/
shadow.go
190 lines (153 loc) · 4.22 KB
/
shadow.go
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package linuxuser
// https://en.wikipedia.org/wiki/Passwd#Shadow_file
import (
"bufio"
"crypto/subtle"
"errors"
"fmt"
"os"
"strconv"
"strings"
"github.com/tredoe/osutil/user/crypt/sha512_crypt"
)
type Account struct {
Username string
passwordHash string
Uid uint32
GidPrimary uint32
GidsSupplementary []uint32
Homedir string
Shell string
}
func FindByUsername(username string) (*Account, error) {
shadowFile, err := os.Open("/etc/shadow")
if err != nil {
return nil, err
}
defer shadowFile.Close()
shadowLines := bufio.NewScanner(shadowFile)
for shadowLines.Scan() {
if shadowLines.Text() == "" { // skip empty lines
continue
}
// usbmux:*:18909:0:99999:7:::
parts := strings.Split(shadowLines.Text(), ":")
if len(parts) < 9 {
return nil, fmt.Errorf("/etc/shadow invalid parts number: %d", len(parts))
}
itemUsername := parts[0]
if itemUsername == username {
uid, gid, homedir, shell, err := resolveUserDetails(itemUsername)
if err != nil {
return nil, fmt.Errorf("resolveUserDetails: %w", err)
}
groups, err := resolveSupplementaryGids(itemUsername)
if err != nil {
return nil, fmt.Errorf("resolveSupplementaryGids: %w", err)
}
return &Account{
Username: itemUsername,
passwordHash: parts[1],
Uid: uid,
GidPrimary: gid,
GidsSupplementary: groups,
Homedir: homedir,
Shell: shell,
}, nil
}
}
if err := shadowLines.Err(); err != nil {
return nil, err
}
return nil, fmt.Errorf("username not found: %s", username)
}
func ValidatePassword(givenPassword string, account Account) error {
salt, err := extractSHA512CryptSalt(account)
if err != nil {
return err
}
givenPasswordHash, err := hashPassword(givenPassword, salt)
if err != nil {
return err
}
if subtle.ConstantTimeCompare([]byte(givenPasswordHash), []byte(account.passwordHash)) != 1 {
return errors.New("wrong password")
}
return nil
}
func hashPassword(givenPassword string, salt []byte) (string, error) {
hash, err := sha512_crypt.New().Generate([]byte(givenPassword), salt)
if err != nil {
return "", err
}
return hash, nil
}
func extractSHA512CryptSalt(account Account) ([]byte, error) {
// $6 prefix indicates sha512_crypt
if !strings.HasPrefix(account.passwordHash, "$6$") {
return nil, errors.New("unexpected passwordHash type")
}
return []byte(account.passwordHash[:11]), nil
}
// /etc/shadow doesn't contain uid & gid, so we have to read it from a separate file
func resolveUserDetails(username string) (uint32, uint32, string, string, error) {
passwdFile, err := os.Open("/etc/passwd")
if err != nil {
return 0, 0, "", "", err
}
defer passwdFile.Close()
passwdLines := bufio.NewScanner(passwdFile)
for passwdLines.Scan() {
// usbmux:x:106:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
parts := strings.Split(passwdLines.Text(), ":")
if len(parts) < 7 {
return 0, 0, "", "", fmt.Errorf("/etc/passwd invalid parts number: %d", len(parts))
}
name := parts[0]
if name == username {
uid, err := strconv.Atoi(parts[2])
if err != nil {
return 0, 0, "", "", err
}
gid, err := strconv.Atoi(parts[3])
if err != nil {
return 0, 0, "", "", err
}
homedir := parts[5]
shell := parts[6]
return uint32(uid), uint32(gid), homedir, shell, nil
}
}
if err := passwdLines.Err(); err != nil {
return 0, 0, "", "", err
}
return 0, 0, "", "", fmt.Errorf("user '%s' not found from /etc/passwd", username)
}
func resolveSupplementaryGids(username string) ([]uint32, error) {
groups := []uint32{}
groupFile, err := os.Open("/etc/group")
if err != nil {
return nil, err
}
defer groupFile.Close()
groupLines := bufio.NewScanner(groupFile)
for groupLines.Scan() {
// docker:x:129:joonas
parts := strings.Split(groupLines.Text(), ":")
if len(parts) < 4 {
return nil, fmt.Errorf("/etc/group invalid parts number: %d", len(parts))
}
lineUsername := parts[3]
if lineUsername == username {
gid, err := strconv.Atoi(parts[2])
if err != nil {
return nil, err
}
groups = append(groups, uint32(gid))
}
}
if err := groupLines.Err(); err != nil {
return nil, err
}
return groups, nil
}