sched: Avoid dereferencing skb pointer after child enqueue

Parent qdiscs may dereference the pointer to the enqueued skb after
enqueue. However, both CAKE and TBF call consume_skb() on the original skb
when splitting GSO packets, leading to a potential use-after-free in the
parent. Fix this by avoiding dereferencing the skb pointer after enqueueing
to the child.
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_cbs.c

@@ -88,13 +88,14 @@ static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			     struct Qdisc *child,
 			     struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb);
 	int err;
 
 	err = child->ops->enqueue(skb, child, to_free);
 	if (err != NET_XMIT_SUCCESS)
 		return err;
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 
 	return NET_XMIT_SUCCESS;

net/sched/sch_drr.c

@@ -350,6 +350,7 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
 static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		       struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb);
 	struct drr_sched *q = qdisc_priv(sch);
 	struct drr_class *cl;
 	int err = 0;
@@ -376,7 +377,7 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		cl->deficit = cl->quantum;
 	}
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 	return err;
 }

net/sched/sch_dsmark.c

@@ -199,6 +199,7 @@ static struct tcf_block *dsmark_tcf_block(struct Qdisc *sch, unsigned long cl,
 static int dsmark_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			  struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb);
 	struct dsmark_qdisc_data *p = qdisc_priv(sch);
 	int err;
 
@@ -271,7 +272,7 @@ static int dsmark_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 
 	return NET_XMIT_SUCCESS;

net/sched/sch_hfsc.c

@@ -1539,6 +1539,7 @@ hfsc_dump_qdisc(struct Qdisc *sch, struct sk_buff *skb)
 static int
 hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb);
 	struct hfsc_class *cl;
 	int uninitialized_var(err);
 
@@ -1560,8 +1561,6 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 	}
 
 	if (cl->qdisc->q.qlen == 1) {
-		unsigned int len = qdisc_pkt_len(skb);
-
 		if (cl->cl_flags & HFSC_RSC)
 			init_ed(cl, len);
 		if (cl->cl_flags & HFSC_FSC)
@@ -1576,7 +1575,7 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 
 	}
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 
 	return NET_XMIT_SUCCESS;

net/sched/sch_htb.c

@@ -581,6 +581,7 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		       struct sk_buff **to_free)
 {
 	int uninitialized_var(ret);
+	unsigned int len = qdisc_pkt_len(skb);
 	struct htb_sched *q = qdisc_priv(sch);
 	struct htb_class *cl = htb_classify(skb, sch, &ret);
 
@@ -610,7 +611,7 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		htb_activate(q, cl);
 	}
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 	return NET_XMIT_SUCCESS;
 }

net/sched/sch_prio.c

@@ -72,6 +72,7 @@ prio_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
 static int
 prio_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb);
 	struct Qdisc *qdisc;
 	int ret;
 
@@ -88,7 +89,7 @@ prio_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 
 	ret = qdisc_enqueue(skb, qdisc, to_free);
 	if (ret == NET_XMIT_SUCCESS) {
-		qdisc_qstats_backlog_inc(sch, skb);
+		sch->qstats.backlog += len;
 		sch->q.qlen++;
 		return NET_XMIT_SUCCESS;
 	}

net/sched/sch_qfq.c

@@ -1210,6 +1210,7 @@ static struct qfq_aggregate *qfq_choose_next_agg(struct qfq_sched *q)
 static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		       struct sk_buff **to_free)
 {
+	unsigned int len = qdisc_pkt_len(skb), gso_segs;
 	struct qfq_sched *q = qdisc_priv(sch);
 	struct qfq_class *cl;
 	struct qfq_aggregate *agg;
@@ -1224,17 +1225,17 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	}
 	pr_debug("qfq_enqueue: cl = %x\n", cl->common.classid);
 
-	if (unlikely(cl->agg->lmax < qdisc_pkt_len(skb))) {
+	if (unlikely(cl->agg->lmax < len)) {
 		pr_debug("qfq: increasing maxpkt from %u to %u for class %u",
-			 cl->agg->lmax, qdisc_pkt_len(skb), cl->common.classid);
-		err = qfq_change_agg(sch, cl, cl->agg->class_weight,
-				     qdisc_pkt_len(skb));
+			 cl->agg->lmax, len, cl->common.classid);
+		err = qfq_change_agg(sch, cl, cl->agg->class_weight, len);
 		if (err) {
 			cl->qstats.drops++;
 			return qdisc_drop(skb, sch, to_free);
 		}
 	}
 
+	gso_segs = skb_is_gso(skb) ? skb_shinfo(skb)->gso_segs : 1;
 	err = qdisc_enqueue(skb, cl->qdisc, to_free);
 	if (unlikely(err != NET_XMIT_SUCCESS)) {
 		pr_debug("qfq_enqueue: enqueue failed %d\n", err);
@@ -1245,8 +1246,9 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return err;
 	}
 
-	bstats_update(&cl->bstats, skb);
-	qdisc_qstats_backlog_inc(sch, skb);
+	cl->bstats.bytes += len;
+	cl->bstats.packets += gso_segs;
+	sch->qstats.backlog += len;
 	++sch->q.qlen;
 
 	agg = cl->agg;
@@ -1254,7 +1256,7 @@ static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	if (cl->qdisc->q.qlen != 1) {
 		if (unlikely(skb == cl->qdisc->ops->peek(cl->qdisc)) &&
 		    list_first_entry(&agg->active, struct qfq_class, alist)
-		    == cl && cl->deficit < qdisc_pkt_len(skb))
+		    == cl && cl->deficit < len)
 			list_move_tail(&cl->alist, &agg->active);
 
 		return err;

net/sched/sch_tbf.c

@@ -185,6 +185,7 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		       struct sk_buff **to_free)
 {
 	struct tbf_sched_data *q = qdisc_priv(sch);
+	unsigned int len = qdisc_pkt_len(skb);
 	int ret;
 
 	if (qdisc_pkt_len(skb) > q->max_size) {
@@ -200,7 +201,7 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return ret;
 	}
 
-	qdisc_qstats_backlog_inc(sch, skb);
+	sch->qstats.backlog += len;
 	sch->q.qlen++;
 	return NET_XMIT_SUCCESS;
 }