template.go

// +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 apparmor

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path"
	"strconv"
	"strings"
	"text/template"

	"github.com/pkg/errors"
)

const dir = "/etc/apparmor.d"

const defaultTemplate = `
{{range $value := .Imports}}
{{$value}}
{{end}}

profile {{.Name}} flags=(attach_disconnected,mediate_deleted) {
{{range $value := .InnerImports}}
  {{$value}}
{{end}}

  network,
  capability,
  file,
  umount,

  deny @{PROC}/* w,   # deny write for all files directly in /proc (not in a subdir)
  # deny write to files not in /proc/<number>/** or /proc/sys/**
  deny @{PROC}/{[^1-9],[^1-9][^0-9],[^1-9s][^0-9y][^0-9s],[^1-9][^0-9][^0-9][^0-9]*}/** w,
  deny @{PROC}/sys/[^k]** w,  # deny /proc/sys except /proc/sys/k* (effectively /proc/sys/kernel)
  deny @{PROC}/sys/kernel/{?,??,[^s][^h][^m]**} w,  # deny everything except shm* in /proc/sys/kernel/
  deny @{PROC}/sysrq-trigger rwklx,
  deny @{PROC}/mem rwklx,
  deny @{PROC}/kmem rwklx,
  deny @{PROC}/kcore rwklx,

  deny mount,

  deny /sys/[^f]*/** wklx,
  deny /sys/f[^s]*/** wklx,
  deny /sys/fs/[^c]*/** wklx,
  deny /sys/fs/c[^g]*/** wklx,
  deny /sys/fs/cg[^r]*/** wklx,
  deny /sys/firmware/** rwklx,
  deny /sys/kernel/security/** rwklx,

{{if ge .Version 208095}}
  ptrace (trace,read) peer={{.Name}},
{{end}}
}
`

type data struct {
	Name         string
	Imports      []string
	InnerImports []string
	Version      int
}

func loadData(name string) (*data, error) {
	p := data{
		Name: name,
	}

	if macroExists("tunables/global") {
		p.Imports = append(p.Imports, "#include <tunables/global>")
	} else {
		p.Imports = append(p.Imports, "@{PROC}=/proc/")
	}
	if macroExists("abstractions/base") {
		p.InnerImports = append(p.InnerImports, "#include <abstractions/base>")
	}
	ver, err := getVersion()
	if err != nil {
		return nil, errors.Wrap(err, "get apparmor_parser version")
	}
	p.Version = ver
	return &p, nil
}

func generate(p *data, o io.Writer) error {
	t, err := template.New("apparmor_profile").Parse(defaultTemplate)
	if err != nil {
		return err
	}
	return t.Execute(o, p)
}

func load(path string) error {
	out, err := aaParser("-Kr", path)
	if err != nil {
		return errors.Errorf("%s: %s", err, out)
	}
	return nil
}

// macrosExists checks if the passed macro exists.
func macroExists(m string) bool {
	_, err := os.Stat(path.Join(dir, m))
	return err == nil
}

func aaParser(args ...string) (string, error) {
	out, err := exec.Command("apparmor_parser", args...).CombinedOutput()
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func getVersion() (int, error) {
	out, err := aaParser("--version")
	if err != nil {
		return -1, err
	}
	return parseVersion(out)
}

// parseVersion takes the output from `apparmor_parser --version` and returns
// a representation of the {major, minor, patch} version as a single number of
// the form MMmmPPP {major, minor, patch}.
func parseVersion(output string) (int, error) {
	// output is in the form of the following:
	// AppArmor parser version 2.9.1
	// Copyright (C) 1999-2008 Novell Inc.
	// Copyright 2009-2012 Canonical Ltd.

	lines := strings.SplitN(output, "\n", 2)
	words := strings.Split(lines[0], " ")
	version := words[len(words)-1]

	// split by major minor version
	v := strings.Split(version, ".")
	if len(v) == 0 || len(v) > 3 {
		return -1, fmt.Errorf("parsing version failed for output: `%s`", output)
	}

	// Default the versions to 0.
	var majorVersion, minorVersion, patchLevel int

	majorVersion, err := strconv.Atoi(v[0])
	if err != nil {
		return -1, err
	}

	if len(v) > 1 {
		minorVersion, err = strconv.Atoi(v[1])
		if err != nil {
			return -1, err
		}
	}
	if len(v) > 2 {
		patchLevel, err = strconv.Atoi(v[2])
		if err != nil {
			return -1, err
		}
	}

	// major*10^5 + minor*10^3 + patch*10^0
	numericVersion := majorVersion*1e5 + minorVersion*1e3 + patchLevel
	return numericVersion, nil
}

func isLoaded(name string) (bool, error) {
	f, err := os.Open("/sys/kernel/security/apparmor/profiles")
	if err != nil {
		return false, err
	}
	defer f.Close()
	r := bufio.NewReader(f)
	for {
		p, err := r.ReadString('\n')
		if err == io.EOF {
			break
		}
		if err != nil {
			return false, err
		}
		if strings.HasPrefix(p, name+" ") {
			return true, nil
		}
	}
	return false, nil
}