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4.13. File Name Transition

The file name transition feature allows policy writers to specify the file name when writing policy transition rules. It is possible to write a rule that states: If a process labeled A_t creates a specified object class in a directory labeled B_t and the specified object class is named objectname, it gets the label C_t. This mechanism provides more fine-grained control over processes on the system.
Without file name transition, there are three possible ways how to label an object:
The file name transition feature decreases problems related to incorrect labeling and improves the system to be more secure. Policy writers are able to state properly that a certain application can only create a file with a specified name in a specified directory. The rules take into account the file name, not the file path. This is the basename of the file path. Note that file name transition uses an exact match done by the strcmp() function. Use of regular expressions or wildcard characters is not considered.

Note

File paths can vary in the kernel and file name transition does not use the paths to determine labels. Consequently, this feature only affects initial file creation and does not fix incorrect labels of already created objects.
Example 4.1. Examples of Policy Rules Written with File Name Transition
The example below shows a policy rule with file name transition:
filetrans_pattern(unconfined_t, admin_home_t, ssh_home_t, dir, ".ssh")
This rule states that if a process with the unconfined_t type creates the ~/.ssh/ directory in a directory labeled admin_home_t, the ~/.ssh/ directory gets the label ssh_home_t.
Similar examples of policy rules written with file name transition are presented below:
filetrans_pattern(staff_t, user_home_dir_t, httpd_user_content_t, dir, "public_html")
filetrans_pattern(thumb_t, user_home_dir_t, thumb_home_t, file, "missfont.log")
filetrans_pattern(kernel_t, device_t, xserver_misc_device_t, chr_file, "nvidia0")
filetrans_pattern(puppet_t, etc_t, krb5_conf_t, file, "krb5.conf")

Note

The file name transition feature affects mainly policy writers, but users can notice that instead of file objects almost always created with the default label of the containing directory, some file objects have a different label as specified in policy.