From fb37780ed99b1eeaa5e71845edbe8121365e316b Mon Sep 17 00:00:00 2001 From: Sasha Levin Date: Mon, 3 Feb 2025 16:58:40 -0800 Subject: [PATCH] netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() [ Upstream commit 638ba5089324796c2ee49af10427459c2de35f71 ] qdisc_tree_reduce_backlog() notifies parent qdisc only if child qdisc becomes empty, therefore we need to reduce the backlog of the child qdisc before calling it. Otherwise it would miss the opportunity to call cops->qlen_notify(), in the case of DRR, it resulted in UAF since DRR uses ->qlen_notify() to maintain its active list. Fixes: f8d4bc455047 ("net/sched: netem: account for backlog updates from child qdisc") Cc: Martin Ottens Reported-by: Mingi Cho Signed-off-by: Cong Wang Link: https://patch.msgid.link/20250204005841.223511-4-xiyou.wangcong@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin Gbp-Pq: Topic bugfix/all Gbp-Pq: Name netem-update-sch-q.qlen-before-qdisc_tree_reduce_bac.patch --- net/sched/sch_netem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index f459e34684a..22f5d9421f6 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -739,9 +739,9 @@ deliver: if (err != NET_XMIT_SUCCESS) { if (net_xmit_drop_count(err)) qdisc_qstats_drop(sch); - qdisc_tree_reduce_backlog(sch, 1, pkt_len); sch->qstats.backlog -= pkt_len; sch->q.qlen--; + qdisc_tree_reduce_backlog(sch, 1, pkt_len); } goto tfifo_dequeue; } -- 2.30.2