net sched actions: fix refcnt when GETing of action after bind

Demonstrating the issue:

.. add a drop action
$sudo $TC actions add action drop index 10

.. retrieve it
$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 2 bind 0 installed 29 sec used 29 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

... bug 1 above: reference is two.
    Reference is actually 1 but we forget to subtract 1.

... do a GET again and we see the same issue
    try a few times and nothing changes
~$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 2 bind 0 installed 31 sec used 31 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

... lets try to bind the action to a filter..
$ sudo $TC qdisc add dev lo ingress
$ sudo $TC filter add dev lo parent ffff: protocol ip prio 1 \
  u32 match ip dst 127.0.0.1/32 flowid 1:1 action gact index 10

... and now a few GETs:
$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 3 bind 1 installed 204 sec used 204 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 4 bind 1 installed 206 sec used 206 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 5 bind 1 installed 235 sec used 235 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

.... as can be observed the reference count keeps going up.

After the fix

$ sudo $TC actions add action drop index 10
$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 1 bind 0 installed 4 sec used 4 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 1 bind 0 installed 6 sec used 6 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

$ sudo $TC qdisc add dev lo ingress
$ sudo $TC filter add dev lo parent ffff: protocol ip prio 1 \
  u32 match ip dst 127.0.0.1/32 flowid 1:1 action gact index 10

$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 2 bind 1 installed 32 sec used 32 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

$ sudo $TC -s actions get action gact index 10

	action order 1: gact action drop
	 random type none pass val 0
	 index 10 ref 2 bind 1 installed 33 sec used 33 sec
 	Action statistics:
	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0

Fixes: aecc5cef ("net sched actions: fix GETing actions")
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -900,8 +900,6 @@ 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);
 	}
 
@@ -914,6 +912,7 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 		return ret;
 	}
 err:
+	if (event != RTM_GETACTION)
 		tcf_action_destroy(&actions, 0);
 	return ret;
 }