package nametransform import ( "bytes" "fmt" "io" "os" "syscall" "libgocryptfs/v2/internal/cryptocore" "libgocryptfs/v2/internal/syscallcompat" ) const ( // DirIVLen is identical to AES block size DirIVLen = 16 // DirIVFilename is the filename used to store directory IV. // Exported because we have to ignore this name in directory listing. DirIVFilename = "gocryptfs.diriv" ) // ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd". // Using the dirfd makes it immune to concurrent renames of the directory. // Retries on EINTR. // If deterministicNames is set it returns an all-zero slice. func (n *NameTransform) ReadDirIVAt(dirfd int) (iv []byte, err error) { if n.deterministicNames { return make([]byte, DirIVLen), nil } fdRaw, err := syscallcompat.Openat(dirfd, DirIVFilename, syscall.O_RDONLY|syscall.O_NOFOLLOW, 0) if err != nil { return nil, err } fd := os.NewFile(uintptr(fdRaw), DirIVFilename) defer fd.Close() return fdReadDirIV(fd) } // allZeroDirIV is preallocated to quickly check if the data read from disk is all zero var allZeroDirIV = make([]byte, DirIVLen) // fdReadDirIV reads and verifies the DirIV from an opened gocryptfs.diriv file. func fdReadDirIV(fd *os.File) (iv []byte, err error) { // We want to detect if the file is bigger than DirIVLen, so // make the buffer 1 byte bigger than necessary. iv = make([]byte, DirIVLen+1) n, err := fd.Read(iv) if err != nil && err != io.EOF { return nil, fmt.Errorf("read failed: %v", err) } iv = iv[0:n] if len(iv) != DirIVLen { return nil, fmt.Errorf("wanted %d bytes, got %d", DirIVLen, len(iv)) } if bytes.Equal(iv, allZeroDirIV) { return nil, fmt.Errorf("diriv is all-zero") } return iv, nil } // WriteDirIVAt - create a new gocryptfs.diriv file in the directory opened at // "dirfd". On error we try to delete the incomplete file. // This function is exported because it is used from fusefrontend, main, // and also the automated tests. func WriteDirIVAt(dirfd int) error { iv := cryptocore.RandBytes(DirIVLen) // 0400 permissions: gocryptfs.diriv should never be modified after creation. // Don't use "ioutil.WriteFile", it causes trouble on NFS: // https://github.com/rfjakob/gocryptfs/commit/7d38f80a78644c8ec4900cc990bfb894387112ed fd, err := syscallcompat.Openat(dirfd, DirIVFilename, os.O_WRONLY|os.O_CREATE|os.O_EXCL, dirivPerms) if err != nil { return err } // Wrap the fd in an os.File - we need the write retry logic. f := os.NewFile(uintptr(fd), DirIVFilename) _, err = f.Write(iv) if err != nil { f.Close() // It is normal to get ENOSPC here // Delete incomplete gocryptfs.diriv file syscallcompat.Unlinkat(dirfd, DirIVFilename, 0) return err } err = f.Close() if err != nil { // Delete incomplete gocryptfs.diriv file syscallcompat.Unlinkat(dirfd, DirIVFilename, 0) return err } return nil }