tree 7ce892202d84a69f94fdc77e2310f003514c3cbd
parent 47f55eb971f2b58e913d143165ffe299998de2b7
author Cong Wang <xiyou.wangcong@gmail.com> 1744915650 -0700
committer Anil Altinay <aaltinay@google.com> 1746487216 -0700

net_sched: hfsc: Fix a UAF vulnerability in class handling

[ Upstream commit 3df275ef0a6ae181e8428a6589ef5d5231e58b5c ]

This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class
handling. The issue occurs due to a time-of-check/time-of-use condition
in hfsc_change_class() when working with certain child qdiscs like netem
or codel.

The vulnerability works as follows:
1. hfsc_change_class() checks if a class has packets (q.qlen != 0)
2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,
   codel, netem) might drop packets and empty the queue
3. The code continues assuming the queue is still non-empty, adding
   the class to vttree
4. This breaks HFSC scheduler assumptions that only non-empty classes
   are in vttree
5. Later, when the class is destroyed, this can lead to a Use-After-Free

The fix adds a second queue length check after qdisc_peek_len() to verify
the queue wasn't emptied.

BUG=b/414270820
TEST=presubmit
RELEASE_NOTE=Fixed KCTF-3df275e in the Linux kernel.

cos-patch: security-high
Fixes: 21f4d5cc25ec ("net_sched/hfsc: fix curve activation in hfsc_change_class()")
Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Reviewed-by: Konstantin Khlebnikov <koct9i@gmail.com>
Change-Id: I9648147616a25ce9630773ab9b897896e47053f5
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20250417184732.943057-2-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/+/101581
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Michael Kochera <kochera@google.com>
Reviewed-by: Anil Altinay <aaltinay@google.com>