5.4-stable review patch. If anyone has any objections, please let me know.
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From: Cong Wang xiyou.wangcong@gmail.com
[ Upstream commit 3f981138109f63232a5fb7165938d4c945cc1b9d ]
When enqueuing the first packet to an HFSC class, hfsc_enqueue() calls the child qdisc's peek() operation before incrementing sch->q.qlen and sch->qstats.backlog. If the child qdisc uses qdisc_peek_dequeued(), this may trigger an immediate dequeue and potential packet drop. In such cases, qdisc_tree_reduce_backlog() is called, but the HFSC qdisc's qlen and backlog have not yet been updated, leading to inconsistent queue accounting. This can leave an empty HFSC class in the active list, causing further consequences like use-after-free.
This patch fixes the bug by moving the increment of sch->q.qlen and sch->qstats.backlog before the call to the child qdisc's peek() operation. This ensures that queue length and backlog are always accurate when packet drops or dequeues are triggered during the peek.
Fixes: 12d0ad3be9c3 ("net/sched/sch_hfsc.c: handle corner cases where head may change invalidating calculated deadline") Reported-by: Mingi Cho mincho@theori.io Signed-off-by: Cong Wang xiyou.wangcong@gmail.com Reviewed-by: Simon Horman horms@kernel.org Link: https://patch.msgid.link/20250518222038.58538-2-xiyou.wangcong@gmail.com Reviewed-by: Jamal Hadi Salim jhs@mojatatu.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/sched/sch_hfsc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c index 5d73d02b8dce7..66c33d7e243d5 100644 --- a/net/sched/sch_hfsc.c +++ b/net/sched/sch_hfsc.c @@ -1573,6 +1573,9 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) return err; }
+ sch->qstats.backlog += len; + sch->q.qlen++; + if (first && !cl->cl_nactive) { if (cl->cl_flags & HFSC_RSC) init_ed(cl, len); @@ -1588,9 +1591,6 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
}
- sch->qstats.backlog += len; - sch->q.qlen++; - return NET_XMIT_SUCCESS; }