netdev - Re: [PATCH net] net_sched: sch_sfq: reject invalid perturb period

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Message-ID: <aEs0W32lPsKZiZFp@pop-os.localdomain>
Date: Thu, 12 Jun 2025 13:11:07 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
	netdev@...r.kernel.org, eric.dumazet@...il.com,
	Gerrard Tai <gerrard.tai@...rlabs.sg>, stable@...r.kernel.org
Subject: Re: [PATCH net] net_sched: sch_sfq: reject invalid perturb period

On Wed, Jun 11, 2025 at 08:35:01AM +0000, Eric Dumazet wrote:
> Gerrard Tai reported that SFQ perturb_period has no range check yet,
> and this can be used to trigger a race condition fixed in a separate patch.
> 
> We want to make sure ctl->perturb_period * HZ will not overflow
> and is positive.
> 
> Tested:
> 
> tc qd add dev lo root sfq perturb -10   # negative value : error
> Error: sch_sfq: invalid perturb period.
> 
> tc qd add dev lo root sfq perturb 1000000000 # too big : error
> Error: sch_sfq: invalid perturb period.
> 
> tc qd add dev lo root sfq perturb 2000000 # acceptable value
> tc -s -d qd sh dev lo
> qdisc sfq 8005: root refcnt 2 limit 127p quantum 64Kb depth 127 flows 128 divisor 1024 perturb 2000000sec
>  Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
>  backlog 0b 0p requeues 0

Please kindly provide a selftest (as a separate patch) since it looks
fairly easy to reproduce. With AI copilot today, this becomes much
easier, so hopefully it won't bring you much burden. :)

Thanks.