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[195.231.47.46]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6a59e2ddad2sm12253271a12.30.2026.08.25.01.33.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Aug 2026 01:33:22 -0700 (PDT) Message-ID: <62618ef6-28f1-4d0d-916a-96fc54dfc2e3@redhat.com> Date: Tue, 25 Aug 2026 10:33:19 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v3 4/6] net/sched: fq_pie: clamp default quantum to avoid signed overflow To: Jamal Hadi Salim , netdev@vger.kernel.org Cc: Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , "Mohit P. Tahiliani" , "Sachin D . Patil" , "V. Saicharan" , Mohit Bhasi , Leslie Monis , Gautam Ramakrishnan , stable@vger.kernel.org, vega@nebusec.ai, Victor Nogueira References: <20260822195509.112717-1-jhs@mojatatu.com> <20260822195509.112717-5-jhs@mojatatu.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260822195509.112717-5-jhs@mojatatu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 8/22/26 9:55 PM, Jamal Hadi Salim wrote: > 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: ec97ecf1ebe4 ("net: sched: add Flow Queue PIE packet scheduler") > Reported-by: vega@nebusec.ai > Tested-by: Victor Nogueira > Signed-off-by: Jamal Hadi Salim > --- > net/sched/sch_fq_pie.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c > index 069e1facd413..b27d95418707 100644 > --- a/net/sched/sch_fq_pie.c > +++ b/net/sched/sch_fq_pie.c > @@ -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); Sashiko thinks that the soft lookup is still reachable via pie_change: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260822195509.112717-1-jhs%40mojatatu.com and has similar concerns for patch 6/6, too. It marks the issues as pre-existing, but AFAICS they overlap with the things addressed here. WDYT? /P