net/sched: Prohibit regrafting ingress or clsact Qdiscs

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")
Tested-by: Pedro Tammela <pctammela@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 383195955b7d21337ae4db67c817dd6fbe3269d0..49b9c1bbfdd97bfdf02fccc2f90cf4a740d88d64 100644 (file)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1596,6 +1596,11 @@ replay:
                                        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");