netdev - Re: [PATCH net 4/6] net/sched: Prohibit regrafting ingress or clsact Qdiscs

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Date: Mon, 8 May 2023 07:24:25 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Peilin Ye <yepeilin.cs@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	Peilin Ye <peilin.ye@...edance.com>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.r.fastabend@...el.com>, Vlad Buslov <vladbu@...lanox.com>, 
	Pedro Tammela <pctammela@...atatu.com>, Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH net 4/6] net/sched: Prohibit regrafting ingress or clsact Qdiscs

On Fri, May 5, 2023 at 8:14 PM Peilin Ye <yepeilin.cs@...il.com> wrote:
>
> Currently, after creating an ingress (or clsact) Qdisc and grafting it
> under TC_H_INGRESS (TC_H_CLSACT), it is possible to graft it again under
> e.g. a TBF Qdisc:
>
>   $ ip link add ifb0 type ifb
>   $ tc qdisc add dev ifb0 handle 1: root tbf rate 20kbit buffer 1600 limit 3000
>   $ tc qdisc add dev ifb0 clsact
>   $ tc qdisc link dev ifb0 handle ffff: parent 1:1
>   $ tc qdisc show dev ifb0
>   qdisc tbf 1: root refcnt 2 rate 20Kbit burst 1600b lat 560.0ms
>   qdisc clsact ffff: parent ffff:fff1 refcnt 2
>                                       ^^^^^^^^
>
> clsact's refcount has increased: it is now grafted under both
> TC_H_CLSACT and 1:1.
>
> ingress and clsact Qdiscs should only be used under TC_H_INGRESS
> (TC_H_CLSACT).  Prohibit regrafting them.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Fixes: 1f211a1b929c ("net, sched: add clsact qdisc")
> Signed-off-by: Peilin Ye <peilin.ye@...edance.com>

Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal

> ---
>  net/sched/sch_api.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index 383195955b7d..49b9c1bbfdd9 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1596,6 +1596,11 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
>                                         NL_SET_ERR_MSG(extack, "Invalid qdisc name");
>                                         return -EINVAL;
>                                 }
> +                               if (q->flags & TCQ_F_INGRESS) {
> +                                       NL_SET_ERR_MSG(extack,
> +                                                      "Cannot regraft ingress or clsact Qdiscs");
> +                                       return -EINVAL;
> +                               }
>                                 if (q == p ||
>                                     (p && check_loop(q, p, 0))) {
>                                         NL_SET_ERR_MSG(extack, "Qdisc parent/child loop detected");
> --
> 2.20.1
>