label transitions

[Giorgio Zanin <giorgio.zanin@inwind.it>]

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I'm now investigating the mechanism used in SELinux to change 
something's security label.
I know there is a kernel interface and a system call for applications  
to do it, their name is security_transition_sid.

The configuration language has two constructs: type_transition and 
type_change. The first is used by the kernel and instructs the security 
server to return a particular label for a type pair and a class when the 
security_transition_sid is called to label a new object or a transformed 
process.

If type_transition is used to label a transformed process, it requires 
the transition permission of the class process.
What about type_transition for files? I mean I had a look at 
file_trans_macro and it seems it's not specified anything like the 
transition process permission to change the type of a file. How can I 
control the privilege to change the type of a new object?

Is it correct to argue that permissions relabelto, relabelfrom and 
transition of file class are used to grant applications the ability to 
change labels with a call to security_transition_sid (with the output 
label specified via type_change)?

Thanks in advance for your nth answer ;)

Giorgio