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net/sched: fq_pie: clamp default quantum to avoid signed overflow

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fq_pie_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without
clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0
accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which
overflows the signed flow->deficit to INT_MIN in fq_pie_qdisc_dequeue(),
causing an infinite loop and soft lockup. Emulate fq_pie_policy which
is already bounded to [1, 1 << 20]; clamp the default to [256, 1 << 20].
256 matches fq_codel's floor and is a sane minimum for a DRR quantum.

Conditions to recreate the bug: a device whose MTU (plus
hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy
device with max_mtu == 0 accepting MTU 2147483634). Requires
CAP_NET_ADMIN in a user namespace.

Fixes: ec97ecf1eb ("net: sched: add Flow Queue PIE packet scheduler")
Reported-by: vega@nebusec.ai
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260822195509.112717-5-jhs@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Jamal Hadi Salim
2026-08-22 15:55:07 -04:00
committed by Paolo Abeni
parent 6439461f16
commit c86cd7ed0b
1 changed files with 2 additions and 1 deletions
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3
net/sched/sch_fq_pie.c
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@@ -427,7 +427,8 @@ static int fq_pie_init(struct Qdisc *sch, struct nlattr *opt,
pie_params_init(&q->p_params);
sch->limit = 10 * 1024;
q->p_params.limit = sch->limit;
q->quantum = psched_mtu(qdisc_dev(sch));
q->quantum = clamp_t(u32, psched_mtu(qdisc_dev(sch)),
256, 1 << 20);
q->sch = sch;
q->ecn_prob = 10;
q->flows_cnt = 1024;