Just a quick note that the symptoms described in this thread
<
https://lists.fedoraproject.org/pipermail/buildsys/2012-June/003902.html>:
$ mock --shell
INFO: mock.py version 1.1.18 starting...
State Changed: init plugins
INFO: selinux disabled
State Changed: start
State Changed: lock buildroot
State Changed: shell
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
... are consistent with a mock root on a filesystem mounted "nodev".
Permissions and SELinux aside, you'll suffer EACCES all day long until
the fs is remounted "dev".
-Mike