Peilin Ye 9de95df5d1 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: 1da177e4c3 ("Linux-2.6.12-rc2")
Fixes: 1f211a1b92 ("net, sched: add clsact qdisc")
Tested-by: Pedro Tammela <[email protected]>
Acked-by: Jamal Hadi Salim <[email protected]>
Reviewed-by: Jamal Hadi Salim <[email protected]>
Reviewed-by: Vlad Buslov <[email protected]>
Signed-off-by: Peilin Ye <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
2023-05-30 23:31:05 -07:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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