guest_u is an SELinux User defined in the SELinux policy. SELinux users have default roles, guest_r. The default role has a default type, guest_t, associated with it.
The SELinux user will usually login to a system with a context that looks like:
Linux users are automatically assigned an SELinux users at login. Login programs use the SELinux User to assign initial context to the user's shell.
SELinux policy uses the context to control the user's access.
By default all users are assigned to the SELinux user via the __default__ flag
On Targeted policy systems the __default__ user is assigned to the unconfined_u SELinux user.
You can list all Linux User to SELinux user mapping using:
semanage login -l
If you wanted to change the default user mapping to use the guest_u user, you would execute:
semanage login -m -s guest_u __default__
If you want to map the one Linux user (joe) to the SELinux user guest, you would execute:
$ semanage login -a -s guest_u joe
The SELinux user guest_u is defined in policy as a unprivileged user. SELinux prevents unprivileged users from doing administration tasks without transitioning to a different role.
The SELinux user guest_u is not able to X Windows login.
If you want to deny user domains applications to map a memory region as both executable and writable, this is dangerous and the executable should be reported in bugzilla, you must turn on the deny_execmem boolean. Disabled by default.
setsebool -P deny_execmem 1
If you want to allow all domains to execute in fips_mode, you must turn on the fips_mode boolean. Enabled by default.
setsebool -P fips_mode 1
If you want to allow httpd cgi support, you must turn on the httpd_enable_cgi boolean. Enabled by default.
setsebool -P httpd_enable_cgi 1
If you want to allow confined applications to run with kerberos, you must turn on the kerberos_enabled boolean. Enabled by default.
setsebool -P kerberos_enabled 1
If you want to allow unconfined executables to make their stack executable. This should never, ever be necessary. Probably indicates a badly coded executable, but could indicate an attack. This executable should be reported in bugzilla, you must turn on the selinuxuser_execstack boolean. Enabled by default.
setsebool -P selinuxuser_execstack 1
If you want to allow user to use ssh chroot environment, you must turn on the selinuxuser_use_ssh_chroot boolean. Disabled by default.
setsebool -P selinuxuser_use_ssh_chroot 1
If you want to support NFS home directories, you must turn on the use_nfs_home_dirs boolean. Disabled by default.
setsebool -P use_nfs_home_dirs 1
If you want to support SAMBA home directories, you must turn on the use_samba_home_dirs boolean. Disabled by default.
setsebool -P use_samba_home_dirs 1
The SELinux user guest_u is able execute home content files.
Three things can happen when guest_t attempts to execute a program.
1. SELinux Policy can deny guest_t from executing the program.
Execute the following to see the types that the SELinux user guest_t can execute without transitioning:
sesearch -A -s guest_t -c file -p execute_no_trans
Execute the following to see the types that the SELinux user guest_t can execute and transition:
$ sesearch -A -s guest_t -c process -p transition
The SELinux process type guest_t can manage files labeled with the following file types. The paths listed are the default paths for these file types. Note the processes UID still need to have DAC permissions.
all user home files
all user tmp files
semanage permissive can also be used to manipulate whether or not a process type is permissive.
semanage module can also be used to enable/disable/install/remove policy modules.
semanage boolean can also be used to manipulate the booleans
system-config-selinux is a GUI tool available to customize SELinux policy settings.