Then, (host)local processes need to be granted the permission to connect to the monitoring port using the policy module interface springboot_monitor() with the SELinux domain prefix as the only argument.

Example: springboot_monitoring_port_t(zabbix) to Allow Zabbix to connect to the monitoring port of the Springboot application.

Services consumed by the Springboot application

If the application needs to connect to services such as databases, directory servers, ... the SELinux type of these services network port must be allowed for the Springboot application to connect to. One of the springboot_allow_connectto or springboot_allow_consumed_service interfaces should be used with the prefix name for the service as the only argument.

Examples:

• springboot_allow_connectto(postgresql) to allow the Springboot application to connect to a PostgreSQL database
• springboot_allow_connectto(ldap) to allow connection to LDAP directory services.

SELinux booleans

allow_springboot_connectto_http (default: true)

When switched to true, this boolean allows the Springboot application to connect to remote HTTP/HTTPS ports (locally assigned the http_port_t SELinux type).

allow_springboot_connectto_self (default: false)

When switched to true, this boolean allows the Springboot application to connect to other remote Springboot application (locally assigned the springboot_port_t SELinux type).

allow_springboot_syslog_netsend (default: false)

When switched to true, this boolean allows the Springboot application to use the syslog protocol to send log messages (both UDP and TCP transports).

allow_springboot_connectto_ldap (default: false)

When switched to true, this boolean allows the Springboot application to connect to remote LDAP/LDAPS ports (locally assigned the ldap_port_t SELinux type).

allow_springboot_connectto_smtp (default: false)

When switched to true, this boolean allows the Springboot application to connect to remote SMTP/SMTPS/submission ports (locally assigned the smtp_port_t SELinux type).

Mutiple booleans allow_springboot_connectto_<DB> (default: false)

When switched to true, these boolean allows the Springboot application to connect to remote database server ports: couchdb, mongodb, mysql (MariaDB), oracle, pgsql (PostgreSQL), redis.

allow_springboot_dynamic_libs (default: false)

When switched to true, this boolean allows the Springboot application to create and use (execute) SO libraries and JAR files under the /srv/springboot/.../dynlib directory. Use with care, i.e. only when strictly required, as this would allow a compromised Springboot application to offload arbitrary code and use it.

allow_springboot_purge_logs (default: false)

When switched to true, this boolean allows the Springboot application to delete its log files. It can be useful for "in Java app" logging framework initiated log file rotation. But it can also be useful for attackers who would like to clean after themselves and remove traces of their actions...

allow_springboot_rewrite_logs (default: false)

When switched to true, this boolean allows the Springboot application to rewrite its own log files. It can prove useful when the logging framework cannot work in "append only" mode". But it can also be useful for attackers who would like to clean after themselves and remove traces of their actions...

allow_webadm_read_springboot_files (default: false)

Users running with the webadm_r SELinux role andwebadm_t domain are granted the permissions to browse the directories of the Springboot application and the permission to stop and start the Springboot application systemd services, as well as querying their status.

When switched to true, this boolean allows such users additional permissions to read the contents of Springboot application files: log, configuration, temp and transient/cache files.

allow_sysadm_write_springboot_files (default: false)

When switched to true, this boolean allows users running with the sysadm_r SELinux role and sysadm_t domain to:

• fully manage temporary files,
• delete and rename log files,
• delete and rename transient/cache files,
• modify the contents of configuration files,

Otherwise, such users are only granted read permissions on all Springboot application files, except authentication/credentials files.

allow_sysadm_manage_springboot_auth_files (default: false)

When switched to true, this boolean allows users running with the sysadm_r SELinux role and sysadm_t domain to fully manage Springboot authentication files.

Interfaces for deployment tools

When the deployment tool (Ansible, Puppet, ...) for the Springboot application runs not unconfined on the target host, it becomes necessary to grant it permissions to create/modify/delete the Springboot application files. This is achieved using SELinux code interfaces to create and compile small additionnal SELinux policy modules.

For obvious security reasons, the deployment tool should not be allowed to delete log files.

Each interface takes the SELinux domain prefix of the deployment tool as its first argument. Eg: ansible for Ansible if the SELinux domain is ansible_t.

springboot_deployer interface

This interface grants permissions to deploy (create/read/write) and clean up (delete) Springboot application files and directories. It also allows the deployment tool to manage the Springboot systemd units (services/targets/...).

The scope of actions on the main Linux operating system directories is limited to:

• create a springboot subdirectory under /opt, /var/lib, /var/log, /srv, /run, ...
• create subdirectories in the springboot directores above.

The scope of actions on Springboot application files and directories is limited to the following types:

• fully manage configuration files (and symlinks)
• fully manage transient (tmp, run) files (and symlinks)
• fully manage application (bin, lib, dynlibs) files (and symlinks)

The scope of actions on the systemd units is limited to:

• read the Springboot systemd unit files (and diretcories)
• stop/start/query/reload/enable/disable units

springboot_auth_deployer interface

This interface allows the deployment tool to deploy Springboot application files with sensitive authentication information (i.e. files with springboot_auth_t SELinux type).

springboot_systemd_deployer interface

This interface grants permissions to deploy systemd Springboot unit files (and directories).

The scope of actions on the Linux system main systemd directories is limited to deploying (creating/writing) unit files/diretcories with the resulting SELinux type springboot_unit_file_t. Then the deployment tool is allowed to fully manage those files/directories.

springboot_systemd_unit_instance_deployer interface

This interface should be used when Springboot application services are managed as systemd instances of the springboot@ template service. The springboot_systemd_unit_instance_deployer interface needs the service instance name as its second argument.

Then the deployment tool is granted permission to create unit files/directories for that service instance.

Usage example:

springboot_systemd_unit_instance_deployer(ansible, myapp)

Will allow the Ansible domain ansible_t to create/start/activate/deactivate the [email protected] unit instance.

Starting the Springboot application

The Java Springboot application should always and only be started as a systemd service using thesystemctl command.

The service or target unit files MUST be located in /etc/systemd/system or in /lib/systemd/system, the file name MUST start with springboot. Directories to tune or override unit behaviour are supported. Template/instantiated units are supported provided the master file is named [email protected].

The script(s) used to start or stop the Springboot application MUST be located in the /opt/springboot/service/ directory. The /opt/springboot/bin/springboot_service file name is also supported.

Running multiple Springboot applications on the same host

Without isolation

Nothing special needs to be done. Care must be taken to name each Springboot apps properly and to properly use systemd/systemctl to manage each one.

With isolation between the Springboot apps

TO DO

Related projects

While having a look at this SELinux policy module for Springboot application, you should probably take a glance at:

• A Puppet module module to deploy Springboot applications: https://github.com/lhqg/puppet-springboot
• Ansible roles to deloy Springboot applications: https://github.com/lhqg/ansible-springboot
• A SElinux policy module for batches running using Springboot: https://github.com/lhqg/selinux_springbatch

Disclaimer

The code of the this SELinux policy module is provided AS-IS. People and organisation willing to use it must be fully aware that they are doing so at their own risks and expenses.

The Author(s) of this SELinux policy module SHALL NOT be held liable nor accountable, in any way, of any malfunction or limitation of said module, nor of the resulting damage, of any kind, resulting, directly or indirectly, of the usage of this SELinux policy module.

It is strongly advised to always use the last version of the code, to check for the compatibility of the platform where it is about to be deployed, to compile the module on the target specific Linux distribution and version where it is intended to be used.

Finally, users should check regularly for updates.