I see several selinux alert messages during a mock build. I'm attaching the alert file from setroubleshoot
Created attachment 267161 [details] setroubleshoot alert groupadd output
This should be against selinux-policy, not mock.
As an aside, this doesnt prevent mock from functioning, it simply produces log messages.
I have fixed this in mock by doing a "chcon --reference=/dev/FILE /mock/build/root/dev/FILE". This specific bug I am going to mark as FIXED - NEXTRELEASE. I dont intend to make another release for a few weeks, at least. If you would like to check out the fixed version, please look in the git repository for mock.