From: Jamal Hadi Salim <jhs@mojatatu.com> mainline inclusion from mainline-v6.19-rc7 commit 50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13607 CVE: CVE-2026-23074 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Design intent of teql is that it is only supposed to be used as root qdisc. We need to check for that constraint. Although not important, I will describe the scenario that unearthed this issue for the curious. GangMin Kim <km.kim1503@gmail.com> managed to concot a scenario as follows: ROOT qdisc 1:0 (QFQ) ├── class 1:1 (weight=15, lmax=16384) netem with delay 6.4s └── class 1:2 (weight=1, lmax=1514) teql GangMin sends a packet which is enqueued to 1:1 (netem). Any invocation of dequeue by QFQ from this class will not return a packet until after 6.4s. In the meantime, a second packet is sent and it lands on 1:2. teql's enqueue will return success and this will activate class 1:2. Main issue is that teql only updates the parent visible qlen (sch->q.qlen) at dequeue. Since QFQ will only call dequeue if peek succeeds (and teql's peek always returns NULL), dequeue will never be called and thus the qlen will remain as 0. With that in mind, when GangMin updates 1:2's lmax value, the qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc's qlen was not incremented, qfq fails to deactivate the class, but still frees its pointers from the aggregate. So when the first packet is rescheduled after 6.4 seconds (netem's delay), a dangling pointer is accessed causing GangMin's causing a UAF. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: GangMin Kim <km.kim1503@gmail.com> Tested-by: Victor Nogueira <victor@mojatatu.com> Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com> Link: https://patch.msgid.link/20260114160243.913069-2-jhs@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> --- net/sched/sch_teql.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/sched/sch_teql.c b/net/sched/sch_teql.c index 163364124691..18d219546cc2 100644 --- a/net/sched/sch_teql.c +++ b/net/sched/sch_teql.c @@ -183,6 +183,11 @@ static int teql_qdisc_init(struct Qdisc *sch, struct nlattr *opt, if (m->dev == dev) return -ELOOP; + if (sch->parent != TC_H_ROOT) { + NL_SET_ERR_MSG_MOD(extack, "teql can only be used as root"); + return -EOPNOTSUPP; + } + q->m = m; skb_queue_head_init(&q->q); -- 2.43.0