lsm: security_task_getsecid_subj() -> security_current_getsecid_subj()

The security_task_getsecid_subj() LSM hook invites misuse by allowing
callers to specify a task even though the hook is only safe when the
current task is referenced.  Fix this by removing the task_struct
argument to the hook, requiring LSM implementations to use the
current task.  While we are changing the hook declaration we also
rename the function to security_current_getsecid_subj() in an effort
to reinforce that the hook captures the subjective credentials of the
current task and not an arbitrary task on the system.

Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/security/security.c b/security/security.c
index c88167a..edb922b8 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1808,12 +1808,12 @@ int security_task_getsid(struct task_struct *p)
 	return call_int_hook(task_getsid, 0, p);
 }
 
-void security_task_getsecid_subj(struct task_struct *p, u32 *secid)
+void security_current_getsecid_subj(u32 *secid)
 {
 	*secid = 0;
-	call_void_hook(task_getsecid_subj, p, secid);
+	call_void_hook(current_getsecid_subj, secid);
 }
-EXPORT_SYMBOL(security_task_getsecid_subj);
+EXPORT_SYMBOL(security_current_getsecid_subj);
 
 void security_task_getsecid_obj(struct task_struct *p, u32 *secid)
 {