Security-Enhanced Linux with MariaDB
Contents
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 SELinux Is Enabled
To verify whether SELinux is enabled, execute the getenforce
command. For example:
getenforce
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.
Configuring a MariaDB Server SELinux Policy
MariaDB Server should work with your default distribution policy (which is usually part of the selinux-policy
or selinux-policy-targeted
system package). If you use mysqld_safe
, you will need an additional policy file, mariadb.pp
, which is installed together with the MariaDB Server. It will be loaded automatically if you have /usr/sbin/semodule
installed, but you can load it manually anytime with
/usr/sbin/semodule -i /usr/share/mysql/policy/selinux/mariadb.pp
Note that this policy file extends, but not replaces the system policy.
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
Setting the Unix Socket
A custom location for the socket means it needs to have the right file context of mysqld_var_run_t
for permitted application to connect to the socket.
sudo semanage fcontext -a -t mysqld_var_run_t "/mariadb/run/mariadb.sock"
A newly created socket with get the right context.
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.
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/).