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

From: Pedro Tammela
Date: Wed May 24 2023 - 11:41:22 EST

On 23/05/2023 22:19, Peilin Ye wrote:
From: Peilin Ye <>

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 <>

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");