Red Hat Summit6.9. Defining a secure terminal in MLS
The SELinux policy checks the type of the terminal from which a user is connected, and allows running of certain SELinux applications, for example newrole, only from secure terminals. Attempting this from a non-secure terminal produces an error: Error: you are not allowed to change levels on a non secure terminal;.
The /etc/selinux/mls/contexts/securetty_types file defines secure terminals for the Multi-Level Security (MLS) policy.
Default contents of the file:
console_device_t
sysadm_tty_device_t
user_tty_device_t
staff_tty_device_t
auditadm_tty_device_t
secureadm_tty_device_tAdding terminal types to the list of secure terminals can expose your system to security risks.
Prerequisites
-
SELinux policy is set to
mls. - You are connected from an already secure terminal, or SELinux is in permissive mode.
You have security administration rights, which means that you are assigned to either:
-
The
secadm_rrole. -
If the
sysadm_secadmmodule is enabled, to thesysadm_rrole. Thesysadm_secadmmodule is enabled by default.
-
The
-
The
policycoreutils-python-utilspackage is installed.
Procedure
Determine the current terminal type:
# ls -Z `tty` root:object_r:user_devpts_t:s0 /dev/pts/0In this example output,
user_devpts_tis the current terminal type.-
Add the relevant SELinux type on a new line in the
/etc/selinux/mls/contexts/securetty_typesfile. Optional: Switch SELinux to enforcing mode:
# setenforce 1
Verification
-
Log in from the previously insecure terminal you have added to the
/etc/selinux/mls/contexts/securetty_typesfile.
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