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netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()

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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: f8d4bc4550 ("net/sched: netem: account for backlog updates from child qdisc")
Cc: Martin Ottens <martin.ottens@fau.de>
Reported-by: Mingi Cho <mincho@theori.io>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Link: https://patch.msgid.link/20250204005841.223511-4-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Cong Wang 2025-02-03 16:58:40 -08:00 • committed by Jakub Kicinski
parent 3fe5648d1d
commit 638ba50893
1 changed files with 1 additions and 1 deletions
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2
net/sched/sch_netem.c
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@ -749,9 +749,9 @@ 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;
}