package fusefrontend_reverse import ( "fmt" "log" "path/filepath" "syscall" "golang.org/x/sys/unix" "github.com/hanwen/go-fuse/fuse" "github.com/hanwen/go-fuse/fuse/nodefs" "github.com/hanwen/go-fuse/fuse/pathfs" "github.com/rfjakob/gocryptfs/internal/configfile" "github.com/rfjakob/gocryptfs/internal/contentenc" "github.com/rfjakob/gocryptfs/internal/cryptocore" "github.com/rfjakob/gocryptfs/internal/fusefrontend" "github.com/rfjakob/gocryptfs/internal/nametransform" "github.com/rfjakob/gocryptfs/internal/pathiv" "github.com/rfjakob/gocryptfs/internal/syscallcompat" "github.com/rfjakob/gocryptfs/internal/tlog" ) // ReverseFS implements the pathfs.FileSystem interface and provides an // encrypted view of a plaintext directory. type ReverseFS struct { // Embed pathfs.defaultFileSystem for a ENOSYS implementation of all methods pathfs.FileSystem // pathfs.loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go loopbackfs pathfs.FileSystem // Stores configuration arguments args fusefrontend.Args // Filename encryption helper nameTransform *nametransform.NameTransform // Content encryption helper contentEnc *contentenc.ContentEnc } var _ pathfs.FileSystem = &ReverseFS{} // NewFS returns an encrypted FUSE overlay filesystem. // In this case (reverse mode) the backing directory is plain-text and // ReverseFS provides an encrypted view. func NewFS(masterkey []byte, args fusefrontend.Args) *ReverseFS { if args.CryptoBackend != cryptocore.BackendAESSIV { log.Panic("reverse mode must use AES-SIV, everything else is insecure") } initLongnameCache() cryptoCore := cryptocore.New(masterkey, args.CryptoBackend, contentenc.DefaultIVBits, args.HKDF, false) contentEnc := contentenc.New(cryptoCore, contentenc.DefaultBS, false) nameTransform := nametransform.New(cryptoCore.EMECipher, args.LongNames, args.Raw64) return &ReverseFS{ // pathfs.defaultFileSystem returns ENOSYS for all operations FileSystem: pathfs.NewDefaultFileSystem(), loopbackfs: pathfs.NewLoopbackFileSystem(args.Cipherdir), args: args, nameTransform: nameTransform, contentEnc: contentEnc, } } // relDir is identical to filepath.Dir excepts that it returns "" when // filepath.Dir would return ".". // In the FUSE API, the root directory is called "", and we actually want that. func relDir(path string) string { dir := filepath.Dir(path) if dir == "." { return "" } return dir } // isDirIV determines if the path points to a gocryptfs.diriv file func (rfs *ReverseFS) isDirIV(relPath string) bool { if rfs.args.PlaintextNames { return false } return filepath.Base(relPath) == nametransform.DirIVFilename } // isNameFile determines if the path points to a gocryptfs.longname.*.name // file func (rfs *ReverseFS) isNameFile(relPath string) bool { if rfs.args.PlaintextNames { return false } fileType := nametransform.NameType(filepath.Base(relPath)) return fileType == nametransform.LongNameFilename } // isTranslatedConfig returns true if the default config file name is in use // and the ciphertext path is "gocryptfs.conf". // "gocryptfs.conf" then maps to ".gocryptfs.reverse.conf" in the plaintext // directory. func (rfs *ReverseFS) isTranslatedConfig(relPath string) bool { if rfs.args.ConfigCustom { return false } if relPath == configfile.ConfDefaultName { return true } return false } // GetAttr - FUSE call // "relPath" is the relative ciphertext path func (rfs *ReverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) { // Handle "gocryptfs.conf" if rfs.isTranslatedConfig(relPath) { absConfPath, _ := rfs.abs(configfile.ConfReverseName, nil) var st syscall.Stat_t err := syscall.Lstat(absConfPath, &st) if err != nil { return nil, fuse.ToStatus(err) } var a fuse.Attr a.FromStat(&st) if rfs.args.ForceOwner != nil { a.Owner = *rfs.args.ForceOwner } return &a, fuse.OK } // Handle virtual files (gocryptfs.diriv, *.name) var f nodefs.File var status fuse.Status virtual := false if rfs.isDirIV(relPath) { virtual = true f, status = rfs.newDirIVFile(relPath) } if rfs.isNameFile(relPath) { virtual = true f, status = rfs.newNameFile(relPath) } if virtual { if !status.Ok() { tlog.Warn.Printf("GetAttr %q: newXFile failed: %v\n", relPath, status) return nil, status } var a fuse.Attr status = f.GetAttr(&a) if rfs.args.ForceOwner != nil { a.Owner = *rfs.args.ForceOwner } return &a, status } dirfd, name, err := rfs.openBackingDir(relPath) if err != nil { return nil, fuse.ToStatus(err) } // Stat the backing file/dir using Fstatat var st unix.Stat_t err = syscallcompat.Fstatat(dirfd, name, &st, unix.AT_SYMLINK_NOFOLLOW) syscall.Close(dirfd) if err != nil { return nil, fuse.ToStatus(err) } // Instead of risking an inode number collision, we return an error. if st.Ino > inoBaseMin { tlog.Warn.Printf("GetAttr %q: backing file inode number %d crosses reserved space, max=%d. Returning EOVERFLOW.", relPath, st.Ino, inoBaseMin) return nil, fuse.ToStatus(syscall.EOVERFLOW) } var a fuse.Attr st2 := syscallcompat.Unix2syscall(st) a.FromStat(&st2) // Calculate encrypted file size if a.IsRegular() { a.Size = rfs.contentEnc.PlainSizeToCipherSize(a.Size) } else if a.IsSymlink() { var linkTarget string var readlinkStatus fuse.Status linkTarget, readlinkStatus = rfs.Readlink(relPath, context) if !readlinkStatus.Ok() { return nil, readlinkStatus } a.Size = uint64(len(linkTarget)) } if rfs.args.ForceOwner != nil { a.Owner = *rfs.args.ForceOwner } return &a, fuse.OK } // Access - FUSE call func (rfs *ReverseFS) Access(relPath string, mode uint32, context *fuse.Context) fuse.Status { if rfs.isTranslatedConfig(relPath) || rfs.isDirIV(relPath) || rfs.isNameFile(relPath) { // access(2) R_OK flag for checking if the file is readable, always 4 as defined in POSIX. ROK := uint32(0x4) // Virtual files can always be read and never written if mode == ROK || mode == 0 { return fuse.OK } return fuse.EPERM } dirfd, name, err := rfs.openBackingDir(relPath) if err != nil { return fuse.ToStatus(err) } err = syscallcompat.Faccessat(dirfd, name, mode) if err != nil { fmt.Printf("name=%q err=%v", name, err) } syscall.Close(dirfd) return fuse.ToStatus(err) } // Open - FUSE call func (rfs *ReverseFS) Open(relPath string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) { if rfs.isTranslatedConfig(relPath) { return rfs.loopbackfs.Open(configfile.ConfReverseName, flags, context) } if rfs.isDirIV(relPath) { return rfs.newDirIVFile(relPath) } if rfs.isNameFile(relPath) { return rfs.newNameFile(relPath) } return rfs.newFile(relPath) } func (rfs *ReverseFS) openDirPlaintextnames(relPath string, entries []fuse.DirEntry) ([]fuse.DirEntry, fuse.Status) { if relPath != "" || rfs.args.ConfigCustom { return entries, fuse.OK } // We are in the root dir and the default config file name // ".gocryptfs.reverse.conf" is used. We map it to "gocryptfs.conf". dupe := -1 status := fuse.OK for i := range entries { if entries[i].Name == configfile.ConfReverseName { entries[i].Name = configfile.ConfDefaultName } else if entries[i].Name == configfile.ConfDefaultName { dupe = i } } if dupe >= 0 { // Warn the user loudly: The gocryptfs.conf_NAME_COLLISION file will // throw ENOENT errors that are hard to miss. tlog.Warn.Printf("The file %s is mapped to %s and shadows another file. Please rename %s in %s .", configfile.ConfReverseName, configfile.ConfDefaultName, configfile.ConfDefaultName, rfs.args.Cipherdir) entries[dupe].Name = "gocryptfs.conf_NAME_COLLISION_" + fmt.Sprintf("%d", cryptocore.RandUint64()) } return entries, status } // OpenDir - FUSE readdir call func (rfs *ReverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) { relPath, err := rfs.decryptPath(cipherPath) if err != nil { return nil, fuse.ToStatus(err) } // Read plaintext dir fd, err := syscallcompat.OpenNofollow(rfs.args.Cipherdir, relPath, syscall.O_RDONLY|syscall.O_DIRECTORY, 0) if err != nil { return nil, fuse.ToStatus(err) } entries, err := syscallcompat.Getdents(fd) syscall.Close(fd) if err != nil { return nil, fuse.ToStatus(err) } if rfs.args.PlaintextNames { return rfs.openDirPlaintextnames(cipherPath, entries) } // Allocate maximum possible number of virtual files. // If all files have long names we need a virtual ".name" file for each, // plus one for gocryptfs.diriv. virtualFiles := make([]fuse.DirEntry, len(entries)+1) // Virtual gocryptfs.diriv file virtualFiles[0] = fuse.DirEntry{ Mode: virtualFileMode, Name: nametransform.DirIVFilename, } // Actually used entries nVirtual := 1 // Encrypt names dirIV := pathiv.Derive(cipherPath, pathiv.PurposeDirIV) for i := range entries { var cName string // ".gocryptfs.reverse.conf" in the root directory is mapped to "gocryptfs.conf" if cipherPath == "" && entries[i].Name == configfile.ConfReverseName { cName = configfile.ConfDefaultName } else { cName = rfs.nameTransform.EncryptName(entries[i].Name, dirIV) if len(cName) > unix.NAME_MAX { cName = rfs.nameTransform.HashLongName(cName) dotNameFile := fuse.DirEntry{ Mode: virtualFileMode, Name: cName + nametransform.LongNameSuffix, } virtualFiles[nVirtual] = dotNameFile nVirtual++ } } entries[i].Name = cName } entries = append(entries, virtualFiles[:nVirtual]...) return entries, fuse.OK } // StatFs - FUSE call. Returns information about the filesystem (free space // etc). // Securing statfs against symlink races seems to be more trouble than // it's worth, so we just ignore the path and always return info about the // backing storage root dir. func (rfs *ReverseFS) StatFs(path string) *fuse.StatfsOut { var s syscall.Statfs_t err := syscall.Statfs(rfs.args.Cipherdir, &s) if err != nil { return nil } out := &fuse.StatfsOut{} out.FromStatfsT(&s) return out } // Readlink - FUSE call func (rfs *ReverseFS) Readlink(relPath string, context *fuse.Context) (string, fuse.Status) { dirfd, name, err := rfs.openBackingDir(relPath) if err != nil { return "", fuse.ToStatus(err) } // read the link target using Readlinkat plainTarget, err := syscallcompat.Readlinkat(dirfd, name) syscall.Close(dirfd) if err != nil { return "", fuse.ToStatus(err) } if rfs.args.PlaintextNames { return plainTarget, fuse.OK } nonce := pathiv.Derive(relPath, pathiv.PurposeSymlinkIV) // Symlinks are encrypted like file contents and base64-encoded cBinTarget := rfs.contentEnc.EncryptBlockNonce([]byte(plainTarget), 0, nil, nonce) cTarget := rfs.nameTransform.B64.EncodeToString(cBinTarget) // The kernel will reject a symlink target above 4096 chars and return // and I/O error to the user. Better emit the proper error ourselves. const PATH_MAX = 4096 // not defined on Darwin if len(cTarget) > PATH_MAX { return "", fuse.Status(syscall.ENAMETOOLONG) } return cTarget, fuse.OK }