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// Package readpassword reads a password from the terminal of from stdin.
package readpassword
import (
"fmt"
"io"
"os"
"os/exec"
"strings"
"sync"
"time"
"golang.org/x/crypto/ssh/terminal"
"github.com/rfjakob/gocryptfs/internal/exitcodes"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
const (
// 2kB limit like EncFS
maxPasswordLen = 2048
)
// Once tries to get a password from the user, either from the terminal, extpass
// or stdin.
func Once(extpass string) string {
if extpass != "" {
return readPasswordExtpass(extpass)
}
if !terminal.IsTerminal(int(os.Stdin.Fd())) {
return readPasswordStdin()
}
return readPasswordTerminal("Password: ")
}
// Twice is the same as Once but will prompt twice if we get the password from
// the terminal.
func Twice(extpass string) string {
if extpass != "" {
return readPasswordExtpass(extpass)
}
if !terminal.IsTerminal(int(os.Stdin.Fd())) {
return readPasswordStdin()
}
p1 := readPasswordTerminal("Password: ")
p2 := readPasswordTerminal("Repeat: ")
if p1 != p2 {
tlog.Fatal.Println("Passwords do not match")
os.Exit(exitcodes.ReadPassword)
}
return p1
}
// readPasswordTerminal reads a line from the terminal.
// Exits on read error or empty result.
func readPasswordTerminal(prompt string) string {
fd := int(os.Stdin.Fd())
fmt.Fprintf(os.Stderr, prompt)
// terminal.ReadPassword removes the trailing newline
p, err := terminal.ReadPassword(fd)
if err != nil {
tlog.Fatal.Printf("Could not read password from terminal: %v\n", err)
os.Exit(exitcodes.ReadPassword)
}
fmt.Fprintf(os.Stderr, "\n")
if len(p) == 0 {
tlog.Fatal.Println("Password is empty")
os.Exit(exitcodes.ReadPassword)
}
return string(p)
}
// readPasswordStdin reads a line from stdin.
// It exits with a fatal error on read error or empty result.
func readPasswordStdin() string {
tlog.Info.Println("Reading password from stdin")
p := readLineUnbuffered(os.Stdin)
if len(p) == 0 {
tlog.Fatal.Println("Got empty password from stdin")
os.Exit(exitcodes.ReadPassword)
}
return p
}
// readPasswordExtpass executes the "extpass" program and returns the first line
// of the output.
// Exits on read error or empty result.
func readPasswordExtpass(extpass string) string {
tlog.Info.Println("Reading password from extpass program")
var parts []string
// The option "-passfile=FILE" gets transformed to
// "-extpass="/bin/cat -- FILE". We don't want to split FILE on spaces,
// so let's handle it manually.
passfileCat := "/bin/cat -- "
if strings.HasPrefix(extpass, passfileCat) {
parts = []string{"/bin/cat", "--", extpass[len(passfileCat):]}
} else {
parts = strings.Split(extpass, " ")
}
cmd := exec.Command(parts[0], parts[1:]...)
cmd.Stderr = os.Stderr
pipe, err := cmd.StdoutPipe()
if err != nil {
tlog.Fatal.Printf("extpass pipe setup failed: %v", err)
os.Exit(exitcodes.ReadPassword)
}
err = cmd.Start()
if err != nil {
tlog.Fatal.Printf("extpass cmd start failed: %v", err)
os.Exit(exitcodes.ReadPassword)
}
p := readLineUnbuffered(pipe)
pipe.Close()
err = cmd.Wait()
if err != nil {
tlog.Fatal.Printf("extpass program returned an error: %v", err)
os.Exit(exitcodes.ReadPassword)
}
if len(p) == 0 {
tlog.Fatal.Println("extpass: password is empty")
os.Exit(exitcodes.ReadPassword)
}
return p
}
// readLineUnbuffered reads single bytes from "r" util it gets "\n" or EOF.
// The returned string does NOT contain the trailing "\n".
func readLineUnbuffered(r io.Reader) (l string) {
b := make([]byte, 1)
for {
if len(l) > maxPasswordLen {
tlog.Fatal.Printf("fatal: maximum password length of %d bytes exceeded", maxPasswordLen)
os.Exit(exitcodes.ReadPassword)
}
n, err := r.Read(b)
if err == io.EOF {
return l
}
if err != nil {
tlog.Fatal.Printf("readLineUnbuffered: %v", err)
os.Exit(exitcodes.ReadPassword)
}
if n == 0 {
continue
}
if b[0] == '\n' {
return l
}
l = l + string(b)
}
}
// CheckTrailingGarbage tries to read one byte from stdin and exits with a
// fatal error if the read returns any data.
// This is meant to be called after reading the password, when there is no more
// data expected. This helps to catch problems with third-party tools that
// interface with gocryptfs.
//
// This is tested via TestInitTrailingGarbage() in tests/cli/cli_test.go.
func CheckTrailingGarbage() {
if terminal.IsTerminal(int(os.Stdin.Fd())) {
// Be lenient when interacting with a human.
return
}
var wg sync.WaitGroup
wg.Add(1)
go func() {
b := make([]byte, 1)
wg.Done()
n, _ := os.Stdin.Read(b)
if n > 0 {
tlog.Fatal.Printf("Received trailing garbage after the password")
os.Exit(exitcodes.ReadPassword)
}
}()
// Wait for the goroutine to start up plus one millisecond for the read to
// return. If there is data available, this SHOULD be plenty of time to
// read one byte. However, I don't see a way to be sure.
wg.Wait()
time.Sleep(1 * time.Millisecond)
}
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