Description: cgroup: verify that source is a string
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=2034514
Notes:
 carnil> Commit fixes 8d2451f4994f ("cgroup1: switch to option-by-option
 carnil> parsing") in 5.1-rc1.
Bugs:
upstream: released (5.14-rc2) [3b0462726e7ef281c35a7a4ae33e93ee2bc9975b]
5.10-upstream-stable: released (5.10.52) [811763e3beb6c922d168e9f509ec593e9240842e]
4.19-upstream-stable: N/A "Vulnerable code not present"
4.9-upstream-stable: N/A "Vulnerable code not present"
sid: released (5.14.6-1)
5.10-bullseye-security: released (5.10.70-1)
4.19-buster-security: N/A "Vulnerable code not present"
4.9-stretch-security: N/A "Vulnerable code not present"