xs/hkexauth.go

// Authentication routines for the HKExSh

package herradurakex

import (
	"bytes"
	"encoding/csv"
	"io"
	"io/ioutil"
	"log"
	"runtime"

	"github.com/jameskeane/bcrypt"
	"golang.org/x/sys/unix"
)

func AuthUser(username string, auth string, fname string) (valid bool, allowedCmds string) {
	b, e := ioutil.ReadFile(fname)
	if e != nil {
		valid = false
		log.Println("ERROR: Cannot read hkexsh.passwd file!")
		log.Fatal(e)
	}
	r := csv.NewReader(bytes.NewReader(b))

	b = nil
	runtime.GC() // Paranoia and prob. not effective; kill authFile in b[]

	r.Comma = ':'
	r.Comment = '#'
	r.FieldsPerRecord = 4 // username:salt:authCookie:disallowedCmdList (a,b,...)
	for {
		record, err := r.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatal(err)
		}

		if username == record[0] {
			tmp, _ := bcrypt.Hash(auth, record[1])
			if tmp == record[2] {
				valid = true
			}
			break
		}
	}
	return
}

/* ------------- minimal terminal APIs brought in from ssh/terminal
 * (they have no real business being there as they aren't specific to
 * ssh, but as of v1.10, early 2018, core go stdlib hasn't yet done
 * the planned terminal lib reorgs.)
 * -------------
 */

// From github.com/golang/crypto/blob/master/ssh/terminal/util_linux.go
const ioctlReadTermios = unix.TCGETS
const ioctlWriteTermios = unix.TCSETS

// From github.com/golang/crypto/blob/master/ssh/terminal/util.go
// State contains the state of a terminal.
type State struct {
	termios unix.Termios
}

// MakeRaw put the terminal connected to the given file descriptor into raw
// mode and returns the previous state of the terminal so that it can be
// restored.
func MakeRaw(fd int) (*State, error) {
	termios, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
	if err != nil {
		return nil, err
	}

	oldState := State{termios: *termios}

	// This attempts to replicate the behaviour documented for cfmakeraw in
	// the termios(3) manpage.
	termios.Iflag &^= unix.IGNBRK | unix.BRKINT | unix.PARMRK | unix.ISTRIP | unix.INLCR | unix.IGNCR | unix.ICRNL | unix.IXON
	termios.Oflag &^= unix.OPOST
	termios.Lflag &^= unix.ECHO | unix.ECHONL | unix.ICANON | unix.ISIG | unix.IEXTEN
	termios.Cflag &^= unix.CSIZE | unix.PARENB
	termios.Cflag |= unix.CS8
	termios.Cc[unix.VMIN] = 1
	termios.Cc[unix.VTIME] = 0
	if err := unix.IoctlSetTermios(fd, ioctlWriteTermios, termios); err != nil {
		return nil, err
	}

	return &oldState, nil
}

// GetState returns the current state of a terminal which may be useful to
// restore the terminal after a signal.
func GetState(fd int) (*State, error) {
	termios, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
	if err != nil {
		return nil, err
	}

	return &State{termios: *termios}, nil
}

// Restore restores the terminal connected to the given file descriptor to a
// previous state.
func Restore(fd int, state *State) error {
	return unix.IoctlSetTermios(fd, ioctlWriteTermios, &state.termios)
}

// ReadPassword reads a line of input from a terminal without local echo.  This
// is commonly used for inputting passwords and other sensitive data. The slice
// returned does not include the \n.
func ReadPassword(fd int) ([]byte, error) {
	termios, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
	if err != nil {
		return nil, err
	}

	newState := *termios
	newState.Lflag &^= unix.ECHO
	newState.Lflag |= unix.ICANON | unix.ISIG
	newState.Iflag |= unix.ICRNL
	if err := unix.IoctlSetTermios(fd, ioctlWriteTermios, &newState); err != nil {
		return nil, err
	}

	defer func() {
		unix.IoctlSetTermios(fd, ioctlWriteTermios, termios)
	}()

	return readPasswordLine(passwordReader(fd))
}

// passwordReader is an io.Reader that reads from a specific file descriptor.
type passwordReader int

func (r passwordReader) Read(buf []byte) (int, error) {
	return unix.Read(int(r), buf)
}

// readPasswordLine reads from reader until it finds \n or io.EOF.
// The slice returned does not include the \n.
// readPasswordLine also ignores any \r it finds.
func readPasswordLine(reader io.Reader) ([]byte, error) {
	var buf [1]byte
	var ret []byte

	for {
		n, err := reader.Read(buf[:])
		if n > 0 {
			switch buf[0] {
			case '\n':
				return ret, nil
			case '\r':
				// remove \r from passwords on Windows
			default:
				ret = append(ret, buf[0])
			}
			continue
		}
		if err != nil {
			if err == io.EOF && len(ret) > 0 {
				return ret, nil
			}
			return ret, err
		}
	}
}