compatible.go

package utils

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"regexp"
	"runtime"
	"strings"

	"github.com/coreos/go-semver/semver"
)

const supportKernelVersion = "5.8.0"
const btfFile = "/sys/kernel/btf/vmlinux"

func isLinux() bool {
	return runtime.GOOS == "linux"
}

func currentKernelVersion() (*semver.Version, error) {
	buf, err := rawKernelVersion()
	if err != nil {
		return nil, err
	}

	ver, err := parseKernelVersion(buf)
	if err != nil {
		return nil, err
	}

	return ver, nil
}

func parseKernelVersion(buf []byte) (*semver.Version, error) {
	// Formats like 5.11.0-34-generic.
	// Only keep the major, minor, and patch version.
	parts := bytes.Split(buf, []byte("-"))
	s := strings.TrimSpace(string(parts[0]))

	ver, err := semver.NewVersion(s)
	if err != nil {
		return nil, err
	}

	return ver, nil
}

func hasSupportKernelVersion() error {
	supportVersion := semver.New(supportKernelVersion)
	version, err := currentKernelVersion()
	if err != nil {
		return err
	}

	if version.LessThan(*supportVersion) {
		return fmt.Errorf("current kernel version not supported. minimum supported kernel version is %v", supportKernelVersion)
	}

	return nil
}

func hasBTF() error {
	f, err := os.Open(btfFile)

	if err != nil {
		// lint:ignore ST1005
		return fmt.Errorf("Current kernel is not supported for BTF. Requires kernel with `CONFIG_DEBUG_INFO_BTF` enabled")
	}

	defer f.Close()

	return nil
}

func rawKernelVersion() ([]byte, error) {
	f, err := os.Open("/proc/sys/kernel/osrelease")
	if err != nil {
		return nil, err
	}
	defer f.Close()

	buf, err := ioutil.ReadAll(f)
	if err != nil {
		return nil, err
	}

	return buf, nil
}

func readKernelConfig() (string, error) {
	buf, err := rawKernelVersion()
	if err != nil {
		return "", err
	}

	configPath := fmt.Sprintf("/boot/config-%s", strings.Replace(string(buf), "\n", "", -1))
	f, err := os.Open(configPath)
	if err != nil {
		return "", err
	}
	defer f.Close()

	kernelConfig, err := ioutil.ReadAll(f)
	if err != nil {
		return "", err
	}

	return string(kernelConfig), err
}

func readCmdline() (string, error) {
	f, err := os.Open("/proc/cmdline")
	if err != nil {
		return "", err
	}

	defer f.Close()

	cmdline, err := ioutil.ReadAll(f)
	if err != nil {
		return "", err
	}

	return string(cmdline), err
}

func hasBPFLSM() error {
	kernelConfig, err := readKernelConfig()
	if err != nil {
		return err
	}

	// check Kernel config
	re := regexp.MustCompile(`CONFIG_LSM="(.*)"`)
	matches := re.FindStringSubmatch(kernelConfig)
	if len(matches) > 0 && strings.Contains(matches[1], "bpf") {
		return nil
	}

	// check boot params
	cmdline, err := readCmdline()
	if err != nil {
		return err
	}

	re = regexp.MustCompile(`lsm=(.*)`)
	matches = re.FindStringSubmatch(cmdline)
	if len(matches) > 0 && strings.Contains(matches[1], "bpf") {
		return nil
	}

	return fmt.Errorf("BPF LSM is not enabled. Build the kernel enabled in CONFIG_LSM or add it to the boot parameters")
}

func AmIRootUser() bool {
	return os.Geteuid() == 0
}

func IsCompatible() error {
	if !isLinux() {
		return errors.New("required to run on Linux")
	}

	if err := hasSupportKernelVersion(); err != nil {
		return err
	}

	if err := hasBTF(); err != nil {
		return err
	}

	if err := hasBPFLSM(); err != nil {
		return err
	}

	return nil
}