cgroup2: devices: switch to emulator for cgroupv1 parity

There were several issues with the previous cgroupv2 devices filter
generator implementation, stemming from the previous implementation
using a few too many tricks to implement the correct cgroup behaviour
(rules were handled in reverse order, with wildcards having particularly
special interpretations). As a result, some slightly odd configurations
with rules in specific orders could result in incorrect filters being
generated.

By switching to the emulator which is already used by cgroupv1, we can
guarantee that the behaviour of filters in both cgroup versions will be
identical, as well as making use of the hardenings in the emulator (not
allowing users to add deny rules the kernel will ignore).

(Note that because the ordering of the devices emulator rules is
deterministic and based on the rule value, the existing test rules had
to be reordered slightly.)

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

libcontainer/cgroups/fs2/devices.go

@@ -58,9 +58,6 @@ func setDevices(dirPath string, r *configs.Resources) error {
 	if r.SkipDevices {
 		return nil
 	}
-	// XXX: This is currently a white-list (but all callers pass a blacklist of
-	//      devices). This is bad for a whole variety of reasons, but will need
-	//      to be fixed with co-ordinated effort with downstreams.
 	insts, license, err := devicefilter.DeviceFilter(r.Devices)
 	if err != nil {
 		return err