cls_fw: use tcf_exts_get_net() before call_rcu()

Hold netns refcnt before call_rcu() and release it after
the tcf_exts_destroy() is done.

Note, on ->destroy() path we have to respect the return value
of tcf_exts_get_net(), on other paths it should always return
true, so we don't need to care.

Cc: Lucas Bates <lucasb@mojatatu.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_fw.c

@@ -122,13 +122,19 @@ static int fw_init(struct tcf_proto *tp)
 	return 0;
 }
 
+static void __fw_delete_filter(struct fw_filter *f)
+{
+	tcf_exts_destroy(&f->exts);
+	tcf_exts_put_net(&f->exts);
+	kfree(f);
+}
+
 static void fw_delete_filter_work(struct work_struct *work)
 {
 	struct fw_filter *f = container_of(work, struct fw_filter, work);
 
 	rtnl_lock();
-	tcf_exts_destroy(&f->exts);
-	kfree(f);
+	__fw_delete_filter(f);
 	rtnl_unlock();
 }
 
@@ -154,7 +160,10 @@ static void fw_destroy(struct tcf_proto *tp)
 			RCU_INIT_POINTER(head->ht[h],
 					 rtnl_dereference(f->next));
 			tcf_unbind_filter(tp, &f->res);
+			if (tcf_exts_get_net(&f->exts))
 				call_rcu(&f->rcu, fw_delete_filter);
+			else
+				__fw_delete_filter(f);
 		}
 	}
 	kfree_rcu(head, rcu);
@@ -179,6 +188,7 @@ static int fw_delete(struct tcf_proto *tp, void *arg, bool *last)
 		if (pfp == f) {
 			RCU_INIT_POINTER(*fp, rtnl_dereference(f->next));
 			tcf_unbind_filter(tp, &f->res);
+			tcf_exts_get_net(&f->exts);
 			call_rcu(&f->rcu, fw_delete_filter);
 			ret = 0;
 			break;
@@ -299,6 +309,7 @@ static int fw_change(struct net *net, struct sk_buff *in_skb,
 		RCU_INIT_POINTER(fnew->next, rtnl_dereference(pfp->next));
 		rcu_assign_pointer(*fp, fnew);
 		tcf_unbind_filter(tp, &f->res);
+		tcf_exts_get_net(&f->exts);
 		call_rcu(&f->rcu, fw_delete_filter);
 
 		*arg = fnew;