Remove remaining uses of libcontainer/system package

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

sys/oom_unix.go

@@ -24,8 +24,6 @@ import (
 	"os"
 	"strconv"
 	"strings"
-
-	"github.com/opencontainers/runc/libcontainer/system"
 )
 
 // OOMScoreMaxKillable is the maximum score keeping the process killable by the oom killer
@@ -40,7 +38,7 @@ func SetOOMScore(pid, score int) error {
 	}
 	defer f.Close()
 	if _, err = f.WriteString(strconv.Itoa(score)); err != nil {
-		if os.IsPermission(err) && (system.RunningInUserNS() || RunningUnprivileged()) {
+		if os.IsPermission(err) && (RunningInUserNS() || RunningUnprivileged()) {
 			return nil
 		}
 		return err

sys/userns_linux.go

@@ -0,0 +1,39 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package sys
+
+import (
+	"github.com/opencontainers/runc/libcontainer/user"
+)
+
+// RunningInUserNS detects whether we are currently running in a user namespace.
+// Originally copied from github.com/lxc/lxd/shared/util.go
+func RunningInUserNS() bool {
+	uidmap, err := user.CurrentProcessUIDMap()
+	if err != nil {
+		// This kernel-provided file only exists if user namespaces are supported
+		return false
+	}
+	/*
+	 * We assume we are in the initial user namespace if we have a full
+	 * range - 4294967295 uids starting at uid 0.
+	 */
+	if len(uidmap) == 1 && uidmap[0].ID == 0 && uidmap[0].ParentID == 0 && uidmap[0].Count == 4294967295 {
+		return false
+	}
+	return true
+}

sys/userns_unsupported.go

@@ -0,0 +1,25 @@
+// +build !linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package sys
+
+// RunningInUserNS is a stub for non-Linux systems
+// Always returns false
+func RunningInUserNS() bool {
+	return false
+}