Soluciones de Problemas Relativos con SELinux

Siga solamente los pasos necesarios desde este procedimiento; en muchos casos, necesita realizar tan solo el paso 1.

Procedimiento

Si el problema aún sucede, algo diferente que SELinux está bloqueando su escenario.

Tras identificar que SELinux está bloqueando su escenario, tal vez necesita analizar la causa raíz antes de elegir una reparación.

Prerequisitos

Procedimiento

Additional resources

In most cases, suggestions provided by the sealert tool give you the right guidance about how to fix problems related to the SELinux policy. See Analyzing SELinux denial messages for information how to use sealert to analyze SELinux denials.

Be careful when the tool suggests using the audit2allow tool for configuration changes. You should not use audit2allow to generate a local policy module as your first option when you see an SELinux denial. Troubleshooting should start with a check if there is a labeling problem. The second most often case is that you have changed a process configuration, and you forgot to tell SELinux about it.

Labeling problems

A common cause of labeling problems is when a non-standard directory is used for a service. For example, instead of using /var/www/html/ for a website, an administrator might want to use /srv/myweb/. On Red Hat Enterprise Linux, the /srv directory is labeled with the var_t type. Files and directories created in /srv inherit this type. Also, newly-created objects in top-level directories, such as /myserver, can be labeled with the default_t type. SELinux prevents the Apache HTTP Server (httpd) from accessing both of these types. To allow access, SELinux must know that the files in /srv/myweb/ are to be accessible by httpd:

This semanage command adds the context for the /srv/myweb/ directory and all files and directories under it to the SELinux file-context configuration. The semanage utility does not change the context. As root, use the restorecon utility to apply the changes:

Incorrect Context The matchpathcon utility checks the context of a file path and compares it to the default label for that path. The following example demonstrates the use of matchpathcon on a directory that contains incorrectly labeled files:

In this example, the index.html and page1.html files are labeled with the user_home_t type. This type is used for files in user home directories. Using the mv command to move files from your home directory may result in files being labeled with the user_home_t type. This type should not exist outside of home directories. Use the restorecon utility to restore such files to their correct type:

To restore the context for all files under a directory, use the -R option:

Confined applications configured in non-standard ways

Services can be run in a variety of ways. To account for that, you need to specify how you run your services. You can achieve this through SELinux booleans that allow parts of SELinux policy to be changed at runtime. This enables changes, such as allowing services access to NFS volumes, without reloading or recompiling SELinux policy. Also, running services on non-default port numbers requires policy configuration to be updated using the semanage command.

For example, to allow the Apache HTTP Server to communicate with MariaDB, enable the httpd_can_network_connect_db boolean:

Note that the -P option makes the setting persistent across reboots of the system.

If access is denied for a particular service, use the getsebool and grep utilities to see if any booleans are available to allow access. For example, use the getsebool -a | grep ftp command to search for FTP related booleans:

To get a list of booleans and to find out if they are enabled or disabled, use the getsebool -a command. To get a list of booleans including their meaning, and to find out if they are enabled or disabled, install the selinux-policy-devel package and use the semanage boolean -l command as root.

*Port numbers

Depending on policy configuration, services can only be allowed to run on certain port numbers. Attempting to change the port a service runs on without changing policy may result in the service failing to start. For example, run the semanage port -l | grep http command as root to list http related ports:

The http_port_t port type defines the ports Apache HTTP Server can listen on, which in this case, are TCP ports 80, 443, 488, 8008, 8009, and 8443. If an administrator configures httpd.conf so that httpd listens on port 9876 (Listen 9876), but policy is not updated to reflect this, the following command fails:

An SELinux denial message similar to the following is logged to /var/log/audit/audit.log:

To allow httpd to listen on a port that is not listed for the http_port_t port type, use the semanage port command to assign a different label to the port:

The -a `option adds a new record; the `-t option defines a type; and the -p option defines a protocol. The last argument is the port number to add.

Corner cases, evolving or broken applications, and compromised systems

Applications may contain bugs, causing SELinux to deny access. Also, SELinux rules are evolving – SELinux may not have seen an application running in a certain way, possibly causing it to deny access, even though the application is working as expected. For example, if a new version of PostgreSQL is released, it may perform actions the current policy does not account for, causing access to be denied, even though access should be allowed.

For these situations, after access is denied, use the audit2allow utility to create a custom policy module to allow access. You can report missing rules in the SELinux policy in Red Hat Bugzilla. For Red Hat Enterprise Linux 8, create bugs against the Red Hat Enterprise Linux 8 product, and select the selinux-policy component. Include the output of the audit2allow -w -a and audit2allow -a commands in such bug reports.

If an application asks for major security privileges, it could be a signal that the application is compromised. Use intrusion detection tools to inspect such suspicious behavior.

The Solution Engine on the Red Hat Customer Portal can also provide guidance in the form of an article containing a possible solution for the same or very similar problem you have. Select the relevant product and version and use SELinux-related keywords, such as selinux or avc, together with the name of your blocked service or application, for example: selinux samba.

The Linux Audit system stores log entries in the /var/log/audit/audit.log file by default.

To list only SELinux-related records, use the ausearch command with the message type parameter set to AVC and AVC_USER at a minimum, for example:

An SELinux denial entry in the Audit log file can look as follows:

The most important parts of this entry are:

The previous log entry can be translated to:

SELinux denied the httpd process with PID 6591 and the httpd_t type to read from a directory with the nfs_t type.

The following SELinux denial message occurs when the Apache HTTP Server attempts to access a directory labeled with a type for the Samba suite:

This SELinux denial can be translated to:

SELinux denied the httpd process with PID 2465 to access the /var/www/html/file1 file with the samba_share_t type, which is not accessible to processes running in the httpd_t domain unless configured otherwise.

Additional resources