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

[Cong Wang <xiyou.wangcong@gmail.com>]

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.