pkt_sched: Fix return value corruption in HTB and TBF.

Based upon a bug report by Josip Rodin.

Packet schedulers should only return NET_XMIT_DROP iff
the packet really was dropped.  If the packet does reach
the device after we return NET_XMIT_DROP then TCP can
crash because it depends upon the enqueue path return
values being accurate.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -577,7 +577,7 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 			sch->qstats.drops++;
 			cl->qstats.drops++;
 		}
-		return NET_XMIT_DROP;
+		return ret;
 	} else {
 		cl->bstats.packets +=
 			skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
@@ -623,7 +623,7 @@ static int htb_requeue(struct sk_buff *skb, struct Qdisc *sch)
 			sch->qstats.drops++;
 			cl->qstats.drops++;
 		}
-		return NET_XMIT_DROP;
+		return ret;
 	} else
 		htb_activate(q, cl);
 

net/sched/sch_tbf.c

@@ -123,15 +123,8 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc* sch)
 	struct tbf_sched_data *q = qdisc_priv(sch);
 	int ret;
 
-	if (qdisc_pkt_len(skb) > q->max_size) {
-		sch->qstats.drops++;
-#ifdef CONFIG_NET_CLS_ACT
-		if (sch->reshape_fail == NULL || sch->reshape_fail(skb, sch))
-#endif
-			kfree_skb(skb);
-
-		return NET_XMIT_DROP;
-	}
+	if (qdisc_pkt_len(skb) > q->max_size)
+		return qdisc_reshape_fail(skb, sch);
 
 	ret = qdisc_enqueue(skb, q->qdisc);
 	if (ret != 0) {