[PATCH net v3 4/9] net/sched: hhf: clamp quantum in change and init paths
From: Jamal Hadi Salim <jhs@mojatatu.com>
Date: 2026-09-01 21:39:53
Also in:
stable
Subsystem:
networking [general], tc subsystem, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Jamal Hadi Salim, Jiri Pirko, Linus Torvalds
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 <redacted>
Reviewed-by: Toke Høiland-Jørgensen <redacted>
Tested-by: Victor Nogueira <redacted>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
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 96acab6a8da0..fc72f825fbd9 100644
--- a/net/sched/sch_hhf.c
+++ b/net/sched/sch_hhf.c@@ -551,7 +551,7 @@ 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]);
@@ -613,7 +613,7 @@ 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);
@@ -624,10 +624,6 @@ 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);
--
2.43.0