When use the following command to test:
1)ip link add bond0 type bond
2)ip link set bond0 up
3)tc qdisc add dev bond0 root handle ffff: mq
4)tc qdisc replace dev bond0 parent ffff:fff1 handle ffff: mq
This is because when mq is added for the first time, qdiscs in mq is set
to NULL in mq_attach(). Therefore, when replacing mq after adding mq, we
need to initialize qdiscs in the mq before continuing to graft. Otherwise,
it will couse NULL pointer dereference issue in mq_attach(). And the same
issue will occur in the attach functions of mqprio, taprio and htb.
ffff:fff1 means that the repalce qdisc is ingress. Ingress does not allow
any qdisc to be attached. Therefore, ffff:fff1 is incorrectly used, and
the command should be dropped.
Fixes: 6ec1c69a8f64 ("net_sched: add classful multiqueue dummy scheduler") Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com> Tested-by: Peilin Ye <peilin.ye@bytedance.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Link: https://lore.kernel.org/r/20230527093747.3583502-1-shaozhengchao@huawei.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>