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

[Pedro Tammela]

On 23/05/2023 22:19, Peilin Ye wrote:
> From: Peilin Ye <peilin.ye@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxx>
> Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
> Signed-off-by: Peilin Ye <peilin.ye@xxxxxxxxxxxxx>

Tested-by: Pedro Tammela <pctammela@xxxxxxxxxxxx>

> ---
> 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");