smack: differentiate between subjective and objective task credentials

With the split of the security_task_getsecid() into subjective and
objective variants it's time to update Smack to ensure it is using
the correct task creds.

Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/smack/smack.h

@@ -383,7 +383,23 @@ static inline struct smack_known *smk_of_task(const struct task_smack *tsp)
 	return tsp->smk_task;
 }
 
-static inline struct smack_known *smk_of_task_struct(
+static inline struct smack_known *smk_of_task_struct_subj(
+						const struct task_struct *t)
+{
+	struct smack_known *skp;
+	const struct cred *cred;
+
+	rcu_read_lock();
+
+	cred = rcu_dereference(t->cred);
+	skp = smk_of_task(smack_cred(cred));
+
+	rcu_read_unlock();
+
+	return skp;
+}
+
+static inline struct smack_known *smk_of_task_struct_obj(
 						const struct task_struct *t)
 {
 	struct smack_known *skp;