aboutsummaryrefslogtreecommitdiff
path: root/internal/fusefrontend/fs.go
blob: e8dae9f97e5565464482590387ad32023d9611f6 (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
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
// Package fusefrontend interfaces directly with the go-fuse library.
package fusefrontend

// FUSE operations on paths

import (
	"os"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"golang.org/x/sys/unix"

	"github.com/hanwen/go-fuse/v2/fuse"
	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
	"github.com/hanwen/go-fuse/v2/fuse/pathfs"

	"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"
)

// FS implements the go-fuse virtual filesystem interface.
type FS struct {
	// Embed pathfs.defaultFileSystem to avoid compile failure when the
	// pathfs.FileSystem interface gets new functions. defaultFileSystem
	// provides a no-op implementation for all functions.
	pathfs.FileSystem
	args Args // Stores configuration arguments
	// 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
	// This 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 dirCacheStruct
	// inoMap translates inode numbers from different devices to unique inode
	// numbers.
	inoMap *inomap.InoMap
}

//var _ pathfs.FileSystem = &FS{} // Verify that interface is implemented.

// NewFS returns a new encrypted FUSE overlay filesystem.
func NewFS(args Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *FS {
	if args.SerializeReads {
		serialize_reads.InitSerializer()
	}
	if len(args.Exclude) > 0 {
		tlog.Warn.Printf("Forward mode does not support -exclude")
	}
	var st syscall.Stat_t
	err := syscall.Stat(args.Cipherdir, &st)
	if err != nil {
		tlog.Warn.Printf("NewFS: could not stat cipherdir: %v", err)
		st.Dev = 0
	}
	return &FS{
		FileSystem:    pathfs.NewDefaultFileSystem(),
		args:          args,
		nameTransform: n,
		contentEnc:    c,
		inoMap:        inomap.New(),
	}
}

// GetAttr implements pathfs.Filesystem.
//
// GetAttr is symlink-safe through use of openBackingDir() and Fstatat().
func (fs *FS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
	tlog.Debug.Printf("FS.GetAttr(%q)", relPath)
	if fs.isFiltered(relPath) {
		return nil, fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(relPath)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	var st unix.Stat_t
	err = syscallcompat.Fstatat(dirfd, cName, &st, unix.AT_SYMLINK_NOFOLLOW)
	syscall.Close(dirfd)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	a := &fuse.Attr{}
	st2 := syscallcompat.Unix2syscall(st)
	fs.inoMap.TranslateStat(&st2)
	a.FromStat(&st2)
	if a.IsRegular() {
		a.Size = fs.contentEnc.CipherSizeToPlainSize(a.Size)
	} else if a.IsSymlink() {
		target, _ := fs.Readlink(relPath, context)
		a.Size = uint64(len(target))
	}
	if fs.args.ForceOwner != nil {
		a.Owner = *fs.args.ForceOwner
	}
	return a, fuse.OK
}

// 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 (fs *FS) 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
}

// Open - FUSE call. Open already-existing file.
//
// Symlink-safe through Openat().
func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
	if fs.isFiltered(path) {
		return nil, fuse.EPERM
	}
	newFlags := fs.mangleOpenFlags(flags)
	// Taking this lock makes sure we don't race openWriteOnlyFile()
	fs.openWriteOnlyLock.RLock()
	defer fs.openWriteOnlyLock.RUnlock()
	// Symlink-safe open
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	fd, err := syscallcompat.Openat(dirfd, cName, newFlags, 0)
	// Handle a few specific errors
	if err != nil {
		if err == syscall.EMFILE {
			var lim syscall.Rlimit
			syscall.Getrlimit(syscall.RLIMIT_NOFILE, &lim)
			tlog.Warn.Printf("Open %q: too many open files. Current \"ulimit -n\": %d", cName, lim.Cur)
		}
		if err == syscall.EACCES && (int(flags)&syscall.O_ACCMODE) == syscall.O_WRONLY {
			return fs.openWriteOnlyFile(dirfd, cName, newFlags)
		}
		return nil, fuse.ToStatus(err)
	}
	f := os.NewFile(uintptr(fd), cName)
	return NewFile(f, fs)
}

// openBackingFile opens the ciphertext file that backs relative plaintext
// path "relPath". Always adds O_NOFOLLOW to the flags.
func (fs *FS) openBackingFile(relPath string, flags int) (fd int, err error) {
	dirfd, cName, err := fs.openBackingDir(relPath)
	if err != nil {
		return -1, err
	}
	defer syscall.Close(dirfd)
	return syscallcompat.Openat(dirfd, cName, flags|syscall.O_NOFOLLOW, 0)
}

// 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 (fs *FS) openWriteOnlyFile(dirfd int, cName string, newFlags int) (*File, fuse.Status) {
	woFd, err := syscallcompat.Openat(dirfd, cName, syscall.O_WRONLY|syscall.O_NOFOLLOW, 0)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	defer syscall.Close(woFd)
	var st syscall.Stat_t
	err = syscall.Fstat(woFd, &st)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	// 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)
		return nil, fuse.ToStatus(syscall.EPERM)
	}
	// Upgrade the lock to block other Open()s and downgrade again on return
	fs.openWriteOnlyLock.RUnlock()
	fs.openWriteOnlyLock.Lock()
	defer func() {
		fs.openWriteOnlyLock.Unlock()
		fs.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 nil, fuse.ToStatus(err)
	}
	defer func() {
		err2 := syscall.Fchmod(woFd, perms)
		if err2 != nil {
			tlog.Warn.Printf("openWriteOnlyFile: reverting permissions failed: %v", err2)
		}
	}()
	rwFd, err := syscallcompat.Openat(dirfd, cName, newFlags, 0)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	f := os.NewFile(uintptr(rwFd), cName)
	return NewFile(f, fs)
}

// Create - FUSE call. Creates a new file.
//
// Symlink-safe through the use of Openat().
func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Context) (nodefs.File, fuse.Status) {
	if fs.isFiltered(path) {
		return nil, fuse.EPERM
	}
	newFlags := fs.mangleOpenFlags(flags)
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	fd := -1
	// Make sure context is nil if we don't want to preserve the owner
	if !fs.args.PreserveOwner {
		context = nil
	}
	// Handle long file name
	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
		// Create ".name"
		err = fs.nameTransform.WriteLongNameAt(dirfd, cName, path)
		if err != nil {
			return nil, fuse.ToStatus(err)
		}
		// Create content
		fd, err = syscallcompat.OpenatUser(dirfd, cName, newFlags|syscall.O_CREAT|syscall.O_EXCL, mode, context)
		if err != nil {
			nametransform.DeleteLongNameAt(dirfd, cName)
		}
	} else {
		// Create content, normal (short) file name
		fd, err = syscallcompat.OpenatUser(dirfd, cName, newFlags|syscall.O_CREAT|syscall.O_EXCL, mode, context)
	}
	if err != nil {
		// xfstests generic/488 triggers this
		if err == syscall.EMFILE {
			var lim syscall.Rlimit
			syscall.Getrlimit(syscall.RLIMIT_NOFILE, &lim)
			tlog.Warn.Printf("Create %q: too many open files. Current \"ulimit -n\": %d", cName, lim.Cur)
		}
		return nil, fuse.ToStatus(err)
	}
	f := os.NewFile(uintptr(fd), cName)
	return NewFile(f, fs)
}

// Chmod - FUSE call. Change permissions on "path".
//
// Symlink-safe through use of Fchmodat().
func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(path) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	// os.Chmod goes through the "syscallMode" translation function that messes
	// up the suid and sgid bits. So use a syscall directly.
	err = syscallcompat.FchmodatNofollow(dirfd, cName, mode)
	return fuse.ToStatus(err)
}

// Chown - FUSE call. Change the owner of "path".
//
// Symlink-safe through use of Fchownat().
func (fs *FS) Chown(path string, uid uint32, gid uint32, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(path) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	err = syscallcompat.Fchownat(dirfd, cName, int(uid), int(gid), unix.AT_SYMLINK_NOFOLLOW)
	return fuse.ToStatus(err)
}

// Mknod - FUSE call. Create a device file.
//
// Symlink-safe through use of Mknodat().
func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(path) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	// Make sure context is nil if we don't want to preserve the owner
	if !fs.args.PreserveOwner {
		context = nil
	}
	// Create ".name" file to store long file name (except in PlaintextNames mode)
	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
		err = fs.nameTransform.WriteLongNameAt(dirfd, cName, path)
		if err != nil {
			return fuse.ToStatus(err)
		}
		// Create "gocryptfs.longfile." device node
		err = syscallcompat.MknodatUser(dirfd, cName, mode, int(dev), context)
		if err != nil {
			nametransform.DeleteLongNameAt(dirfd, cName)
		}
	} else {
		// Create regular device node
		err = syscallcompat.MknodatUser(dirfd, cName, mode, int(dev), context)
	}
	return fuse.ToStatus(err)
}

// Truncate - FUSE call. Truncates a file.
//
// Support truncate(2) by opening the file and calling ftruncate(2)
// While the glibc "truncate" wrapper seems to always use ftruncate, fsstress from
// xfstests uses this a lot by calling "truncate64" directly.
//
// Symlink-safe by letting file.Truncate() do all the work.
func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
	file, code := fs.Open(path, uint32(os.O_RDWR), context)
	if code != fuse.OK {
		return code
	}
	code = file.Truncate(offset)
	file.Release()
	return code
}

// Utimens - FUSE call. Set the timestamps on file "path".
//
// Symlink-safe through UtimesNanoAt.
func (fs *FS) Utimens(path string, a *time.Time, m *time.Time, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(path) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	err = syscallcompat.UtimesNanoAtNofollow(dirfd, cName, a, m)
	return fuse.ToStatus(err)
}

// StatFs - FUSE call. Returns information about the filesystem.
//
// Symlink-safe because the passed path is ignored.
func (fs *FS) StatFs(path string) *fuse.StatfsOut {
	var st syscall.Statfs_t
	err := syscall.Statfs(fs.args.Cipherdir, &st)
	if err == nil {
		var out fuse.StatfsOut
		out.FromStatfsT(&st)
		return &out
	}
	return nil
}

// 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 (fs *FS) decryptSymlinkTarget(cData64 string) (string, error) {
	if cData64 == "" {
		return "", nil
	}
	cData, err := fs.nameTransform.B64DecodeString(cData64)
	if err != nil {
		return "", err
	}
	data, err := fs.contentEnc.DecryptBlock([]byte(cData), 0, nil)
	if err != nil {
		return "", err
	}
	return string(data), nil
}

// Readlink - FUSE call.
//
// Symlink-safe through openBackingDir() + Readlinkat().
func (fs *FS) Readlink(relPath string, context *fuse.Context) (out string, status fuse.Status) {
	dirfd, cName, err := fs.openBackingDir(relPath)
	if err != nil {
		return "", fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	cTarget, err := syscallcompat.Readlinkat(dirfd, cName)
	if err != nil {
		return "", fuse.ToStatus(err)
	}
	if fs.args.PlaintextNames {
		return cTarget, fuse.OK
	}
	// Symlinks are encrypted like file contents (GCM) and base64-encoded
	target, err := fs.decryptSymlinkTarget(cTarget)
	if err != nil {
		tlog.Warn.Printf("Readlink %q: decrypting target failed: %v", cName, err)
		return "", fuse.EIO
	}
	return string(target), fuse.OK
}

// Unlink - FUSE call. Delete a file.
//
// Symlink-safe through use of Unlinkat().
func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(path) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(path)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	// Delete content
	err = syscallcompat.Unlinkat(dirfd, cName, 0)
	if err != nil {
		return fuse.ToStatus(err)
	}
	// Delete ".name" file
	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
		err = nametransform.DeleteLongNameAt(dirfd, cName)
		if err != nil {
			tlog.Warn.Printf("Unlink: could not delete .name file: %v", err)
		}
	}
	return fuse.ToStatus(err)
}

// 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 (fs *FS) encryptSymlinkTarget(data string) (cData64 string) {
	if data == "" {
		return ""
	}
	cData := fs.contentEnc.EncryptBlock([]byte(data), 0, nil)
	cData64 = fs.nameTransform.B64EncodeToString(cData)
	return cData64
}

// Symlink - FUSE call. Create a symlink.
//
// Symlink-safe through use of Symlinkat.
func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (code fuse.Status) {
	tlog.Debug.Printf("Symlink(\"%s\", \"%s\")", target, linkName)
	if fs.isFiltered(linkName) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(linkName)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(dirfd)
	// Make sure context is nil if we don't want to preserve the owner
	if !fs.args.PreserveOwner {
		context = nil
	}
	cTarget := target
	if !fs.args.PlaintextNames {
		// Symlinks are encrypted like file contents (GCM) and base64-encoded
		cTarget = fs.encryptSymlinkTarget(target)
	}
	// Create ".name" file to store long file name (except in PlaintextNames mode)
	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
		err = fs.nameTransform.WriteLongNameAt(dirfd, cName, linkName)
		if err != nil {
			return fuse.ToStatus(err)
		}
		// Create "gocryptfs.longfile." symlink
		err = syscallcompat.SymlinkatUser(cTarget, dirfd, cName, context)
		if err != nil {
			nametransform.DeleteLongNameAt(dirfd, cName)
		}
	} else {
		// Create symlink
		err = syscallcompat.SymlinkatUser(cTarget, dirfd, cName, context)
	}
	return fuse.ToStatus(err)
}

// Rename - FUSE call.
//
// Symlink-safe through Renameat().
func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
	defer fs.dirCache.Clear()
	if fs.isFiltered(newPath) {
		return fuse.EPERM
	}
	oldDirfd, oldCName, err := fs.openBackingDir(oldPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(oldDirfd)
	newDirfd, newCName, err := fs.openBackingDir(newPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(newDirfd)
	// Easy case.
	if fs.args.PlaintextNames {
		return fuse.ToStatus(syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName))
	}
	// Long destination file name: create .name file
	nameFileAlreadyThere := false
	if nametransform.IsLongContent(newCName) {
		err = fs.nameTransform.WriteLongNameAt(newDirfd, newCName, newPath)
		// Failure to write the .name file is expected when the target path already
		// exists. Since hashes are pretty unique, there is no need to modify the
		// .name file in this case, and we ignore the error.
		if err == syscall.EEXIST {
			nameFileAlreadyThere = true
		} else if err != nil {
			return fuse.ToStatus(err)
		}
	}
	// Actual rename
	tlog.Debug.Printf("Renameat %d/%s -> %d/%s\n", oldDirfd, oldCName, newDirfd, newCName)
	err = syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName)
	if err == syscall.ENOTEMPTY || err == syscall.EEXIST {
		// If an empty directory is overwritten we will always get an error as
		// the "empty" directory will still contain gocryptfs.diriv.
		// Interestingly, ext4 returns ENOTEMPTY while xfs returns EEXIST.
		// We handle that by trying to fs.Rmdir() the target directory and trying
		// again.
		tlog.Debug.Printf("Rename: Handling ENOTEMPTY")
		if fs.Rmdir(newPath, context) == fuse.OK {
			err = syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName)
		}
	}
	if err != nil {
		if nametransform.IsLongContent(newCName) && nameFileAlreadyThere == false {
			// Roll back .name creation unless the .name file was already there
			nametransform.DeleteLongNameAt(newDirfd, newCName)
		}
		return fuse.ToStatus(err)
	}
	if nametransform.IsLongContent(oldCName) {
		nametransform.DeleteLongNameAt(oldDirfd, oldCName)
	}
	return fuse.OK
}

// Link - FUSE call. Creates a hard link at "newPath" pointing to file
// "oldPath".
//
// Symlink-safe through use of Linkat().
func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(newPath) {
		return fuse.EPERM
	}
	oldDirFd, cOldName, err := fs.openBackingDir(oldPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(oldDirFd)
	newDirFd, cNewName, err := fs.openBackingDir(newPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer syscall.Close(newDirFd)
	// Handle long file name (except in PlaintextNames mode)
	if !fs.args.PlaintextNames && nametransform.IsLongContent(cNewName) {
		err = fs.nameTransform.WriteLongNameAt(newDirFd, cNewName, newPath)
		if err != nil {
			return fuse.ToStatus(err)
		}
		// Create "gocryptfs.longfile." link
		err = syscallcompat.Linkat(oldDirFd, cOldName, newDirFd, cNewName, 0)
		if err != nil {
			nametransform.DeleteLongNameAt(newDirFd, cNewName)
		}
	} else {
		// Create regular link
		err = syscallcompat.Linkat(oldDirFd, cOldName, newDirFd, cNewName, 0)
	}
	return fuse.ToStatus(err)
}

// Access - FUSE call. Check if a file can be accessed in the specified mode(s)
// (read, write, execute).
//
// From https://github.com/libfuse/libfuse/blob/master/include/fuse.h :
//
// > Check file access permissions
// >
// > If the 'default_permissions' mount option is given, this method is not
// > called.
//
// We always enable default_permissions when -allow_other is passed, so there
// is no need for this function to check the uid in fuse.Context.
//
// Symlink-safe through use of faccessat.
func (fs *FS) Access(relPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
	if fs.isFiltered(relPath) {
		return fuse.EPERM
	}
	dirfd, cName, err := fs.openBackingDir(relPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	err = syscallcompat.Faccessat(dirfd, cName, mode)
	syscall.Close(dirfd)
	return fuse.ToStatus(err)
}

// 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 (fs *FS) reportMitigatedCorruption(item string) {
	if fs.MitigatedCorruptions == nil {
		return
	}
	select {
	case fs.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 (fs *FS) isFiltered(path string) bool {
	atomic.StoreUint32(&fs.IsIdle, 0)

	if !fs.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
}