[SRU][N/P][PATCH 2/2] net/sched: sch_qfq: Avoid triggering might_sleep in atomic context in qfq_delete_class

[Tim Whisonant]

From: Xiang Mei <xmei5 at asu.edu>

might_sleep could be trigger in the atomic context in qfq_delete_class.

qfq_destroy_class was moved into atomic context locked
by sch_tree_lock to avoid a race condition bug on
qfq_aggregate. However, might_sleep could be triggered by
qfq_destroy_class, which introduced sleeping in atomic context (path:
qfq_destroy_class->qdisc_put->__qdisc_destroy->lockdep_unregister_key
->might_sleep).

Considering the race is on the qfq_aggregate objects, keeping
qfq_rm_from_agg in the lock but moving the left part out can solve
this issue.

Fixes: 5e28d5a3f774 ("net/sched: sch_qfq: Fix race condition on qfq_aggregate")
Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
Signed-off-by: Xiang Mei <xmei5 at asu.edu>
Link: https://patch.msgid.link/4a04e0cc-a64b-44e7-9213-2880ed641d77@sabinyo.mountain
Reviewed-by: Cong Wang <xiyou.wangcong at gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter at linaro.org>
Link: https://patch.msgid.link/20250717230128.159766-1-xmei5@asu.edu
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
(cherry picked from commit cf074eca0065bc5142e6004ae236bb35a2687fdf)
CVE-2025-38477
Signed-off-by: Tim Whisonant <tim.whisonant at canonical.com>
---
 net/sched/sch_qfq.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index a202a70c6b294..f54f534071596 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -534,9 +534,6 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 
 static void qfq_destroy_class(struct Qdisc *sch, struct qfq_class *cl)
 {
-	struct qfq_sched *q = qdisc_priv(sch);
-
-	qfq_rm_from_agg(q, cl);
 	gen_kill_estimator(&cl->rate_est);
 	qdisc_put(cl->qdisc);
 	kfree(cl);
@@ -557,10 +554,11 @@ static int qfq_delete_class(struct Qdisc *sch, unsigned long arg,
 
 	qdisc_purge_queue(cl->qdisc);
 	qdisc_class_hash_remove(&q->clhash, &cl->common);
-	qfq_destroy_class(sch, cl);
+	qfq_rm_from_agg(q, cl);
 
 	sch_tree_unlock(sch);
 
+	qfq_destroy_class(sch, cl);
 	return 0;
 }
 
@@ -1503,6 +1501,7 @@ static void qfq_destroy_qdisc(struct Qdisc *sch)
 	for (i = 0; i < q->clhash.hashsize; i++) {
 		hlist_for_each_entry_safe(cl, next, &q->clhash.hash[i],
 					  common.hnode) {
+			qfq_rm_from_agg(q, cl);
 			qfq_destroy_class(sch, cl);
 		}
 	}
-- 
2.43.0