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[209.147.139.51]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7e29f3e52c8sm3436094b3a.10.2025.12.04.17.49.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Dec 2025 17:49:17 -0800 (PST) From: Xiang Mei To: security@kernel.org Cc: netdev@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, Xiang Mei Subject: [PATCH net] net/sched: sch_qfq: Fix NULL deref when deactivating Date: Thu, 4 Dec 2025 18:48:55 -0700 Message-ID: <20251205014855.736723-1-xmei5@asu.edu> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit `qfq_class->leaf_qdisc->q.qlen > 0` does not imply that the class itself is active. Two qfq_class objects may point to the same leaf_qdisc. This happens when: 1. one QFQ qdisc is attached to the dev as the root qdisc, and 2. another QFQ qdisc is temporarily referenced (e.g., via qdisc_get() / qdisc_put()) and is pending to be destroyed, as in function tc_new_tfilter. When packets are enqueued through the root QFQ qdisc, the shared leaf_qdisc->q.qlen increases. At the same time, the second QFQ qdisc triggers qdisc_put and qdisc_destroy: the qdisc enters qfq_reset() with its own q->q.qlen == 0, but its class's leaf qdisc->q.qlen > 0. Therefore, the qfq_reset would wrongly deactivate an inactive aggregate and trigger a null-deref in qfq_deactivate_agg. Fixes: 0545a3037773 ("pkt_sched: QFQ - quick fair queue scheduler") Signed-off-by: Xiang Mei --- net/sched/sch_qfq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c index d920f57dc6d7..f4013b547438 100644 --- a/net/sched/sch_qfq.c +++ b/net/sched/sch_qfq.c @@ -1481,7 +1481,7 @@ static void qfq_reset_qdisc(struct Qdisc *sch) for (i = 0; i < q->clhash.hashsize; i++) { hlist_for_each_entry(cl, &q->clhash.hash[i], common.hnode) { - if (cl->qdisc->q.qlen > 0) + if (cl_is_active(cl)) qfq_deactivate_class(q, cl); qdisc_reset(cl->qdisc); -- 2.43.0