From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Vega <vega@nebusec.ai>,
	=?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>,
	Victor Nogueira <victor@mojatatu.com>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 0694/1102] net/sched: hhf: clamp quantum in change and init paths
Date: Thu, 17 Sep 2026 16:10:37 +0100
Message-ID: <20260917151557.703921279@linuxfoundation.org>
In-Reply-To: <20260917151539.408551884@linuxfoundation.org>
References: <20260917151539.408551884@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Jamal Hadi Salim <jhs@mojatatu.com>

[ Upstream commit eb56a495f59baf6cad5ed80e3ffb9078098b1346 ]

hhf_change() accepts any quantum from userspace, including 1. With a
crafted size table qdisc_pkt_len reaches ~2 GiB, so quantum=1 makes
the deficit-refill loop spin ~2^31 times under the qdisc lock
(a soft lockup / denial of service).

Add max(256U, ...) in hhf_change() matching fq_codel_change(). Clamp
hhf_init() to [256, 1<<20] matching the siblings, and remove the old
fallback that only set quantum=256 on overflow.

Conditions to recreate the bug:
  CONFIG_NET_SCH_HHF=y. Requires CAP_NET_ADMIN (namespace-local via
  unshare -Urn suffices).

  tc qdisc add dev dummy0 root hhf
  tc qdisc change dev dummy0 root hhf quantum 1 stab data 32768 size_log 15 cell_log 0

Fixes: 10239edf86f1 ("net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc")
Reported-by: Vega <vega@nebusec.ai>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/QDISC-0CFC.v3.20260901204856@mojatatu.com.5
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sched/sch_hhf.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/sched/sch_hhf.c b/net/sched/sch_hhf.c
index 0c406d11b22d7..e7df723c9f62e 100644
--- a/net/sched/sch_hhf.c
+++ b/net/sched/sch_hhf.c
@@ -550,7 +550,7 @@ static int hhf_change(struct Qdisc *sch, struct nlattr *opt,
 		return err;
 
 	if (tb[TCA_HHF_QUANTUM])
-		new_quantum = nla_get_u32(tb[TCA_HHF_QUANTUM]);
+		new_quantum = max(256U, nla_get_u32(tb[TCA_HHF_QUANTUM]));
 
 	if (tb[TCA_HHF_NON_HH_WEIGHT])
 		new_hhf_non_hh_weight = nla_get_u32(tb[TCA_HHF_NON_HH_WEIGHT]);
@@ -610,7 +610,7 @@ static int hhf_init(struct Qdisc *sch, struct nlattr *opt,
 	int i;
 
 	sch->limit = 1000;
-	q->quantum = psched_mtu(qdisc_dev(sch));
+	q->quantum = clamp_t(u32, psched_mtu(qdisc_dev(sch)), 256, 1 << 20);
 	get_random_bytes(&q->perturbation, sizeof(q->perturbation));
 	INIT_LIST_HEAD(&q->new_buckets);
 	INIT_LIST_HEAD(&q->old_buckets);
@@ -621,10 +621,6 @@ static int hhf_init(struct Qdisc *sch, struct nlattr *opt,
 	q->hhf_evict_timeout = HZ;      /* 1  sec */
 	q->hhf_non_hh_weight = 2;
 
-	if ((int)q->quantum <= 0 ||
-	    (u64)q->quantum * q->hhf_non_hh_weight > INT_MAX)
-		q->quantum = 256;
-
 	if (opt) {
 		int err = hhf_change(sch, opt, extack);
 
-- 
2.53.0