Cambiando los estados y modos de SELinux

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Permanent changes in SELinux states and modes

As discussed in Introduction to SELinux, SELinux can be enabled or disabled. When enabled, SELinux has two modes: enforcing and permissive.

Use the getenforce or sestatus commands to check in which mode SELinux is running. The getenforce command returns Enforcing, Permissive, or Disabled.

The sestatus command returns the SELinux status and the SELinux policy being used:

~]$ sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Memory protection checking:     actual (secure)
Max kernel policy version:      31

When systems run SELinux in permissive mode, users and processes can label various file-system objects incorrectly. File-system objects created while SELinux is disabled are not labeled at all. This behavior causes problems when changing to enforcing mode because SELinux relies on correct labels of file-system objects.

To prevent incorrectly labeled and unlabeled files from causing problems, file systems are automatically relabeled when changing from the disabled state to permissive or enforcing mode. In permissive mode, use the fixfiles -F onboot command as root to create /.autorelabel file containing the -F option to ensure that files are relabeled upon next reboot.

Habilitando SELinux

Cuando está habilitado, SELinux puede correr en uno de estos dos modos: hacer cumplir o permisiv. Las siguientes secciones muestran como cambiar permanentemente entre estos modos.

Mientras habilita SELinux sobre sistemas que previamente lo tenían deshabilitado, para evitar problemas como sistemas que sean incapaces de arrancar o fallos en procesos, siga este procedimiento.

Requisitos previos

  • Están instalados los paquetes selinux-policy-targeted, selinux-policy, libselinux-utils y grubby. Para comprobar que un paquete concreto está instalado:

    $ rpm -q package_name
Procedimiento

  1. Si su sistema tiene SELinux deshabilitado a nivel de kernel (esta es la manera recomendada, vea [selinux-deshabilitado-selinux]), cambie esto primero. Compruebe si tiene la opción selinux=0 en la línea de comando de kernel:

    $ cat /proc/cmdline
BOOT_IMAGE=... ... selinux=0

    1. Quite la opción selinux=0 de la configuración del cargador de arranque usando grubby:

      $ sudo grubby --update-kernel ALL --remove-args selinux

    2. The change applies after you restart the system in one of the following steps.

  2. Ensure the file system is relabeled on the next boot:

    $ sudo fixfiles onboot

  3. Enable SELinux in permissive mode. For more information, see Changing to permissive mode.

  4. Restart your system:

    $ reboot

  5. Check for SELinux denial messages.

    $ sudo ausearch -m AVC,USER_AVC,SELINUX_ERR,USER_SELINUX_ERR -ts recent

  6. If there are no denials, switch to enforcing mode. For more information, see Cambiando el modo de aplicación.

To run custom applications with SELinux in enforcing mode, choose one of the following scenarios:

Changing to permissive mode

Use the following procedure to permanently change SELinux mode to permissive. When SELinux is running in permissive mode, SELinux policy is not enforced. The system remains operational and SELinux does not deny any operations but only logs AVC messages, which can be then used for troubleshooting, debugging, and SELinux policy improvements. Each AVC is logged only once in this case.

Prerequisites

  • The selinux-policy-targeted, libselinux-utils, and policycoreutils packages are installed on your system.

  • The selinux=0 or enforcing=0 kernel parameters are not used.

Procedimiento

  1. Open the /etc/selinux/config file in a text editor of your choice, for example:

# vi /etc/selinux/config

  1. Configure the SELINUX=permissive option:

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - No SELinux policy is loaded.
SELINUX=*permissive*
# SELINUXTYPE= can take one of these two values:
#       targeted - Targeted processes are protected,
#       mls - Multi Level Security protection.
SELINUXTYPE=targeted

  1. Restart the system:

    # reboot

Cambiando el modo de aplicación

Use the following procedure to switch SELinux to enforcing mode. When SELinux is running in enforcing mode, it enforces the SELinux policy and denies access based on SELinux policy rules. In Fedora, enforcing mode is enabled by default when the system was initially installed with SELinux.

Prerequisites

  • The selinux-policy-targeted, libselinux-utils, and policycoreutils packages are installed on your system.

  • The selinux=0 or enforcing=0 kernel parameters are not used.

Procedimiento

  1. Open the /etc/selinux/config file in a text editor of your choice, for example:

# vi /etc/selinux/config

  1. Configure the SELINUX=enforcing option:

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - No SELinux policy is loaded.
SELINUX=enforcing
# SELINUXTYPE= can take one of these two values:
#       targeted - Targeted processes are protected,
#       mls - Multi Level Security protection.
SELINUXTYPE=targeted

  1. Save the change, and restart the system:

    # reboot

    On the next boot, SELinux relabels all the files and directories within the system and adds SELinux context for files and directories that were created when SELinux was disabled.

Verification

  1. After the system restarts, confirm that the getenforce command returns Enforcing:

$ getenforce
Enforcing

After changing to enforcing mode, SELinux may deny some actions because of incorrect or missing SELinux policy rules. To view what actions SELinux denies, enter the following command as root:

# ausearch -m AVC,USER_AVC,SELINUX_ERR,USER_SELINUX_ERR -ts today

Alternatively, with the setroubleshoot-server package installed, enter:

# grep "SELinux is preventing" /var/log/messages

Standard users can use the GUI setroubleshoot to file bugs directly to Bugzilla.

If SELinux is active and the Audit daemon (auditd) is not running on your system, then search for certain SELinux messages in the output of the dmesg command:

# dmesg | grep -i -e type=1300 -e type=1400

If SELinux denies some actions, see the Troubleshooting problems related to SELinux chapter in the RHEL 8 Using SELinux document for information about troubleshooting.

Disabling SELinux

Use the following procedure to permanently disable SELinux.

When SELinux is disabled, SELinux policy is not loaded at all; it is not enforced and AVC messages are not logged. Therefore, all benefits of running SELinux listed in Benefits of SELinux are lost.

It is recommended to use permissive mode instead of permanently disabling SELinux. See Changing to permissive mode for more information about permissive mode.

Disabling SELinux using the SELINUX=disabled option in the /etc/selinux/config results in a process in which the kernel boots with SELinux enabled and switches to disabled mode later in the boot process. Because memory leaks and race conditions causing kernel panics can occur, prefer disabling SELinux by adding the selinux=0 parameter to the kernel command line as described in Changing SELinux modes at boot time if your scenario really requires to completely disable SELinux.

Requisitos previos

  • The grubby package is installed:

    $ rpm -q grubby
grubby-version
Procedimiento

  1. Open the /etc/selinux/config file in a text editor of your choice, for example:

    # vi /etc/selinux/config

  2. Configure the SELINUX=disabled option:

    # This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - No SELinux policy is loaded.
SELINUX=disabled
# SELINUXTYPE= can take one of these two values:
#       targeted - Targeted processes are protected,
#       mls - Multi Level Security protection.
SELINUXTYPE=targeted

  3. Save the change, and restart your system:

# reboot
Verification

  • After reboot, confirm that the getenforce command returns Disabled:

    $ getenforce
Disabled

Changing SELinux Modes at Boot Time

On boot, you can set several kernel parameters to change the way SELinux runs:

enforcing=0

Setting this parameter causes the system to start in permissive mode, which is useful when troubleshooting issues. Using permissive mode might be the only option to detect a problem if your file system is too corrupted. Moreover, in permissive mode, the system continues to create the labels correctly. The AVC messages that are created in this mode can be different than in enforcing mode.

In permissive mode, only the first denial from a series of the same denials is reported. However, in enforcing mode, you might get a denial related to reading a directory, and an application stops. In permissive mode, you get the same AVC message, but the application continues reading files in the directory and you get an AVC for each denial in addition.

selinux=0

This parameter causes the kernel to not load any part of the SELinux infrastructure. The init scripts notice that the system booted with the selinux=0 parameter and touch the /.autorelabel file. This causes the system to automatically relabel the next time you boot with SELinux enabled.

Using the selinux=0 parameter is not recommended. To debug your system, prefer using permissive mode.
autorelabel=1

This parameter forces the system to relabel similarly to the following commands:

# touch /.autorelabel
# reboot

If a file system contains a large amount of mislabeled objects, start the system in permissive mode to make the autorelabel process successful.

For additional SELinux-related kernel boot parameters, such as checkreqprot, see the kernel-parameters.txt file. This file is available in the source package of your Linux kernel (.src.rpm). To download the source package containing the currently used kernel:

~]# dnf download --source kernel

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