linux-kernel - Re: [PATCH v5 net 4/6] net/sched: Prohibit regrafting ingress or clsact Qdiscs

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Message-ID: <9b58d882-743a-c392-0407-17bb0b075516@mojatatu.com>
Date:   Wed, 24 May 2023 12:38:51 -0300
From:   Pedro Tammela <pctammela@...atatu.com>
To:     Peilin Ye <yepeilin.cs@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     Peilin Ye <peilin.ye@...edance.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH v5 net 4/6] net/sched: Prohibit regrafting ingress or
 clsact Qdiscs

On 23/05/2023 22:19, Peilin Ye wrote:
> From: Peilin Ye <peilin.ye@...edance.com>
> 
> 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")
> Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>
> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
> Signed-off-by: Peilin Ye <peilin.ye@...edance.com>

Tested-by: Pedro Tammela <pctammela@...atatu.com>

> ---
> change in v3, v4:
>    - add in-body From: tag
> 
>   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");