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>

1 files changed, 9 insertions, 7 deletions

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index dc37c4ead439..8d5e55d5bed2 100644
--- a/net/sched/sch_qfq.c
+++ b/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;