aboutsummaryrefslogtreecommitdiff
path: root/internal/nametransform/names_diriv.go
blob: b9473aa83e699aff879c3c6b3789da8576ab9480 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
package nametransform

import (
	"errors"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/rfjakob/gocryptfs/internal/cryptocore"
	"github.com/rfjakob/gocryptfs/internal/tlog"
)

const (
	// identical to AES block size
	dirIVLen = 16
	// dirIV is stored in this file. Exported because we have to ignore this
	// name in directory listing.
	DirIVFilename = "gocryptfs.diriv"
)

// ReadDirIV - read the "gocryptfs.diriv" file from "dir" (absolute ciphertext path)
// This function is exported because it allows for an efficient readdir implementation.
func ReadDirIV(dir string) (iv []byte, err error) {
	dirfd, err := os.Open(dir)
	if err != nil {
		return nil, err
	}
	defer dirfd.Close()

	return ReadDirIVAt(dirfd)
}

// ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
// Using the dirfd makes it immune to concurrent renames of the directory.
func ReadDirIVAt(dirfd *os.File) (iv []byte, err error) {
	fdRaw, err := syscall.Openat(int(dirfd.Fd()), DirIVFilename, syscall.O_RDONLY, 0)
	if err != nil {
		tlog.Warn.Printf("ReadDirIVAt: opening %q in dir %q failed: %v",
			DirIVFilename, dirfd.Name(), err)
		return nil, err
	}
	fd := os.NewFile(uintptr(fdRaw), DirIVFilename)
	defer fd.Close()

	iv = make([]byte, dirIVLen+1)
	n, err := fd.Read(iv)
	if err != nil {
		tlog.Warn.Printf("ReadDirIVAt: Read failed: %v", err)
		return nil, err
	}
	iv = iv[0:n]
	if len(iv) != dirIVLen {
		tlog.Warn.Printf("ReadDirIVAt: wanted %d bytes, got %d", dirIVLen, len(iv))
		return nil, errors.New("invalid iv length")
	}
	return iv, nil
}

// WriteDirIV - create diriv file inside "dir" (absolute ciphertext path)
// This function is exported because it is used from pathfs_frontend, main,
// and also the automated tests.
func WriteDirIV(dir string) error {
	iv := cryptocore.RandBytes(dirIVLen)
	file := filepath.Join(dir, DirIVFilename)
	err := ioutil.WriteFile(file, iv, 0400)
	if err != nil {
		tlog.Warn.Printf("WriteDirIV: %v", err)
	}
	return err
}

// EncryptPathDirIV - encrypt relative plaintext path using EME with DirIV.
// Components that are longer than 255 bytes are hashed if be.longnames == true.
func (be *NameTransform) EncryptPathDirIV(plainPath string, rootDir string) (cipherPath string, err error) {
	// Empty string means root directory
	if plainPath == "" {
		return plainPath, nil
	}
	// Reject names longer than 255 bytes already here. This relieves everybody
	// who uses hashed long names from checking for that later.
	baseName := filepath.Base(plainPath)
	if len(baseName) > syscall.NAME_MAX {
		return "", syscall.ENAMETOOLONG
	}
	// Check if the DirIV is cached
	parentDir := filepath.Dir(plainPath)
	found, iv, cParentDir := be.DirIVCache.lookup(parentDir)
	if found {
		cBaseName := be.EncryptName(baseName, iv)
		if be.longNames && len(cBaseName) > syscall.NAME_MAX {
			cBaseName = HashLongName(cBaseName)
		}
		cipherPath = cParentDir + "/" + cBaseName
		return cipherPath, nil
	}
	// Not cached - walk the directory tree
	var wd = rootDir
	var encryptedNames []string
	plainNames := strings.Split(plainPath, "/")
	for _, plainName := range plainNames {
		iv, err = ReadDirIV(wd)
		if err != nil {
			return "", err
		}
		encryptedName := be.EncryptName(plainName, iv)
		if be.longNames && len(encryptedName) > syscall.NAME_MAX {
			encryptedName = HashLongName(encryptedName)
		}
		encryptedNames = append(encryptedNames, encryptedName)
		wd = filepath.Join(wd, encryptedName)
	}
	cipherPath = strings.Join(encryptedNames, "/")
	// Cache the final DirIV
	cParentDir = filepath.Dir(cipherPath)
	be.DirIVCache.store(parentDir, iv, cParentDir)
	return cipherPath, nil
}

// DecryptPathDirIV - decrypt path using EME with DirIV
//
// TODO This has only a single user, Readlink(), and only for compatability with
// gocryptfs v0.5. Drop?
func (be *NameTransform) DecryptPathDirIV(encryptedPath string, rootDir string) (string, error) {
	var wd = rootDir
	var plainNames []string
	encryptedNames := strings.Split(encryptedPath, "/")
	tlog.Debug.Printf("DecryptPathDirIV: decrypting %v\n", encryptedNames)
	for _, encryptedName := range encryptedNames {
		iv, err := ReadDirIV(wd)
		if err != nil {
			return "", err
		}
		plainName, err := be.DecryptName(encryptedName, iv)
		if err != nil {
			return "", err
		}
		plainNames = append(plainNames, plainName)
		wd = filepath.Join(wd, encryptedName)
	}
	return filepath.Join(plainNames...), nil
}