sch_tbf: Fix potential memory leak in tbf_change().

The allocated child qdisc is not freed in error conditions.
Defer the allocation after user configuration turns out to be
valid and acceptable.

Fixes: cc106e44 ("net: sched: tbf: fix the calculation of max_size")
Signed-off-by: NHiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_tbf.c

@@ -334,18 +334,6 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
 			qdisc_put_rtab(qdisc_get_rtab(&qopt->peakrate,
 						      tb[TCA_TBF_PTAB]));
 
-	if (q->qdisc != &noop_qdisc) {
-		err = fifo_set_limit(q->qdisc, qopt->limit);
-		if (err)
-			goto done;
-	} else if (qopt->limit > 0) {
-		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
-		if (IS_ERR(child)) {
-			err = PTR_ERR(child);
-			goto done;
-		}
-	}
-
 	buffer = min_t(u64, PSCHED_TICKS2NS(qopt->buffer), ~0U);
 	mtu = min_t(u64, PSCHED_TICKS2NS(qopt->mtu), ~0U);
 
@@ -390,6 +378,18 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
 		goto done;
 	}
 
+	if (q->qdisc != &noop_qdisc) {
+		err = fifo_set_limit(q->qdisc, qopt->limit);
+		if (err)
+			goto done;
+	} else if (qopt->limit > 0) {
+		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
+		if (IS_ERR(child)) {
+			err = PTR_ERR(child);
+			goto done;
+		}
+	}
+
 	sch_tree_lock(sch);
 	if (child) {
 		qdisc_tree_decrease_qlen(q->qdisc, q->qdisc->q.qlen);