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|
// +build linux
package chrootuser
import (
"bufio"
"flag"
"fmt"
"io"
"os"
"os/exec"
"os/user"
"strconv"
"strings"
"sync"
"github.com/containers/storage/pkg/reexec"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
const (
openChrootedCommand = "chrootuser-open"
)
func init() {
reexec.Register(openChrootedCommand, openChrootedFileMain)
}
func openChrootedFileMain() {
status := 0
flag.Parse()
if len(flag.Args()) < 1 {
os.Exit(1)
}
// Our first parameter is the directory to chroot into.
if err := unix.Chdir(flag.Arg(0)); err != nil {
fmt.Fprintf(os.Stderr, "chdir(): %v", err)
os.Exit(1)
}
if err := unix.Chroot(flag.Arg(0)); err != nil {
fmt.Fprintf(os.Stderr, "chroot(): %v", err)
os.Exit(1)
}
// Anything else is a file we want to dump out.
for _, filename := range flag.Args()[1:] {
f, err := os.Open(filename)
if err != nil {
fmt.Fprintf(os.Stderr, "open(%q): %v", filename, err)
status = 1
continue
}
_, err = io.Copy(os.Stdout, f)
if err != nil {
fmt.Fprintf(os.Stderr, "read(%q): %v", filename, err)
}
f.Close()
}
os.Exit(status)
}
func openChrootedFile(rootdir, filename string) (*exec.Cmd, io.ReadCloser, error) {
// The child process expects a chroot and one or more filenames that
// will be consulted relative to the chroot directory and concatenated
// to its stdout. Start it up.
cmd := reexec.Command(openChrootedCommand, rootdir, filename)
stdout, err := cmd.StdoutPipe()
if err != nil {
return nil, nil, err
}
err = cmd.Start()
if err != nil {
return nil, nil, err
}
// Hand back the child's stdout for reading, and the child to reap.
return cmd, stdout, nil
}
var (
lookupUser, lookupGroup sync.Mutex
)
type lookupPasswdEntry struct {
name string
uid uint64
gid uint64
}
type lookupGroupEntry struct {
name string
gid uint64
}
func readWholeLine(rc *bufio.Reader) ([]byte, error) {
line, isPrefix, err := rc.ReadLine()
if err != nil {
return nil, err
}
for isPrefix {
// We didn't get a whole line. Keep reading chunks until we find an end of line, and discard them.
for isPrefix {
logrus.Debugf("discarding partial line %q", string(line))
_, isPrefix, err = rc.ReadLine()
if err != nil {
return nil, err
}
}
// That last read was the end of a line, so now we try to read the (beginning of?) the next line.
line, isPrefix, err = rc.ReadLine()
if err != nil {
return nil, err
}
}
return line, nil
}
func parseNextPasswd(rc *bufio.Reader) *lookupPasswdEntry {
line, err := readWholeLine(rc)
if err != nil {
return nil
}
fields := strings.Split(string(line), ":")
if len(fields) < 7 {
return nil
}
uid, err := strconv.ParseUint(fields[2], 10, 32)
if err != nil {
return nil
}
gid, err := strconv.ParseUint(fields[3], 10, 32)
if err != nil {
return nil
}
return &lookupPasswdEntry{
name: fields[0],
uid: uid,
gid: gid,
}
}
func parseNextGroup(rc *bufio.Reader) *lookupGroupEntry {
line, err := readWholeLine(rc)
if err != nil {
return nil
}
fields := strings.Split(string(line), ":")
if len(fields) < 4 {
return nil
}
gid, err := strconv.ParseUint(fields[2], 10, 32)
if err != nil {
return nil
}
return &lookupGroupEntry{
name: fields[0],
gid: gid,
}
}
func lookupUserInContainer(rootdir, username string) (uid uint64, gid uint64, err error) {
cmd, f, err := openChrootedFile(rootdir, "/etc/passwd")
if err != nil {
return 0, 0, err
}
defer func() {
_ = cmd.Wait()
}()
rc := bufio.NewReader(f)
defer f.Close()
lookupUser.Lock()
defer lookupUser.Unlock()
pwd := parseNextPasswd(rc)
for pwd != nil {
if pwd.name != username {
pwd = parseNextPasswd(rc)
continue
}
return pwd.uid, pwd.gid, nil
}
return 0, 0, user.UnknownUserError(fmt.Sprintf("error looking up user %q", username))
}
func lookupGroupForUIDInContainer(rootdir string, userid uint64) (username string, gid uint64, err error) {
cmd, f, err := openChrootedFile(rootdir, "/etc/passwd")
if err != nil {
return "", 0, err
}
defer func() {
_ = cmd.Wait()
}()
rc := bufio.NewReader(f)
defer f.Close()
lookupUser.Lock()
defer lookupUser.Unlock()
pwd := parseNextPasswd(rc)
for pwd != nil {
if pwd.uid != userid {
pwd = parseNextPasswd(rc)
continue
}
return pwd.name, pwd.gid, nil
}
return "", 0, user.UnknownUserError(fmt.Sprintf("error looking up user with UID %d", userid))
}
func lookupGroupInContainer(rootdir, groupname string) (gid uint64, err error) {
cmd, f, err := openChrootedFile(rootdir, "/etc/group")
if err != nil {
return 0, err
}
defer func() {
_ = cmd.Wait()
}()
rc := bufio.NewReader(f)
defer f.Close()
lookupGroup.Lock()
defer lookupGroup.Unlock()
grp := parseNextGroup(rc)
for grp != nil {
if grp.name != groupname {
grp = parseNextGroup(rc)
continue
}
return grp.gid, nil
}
return 0, user.UnknownGroupError(fmt.Sprintf("error looking up group %q", groupname))
}
|
