Re: [syzbot] [net?] general protection fault in qdisc_tree_reduce_backlog

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Subject: Re: [syzbot] [net?] general protection fault in qdisc_tree_reduce_backlog
Author: lizhi.xu@xxxxxxxxxxxxx

#syz test

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index d8a33486c51..7f32347971f 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -803,12 +803,13 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, int n, int len)
 			break;
 		}
 		cops = sch->ops->cl_ops;
-		if (notify && cops->qlen_notify) {
+		if (cops && notify && cops->qlen_notify) {
 			/* Note that qlen_notify must be idempotent as it may get called
 			 * multiple times.
 			 */
 			cl = cops->find(sch, parentid);
-			cops->qlen_notify(sch, cl);
+			if (virt_addr_valid(cl))
+				cops->qlen_notify(sch, cl);
 		}
 		sch->q.qlen -= n;
 		sch->qstats.backlog -= len;