summaryrefslogtreecommitdiff
path: root/internal/fusefrontend/root_node.go
blob: 2b4ad247a04bf4e70470fb69a6c4eeed312e135d (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
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
package fusefrontend

import (
	"os"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/rfjakob/gocryptfs/internal/configfile"
	"github.com/rfjakob/gocryptfs/internal/contentenc"
	"github.com/rfjakob/gocryptfs/internal/inomap"
	"github.com/rfjakob/gocryptfs/internal/nametransform"
	"github.com/rfjakob/gocryptfs/internal/serialize_reads"
	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
	"github.com/rfjakob/gocryptfs/internal/tlog"
)

// RootNode is the root of the filesystem tree of Nodes.
type RootNode struct {
	Node
	// args stores configuration arguments
	args Args
	// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
	// Readers must RLock() it to prevent them from seeing intermediate
	// states
	dirIVLock sync.RWMutex
	// Filename encryption helper
	nameTransform nametransform.NameTransformer
	// Content encryption helper
	contentEnc *contentenc.ContentEnc
	// This lock is used by openWriteOnlyFile() to block concurrent opens while
	// it relaxes the permissions on a file.
	openWriteOnlyLock sync.RWMutex
	// MitigatedCorruptions is used to report data corruption that is internally
	// mitigated by ignoring the corrupt item. For example, when OpenDir() finds
	// a corrupt filename, we still return the other valid filenames.
	// The corruption is logged to syslog to inform the user,	and in addition,
	// the corrupt filename is logged to this channel via
	// reportMitigatedCorruption().
	// "gocryptfs -fsck" reads from the channel to also catch these transparently-
	// mitigated corruptions.
	MitigatedCorruptions chan string
	// IsIdle flag is set to zero each time fs.isFiltered() is called
	// (uint32 so that it can be reset with CompareAndSwapUint32).
	// When -idle was used when mounting, idleMonitor() sets it to 1
	// periodically.
	IsIdle uint32
	// dirCache caches directory fds
	dirCache dirCache
	// inoMap translates inode numbers from different devices to unique inode
	// numbers.
	inoMap inomap.TranslateStater
}

func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *RootNode {
	if args.SerializeReads {
		serialize_reads.InitSerializer()
	}
	if len(args.Exclude) > 0 {
		tlog.Warn.Printf("Forward mode does not support -exclude")
	}
	rn := &RootNode{
		args:          args,
		nameTransform: n,
		contentEnc:    c,
		inoMap:        inomap.New(),
	}
	// In `-sharedstorage` mode we always set the inode number to zero.
	// This makes go-fuse generate a new inode number for each lookup.
	if args.SharedStorage {
		rn.inoMap = &inomap.TranslateStatZero{}
	}
	return rn
}

// mangleOpenFlags is used by Create() and Open() to convert the open flags the user
// wants to the flags we internally use to open the backing file.
// The returned flags always contain O_NOFOLLOW.
func (rn *RootNode) mangleOpenFlags(flags uint32) (newFlags int) {
	newFlags = int(flags)
	// Convert WRONLY to RDWR. We always need read access to do read-modify-write cycles.
	if (newFlags & syscall.O_ACCMODE) == syscall.O_WRONLY {
		newFlags = newFlags ^ os.O_WRONLY | os.O_RDWR
	}
	// We also cannot open the file in append mode, we need to seek back for RMW
	newFlags = newFlags &^ os.O_APPEND
	// O_DIRECT accesses must be aligned in both offset and length. Due to our
	// crypto header, alignment will be off, even if userspace makes aligned
	// accesses. Running xfstests generic/013 on ext4 used to trigger lots of
	// EINVAL errors due to missing alignment. Just fall back to buffered IO.
	newFlags = newFlags &^ syscallcompat.O_DIRECT
	// Create and Open are two separate FUSE operations, so O_CREAT should not
	// be part of the open flags.
	newFlags = newFlags &^ syscall.O_CREAT
	// We always want O_NOFOLLOW to be safe against symlink races
	newFlags |= syscall.O_NOFOLLOW
	return newFlags
}

// reportMitigatedCorruption is used to report a corruption that was transparently
// mitigated and did not return an error to the user. Pass the name of the corrupt
// item (filename for OpenDir(), xattr name for ListXAttr() etc).
// See the MitigatedCorruptions channel for more info.
func (rn *RootNode) reportMitigatedCorruption(item string) {
	if rn.MitigatedCorruptions == nil {
		return
	}
	select {
	case rn.MitigatedCorruptions <- item:
	case <-time.After(1 * time.Second):
		tlog.Warn.Printf("BUG: reportCorruptItem: timeout")
		//debug.PrintStack()
		return
	}
}

// isFiltered - check if plaintext "path" should be forbidden
//
// Prevents name clashes with internal files when file names are not encrypted
func (rn *RootNode) isFiltered(path string) bool {
	atomic.StoreUint32(&rn.IsIdle, 0)

	if !rn.args.PlaintextNames {
		return false
	}
	// gocryptfs.conf in the root directory is forbidden
	if path == configfile.ConfDefaultName {
		tlog.Info.Printf("The name /%s is reserved when -plaintextnames is used\n",
			configfile.ConfDefaultName)
		return true
	}
	// Note: gocryptfs.diriv is NOT forbidden because diriv and plaintextnames
	// are exclusive
	return false
}

// decryptSymlinkTarget: "cData64" is base64-decoded and decrypted
// like file contents (GCM).
// The empty string decrypts to the empty string.
//
// This function does not do any I/O and is hence symlink-safe.
func (rn *RootNode) decryptSymlinkTarget(cData64 string) (string, error) {
	if cData64 == "" {
		return "", nil
	}
	cData, err := rn.nameTransform.B64DecodeString(cData64)
	if err != nil {
		return "", err
	}
	data, err := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
	if err != nil {
		return "", err
	}
	return string(data), nil
}

// Due to RMW, we always need read permissions on the backing file. This is a
// problem if the file permissions do not allow reading (i.e. 0200 permissions).
// This function works around that problem by chmod'ing the file, obtaining a fd,
// and chmod'ing it back.
func (rn *RootNode) openWriteOnlyFile(dirfd int, cName string, newFlags int) (rwFd int, err error) {
	woFd, err := syscallcompat.Openat(dirfd, cName, syscall.O_WRONLY|syscall.O_NOFOLLOW, 0)
	if err != nil {
		return
	}
	defer syscall.Close(woFd)
	var st syscall.Stat_t
	err = syscall.Fstat(woFd, &st)
	if err != nil {
		return
	}
	// The cast to uint32 fixes a build failure on Darwin, where st.Mode is uint16.
	perms := uint32(st.Mode)
	// Verify that we don't have read permissions
	if perms&0400 != 0 {
		tlog.Warn.Printf("openWriteOnlyFile: unexpected permissions %#o, returning EPERM", perms)
		err = syscall.EPERM
		return
	}
	// Upgrade the lock to block other Open()s and downgrade again on return
	rn.openWriteOnlyLock.RUnlock()
	rn.openWriteOnlyLock.Lock()
	defer func() {
		rn.openWriteOnlyLock.Unlock()
		rn.openWriteOnlyLock.RLock()
	}()
	// Relax permissions and revert on return
	err = syscall.Fchmod(woFd, perms|0400)
	if err != nil {
		tlog.Warn.Printf("openWriteOnlyFile: changing permissions failed: %v", err)
		return
	}
	defer func() {
		err2 := syscall.Fchmod(woFd, perms)
		if err2 != nil {
			tlog.Warn.Printf("openWriteOnlyFile: reverting permissions failed: %v", err2)
		}
	}()
	return syscallcompat.Openat(dirfd, cName, newFlags, 0)
}

// openBackingDir opens the parent ciphertext directory of plaintext path
// "relPath". It returns the dirfd (opened with O_PATH) and the encrypted
// basename.
//
// The caller should then use Openat(dirfd, cName, ...) and friends.
// For convenience, if relPath is "", cName is going to be ".".
//
// openBackingDir is secure against symlink races by using Openat and
// ReadDirIVAt.
//
// Retries on EINTR.
func (rn *RootNode) openBackingDir(relPath string) (dirfd int, cName string, err error) {
	dirRelPath := nametransform.Dir(relPath)
	// With PlaintextNames, we don't need to read DirIVs. Easy.
	if rn.args.PlaintextNames {
		dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, dirRelPath)
		if err != nil {
			return -1, "", err
		}
		// If relPath is empty, cName is ".".
		cName = filepath.Base(relPath)
		return dirfd, cName, nil
	}
	// Open cipherdir (following symlinks)
	dirfd, err = syscallcompat.Open(rn.args.Cipherdir, syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
	if err != nil {
		return -1, "", err
	}
	// If relPath is empty, cName is ".".
	if relPath == "" {
		return dirfd, ".", nil
	}
	// Walk the directory tree
	parts := strings.Split(relPath, "/")
	for i, name := range parts {
		iv, err := nametransform.ReadDirIVAt(dirfd)
		if err != nil {
			syscall.Close(dirfd)
			return -1, "", err
		}
		cName, err = rn.nameTransform.EncryptAndHashName(name, iv)
		if err != nil {
			syscall.Close(dirfd)
			return -1, "", err
		}
		// Last part? We are done.
		if i == len(parts)-1 {
			break
		}
		// Not the last part? Descend into next directory.
		dirfd2, err := syscallcompat.Openat(dirfd, cName, syscall.O_NOFOLLOW|syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
		syscall.Close(dirfd)
		if err != nil {
			return -1, "", err
		}
		dirfd = dirfd2
	}
	return dirfd, cName, nil
}

// encryptSymlinkTarget: "data" is encrypted like file contents (GCM)
// and base64-encoded.
// The empty string encrypts to the empty string.
//
// Symlink-safe because it does not do any I/O.
func (rn *RootNode) encryptSymlinkTarget(data string) (cData64 string) {
	if data == "" {
		return ""
	}
	cData := rn.contentEnc.EncryptBlock([]byte(data), 0, nil)
	cData64 = rn.nameTransform.B64EncodeToString(cData)
	return cData64
}

// encryptXattrValue encrypts the xattr value "data".
// The data is encrypted like a file content block, but without binding it to
// a file location (block number and file id are set to zero).
// Special case: an empty value is encrypted to an empty value.
func (rn *RootNode) encryptXattrValue(data []byte) (cData []byte) {
	if len(data) == 0 {
		return []byte{}
	}
	return rn.contentEnc.EncryptBlock(data, 0, nil)
}

// decryptXattrValue decrypts the xattr value "cData".
func (rn *RootNode) decryptXattrValue(cData []byte) (data []byte, err error) {
	if len(cData) == 0 {
		return []byte{}, nil
	}
	data, err1 := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
	if err1 == nil {
		return data, nil
	}
	// This backward compatibility is needed to support old
	// file systems having xattr values base64-encoded.
	cData, err2 := rn.nameTransform.B64DecodeString(string(cData))
	if err2 != nil {
		// Looks like the value was not base64-encoded, but just corrupt.
		// Return the original decryption error: err1
		return nil, err1
	}
	return rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
}

// encryptXattrName transforms "user.foo" to "user.gocryptfs.a5sAd4XAa47f5as6dAf"
func (rn *RootNode) encryptXattrName(attr string) (cAttr string) {
	// xattr names are encrypted like file names, but with a fixed IV.
	cAttr = xattrStorePrefix + rn.nameTransform.EncryptName(attr, xattrNameIV)
	return cAttr
}

func (rn *RootNode) decryptXattrName(cAttr string) (attr string, err error) {
	// Reject anything that does not start with "user.gocryptfs."
	if !strings.HasPrefix(cAttr, xattrStorePrefix) {
		return "", syscall.EINVAL
	}
	// Strip "user.gocryptfs." prefix
	cAttr = cAttr[len(xattrStorePrefix):]
	attr, err = rn.nameTransform.DecryptName(cAttr, xattrNameIV)
	if err != nil {
		return "", err
	}
	return attr, nil
}