SELinux

Security-Enhanced Linux (SELinux) is a Linux kernel module that provides a framework for configuring mandatory access control (MAC) system for many resources on the system. It is enabled by default on some Linux distributions, including RHEL, CentOS, Fedora, and other similar Linux distribution. SELinux prevents programs from accessing files, directories or ports unless it is configured to access those resources.

Verifying Whether SELinix Is Enabled

To verify whether SELinux is enabled, execute the getenforce command. For example:

getenforce

Changing SELinux's Mode

Sometimes it can be helpful to permanently set SELinux to permissive mode or to permanently disable SELinux entirely. To do so, you have to update the SELinux configuration file. On many systems, it is at the following path:

  • /etc/selinux/config

To set it to permissive mode, set SELINUX=permissive.

To disable it entirely, set SELINUX=disabled.

To re-enable it again later, set SELINUX=enforcing.

After you make a change to this configuration file, you have to reboot the system in order for the changes to go into effect.

Building and Loading the Server's SELinux Policy

MariaDB Server comes with an SELinux policy that is not build or loaded by default. On many systems, the policy is installed to /usr/share/mysql/policy/selinux/mariadb-server.fc. In order to build it and load it, execute the following:

sudo yum install selinux-policy-devel
cd /usr/share/mysql/policy/selinux/
make -f /usr/share/selinux/devel/Makefile mariadb-server.pp
sudo semodule -i mariadb-server.pp

Setting File Contexts

SELinux uses file contexts as a way to determine who should be able to access that file.

File contexts are managed with the semanage fcontext and restorecon commands.

On many systems, the semanage utility is installed by the policycoreutils-python package, and the restorecon utility is installed by the policycoreutils package. You can install these with the following command:

sudo yum install policycoreutils policycoreutils-python

A file or directory's current context can be checked by executing ls with the --context or --scontext options.

Setting the File Context for the Data Directory

If you use a custom directory for datadir, then you may need to set the file context for that directory. The SELinux file context for MariaDB data files is mysqld_db_t. You can determine if this file context is present on your system and which files or directories it is associated with by executing the following command:

sudo semanage fcontext --list | grep mysqld_db_t

If you would like to set the file context for your custom directory for your datadir, then that can be done by executing the semanage fcontext and restorecon commands. For example:

sudo semanage fcontext -a -t mysqld_db_t "/mariadb/data(/.*)?"
sudo restorecon -Rv /mariadb/data

If you would like to check the current file context, you can do so by by executing ls with the --context or --scontext options. For example:

ls --directory --scontext /mariadb/data

Setting the File Context for Log Files

If you use a custom directory for log files, then you may need to set the file context for that directory. The SELinux file context for MariaDB log files is mysqld_log_t. You can determine if this file context is present on your system and which files or directories it is associated with by executing the following command:

sudo semanage fcontext --list | grep mysqld_log_t

If you would like to set the file context for your custom directory for log files, then that can be done by executing the semanage fcontext and restorecon commands. For example:

sudo semanage fcontext -a -t mysqld_log_t "/var/log/mysql(/.*)?"
sudo restorecon -Rv /var/log/mysql

If you would like to check the current file context, you can do so by by executing ls with the --context or --scontext options. For example:

ls --directory --scontext /var/log/mysql

Setting the File Context for Option Files

If you use a custom directory for option files, then you may need to set the file context for that directory. The SELinux file context for MariaDB option files is mysqld_etc_t. You can determine if this file context is present on your system and which files or directories it is associated with by executing the following command:

sudo semanage fcontext --list | grep mysqld_etc_t

If you would like to set the file context for your custom directory for option files, then that can be done by executing the semanage fcontext and restorecon commands. For example:

sudo semanage fcontext -a -t mysqld_etc_t "/etc/mariadb(/.*)?"
sudo restorecon -Rv /etc/mariadb

If you would like to check the current file context, you can do so by by executing ls with the --context or --scontext options. For example:

ls --directory --scontext /etc/mariadb

Allowing Access to the Tmpfs File Context

If you wanted to mount your tmpdir on a tmpfs file system or wanted to use a tmpfs file system on /run/shm, then you might need to allow mysqld_t to have access to a couple tmpfs-related file contexts. For example:

cd /usr/share/mysql/policy/selinux/
tee ./mysqld_tmpfs.te <<EOF
module mysqld_tmpfs 1.0;

require {
type tmpfs_t;
type mysqld_t;
class dir { write search read remove_name open getattr add_name };
class file { write getattr read lock create unlink open };
}

allow mysqld_t tmpfs_t:dir { write search read remove_name open getattr add_name };

allow mysqld_t tmpfs_t:file { write getattr read lock create unlink open }
EOF
sudo checkmodule -M -m mysqld_tmpfs.te -o mysqld_tmpfs.mod
sudo semodule_package -m mysqld_tmpfs.mod -o mysqld_tmpfs.pp 
sudo semodule -i mysqld_tmpfs.pp

Troubleshooting SELinux Issues

You might need to troubleshoot SELinux-related issues in cases, such as:

  • MariaDB is using a non-default port.
  • MariaDB is reading from or writing to some files (datadir, log files, option files, etc.) located at non-default paths.
  • MariaDB is using a plugin that requires access to resources that default installations do not use.

Temporarily Putting mysqld Into Permissive Mode

When you are troubleshooting issues that you think SELinux might be causing, it can help to temporarily put mysqld_t into permissive mode. This can be done by executing the semanage command. For example:

sudo semanage permissive -a mysqld_t

If that solved the problem, then it means that the current SELinux policy is the culprit. You need to adjust the SELinux policy or labels for MariaDB.

File System Permission Errors

If the file system permissions for some MariaDB directory look fine, but the MariaDB error log still has errors that look similar to the following:

130321 11:50:51 mysqld_safe Starting mysqld daemon with databases from /datadir
...
2013-03-21 11:50:52 2119 [Warning] Can't create test file /datadir/
2013-03-21 11:50:52 2119 [Warning] Can't create test file /datadir/
...
2013-03-21 11:50:52 2119 [ERROR] /usr/sbin/mysqld: Can't create/write to file 
    '/datadir/boxy.pid' (Errcode: 13 - Permission denied)
2013-03-21 11:50:52 2119 [ERROR] Can't start server: can't create PID file: 
    Permission denied
130321 11:50:52 mysqld_safe mysqld from pid file /datadir/boxy.pid ended

Then check SELinux's /var/log/audit/audit.log for log entries that look similar to the following:

type=AVC msg=audit(1363866652.030:24): avc:  denied  { write } for  pid=2119 
    comm="mysqld" name="datadir" dev=dm-0 ino=394 
    scontext=unconfined_u:system_r:mysqld_t:s0 
    tcontext=unconfined_u:object_r:default_t:s0 tclass=dir

If you see any entries that look similar to this, then you most likely need to adjust the file contexts for some files or directories. See Setting File Contexts for more information on how to do that.

SELinux and MariaDB On a Different Port

TCP and UDP ports are enabled for permission to bind too. If you are using a different port, or some Galera ports, configure SELinux to be able to use those ports:

sudo semanage port -a -t mysqld_port_t -p tcp 3307 

Generating SELinux Policies with audit2allow

In some cases, a MariaDB system might need non-standard policies. It is possible to create these policies from the SELinux audit log using the audit2allow utility. The semanage and semodule utilities will also be needed.

On many systems, the audit2allow and semanage utilities are installed by the policycoreutils-python package, and the semodule utility is installed by the policycoreutils package. You can install these with the following command:

sudo yum install policycoreutils policycoreutils-python

The following process can be used to generate a policy from the audit log:

  • Remove dontaudits from the policy:
sudo semodule -DB
  • Temporarily put mysqld_t into permissive mode. For example:
sudo semanage permissive -a mysqld_t
  • Do whatever was causing SELinux errors.
  • Use the generated audit log to create a policy:
sudo grep mysqld /var/log/audit/audit.log | audit2allow -M mariadb_local
sudo semodule -i mariadb_local.pp
  • Pull mysqld_t out of permissive mode. For example:
sudo semanage permissive -d mysqld_t
  • Restore dontaudits for the policy:
sudo setmodule -B

The same procedure can be used if MariaDB starts but SELinux prevents it from functioning correctly. For example, SELinux may prevent PAM plugin from authenticating users. The solution is the same — enable auditing, switch to permissive, do, whatever SELinux didn't allow you to, create a policy from the audit log.

When you discover any needed SELinux permissions, please report the needed permissions to your operating system bug tracking so all users can benefit from your work (e.g. Red Hat Bugzilla https://bugzilla.redhat.com/).

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