remove libseccomp cgo dependency

The CRI plugin was depending on libseccomp cgo dependency via
libseccomp-golang via libcontainer.

https://github.com/seccomp/libseccomp-golang/blob/v0.9.1/seccomp_internal.go#L17

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

pkg/seccomp/seccomp_linux.go

@@ -0,0 +1,88 @@
+/*
+   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.
+*/
+
+/*
+   Copyright The runc 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 seccomp
+
+import (
+	"bufio"
+	"os"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+// IsEnabled returns if the kernel has been configured to support seccomp.
+// From https://github.com/opencontainers/runc/blob/v1.0.0-rc91/libcontainer/seccomp/seccomp_linux.go#L86-L102
+func IsEnabled() bool {
+	// Try to read from /proc/self/status for kernels > 3.8
+	s, err := parseStatusFile("/proc/self/status")
+	if err != nil {
+		// Check if Seccomp is supported, via CONFIG_SECCOMP.
+		if err := unix.Prctl(unix.PR_GET_SECCOMP, 0, 0, 0, 0); err != unix.EINVAL {
+			// Make sure the kernel has CONFIG_SECCOMP_FILTER.
+			if err := unix.Prctl(unix.PR_SET_SECCOMP, unix.SECCOMP_MODE_FILTER, 0, 0, 0); err != unix.EINVAL {
+				return true
+			}
+		}
+		return false
+	}
+	_, ok := s["Seccomp"]
+	return ok
+}
+
+// parseStatusFile is from https://github.com/opencontainers/runc/blob/v1.0.0-rc91/libcontainer/seccomp/seccomp_linux.go#L243-L268
+func parseStatusFile(path string) (map[string]string, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	s := bufio.NewScanner(f)
+	status := make(map[string]string)
+
+	for s.Scan() {
+		text := s.Text()
+		parts := strings.Split(text, ":")
+
+		if len(parts) <= 1 {
+			continue
+		}
+
+		status[parts[0]] = parts[1]
+	}
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
+
+	return status, nil
+}