8.3 Flask-Related Declarations

     

8.3 Flask - Related Declarations

The flask directory contains several files that are part of the SELinux policy:

security_classes

Specifies the SELinux security classes.

initial_sids

Specifies the initial SIDs.

access_vectors

Specifies the permissions includes in access vectors.

The following subsections explain the syntax of declarations residing in these files. Generally, only SELinux developers should change these declarations. However, administrators may find it helpful to understand these files and the declarations they contain.

8.3.1 Syntax of security_classes

The flask/security_classes file specifies the security classes handled by SELinux. Entries in the file have the syntax shown in Figure 8-10. A class declaration contains only the keyword class and an identifier giving the class name .

Figure 8-10. Flask class declaration

The example policy defines between two and three dozen classes. Here is a typical class declaration:

 class security 

Appendix A summarizes the standard security object classes.

8.3.2 Syntax of initial_sids

The flask/initial_sids file specifies the symbols corresponding to initial SIDs. Entries in the file have the syntax shown in Figure 8-11, consisting of the keyword sid and an identifier naming the SID.

Figure 8-11. Flask initial SID declaration

The sample policy defines a few more than two dozen initial SIDs. A typical SID declaration follows :

 sid kernel 

Don't confuse the flask/initial_sids file and its sid declarations with the sid declarations residing in the initial_sid_contexts file. The former declarations include no security context, whereas the latter declarations do.

8.3.3 Syntax of access_vectors

The flask/access_vectors file specifies the form of SELinux access vectors. Declarations in the flask/access_vectors file have the forms given in Figure 8-12 and 8-13. The common declaration, shown in Figure 8-12, is used to define access vector components common to multiple classes. The sample policy includes several such declarations. A typical common declaration is:

Figure 8-12. Common declaration

 common file {     ioctl     read     write     create     getattr     setattr     lock     relabelfrom     relabelto     append     unlink     link     rename     execute     swapon     quotaon     mounton } 

This declaration specifies the permissions associated with file-like objects.

A second type of declaration, class , specifies the permissions associated with a class. Figure 8-13 shows the related syntax. The sample policy specifies between two and three dozen sets of permissions, one for each class.

Figure 8-13. Access vector declaration

Within a class declaration, permissions can be enumerated directly, inherited from a common declaration, or both. For example, the class filesystem enumerates its permissions:

 class filesystem {     mount     remount     unmount     getattr     relabelfrom     relabelto     transition     associate     quotamod     quotaget } 

The lnk_file class, on the other hand, inherits all its permissions from the common declaration named file :

 class lnk_file inherits file 

The dir class both enumerates and inherits permissions:

 class dir inherits file {     add_name     remove_name     reparent     search     rmdir } 

Appendix B summarizes the operations that appear in SELinux access vectors.