From: Victor Nogueira <victor@mojatatu.com>
To: netdev@vger.kernel.org
Cc: jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, toke@redhat.com, gerrard.tai@starlabs.sg,
	pctammela@mojatatu.com, stephen@networkplumber.org
Subject: [PATCH net v3 2/5] net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc
Date: Fri, 25 Apr 2025 19:07:06 -0300	[thread overview]
Message-ID: <20250425220710.3964791-3-victor@mojatatu.com> (raw)
In-Reply-To: <20250425220710.3964791-1-victor@mojatatu.com>

As described in Gerrard's report [1], we have a UAF case when an hfsc class
has a netem child qdisc. The crux of the issue is that hfsc is assuming
that checking for cl->qdisc->q.qlen == 0 guarantees that it hasn't inserted
the class in the vttree or eltree (which is not true for the netem
duplicate case).

This patch checks the n_active class variable to make sure that the code
won't insert the class in the vttree or eltree twice, catering for the
reentrant case.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/

Fixes: 37d9cf1a3ce3 ("sched: Fix detection of empty queues in child qdiscs")
Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
---
 net/sched/sch_hfsc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index 6c8ef826cec0..cb8c525ea20e 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -1569,7 +1569,7 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
 		return err;
 	}
 
-	if (first) {
+	if (first && !cl->cl_nactive) {
 		if (cl->cl_flags & HFSC_RSC)
 			init_ed(cl, len);
 		if (cl->cl_flags & HFSC_FSC)
-- 
2.34.1

next prev parent reply	other threads:[~2025-04-25 22:07 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-25 22:07 [PATCH net v3 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases Victor Nogueira
2025-04-25 22:07 ` [PATCH net v3 1/5] net_sched: drr: Fix double list add in class with netem as child qdisc Victor Nogueira
2025-04-25 22:07 ` Victor Nogueira [this message]
2025-04-25 22:07 ` [PATCH net v3 3/5] net_sched: ets: " Victor Nogueira
2025-04-25 22:07 ` [PATCH net v3 4/5] net_sched: qfq: " Victor Nogueira
2025-04-25 22:07 ` [PATCH net v3 5/5] selftests: tc-testing: Add TDC tests that exercise reentrant enqueue behaviour Victor Nogueira
2025-04-28 23:00 ` [PATCH net v3 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases patchwork-bot+netdevbpf

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