10.3.2. Unconfined Processes

⁠10.3.2. Unconfined Processes

Unconfined processes run in unconfined domains, for example, init programs run in the unconfined initrc_t domain, unconfined kernel processes run in the kernel_t domain, and unconfined Linux users run in the unconfined_t domain. For unconfined processes, SELinux policy rules are applied, but policy rules exist that allow processes running in unconfined domains almost all access. Processes running in unconfined domains fall back to using DAC rules exclusively. If an unconfined process is compromised, SELinux does not prevent an attacker from gaining access to system resources and data, but of course, DAC rules are still used. SELinux is a security enhancement on top of DAC rules – it does not replace them.

To ensure that SELinux is enabled and the system is prepared to perform the following example, complete the Procedure 10.3, “How to Verify SELinux Status” described in Section 10.3.1, “Confined Processes”.

The following example demonstrates how the Apache HTTP Server (httpd) can access data intended for use by Samba, when running unconfined. Note that in Fedora, the httpd process runs in the confined httpd_t domain by default. This is an example, and should not be used in production. It assumes that the httpd, wget, dbus and audit packages are installed, that the SELinux targeted policy is used, and that SELinux is running in enforcing mode.

⁠

Procedure 10.5. An Example of Unconfined Process

The chcon command relabels files; however, such label changes do not survive when the file system is relabeled. For permanent changes that survive a file system relabel, use the semanage utility, which is discussed later. As the root user, run the following command to change the type to a type used by Samba:
```
~]# chcon -t samba_share_t /var/www/html/testfile
```
View the changes:
```
~]$ ls -Z /var/www/html/testfile
-rw-r--r--  root root unconfined_u:object_r:samba_share_t:s0 /var/www/html/testfile
```

Run the following command to confirm that the httpd process is not running:

~]$ systemctl status httpd.service
httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled)
   Active: inactive (dead)

If the output differs, run the following command as root to stop the httpd process:

~]# systemctl stop httpd.service

To make the httpd process run unconfined, run the following command as root to change the type of the /usr/sbin/httpd file, to a type that does not transition to a confined domain:
```
~]# chcon -t unconfined_exec_t /usr/sbin/httpd
```

Confirm that /usr/sbin/httpd is labeled with the unconfined_exec_t type:

~]$ ls -Z /usr/sbin/httpd
-rwxr-xr-x  root root system_u:object_r:unconfined_exec_t:s0 /usr/sbin/httpd

As root, start the httpd process and confirm, that it started successfully:

~]# systemctl start httpd.service

~]# systemctl status httpd.service
httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled)
   Active: active (running) since Thu 2013-08-15 11:17:01 CEST; 5s ago

Run the following command to view httpd running in the unconfined_t domain:

~]$ ps -eZ | grep httpd
unconfined_u:unconfined_r:unconfined_t:s0 7721 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7723 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7724 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7725 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7726 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7727 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7728 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7729 ?      00:00:00 httpd
unconfined_u:unconfined_r:unconfined_t:s0 7730 ?      00:00:00 httpd

Change into a directory where your Linux user has write access to, and run the following command. Unless there are changes to the default configuration, this command succeeds:
```
~]$ wget http://localhost/testfile
--2009-05-07 01:41:10--  http://localhost/testfile
Resolving localhost... 127.0.0.1
Connecting to localhost|127.0.0.1|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 0 [text/plain]
Saving to: `testfile.1'

[ <=>                            ]--.-K/s   in 0s      
	
2009-05-07 01:41:10 (0.00 B/s) - `testfile.1' saved [0/0]
```
Although the httpd process does not have access to files labeled with the samba_share_t type, httpd is running in the unconfined unconfined_t domain, and falls back to using DAC rules, and as such, the wget command succeeds. Had httpd been running in the confined httpd_t domain, the wget command would have failed.

The restorecon utility restores the default SELinux context for files. As root, run the following command to restore the default SELinux context for /usr/sbin/httpd:

~]# restorecon -v /usr/sbin/httpd
restorecon reset /usr/sbin/httpd context system_u:object_r:unconfined_exec_t:s0->system_u:object_r:httpd_exec_t:s0

Confirm that /usr/sbin/httpd is labeled with the httpd_exec_t type:

~]$ ls -Z /usr/sbin/httpd
-rwxr-xr-x  root root system_u:object_r:httpd_exec_t:s0 /usr/sbin/httpd

As root, run the following command to restart httpd. After restarting, confirm that httpd is running in the confined httpd_t domain:

~]# systemctl restart httpd.service

~]$ ps -eZ | grep httpd
system_u:system_r:httpd_t:s0    8883 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8884 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8885 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8886 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8887 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8888 ?        00:00:00 httpd
system_u:system_r:httpd_t:s0    8889 ?        00:00:00 httpd

As root, remove testfile:

~]# rm -i /var/www/html/testfile
rm: remove regular empty file `/var/www/html/testfile'? y

If you do not require httpd to be running, as root, run the following command to stop httpd:
```
~]# systemctl stop httpd.service
```

The examples in these sections demonstrate how data can be protected from a compromised confined-process (protected by SELinux), as well as how data is more accessible to an attacker from a compromised unconfined-process (not protected by SELinux).