package nametransform import ( "crypto/sha256" "fmt" "io" "os" "path/filepath" "strings" "syscall" "../../rewrites/syscallcompat" ) const ( // LongNameSuffix is the suffix used for files with long names. // Files with long names are stored in two files: // gocryptfs.longname.[sha256] <--- File content, prefix = gocryptfs.longname. // gocryptfs.longname.[sha256].name <--- File name, suffix = .name LongNameSuffix = ".name" longNamePrefix = "gocryptfs.longname." ) // HashLongName - take the hash of a long string "name" and return // "gocryptfs.longname.[sha256]" // // This function does not do any I/O. func (n *NameTransform) HashLongName(name string) string { hashBin := sha256.Sum256([]byte(name)) hashBase64 := n.B64.EncodeToString(hashBin[:]) return longNamePrefix + hashBase64 } // Values returned by IsLongName const ( // LongNameContent is the file that stores the file content. // Example: gocryptfs.longname.URrM8kgxTKYMgCk4hKk7RO9Lcfr30XQof4L_5bD9Iro= LongNameContent = iota // LongNameFilename is the file that stores the full encrypted filename. // Example: gocryptfs.longname.URrM8kgxTKYMgCk4hKk7RO9Lcfr30XQof4L_5bD9Iro=.name LongNameFilename = iota // LongNameNone is used when the file does not have a long name. // Example: i1bpTaVLZq7sRNA9mL_2Ig== LongNameNone = iota ) // NameType - detect if cName is // gocryptfs.longname.[sha256] ........ LongNameContent (content of a long name file) // gocryptfs.longname.[sha256].name .... LongNameFilename (full file name of a long name file) // else ................................ LongNameNone (normal file) // // This function does not do any I/O. func NameType(cName string) int { if !strings.HasPrefix(cName, longNamePrefix) { return LongNameNone } if strings.HasSuffix(cName, LongNameSuffix) { return LongNameFilename } return LongNameContent } // IsLongContent returns true if "cName" is the content store of a long name // file (looks like "gocryptfs.longname.[sha256]"). // // This function does not do any I/O. func IsLongContent(cName string) bool { return NameType(cName) == LongNameContent } // RemoveLongNameSuffix removes the ".name" suffix from cName, returning the corresponding // content file name. // No check is made if cName actually is a LongNameFilename. func RemoveLongNameSuffix(cName string) string { return cName[:len(cName)-len(LongNameSuffix)] } // ReadLongName - read cName + ".name" from the directory opened as dirfd. // // Symlink-safe through Openat(). func ReadLongNameAt(dirfd int, cName string) (string, error) { cName += LongNameSuffix var f *os.File { fd, err := syscallcompat.Openat(dirfd, cName, syscall.O_RDONLY|syscall.O_NOFOLLOW, 0) if err != nil { return "", err } f = os.NewFile(uintptr(fd), "") // fd runs out of scope here } defer f.Close() // 256 (=255 padded to 16) bytes base64-encoded take 344 bytes: "AAAAAAA...AAA==" lim := 344 // Allocate a bigger buffer so we see whether the file is too big buf := make([]byte, lim+1) n, err := f.ReadAt(buf, 0) if err != nil && err != io.EOF { return "", err } if n == 0 { return "", fmt.Errorf("ReadLongName: empty file") } if n > lim { return "", fmt.Errorf("ReadLongName: size=%d > limit=%d", n, lim) } return string(buf[0:n]), nil } // DeleteLongName deletes "hashName.name" in the directory opened at "dirfd". // // This function is symlink-safe through the use of Unlinkat(). func DeleteLongNameAt(dirfd int, hashName string) error { return syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0) } // WriteLongName encrypts plainName and writes it into "hashName.name". // For the convenience of the caller, plainName may also be a path and will be // Base()named internally. // // This function is symlink-safe through the use of Openat(). func (n *NameTransform) WriteLongNameAt(dirfd int, hashName string, plainName string) (err error) { plainName = filepath.Base(plainName) // Encrypt the basename dirIV, err := ReadDirIVAt(dirfd) if err != nil { return err } cName := n.EncryptName(plainName, dirIV) // Write the encrypted name into hashName.name fdRaw, err := syscallcompat.Openat(dirfd, hashName+LongNameSuffix, syscall.O_WRONLY|syscall.O_CREAT|syscall.O_EXCL, 0400) if err != nil { return err } fd := os.NewFile(uintptr(fdRaw), hashName+LongNameSuffix) _, err = fd.Write([]byte(cName)) if err != nil { fd.Close() // Delete incomplete longname file syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0) return err } err = fd.Close() if err != nil { // Delete incomplete longname file syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0) return err } return nil }