containerd/contrib/apparmor/template.go

//go:build linux

/*
   Copyright The docker Authors.
   Copyright The Moby Authors.
   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"
	"path"
	"strconv"
	"strings"
	"text/template"

	exec "golang.org/x/sys/execabs"
)

// NOTE: This code is copied from <github.com/docker/docker/profiles/apparmor>.
//       If you plan to make any changes, please make sure they are also sent
//       upstream.

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,
  # Host (privileged) processes may send signals to container processes.
  signal (receive) peer=unconfined,
  # Manager may send signals to container processes.
  signal (receive) peer={{.DaemonProfile}},
  # Container processes may send signals amongst themselves.
  signal (send,receive) peer={{.Name}},

  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,

  # allow processes within the container to trace each other,
  # provided all other LSM and yama setting allow it.
  ptrace (trace,tracedby,read,readby) peer={{.Name}},
}
`

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

func cleanProfileName(profile string) string {
	// Normally profiles are suffixed by " (enforce)". AppArmor profiles cannot
	// contain spaces so this doesn't restrict daemon profile names.
	profile, _, _ = strings.Cut(profile, " ")
	if profile == "" {
		profile = "unconfined"
	}
	return profile
}

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, fmt.Errorf("get apparmor_parser version: %w", err)
	}
	p.Version = ver

	// Figure out the daemon profile.
	currentProfile, err := os.ReadFile("/proc/self/attr/current")
	if err != nil {
		// If we couldn't get the daemon profile, assume we are running
		// unconfined which is generally the default.
		currentProfile = nil
	}
	p.DaemonProfile = cleanProfileName(string(currentProfile))

	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 fmt.Errorf("parser error(%q): %w", strings.TrimSpace(out), err)
	}
	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()
	return string(out), err
}

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.

	version, _, _ := strings.Cut(output, "\n")
	if i := strings.LastIndex(version, " "); i >= 0 {
		version = version[i+1:]
	}

	// trim "-beta1" suffix from version="3.0.0-beta1" if exists
	version, _, _ = strings.Cut(version, "-")
	// also trim tilde
	version, _, _ = strings.Cut(version, "~")

	// split by major minor version
	v := strings.SplitN(version, ".", 4)
	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
}