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package image
import (
"errors"
"fmt"
"os"
"path/filepath"
"strings"
"golang.org/x/sys/unix"
)
type secureOutputStore struct {
options *DownloadOptions
}
func newSecureOutputStore(options *DownloadOptions) secureOutputStore {
return secureOutputStore{options: options}
}
func (s secureOutputStore) openSecureOutputFile(outputPath string) (*os.File, int, string, error) {
baseAbs, err := s.baseAbs()
if err != nil {
return nil, 0, "", err
}
targetAbs, err := filepath.Abs(outputPath)
if err != nil {
return nil, 0, "", fmt.Errorf("resolve output path: %w", err)
}
relPath, err := filepath.Rel(baseAbs, targetAbs)
if err != nil {
return nil, 0, "", fmt.Errorf("relativize output path: %w", err)
}
if relPath == "." || relPath == ".." || strings.HasPrefix(relPath, ".."+string(os.PathSeparator)) {
return nil, 0, "", fmt.Errorf("path escapes base dir")
}
relPath = filepath.Clean(relPath)
parentRel := filepath.Dir(relPath)
finalName := filepath.Base(relPath)
parentFD, err := openDirPathNoFollow(baseAbs, parentRel, s.createDirs())
if err != nil {
return nil, 0, "", err
}
flags := unix.O_WRONLY | unix.O_CREAT | unix.O_CLOEXEC | unix.O_NOFOLLOW
if s.options != nil && s.options.OverwriteExisting {
flags |= unix.O_TRUNC
} else {
flags |= unix.O_EXCL
}
fd, err := unix.Openat(parentFD, finalName, flags, 0o644)
if err != nil {
_ = unix.Close(parentFD)
return nil, 0, "", fmt.Errorf("open output file: %w", err)
}
return os.NewFile(uintptr(fd), targetAbs), parentFD, finalName, nil
}
func (s secureOutputStore) writeSecureRelativeFile(outputPath, relPath string, content []byte, perm os.FileMode) error {
file, parentFD, finalName, err := s.openSecureRelativeFile(outputPath, relPath, perm)
if err != nil {
return err
}
defer func() {
_ = unix.Close(parentFD)
}()
defer func() {
_ = file.Close()
}()
if _, err := file.Write(content); err != nil {
_ = unix.Unlinkat(parentFD, finalName, 0)
return fmt.Errorf("write attribution file: %w", err)
}
if err := file.Sync(); err != nil {
_ = unix.Unlinkat(parentFD, finalName, 0)
return fmt.Errorf("sync attribution file: %w", err)
}
return nil
}
func (s secureOutputStore) openSecureRelativeFile(outputPath, relPath string, perm os.FileMode) (*os.File, int, string, error) {
baseAbs, err := s.baseAbs()
if err != nil {
return nil, 0, "", err
}
targetAbs, err := filepath.Abs(outputPath)
if err != nil {
return nil, 0, "", fmt.Errorf("resolve output path: %w", err)
}
baseRelPath, err := filepath.Rel(baseAbs, targetAbs)
if err != nil {
return nil, 0, "", fmt.Errorf("relativize output path: %w", err)
}
if baseRelPath == "." || baseRelPath == ".." || strings.HasPrefix(baseRelPath, ".."+string(os.PathSeparator)) {
return nil, 0, "", fmt.Errorf("path escapes base dir")
}
parentRel := filepath.Dir(filepath.Clean(baseRelPath))
parentFD, err := openDirPathNoFollow(baseAbs, parentRel, true)
if err != nil {
return nil, 0, "", err
}
flags := unix.O_WRONLY | unix.O_CREAT | unix.O_CLOEXEC | unix.O_NOFOLLOW | unix.O_TRUNC
fd, err := unix.Openat(parentFD, relPath, flags, uint32(perm.Perm()))
if err != nil {
_ = unix.Close(parentFD)
return nil, 0, "", fmt.Errorf("open attribution file: %w", err)
}
return os.NewFile(uintptr(fd), targetAbs), parentFD, relPath, nil
}
func (s secureOutputStore) baseAbs() (string, error) {
baseDir := "./images"
if s.options != nil && s.options.OutputDir != "" {
baseDir = s.options.OutputDir
}
baseAbs, err := filepath.Abs(baseDir)
if err != nil {
return "", fmt.Errorf("resolve base dir: %w", err)
}
return baseAbs, nil
}
func (s secureOutputStore) createDirs() bool {
return s.options != nil && s.options.CreateDir
}
func openDirPathNoFollow(baseAbs, relPath string, createDirs bool) (int, error) {
dirFD, err := openPathDirNoFollow(baseAbs, createDirs)
if err != nil {
return 0, err
}
relPath = filepath.Clean(relPath)
if relPath == "." {
return dirFD, nil
}
parts := strings.Split(relPath, string(os.PathSeparator))
for _, part := range parts {
if part == "" || part == "." {
continue
}
if createDirs {
if err := unix.Mkdirat(dirFD, part, 0o755); err != nil && !errors.Is(err, unix.EEXIST) {
_ = unix.Close(dirFD)
return 0, fmt.Errorf("create dir %q: %w", part, err)
}
}
nextFD, err := unix.Openat(dirFD, part, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
if err != nil {
_ = unix.Close(dirFD)
return 0, fmt.Errorf("open dir %q: %w", part, err)
}
_ = unix.Close(dirFD)
dirFD = nextFD
}
return dirFD, nil
}
func openPathDirNoFollow(absPath string, createDirs bool) (int, error) {
absPath = filepath.Clean(absPath)
if absPath == string(os.PathSeparator) {
return unix.Open(absPath, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
}
parentAbs := filepath.Dir(absPath)
leaf := filepath.Base(absPath)
parentFD, err := openPathDirNoFollow(parentAbs, createDirs)
if err != nil {
return 0, err
}
if createDirs {
if err := unix.Mkdirat(parentFD, leaf, 0o755); err != nil && !errors.Is(err, unix.EEXIST) {
_ = unix.Close(parentFD)
return 0, fmt.Errorf("create dir %q: %w", leaf, err)
}
}
dirFD, err := unix.Openat(parentFD, leaf, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
_ = unix.Close(parentFD)
if err != nil {
return 0, fmt.Errorf("open dir %q: %w", leaf, err)
}
return dirFD, nil
}
|
