net sched actions: fix GETing actions

With the batch changes that translated transient actions into
a temporary list lost in the translation was the fact that
tcf_action_destroy() will eventually delete the action from
the permanent location if the refcount is zero.

Example of what broke:
...add a gact action to drop
sudo $TC actions add action drop index 10
...now retrieve it, looks good
sudo $TC actions get action gact index 10
...retrieve it again and find it is gone!
sudo $TC actions get action gact index 10

Fixes: 22dc13c837 ("net_sched: convert tcf_exts from list to pointer array"),
Fixes: 824a7e8863 ("net_sched: remove an unnecessary list_del()")
Fixes: f07fed82ad ("net_sched: remove the leftover cleanup_a()")

Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -592,6 +592,17 @@ err_out:
 	return ERR_PTR(err);
 }
 
+static void cleanup_a(struct list_head *actions, int ovr)
+{
+	struct tc_action *a;
+
+	if (!ovr)
+		return;
+
+	list_for_each_entry(a, actions, list)
+		a->tcfa_refcnt--;
+}
+
 int tcf_action_init(struct net *net, struct nlattr *nla, struct nlattr *est,
 		    char *name, int ovr, int bind, struct list_head *actions)
 {
@@ -611,8 +622,15 @@ int tcf_action_init(struct net *net, struct nlattr *nla, struct nlattr *est,
 			goto err;
 		}
 		act->order = i;
+		if (ovr)
+			act->tcfa_refcnt++;
 		list_add_tail(&act->list, actions);
 	}
+
+	/* Remove the temp refcnt which was necessary to protect against
+	 * destroying an existing action which was being replaced
+	 */
+	cleanup_a(actions, ovr);
 	return 0;
 
 err:
@@ -882,6 +900,8 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 			goto err;
 		}
 		act->order = i;
+		if (event == RTM_GETACTION)
+			act->tcfa_refcnt++;
 		list_add_tail(&act->list, &actions);
 	}