netdev - [REGRESSION] Userland interface breaks due to hard HFSC

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Message-Id: <297D84E3-736E-4AB4-B825-264279E2043C@flyingcircus.io>
Date: Fri, 6 Oct 2023 10:37:00 +0200
From: Christian Theune <ct@...ingcircus.io>
To: stable@...r.kernel.org,
 netdev@...r.kernel.org
Cc: regressions@...ts.linux.dev,
 davem@...emloft.net,
 edumazet@...gle.com,
 kuba@...nel.org,
 pabeni@...hat.com
Subject: [REGRESSION] Userland interface breaks due to hard HFSC_FSC
 requirement

Hi,

(prefix, I was not aware of the regression reporting process and incorrectly reported this informally with the developers mentioned in the change)

I upgraded from 6.1.38 to 6.1.55 this morning and it broke my traffic shaping script, leaving me with a non-functional uplink on a remote router.

The script errors out like this:

Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ext=ispA
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ext_ingress=ifb0
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + modprobe ifb
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + modprobe act_mirred
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ispA root
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2061]: Error: Cannot delete qdisc with handle of zero.
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ispA ingress
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2064]: Error: Cannot find specified qdisc on specified device.
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ifb0 root
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2066]: Error: Cannot delete qdisc with handle of zero.
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ifb0 ingress
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2067]: Error: Cannot find specified qdisc on specified device.
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc add dev ispA handle ffff: ingress
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ifconfig ifb0 up
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc filter add dev ispA parent ffff: protocol all u32 match u32 0 0 action mirred egress redirect dev ifb0
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc add dev ifb0 root handle 1: hfsc default 1
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc class add dev ifb0 parent 1: classid 1:999 hfsc rt m2 2.5gbit
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc class add dev ifb0 parent 1:999 classid 1:1 hfsc sc rate 50mbit
Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2077]: Error: Invalid parent - parent class must have FSC.

The error message is also a bit weird (but that’s likely due to iproute2 being weird) as the CLI interface for `tc` and the error message do not map well. (I think I would have to choose `hfsc sc` on the parent to enable the FSC option which isn’t mentioned anywhere in the hfsc manpage).

The breaking change was introduced in 6.1.53[1] and a multitude of other currently supported kernels:

----
commit a1e820fc7808e42b990d224f40e9b4895503ac40
Author: Budimir Markovic <markovicbudimir@...il.com>
Date: Thu Aug 24 01:49:05 2023 -0700

net/sched: sch_hfsc: Ensure inner classes have fsc curve

[ Upstream commit b3d26c5702c7d6c45456326e56d2ccf3f103e60f ]

HFSC assumes that inner classes have an fsc curve, but it is currently
possible for classes without an fsc curve to become parents. This leads
to bugs including a use-after-free.

Don't allow non-root classes without HFSC_FSC to become parents.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Budimir Markovic <markovicbudimir@...il.com>
Signed-off-by: Budimir Markovic <markovicbudimir@...il.com>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
Link: https://lore.kernel.org/r/20230824084905.422-1-markovicbudimir@gmail.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
----

Regards,
Christian

[1] https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.1.53

#regzbot introduced: a1e820fc7808e42b990d224f40e9b4895503ac40

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