tree d93e0a4558f3f8f703d5b21bd8ce08fcd79f2dc8
parent 8fd68e02310ed038999ccf777b4a4ea1c4cfc22d
author Cong Wang <cong.wang@bytedance.com> 1738630720 -0800
committer Arnav Kansal <rnv@google.com> 1741213041 -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.

BUG=b/395542329
TEST=presubmit
RELEASE_NOTE=Fixed KCTF-638ba50 in the Linux kernel.

cos-patch: security-high
Fixes: f8d4bc455047 ("net/sched: netem: account for backlog updates from child qdisc")
Cc: Martin Ottens <martin.ottens@fau.de>
Reported-by: Mingi Cho <mincho@theori.io>
Change-Id: Icf659324c3d352aed4152964718714f1c9809900
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/95080
Reviewed-by: Arnav Kansal <rnv@google.com>
Reviewed-by: Kevin Berry <kpberry@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>