From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	Bryam Vargas <hexlabsecurity@proton.me>,
	Victor Nogueira <victor@mojatatu.com>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.1 157/303] net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked
Date: Thu, 20 Aug 2026 16:54:53 +0200
Message-ID: <20260820145258.016935348@linuxfoundation.org>
In-Reply-To: <20260820145253.200766705@linuxfoundation.org>
References: <20260820145253.200766705@linuxfoundation.org>
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6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bryam Vargas <hexlabsecurity@proton.me>

[ Upstream commit e056e1dfcddca877dd46d704e8ec9860cfc9ec44 ]

When taprio's software path peeks a non-work-conserving child qdisc, the
child stashes the peeked skb in its gso_skb; taprio_dequeue_from_txq()
then takes the packet with a direct child ->dequeue() call, which ignores
that stash, orphans the peeked skb and desyncs the child's qlen/backlog.
With a qfq child this re-enters the child on an emptied list and
dereferences NULL, panicking the kernel from softirq on ordinary egress.

Take the packet through qdisc_dequeue_peeked(), as sch_red and sch_sfb
now do. The helper returns the child's stashed skb first and is a no-op
when there is none, so a work-conserving child is unaffected and the
gated path now consumes the skb whose length was charged to the budget.

Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
Cc: stable@vger.kernel.org
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260625-b4-disp-31bcb279-v1-1-85c40b83c529@proton.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/sched/sch_taprio.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -596,7 +596,7 @@ static struct sk_buff *taprio_dequeue_fr
 		return NULL;
 
 skip_peek_checks:
-	skb = child->ops->dequeue(child);
+	skb = qdisc_dequeue_peeked(child);
 	if (unlikely(!skb))
 		return NULL;