2.5.4. SELinux: Avoid SELinux on GFS2

Security Enhanced Linux (SELinux) is highly recommended for security reasons in most situations, but it is not supported for use with GFS2. SELinux stores information using extended attributes about every file system object, and SELinux labels on GFS2 file systems can get out of sync between cluster nodes because of how they are cached in memory.

When mounting a GFS2 file system, you must ensure that SELinux will not attempt to read the seclabel element on each file system object by using one of the context options as described on the mount(8) man page; SELinux will assume that all content in the file system is labeled with the seclabel element provided in the context mount options. This will also speed up processing as it avoids another disk read of the extended attribute block that could contain seclabel elements.

For example, on a system with SELinux in enforcing mode, you can use the following mount command to mount the GFS2 file system if the file system is going to contain Apache content. This label will apply to the entire file system; it remains in memory and is not written to disk.

# mount -t gfs2 -o context=system_u:object_r:httpd_sys_content_t:s0 /dev/mapper/xyz/mnt/gfs2

# mount -t gfs2 -o context=system_u:object_r:httpd_sys_content_t:s0 /dev/mapper/xyz/mnt/gfs2

If you are not sure whether the file system will contain Apache content, you can use the labels public_content_rw_t or public_content_t, or you could define a new label altogether and define a policy around it.

Note that in a Pacemaker cluster you should always use Pacemaker to manage a GFS2 file system. You can specify the mount options when you create a GFS2 file system resource, as described in Chapter 6, Configuring a GFS2 File System in a Pacemaker Cluster.