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net/sched: hhf: clamp quantum in change and init paths

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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: 10239edf86 ("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>
This commit is contained in:
Jamal Hadi Salim 2026-09-01 17:39:25 -04:00 committed by Jakub Kicinski
parent fb9f88a33c
commit eb56a495f5
1 changed files with 2 additions and 6 deletions
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8
net/sched/sch_hhf.c
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@ -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);