allow ptrace(2) by default for kernel >= 4.8

Signed-off-by: Henry Wang <henwang@amazon.com>

contrib/seccomp/kernelversion/kernel_linux.go

@@ -0,0 +1,92 @@
+/*
+   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.
+
+   File copied and customized based on
+   https://github.com/moby/moby/tree/v20.10.14/profiles/seccomp/kernel_linux.go
+*/
+
+package kernelversion
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+
+	"golang.org/x/sys/unix"
+)
+
+// KernelVersion holds information about the kernel.
+type KernelVersion struct {
+	Kernel uint64 // Version of the Kernel (i.e., the "4" in "4.1.2-generic")
+	Major  uint64 // Major revision of the Kernel (i.e., the "1" in "4.1.2-generic")
+}
+
+// String implements fmt.Stringer for KernelVersion
+func (k *KernelVersion) String() string {
+	if k.Kernel > 0 || k.Major > 0 {
+		return fmt.Sprintf("%d.%d", k.Kernel, k.Major)
+	}
+	return ""
+}
+
+var (
+	currentKernelVersion *KernelVersion
+	kernelVersionError   error
+	once                 sync.Once
+)
+
+// getKernelVersion gets the current kernel version.
+func getKernelVersion() (*KernelVersion, error) {
+	once.Do(func() {
+		var uts unix.Utsname
+		if err := unix.Uname(&uts); err != nil {
+			return
+		}
+		// Remove the \x00 from the release for Atoi to parse correctly
+		currentKernelVersion, kernelVersionError = parseRelease(string(uts.Release[:bytes.IndexByte(uts.Release[:], 0)]))
+	})
+	return currentKernelVersion, kernelVersionError
+}
+
+// parseRelease parses a string and creates a KernelVersion based on it.
+func parseRelease(release string) (*KernelVersion, error) {
+	var version = KernelVersion{}
+
+	// We're only make sure we get the "kernel" and "major revision". Sometimes we have
+	// 3.12.25-gentoo, but sometimes we just have 3.12-1-amd64.
+	_, err := fmt.Sscanf(release, "%d.%d", &version.Kernel, &version.Major)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse kernel version %q: %w", release, err)
+	}
+	return &version, nil
+}
+
+// GreaterEqualThan checks if the host's kernel version is greater than, or
+// equal to the given kernel version v. Only "kernel version" and "major revision"
+// can be specified (e.g., "3.12") and will be taken into account, which means
+// that 3.12.25-gentoo and 3.12-1-amd64 are considered equal (kernel: 3, major: 12).
+func GreaterEqualThan(minVersion KernelVersion) (bool, error) {
+	kv, err := getKernelVersion()
+	if err != nil {
+		return false, err
+	}
+	if kv.Kernel > minVersion.Kernel {
+		return true, nil
+	}
+	if kv.Kernel == minVersion.Kernel && kv.Major >= minVersion.Major {
+		return true, nil
+	}
+	return false, nil
+}