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From:   Peilin Ye <yepeilin.cs@gmail.com>
To:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>
Cc:     Peilin Ye <peilin.ye@bytedance.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Vlad Buslov <vladbu@mellanox.com>,
        Pedro Tammela <pctammela@mojatatu.com>,
        Hillf Danton <hdanton@sina.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>,
        Peilin Ye <yepeilin.cs@gmail.com>
Subject: [PATCH v4 net 4/6] net/sched: Prohibit regrafting ingress or clsact Qdiscs
Date:   Tue, 23 May 2023 00:16:16 -0700
Message-Id: <4bc54b82ffc3816058de543f383623a022a36d18.1684825171.git.peilin.ye@bytedance.com>
In-Reply-To: <cover.1684825171.git.peilin.ye@bytedance.com>
References: <cover.1684825171.git.peilin.ye@bytedance.com>
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From: Peilin Ye <peilin.ye@bytedance.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@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
---
change since v2:
  - 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");
-- 
2.20.1