[PATCH 5.15 013/206] net/sched: sch_qfq: do not free existing class in qfq_change_class()

Greg Kroah-Hartman
2026-02-04T14:52:06Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 3879cffd9d07aa0377c4b8835c4f64b4fb24ac78 ]

Fixes qfq_change_class() error case.

cl->qdisc and cl should only be freed if a new class and qdisc
were allocated, or we risk various UAF.

Fixes: 462dbc9101ac ("pkt_sched: QFQ Plus: fair-queueing service at DRR cost")
Reported-by: syzbot+07f3f38f723c335f106d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6965351d.050a0220.eaf7.00c5.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260112175656.17605-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/sch_qfq.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index aa049dd33a74e..d201bcb5edc42 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -532,8 +532,10 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
return 0;

destroy_class:
- qdisc_put(cl->qdisc);
- kfree(cl);
+ if (!existing) {
+ qdisc_put(cl->qdisc);
+ kfree(cl);
+ }
return err;
}

--
2.51.0