net: sched: use Qdisc rcu API instead of relying on rtnl lock

stable inclusion
from linux-4.19.221
commit ae214e04b95ff64a4b0e9aab6742520bfde6ff0c
category: bugfix
CVE: CVE-2021-39713

--------------------------------

[ Upstream commit e368fdb6 ]

As a preparation from removing rtnl lock dependency from rules update path,
use Qdisc rcu and reference counting capabilities instead of relying on
rtnl lock while working with Qdiscs. Create new tcf_block_release()
function, and use it to free resources taken by tcf_block_find().
Currently, this function only releases Qdisc and it is extended in next
patches in this series.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[Lee: Sent to Stable]
Link: https://syzkaller.appspot.com/bug?id=d7e411c5472dd5da33d8cc921ccadc747743a568


Reported-by:  <syzbot+5f229e48cccc804062c0@syzkaller.appspotmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Conflict:
	net/sched/cls_api.c
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>