net: sched: extend Qdisc with rcu

stable inclusion
from linux-4.19.221
commit f602ed9f8574512e7ea1ab65c3db7ba71053bf27
category: bugfix
CVE: CVE-2021-39713

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

[ Upstream commit 3a7d0d07 ]

Currently, Qdisc API functions assume that users have rtnl lock taken. To
implement rtnl unlocked classifiers update interface, Qdisc API must be
extended with functions that do not require rtnl lock.

Extend Qdisc structure with rcu. Implement special version of put function
qdisc_put_unlocked() that is called without rtnl lock taken. This function
only takes rtnl lock if Qdisc reference counter reached zero and is
intended to be used as optimization.

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/sch_generic.c
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>