This is a note to let you know that I've just added the patch titled
netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
netem-update-sch-q.qlen-before-qdisc_tree_reduce_bac.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4a766b515be890c900c2c1cd980088a8df8250ac
Author: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Date: Mon Feb 3 16:58:40 2025 -0800
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 <martin.ottens@xxxxxx>
Reported-by: Mingi Cho <mincho@xxxxxxxxx>
Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20250204005841.223511-4-xiyou.wangcong@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 73c952d482752..27bd18c74e858 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -739,9 +739,9 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
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;
}
