DockerCLI/vendor/github.com/opencontainers/selinux/go-selinux/selinux.go

594 lines
13 KiB
Go

// +build linux
package selinux
import (
"bufio"
"crypto/rand"
"encoding/binary"
"fmt"
"io"
"os"
"path/filepath"
"regexp"
"strconv"
"strings"
"sync"
"syscall"
)
const (
// Enforcing constant indicate SELinux is in enforcing mode
Enforcing = 1
// Permissive constant to indicate SELinux is in permissive mode
Permissive = 0
// Disabled constant to indicate SELinux is disabled
Disabled = -1
selinuxDir = "/etc/selinux/"
selinuxConfig = selinuxDir + "config"
selinuxTypeTag = "SELINUXTYPE"
selinuxTag = "SELINUX"
selinuxPath = "/sys/fs/selinux"
xattrNameSelinux = "security.selinux"
stRdOnly = 0x01
)
type selinuxState struct {
enabledSet bool
enabled bool
selinuxfsSet bool
selinuxfs string
mcsList map[string]bool
sync.Mutex
}
var (
assignRegex = regexp.MustCompile(`^([^=]+)=(.*)$`)
state = selinuxState{
mcsList: make(map[string]bool),
}
)
// Context is a representation of the SELinux label broken into 4 parts
type Context map[string]string
func (s *selinuxState) setEnable(enabled bool) bool {
s.Lock()
defer s.Unlock()
s.enabledSet = true
s.enabled = enabled
return s.enabled
}
func (s *selinuxState) getEnabled() bool {
s.Lock()
enabled := s.enabled
enabledSet := s.enabledSet
s.Unlock()
if enabledSet {
return enabled
}
enabled = false
if fs := getSelinuxMountPoint(); fs != "" {
if con, _ := CurrentLabel(); con != "kernel" {
enabled = true
}
}
return s.setEnable(enabled)
}
// SetDisabled disables selinux support for the package
func SetDisabled() {
state.setEnable(false)
}
func (s *selinuxState) setSELinuxfs(selinuxfs string) string {
s.Lock()
defer s.Unlock()
s.selinuxfsSet = true
s.selinuxfs = selinuxfs
return s.selinuxfs
}
func (s *selinuxState) getSELinuxfs() string {
s.Lock()
selinuxfs := s.selinuxfs
selinuxfsSet := s.selinuxfsSet
s.Unlock()
if selinuxfsSet {
return selinuxfs
}
selinuxfs = ""
f, err := os.Open("/proc/self/mountinfo")
if err != nil {
return selinuxfs
}
defer f.Close()
scanner := bufio.NewScanner(f)
for scanner.Scan() {
txt := scanner.Text()
// Safe as mountinfo encodes mountpoints with spaces as \040.
sepIdx := strings.Index(txt, " - ")
if sepIdx == -1 {
continue
}
if !strings.Contains(txt[sepIdx:], "selinuxfs") {
continue
}
fields := strings.Split(txt, " ")
if len(fields) < 5 {
continue
}
selinuxfs = fields[4]
break
}
if selinuxfs != "" {
var buf syscall.Statfs_t
syscall.Statfs(selinuxfs, &buf)
if (buf.Flags & stRdOnly) == 1 {
selinuxfs = ""
}
}
return s.setSELinuxfs(selinuxfs)
}
// getSelinuxMountPoint returns the path to the mountpoint of an selinuxfs
// filesystem or an empty string if no mountpoint is found. Selinuxfs is
// a proc-like pseudo-filesystem that exposes the selinux policy API to
// processes. The existence of an selinuxfs mount is used to determine
// whether selinux is currently enabled or not.
func getSelinuxMountPoint() string {
return state.getSELinuxfs()
}
// GetEnabled returns whether selinux is currently enabled.
func GetEnabled() bool {
return state.getEnabled()
}
func readConfig(target string) (value string) {
var (
val, key string
bufin *bufio.Reader
)
in, err := os.Open(selinuxConfig)
if err != nil {
return ""
}
defer in.Close()
bufin = bufio.NewReader(in)
for done := false; !done; {
var line string
if line, err = bufin.ReadString('\n'); err != nil {
if err != io.EOF {
return ""
}
done = true
}
line = strings.TrimSpace(line)
if len(line) == 0 {
// Skip blank lines
continue
}
if line[0] == ';' || line[0] == '#' {
// Skip comments
continue
}
if groups := assignRegex.FindStringSubmatch(line); groups != nil {
key, val = strings.TrimSpace(groups[1]), strings.TrimSpace(groups[2])
if key == target {
return strings.Trim(val, "\"")
}
}
}
return ""
}
func getSELinuxPolicyRoot() string {
return selinuxDir + readConfig(selinuxTypeTag)
}
func readCon(name string) (string, error) {
var val string
in, err := os.Open(name)
if err != nil {
return "", err
}
defer in.Close()
_, err = fmt.Fscanf(in, "%s", &val)
return val, err
}
// SetFileLabel sets the SELinux label for this path or returns an error.
func SetFileLabel(path string, label string) error {
return lsetxattr(path, xattrNameSelinux, []byte(label), 0)
}
// Filecon returns the SELinux label for this path or returns an error.
func FileLabel(path string) (string, error) {
label, err := lgetxattr(path, xattrNameSelinux)
if err != nil {
return "", err
}
// Trim the NUL byte at the end of the byte buffer, if present.
if len(label) > 0 && label[len(label)-1] == '\x00' {
label = label[:len(label)-1]
}
return string(label), nil
}
/*
SetFSCreateLabel tells kernel the label to create all file system objects
created by this task. Setting label="" to return to default.
*/
func SetFSCreateLabel(label string) error {
return writeCon(fmt.Sprintf("/proc/self/task/%d/attr/fscreate", syscall.Gettid()), label)
}
/*
FSCreateLabel returns the default label the kernel which the kernel is using
for file system objects created by this task. "" indicates default.
*/
func FSCreateLabel() (string, error) {
return readCon(fmt.Sprintf("/proc/self/task/%d/attr/fscreate", syscall.Gettid()))
}
// CurrentLabel returns the SELinux label of the current process thread, or an error.
func CurrentLabel() (string, error) {
return readCon(fmt.Sprintf("/proc/self/task/%d/attr/current", syscall.Gettid()))
}
// PidLabel returns the SELinux label of the given pid, or an error.
func PidLabel(pid int) (string, error) {
return readCon(fmt.Sprintf("/proc/%d/attr/current", pid))
}
/*
ExecLabel returns the SELinux label that the kernel will use for any programs
that are executed by the current process thread, or an error.
*/
func ExecLabel() (string, error) {
return readCon(fmt.Sprintf("/proc/self/task/%d/attr/exec", syscall.Gettid()))
}
func writeCon(name string, val string) error {
out, err := os.OpenFile(name, os.O_WRONLY, 0)
if err != nil {
return err
}
defer out.Close()
if val != "" {
_, err = out.Write([]byte(val))
} else {
_, err = out.Write(nil)
}
return err
}
/*
SetExecLabel sets the SELinux label that the kernel will use for any programs
that are executed by the current process thread, or an error.
*/
func SetExecLabel(label string) error {
return writeCon(fmt.Sprintf("/proc/self/task/%d/attr/exec", syscall.Gettid()), label)
}
// Get returns the Context as a string
func (c Context) Get() string {
return fmt.Sprintf("%s:%s:%s:%s", c["user"], c["role"], c["type"], c["level"])
}
// NewContext creates a new Context struct from the specified label
func NewContext(label string) Context {
c := make(Context)
if len(label) != 0 {
con := strings.SplitN(label, ":", 4)
c["user"] = con[0]
c["role"] = con[1]
c["type"] = con[2]
c["level"] = con[3]
}
return c
}
// ReserveLabel reserves the MLS/MCS level component of the specified label
func ReserveLabel(label string) {
if len(label) != 0 {
con := strings.SplitN(label, ":", 4)
mcsAdd(con[3])
}
}
func selinuxEnforcePath() string {
return fmt.Sprintf("%s/enforce", selinuxPath)
}
// EnforceMode returns the current SELinux mode Enforcing, Permissive, Disabled
func EnforceMode() int {
var enforce int
enforceS, err := readCon(selinuxEnforcePath())
if err != nil {
return -1
}
enforce, err = strconv.Atoi(string(enforceS))
if err != nil {
return -1
}
return enforce
}
/*
SetEnforce sets the current SELinux mode Enforcing, Permissive.
Disabled is not valid, since this needs to be set at boot time.
*/
func SetEnforceMode(mode int) error {
return writeCon(selinuxEnforcePath(), fmt.Sprintf("%d", mode))
}
/*
DefaultEnforceMode returns the systems default SELinux mode Enforcing,
Permissive or Disabled. Note this is is just the default at boot time.
EnforceMode tells you the systems current mode.
*/
func DefaultEnforceMode() int {
switch readConfig(selinuxTag) {
case "enforcing":
return Enforcing
case "permissive":
return Permissive
}
return Disabled
}
func mcsAdd(mcs string) error {
state.Lock()
defer state.Unlock()
if state.mcsList[mcs] {
return fmt.Errorf("MCS Label already exists")
}
state.mcsList[mcs] = true
return nil
}
func mcsDelete(mcs string) {
state.Lock()
defer state.Unlock()
state.mcsList[mcs] = false
}
func intToMcs(id int, catRange uint32) string {
var (
SETSIZE = int(catRange)
TIER = SETSIZE
ORD = id
)
if id < 1 || id > 523776 {
return ""
}
for ORD > TIER {
ORD = ORD - TIER
TIER--
}
TIER = SETSIZE - TIER
ORD = ORD + TIER
return fmt.Sprintf("s0:c%d,c%d", TIER, ORD)
}
func uniqMcs(catRange uint32) string {
var (
n uint32
c1, c2 uint32
mcs string
)
for {
binary.Read(rand.Reader, binary.LittleEndian, &n)
c1 = n % catRange
binary.Read(rand.Reader, binary.LittleEndian, &n)
c2 = n % catRange
if c1 == c2 {
continue
} else {
if c1 > c2 {
c1, c2 = c2, c1
}
}
mcs = fmt.Sprintf("s0:c%d,c%d", c1, c2)
if err := mcsAdd(mcs); err != nil {
continue
}
break
}
return mcs
}
/*
ReleaseLabel will unreserve the MLS/MCS Level field of the specified label.
Allowing it to be used by another process.
*/
func ReleaseLabel(label string) {
if len(label) != 0 {
con := strings.SplitN(label, ":", 4)
mcsDelete(con[3])
}
}
var roFileLabel string
// ROFileLabel returns the specified SELinux readonly file label
func ROFileLabel() (fileLabel string) {
return roFileLabel
}
/*
ContainerLabels returns an allocated processLabel and fileLabel to be used for
container labeling by the calling process.
*/
func ContainerLabels() (processLabel string, fileLabel string) {
var (
val, key string
bufin *bufio.Reader
)
if !GetEnabled() {
return "", ""
}
lxcPath := fmt.Sprintf("%s/contexts/lxc_contexts", getSELinuxPolicyRoot())
in, err := os.Open(lxcPath)
if err != nil {
return "", ""
}
defer in.Close()
bufin = bufio.NewReader(in)
for done := false; !done; {
var line string
if line, err = bufin.ReadString('\n'); err != nil {
if err == io.EOF {
done = true
} else {
goto exit
}
}
line = strings.TrimSpace(line)
if len(line) == 0 {
// Skip blank lines
continue
}
if line[0] == ';' || line[0] == '#' {
// Skip comments
continue
}
if groups := assignRegex.FindStringSubmatch(line); groups != nil {
key, val = strings.TrimSpace(groups[1]), strings.TrimSpace(groups[2])
if key == "process" {
processLabel = strings.Trim(val, "\"")
}
if key == "file" {
fileLabel = strings.Trim(val, "\"")
}
if key == "ro_file" {
roFileLabel = strings.Trim(val, "\"")
}
}
}
if processLabel == "" || fileLabel == "" {
return "", ""
}
if roFileLabel == "" {
roFileLabel = fileLabel
}
exit:
mcs := uniqMcs(1024)
scon := NewContext(processLabel)
scon["level"] = mcs
processLabel = scon.Get()
scon = NewContext(fileLabel)
scon["level"] = mcs
fileLabel = scon.Get()
return processLabel, fileLabel
}
// SecurityCheckContext validates that the SELinux label is understood by the kernel
func SecurityCheckContext(val string) error {
return writeCon(fmt.Sprintf("%s.context", selinuxPath), val)
}
/*
CopyLevel returns a label with the MLS/MCS level from src label replaces on
the dest label.
*/
func CopyLevel(src, dest string) (string, error) {
if src == "" {
return "", nil
}
if err := SecurityCheckContext(src); err != nil {
return "", err
}
if err := SecurityCheckContext(dest); err != nil {
return "", err
}
scon := NewContext(src)
tcon := NewContext(dest)
mcsDelete(tcon["level"])
mcsAdd(scon["level"])
tcon["level"] = scon["level"]
return tcon.Get(), nil
}
// Prevent users from relabing system files
func badPrefix(fpath string) error {
var badprefixes = []string{"/usr"}
for _, prefix := range badprefixes {
if fpath == prefix || strings.HasPrefix(fpath, fmt.Sprintf("%s/", prefix)) {
return fmt.Errorf("relabeling content in %s is not allowed", prefix)
}
}
return nil
}
// Chcon changes the fpath file object to the SELinux label label.
// If the fpath is a directory and recurse is true Chcon will walk the
// directory tree setting the label
func Chcon(fpath string, label string, recurse bool) error {
if label == "" {
return nil
}
if err := badPrefix(fpath); err != nil {
return err
}
callback := func(p string, info os.FileInfo, err error) error {
return SetFileLabel(p, label)
}
if recurse {
return filepath.Walk(fpath, callback)
}
return SetFileLabel(fpath, label)
}
// DupSecOpt takes an SELinux process label and returns security options that
// can will set the SELinux Type and Level for future container processes
func DupSecOpt(src string) []string {
if src == "" {
return nil
}
con := NewContext(src)
if con["user"] == "" ||
con["role"] == "" ||
con["type"] == "" ||
con["level"] == "" {
return nil
}
return []string{"user:" + con["user"],
"role:" + con["role"],
"type:" + con["type"],
"level:" + con["level"]}
}
// DisableSecOpt returns a security opt that can be used to disabling SELinux
// labeling support for future container processes
func DisableSecOpt() []string {
return []string{"disable"}
}