net/sched: sch_qfq: Fix null-deref in agg_dequeue

To prevent a potential crash in agg_dequeue (net/sched/sch_qfq.c)
when cl->qdisc->ops->peek(cl->qdisc) returns NULL, we check the return
value before using it, similar to the existing approach in sch_hfsc.c.

To avoid code duplication, the following changes are made:

1. Changed qdisc_warn_nonwc(include/net/pkt_sched.h) into a static
inline function.

2. Moved qdisc_peek_len from net/sched/sch_hfsc.c to
include/net/pkt_sched.h so that sch_qfq can reuse it.

3. Applied qdisc_peek_len in agg_dequeue to avoid crashing.

Signed-off-by: Xiang Mei <xmei5@asu.edu>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Link: https://patch.msgid.link/20250705212143.3982664-1-xmei5@asu.edu
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: n132

include/net/pkt_sched.h

@@ -114,7 +114,6 @@ struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
 					struct netlink_ext_ack *extack);
 void qdisc_put_rtab(struct qdisc_rate_table *tab);
 void qdisc_put_stab(struct qdisc_size_table *tab);
-void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc);
 bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
 		     struct net_device *dev, struct netdev_queue *txq,
 		     spinlock_t *root_lock, bool validate);
@@ -290,4 +289,28 @@ static inline bool tc_qdisc_stats_dump(struct Qdisc *sch,
 	return true;
 }
 
+static inline void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc)
+{
+	if (!(qdisc->flags & TCQ_F_WARN_NONWC)) {
+		pr_warn("%s: %s qdisc %X: is non-work-conserving?\n",
+			txt, qdisc->ops->id, qdisc->handle >> 16);
+		qdisc->flags |= TCQ_F_WARN_NONWC;
+	}
+}
+
+static inline unsigned int qdisc_peek_len(struct Qdisc *sch)
+{
+	struct sk_buff *skb;
+	unsigned int len;
+
+	skb = sch->ops->peek(sch);
+	if (unlikely(skb == NULL)) {
+		qdisc_warn_nonwc("qdisc_peek_len", sch);
+		return 0;
+	}
+	len = qdisc_pkt_len(skb);
+
+	return len;
+}
+
 #endif

net/sched/sch_api.c

@@ -601,16 +601,6 @@ void __qdisc_calculate_pkt_len(struct sk_buff *skb,
 	qdisc_skb_cb(skb)->pkt_len = pkt_len;
 }
 
-void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc)
-{
-	if (!(qdisc->flags & TCQ_F_WARN_NONWC)) {
-		pr_warn("%s: %s qdisc %X: is non-work-conserving?\n",
-			txt, qdisc->ops->id, qdisc->handle >> 16);
-		qdisc->flags |= TCQ_F_WARN_NONWC;
-	}
-}
-EXPORT_SYMBOL(qdisc_warn_nonwc);
-
 static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer)
 {
 	struct qdisc_watchdog *wd = container_of(timer, struct qdisc_watchdog,

net/sched/sch_hfsc.c

@@ -835,22 +835,6 @@ update_vf(struct hfsc_class *cl, unsigned int len, u64 cur_time)
 	}
 }
 
-static unsigned int
-qdisc_peek_len(struct Qdisc *sch)
-{
-	struct sk_buff *skb;
-	unsigned int len;
-
-	skb = sch->ops->peek(sch);
-	if (unlikely(skb == NULL)) {
-		qdisc_warn_nonwc("qdisc_peek_len", sch);
-		return 0;
-	}
-	len = qdisc_pkt_len(skb);
-
-	return len;
-}
-
 static void
 hfsc_adjust_levels(struct hfsc_class *cl)
 {

net/sched/sch_qfq.c

@@ -989,7 +989,7 @@ static struct sk_buff *agg_dequeue(struct qfq_aggregate *agg,
 
 	if (cl->qdisc->q.qlen == 0) /* no more packets, remove from list */
 		list_del_init(&cl->alist);
-	else if (cl->deficit < qdisc_pkt_len(cl->qdisc->ops->peek(cl->qdisc))) {
+	else if (cl->deficit < qdisc_peek_len(cl->qdisc)) {
 		cl->deficit += agg->lmax;
 		list_move_tail(&cl->alist, &agg->active);
 	}