[PATCH 2/2] hijack: update task_alloc_security

[Serge E. Hallyn]

Quoting Crispin Cowan (crispin at crispincowan.com):
> Serge E. Hallyn wrote:
> > Quoting Stephen Smalley (sds at tycho.nsa.gov):
> >   
> >> I agree with this part - we don't want people to have to choose between
> >> using containers and using selinux, so if hijack is going to be a
> >> requirement for effective use of containers, then we need to make them
> >> work together.
> >>     
> > Absolutely, we just need to decide how to properly make it work with
> > selinux.  Maybe we check for
> >
> > 	allow (current_domain):(hijacked_process_domain) hijack
> > 	type_transition hijacked_process_domain \
> > 		vserver_enter_binary_t:process vserver1_hijack_admin_t;
> >   
> Is there to be an LSM hook, so that modules can decide on an arbitrary
> decision of whether to allow a hijack? So that this "do the right
> SELinux" thing can be generalized for all LSMs to do the right thing.

Currently:

	1. the permission is granted through ptrace
	2. the lsm knows a hijack is going in security_task_alloc()
		when task != current

so the lsm has all the information it needs.  But I have no objection
to a separate security_task_hijack() hook if you find the ptrace hook
insufficient.

-serge