chroot_fs.go

package syslutil

import (
	"errors"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"time"

	"github.com/spf13/afero"
)

const windows = "windows"

type ChrootFs struct {
	fs   afero.Fs
	root string
}

var _ afero.Fs = &ChrootFs{}

// NewChrootFs returns a filesystem that is rooted at root argument
func NewChrootFs(fs afero.Fs, root string) *ChrootFs {
	if !filepath.IsAbs(root) {
		var err error
		root, err = filepath.Abs(root)
		if err != nil {
			panic(err)
		}
	}
	return &ChrootFs{fs: fs, root: cleanPathForMemFs(fs, root)}
}

func trimVolumeName(name string) string {
	return strings.TrimLeft(name, filepath.VolumeName(name))
}

func cleanPathForMemFs(fs afero.Fs, p string) string {
	// this is a workaround for afero.MemMapFs because it does not work if path has volume names.
	if _, isMemFs := fs.(*afero.MemMapFs); runtime.GOOS == windows && isMemFs {
		p = trimVolumeName(p)
	}
	return p
}

func (fs *ChrootFs) join(name string) (string, error) {
	// this is to avoid windows joining volume name twice in a nested fs
	name = trimVolumeName(name)
	p, err := filepath.Abs(filepath.Join(fs.root, name))
	if err != nil {
		return "", err
	}
	return cleanPathForMemFs(fs.fs, p), nil
}

func (fs *ChrootFs) Create(name string) (afero.File, error) {
	data, err := fs.wrapCallWithData(name,
		func(fixedPath string) (interface{}, error) {
			return fs.fs.Create(fixedPath)
		})
	if err != nil {
		return nil, err
	}
	return data.(afero.File), err
}

func (fs *ChrootFs) Mkdir(name string, perm os.FileMode) error {
	return fs.wrapCall(name, func(fixedPath string) error {
		return fs.fs.Mkdir(fixedPath, perm)
	})
}

func (fs *ChrootFs) MkdirAll(path string, perm os.FileMode) error {
	return fs.wrapCall(path, func(fixedPath string) error {
		return fs.fs.MkdirAll(fixedPath, perm)
	})
}

func (fs *ChrootFs) Open(name string) (afero.File, error) {
	data, err := fs.wrapCallWithData(name,
		func(fixedPath string) (interface{}, error) {
			return fs.fs.Open(fixedPath)
		})
	if err != nil {
		return nil, err
	}
	return data.(afero.File), err
}

func (fs *ChrootFs) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
	data, err := fs.wrapCallWithData(name,
		func(fixedPath string) (interface{}, error) {
			return fs.fs.OpenFile(fixedPath, flag, perm)
		})
	if err != nil {
		return nil, err
	}
	return data.(afero.File), err
}

func (fs *ChrootFs) Remove(name string) error {
	return fs.wrapCall(name, func(fixedPath string) error {
		return fs.fs.Remove(fixedPath)
	})
}

func (fs *ChrootFs) RemoveAll(path string) error {
	return fs.wrapCall(path, func(fixedPath string) error {
		return fs.fs.RemoveAll(fixedPath)
	})
}

func (fs *ChrootFs) Rename(oldname, newname string) error {
	return fs.wrapCall(oldname, func(fixedPath string) error {
		newFile, err := fs.join(newname)
		if err != nil {
			return err
		}
		return fs.fs.Rename(fixedPath, newFile)
	})
}

func (fs *ChrootFs) Stat(name string) (os.FileInfo, error) {
	data, err := fs.wrapCallWithData(name,
		func(fixedPath string) (interface{}, error) {
			return fs.fs.Stat(fixedPath)
		})
	if err != nil {
		return nil, err
	}
	return data.(os.FileInfo), err
}

func (fs *ChrootFs) Name() string {
	return "ChrootFS"
}

func (fs *ChrootFs) Chmod(name string, mode os.FileMode) error {
	return fs.wrapCall(name, func(fixedPath string) error {
		return fs.fs.Chmod(fixedPath, mode)
	})
}

func (fs *ChrootFs) Chown(name string, uid, gid int) error {
	return fs.wrapCall(name, func(fixedPath string) error {
		return fs.fs.Chown(fixedPath, uid, gid)
	})
}

func (fs *ChrootFs) Chtimes(name string, atime time.Time, mtime time.Time) error {
	return fs.wrapCall(name, func(fixedPath string) error {
		return fs.fs.Chtimes(fixedPath, atime, mtime)
	})
}

func (fs *ChrootFs) Root() string {
	return fs.root
}

func (fs *ChrootFs) openAllowed(fullPath string) error {
	relativePath, err := filepath.Rel(fs.root, fullPath)
	if err != nil {
		return err
	}

	if relativePath != "" && strings.Split(relativePath, string(os.PathSeparator))[0] == ".." {
		return errors.New("permission denied, file outside root")
	}

	return nil
}

func (fs *ChrootFs) wrapCall(path string, fn func(string) error) error {
	filename, err := fs.join(path)
	if err != nil {
		return err
	}
	if err := fs.openAllowed(filename); err != nil {
		return err
	}
	return fn(filename)
}

func (fs *ChrootFs) wrapCallWithData(
	path string,
	fn func(string) (interface{}, error)) (interface{}, error) {
	filename, err := fs.join(path)
	if err != nil {
		return nil, err
	}
	if err := fs.openAllowed(filename); err != nil {
		return nil, err
	}
	return fn(filename)
}