net: sched: fix clsact init error path

Since in qdisc_create, the destroy op is called when init fails, we
don't do cleanup in init and leave it up to destroy.
This fixes use-after-free when trying to put already freed block.

Fixes: 6e40cf2 ("net: sched: use extended variants of block_get/put in ingress and clsact qdiscs")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_api.c

@@ -351,6 +351,8 @@ void tcf_block_put_ext(struct tcf_block *block, struct Qdisc *q,
 {
 	struct tcf_chain *chain;
 
+	if (!block)
+		return;
 	/* Hold a refcnt for all chains, except 0, so that they don't disappear
 	 * while we are iterating.
 	 */
@@ -377,8 +379,6 @@ void tcf_block_put(struct tcf_block *block)
 {
 	struct tcf_block_ext_info ei = {0, };
 
-	if (!block)
-		return;
 	tcf_block_put_ext(block, block->q, &ei);
 }
 

net/sched/sch_ingress.c

@@ -190,18 +190,14 @@ static int clsact_init(struct Qdisc *sch, struct nlattr *opt)
 
 	err = tcf_block_get_ext(&q->egress_block, sch, &q->egress_block_info);
 	if (err)
-		goto err_egress_block_get;
+		return err;
 
 	net_inc_ingress_queue();
 	net_inc_egress_queue();
 
 	sch->flags |= TCQ_F_CPUSTATS;
 
 	return 0;
-
-err_egress_block_get:
-	tcf_block_put_ext(q->ingress_block, sch, &q->ingress_block_info);
-	return err;
 }
 
 static void clsact_destroy(struct Qdisc *sch)