Description: cgroup: add missing skcd->no_refcnt check in cgroup_sk_clone()
References:
 https://www.spinics.net/lists/stable/msg405099.html
 http://blog.pi3.com.pl/?p=720
Notes:
 carnil> Exists because of a backporting issue in the v4.9.y, v4.14.y
 carnil> and v4.19.y stable series when backporting fix for CVE-2020-
 carnil> 14356.
Bugs:
upstream: N/A "Vulnerable code not present"
4.19-upstream-stable: released (4.19.140) [38de4308c5c3319ae9c815b6d6aa8d2b5804bace]
4.9-upstream-stable: released (4.9.233) [f3b1d647251a94a6968a35e3d685dc8b1b24c3ff]
sid: N/A "Vulnerable code not present"
4.19-buster-security: N/A "No released version contains broken backport"
4.9-stretch-security: N/A "No released version contains broken backport"