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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2017 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package x11
import (
"encoding/binary"
"fmt"
"io"
"os"
)
// See https://cgit.freedesktop.org/xorg/lib/libXau/tree/AuRead.c and
// https://cgit.freedesktop.org/xorg/lib/libXau/tree/include/X11/Xauth.h
// for details about the actual file format.
type xauth struct {
Family uint16
Address []byte
Number []byte
Name []byte
Data []byte
}
func readChunk(r io.Reader) ([]byte, error) {
// A chunk consists of a length encoded by two bytes (so max 64K)
// and additional data which is the real value of the item we're
// reading here from the file.
b := [2]byte{}
if _, err := io.ReadFull(r, b[:]); err != nil {
return nil, err
}
size := int(binary.BigEndian.Uint16(b[:]))
chunk := make([]byte, size)
if _, err := io.ReadFull(r, chunk); err != nil {
return nil, err
}
return chunk, nil
}
func (xa *xauth) readFromFile(r io.Reader) error {
b := [2]byte{}
if _, err := io.ReadFull(r, b[:]); err != nil {
return err
}
// The family field consists of two bytes
xa.Family = binary.BigEndian.Uint16(b[:])
var err error
if xa.Address, err = readChunk(r); err != nil {
return err
}
if xa.Number, err = readChunk(r); err != nil {
return err
}
if xa.Name, err = readChunk(r); err != nil {
return err
}
if xa.Data, err = readChunk(r); err != nil {
return err
}
return nil
}
// ValidateXauthority validates a given Xauthority file. The file is valid
// if it can be parsed and contains at least one cookie.
func ValidateXauthorityFile(path string) error {
f, err := os.Open(path)
if err != nil {
return err
}
defer f.Close()
return ValidateXauthority(f)
}
// ValidateXauthority validates a given Xauthority file. The file is valid
// if it can be parsed and contains at least one cookie.
func ValidateXauthority(r io.Reader) error {
cookies := 0
for {
xa := &xauth{}
err := xa.readFromFile(r)
if err == io.EOF {
break
} else if err != nil {
return err
}
cookies++
}
if cookies <= 0 {
return fmt.Errorf("Xauthority file is invalid")
}
return nil
}
// MockXauthority will create a fake xauthority file and place it
// on a temporary path which is returned as result.
func MockXauthority(cookies int) (string, error) {
f, err := os.CreateTemp("", "xauth")
if err != nil {
return "", err
}
defer f.Close()
for n := 0; n < cookies; n++ {
data := []byte{
// Family
0x01, 0x00,
// Address
0x00, 0x04, 0x73, 0x6e, 0x61, 0x70,
// Number
0x00, 0x01, 0xff,
// Name
0x00, 0x05, 0x73, 0x6e, 0x61, 0x70, 0x64,
// Data
0x00, 0x01, 0xff,
}
m, err := f.Write(data)
if err != nil {
return "", err
} else if m != len(data) {
return "", fmt.Errorf("Could write cookie")
}
}
return f.Name(), nil
}
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