1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Overlayfs NFS export support.
4 *
5 * Amir Goldstein <amir73il@gmail.com>
6 *
7 * Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved.
8 */
9
10#include <linux/fs.h>
11#include <linux/cred.h>
12#include <linux/mount.h>
13#include <linux/namei.h>
14#include <linux/xattr.h>
15#include <linux/exportfs.h>
16#include <linux/ratelimit.h>
17#include "overlayfs.h"
18
19static int ovl_encode_maybe_copy_up(struct dentry *dentry)
20{
21 int err;
22
23 if (ovl_dentry_upper(dentry))
24 return 0;
25
26 err = ovl_copy_up(dentry);
27 if (err) {
28 pr_warn_ratelimited("failed to copy up on encode (%pd2, err=%i)\n",
29 dentry, err);
30 }
31
32 return err;
33}
34
35/*
36 * Before encoding a non-upper directory file handle from real layer N, we need
37 * to check if it will be possible to reconnect an overlay dentry from the real
38 * lower decoded dentry. This is done by following the overlay ancestry up to a
39 * "layer N connected" ancestor and verifying that all parents along the way are
40 * "layer N connectable". If an ancestor that is NOT "layer N connectable" is
41 * found, we need to copy up an ancestor, which is "layer N connectable", thus
42 * making that ancestor "layer N connected". For example:
43 *
44 * layer 1: /a
45 * layer 2: /a/b/c
46 *
47 * The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is
48 * copied up and renamed, upper dir /a will be indexed by lower dir /a from
49 * layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*)
50 * in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay
51 * dentry from the connected lower dentry /a/b/c.
52 *
53 * To avoid this problem on decode time, we need to copy up an ancestor of
54 * /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is
55 * /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected"
56 * and when the time comes to decode the file handle from lower dentry /a/b/c,
57 * ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding
58 * a connected overlay dentry will be accomplished.
59 *
60 * (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an
61 * entry /a in the lower layers above layer N and find the indexed dir /a from
62 * layer 1. If that improvement is made, then the check for "layer N connected"
63 * will need to verify there are no redirects in lower layers above N. In the
64 * example above, /a will be "layer 2 connectable". However, if layer 2 dir /a
65 * is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable":
66 *
67 * layer 1: /A (redirect = /a)
68 * layer 2: /a/b/c
69 */
70
71/* Return the lowest layer for encoding a connectable file handle */
72static int ovl_connectable_layer(struct dentry *dentry)
73{
74 struct ovl_entry *oe = OVL_E(dentry);
75
76 /* We can get overlay root from root of any layer */
77 if (dentry == dentry->d_sb->s_root)
78 return ovl_numlower(oe);
79
80 /*
81 * If it's an unindexed merge dir, then it's not connectable with any
82 * lower layer
83 */
84 if (ovl_dentry_upper(dentry) &&
85 !ovl_test_flag(flag: OVL_INDEX, inode: d_inode(dentry)))
86 return 0;
87
88 /* We can get upper/overlay path from indexed/lower dentry */
89 return ovl_lowerstack(oe)->layer->idx;
90}
91
92/*
93 * @dentry is "connected" if all ancestors up to root or a "connected" ancestor
94 * have the same uppermost lower layer as the origin's layer. We may need to
95 * copy up a "connectable" ancestor to make it "connected". A "connected" dentry
96 * cannot become non "connected", so cache positive result in dentry flags.
97 *
98 * Return the connected origin layer or < 0 on error.
99 */
100static int ovl_connect_layer(struct dentry *dentry)
101{
102 struct dentry *next, *parent = NULL;
103 struct ovl_entry *oe = OVL_E(dentry);
104 int origin_layer;
105 int err = 0;
106
107 if (WARN_ON(dentry == dentry->d_sb->s_root) ||
108 WARN_ON(!ovl_dentry_lower(dentry)))
109 return -EIO;
110
111 origin_layer = ovl_lowerstack(oe)->layer->idx;
112 if (ovl_dentry_test_flag(flag: OVL_E_CONNECTED, dentry))
113 return origin_layer;
114
115 /* Find the topmost origin layer connectable ancestor of @dentry */
116 next = dget(dentry);
117 for (;;) {
118 parent = dget_parent(dentry: next);
119 if (WARN_ON(parent == next)) {
120 err = -EIO;
121 break;
122 }
123
124 /*
125 * If @parent is not origin layer connectable, then copy up
126 * @next which is origin layer connectable and we are done.
127 */
128 if (ovl_connectable_layer(dentry: parent) < origin_layer) {
129 err = ovl_encode_maybe_copy_up(dentry: next);
130 break;
131 }
132
133 /* If @parent is connected or indexed we are done */
134 if (ovl_dentry_test_flag(flag: OVL_E_CONNECTED, dentry: parent) ||
135 ovl_test_flag(flag: OVL_INDEX, inode: d_inode(dentry: parent)))
136 break;
137
138 dput(next);
139 next = parent;
140 }
141
142 dput(parent);
143 dput(next);
144
145 if (!err)
146 ovl_dentry_set_flag(flag: OVL_E_CONNECTED, dentry);
147
148 return err ?: origin_layer;
149}
150
151/*
152 * We only need to encode origin if there is a chance that the same object was
153 * encoded pre copy up and then we need to stay consistent with the same
154 * encoding also after copy up. If non-pure upper is not indexed, then it was
155 * copied up before NFS export was enabled. In that case we don't need to worry
156 * about staying consistent with pre copy up encoding and we encode an upper
157 * file handle. Overlay root dentry is a private case of non-indexed upper.
158 *
159 * The following table summarizes the different file handle encodings used for
160 * different overlay object types:
161 *
162 * Object type | Encoding
163 * --------------------------------
164 * Pure upper | U
165 * Non-indexed upper | U
166 * Indexed upper | L (*)
167 * Non-upper | L (*)
168 *
169 * U = upper file handle
170 * L = lower file handle
171 *
172 * (*) Decoding a connected overlay dir from real lower dentry is not always
173 * possible when there are redirects in lower layers and non-indexed merge dirs.
174 * To mitigate those case, we may copy up the lower dir ancestor before encode
175 * of a decodable file handle for non-upper dir.
176 *
177 * Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
178 */
179static int ovl_check_encode_origin(struct dentry *dentry)
180{
181 struct ovl_fs *ofs = OVL_FS(sb: dentry->d_sb);
182 bool decodable = ofs->config.nfs_export;
183
184 /* Lower file handle for non-upper non-decodable */
185 if (!ovl_dentry_upper(dentry) && !decodable)
186 return 1;
187
188 /* Upper file handle for pure upper */
189 if (!ovl_dentry_lower(dentry))
190 return 0;
191
192 /*
193 * Root is never indexed, so if there's an upper layer, encode upper for
194 * root.
195 */
196 if (dentry == dentry->d_sb->s_root)
197 return 0;
198
199 /*
200 * Upper decodable file handle for non-indexed upper.
201 */
202 if (ovl_dentry_upper(dentry) && decodable &&
203 !ovl_test_flag(flag: OVL_INDEX, inode: d_inode(dentry)))
204 return 0;
205
206 /*
207 * Decoding a merge dir, whose origin's ancestor is under a redirected
208 * lower dir or under a non-indexed upper is not always possible.
209 * ovl_connect_layer() will try to make origin's layer "connected" by
210 * copying up a "connectable" ancestor.
211 */
212 if (d_is_dir(dentry) && ovl_upper_mnt(ofs) && decodable)
213 return ovl_connect_layer(dentry);
214
215 /* Lower file handle for indexed and non-upper dir/non-dir */
216 return 1;
217}
218
219static int ovl_dentry_to_fid(struct ovl_fs *ofs, struct dentry *dentry,
220 u32 *fid, int buflen)
221{
222 struct ovl_fh *fh = NULL;
223 int err, enc_lower;
224 int len;
225
226 /*
227 * Check if we should encode a lower or upper file handle and maybe
228 * copy up an ancestor to make lower file handle connectable.
229 */
230 err = enc_lower = ovl_check_encode_origin(dentry);
231 if (enc_lower < 0)
232 goto fail;
233
234 /* Encode an upper or lower file handle */
235 fh = ovl_encode_real_fh(ofs, real: enc_lower ? ovl_dentry_lower(dentry) :
236 ovl_dentry_upper(dentry), is_upper: !enc_lower);
237 if (IS_ERR(ptr: fh))
238 return PTR_ERR(ptr: fh);
239
240 len = OVL_FH_LEN(fh);
241 if (len <= buflen)
242 memcpy(fid, fh, len);
243 err = len;
244
245out:
246 kfree(objp: fh);
247 return err;
248
249fail:
250 pr_warn_ratelimited("failed to encode file handle (%pd2, err=%i)\n",
251 dentry, err);
252 goto out;
253}
254
255static int ovl_encode_fh(struct inode *inode, u32 *fid, int *max_len,
256 struct inode *parent)
257{
258 struct ovl_fs *ofs = OVL_FS(sb: inode->i_sb);
259 struct dentry *dentry;
260 int bytes, buflen = *max_len << 2;
261
262 /* TODO: encode connectable file handles */
263 if (parent)
264 return FILEID_INVALID;
265
266 dentry = d_find_any_alias(inode);
267 if (!dentry)
268 return FILEID_INVALID;
269
270 bytes = ovl_dentry_to_fid(ofs, dentry, fid, buflen);
271 dput(dentry);
272 if (bytes <= 0)
273 return FILEID_INVALID;
274
275 *max_len = bytes >> 2;
276 if (bytes > buflen)
277 return FILEID_INVALID;
278
279 return OVL_FILEID_V1;
280}
281
282/*
283 * Find or instantiate an overlay dentry from real dentries and index.
284 */
285static struct dentry *ovl_obtain_alias(struct super_block *sb,
286 struct dentry *upper_alias,
287 struct ovl_path *lowerpath,
288 struct dentry *index)
289{
290 struct dentry *lower = lowerpath ? lowerpath->dentry : NULL;
291 struct dentry *upper = upper_alias ?: index;
292 struct inode *inode = NULL;
293 struct ovl_entry *oe;
294 struct ovl_inode_params oip = {
295 .index = index,
296 };
297
298 /* We get overlay directory dentries with ovl_lookup_real() */
299 if (d_is_dir(dentry: upper ?: lower))
300 return ERR_PTR(error: -EIO);
301
302 oe = ovl_alloc_entry(numlower: !!lower);
303 if (!oe)
304 return ERR_PTR(error: -ENOMEM);
305
306 oip.upperdentry = dget(dentry: upper);
307 if (lower) {
308 ovl_lowerstack(oe)->dentry = dget(dentry: lower);
309 ovl_lowerstack(oe)->layer = lowerpath->layer;
310 }
311 oip.oe = oe;
312 inode = ovl_get_inode(sb, oip: &oip);
313 if (IS_ERR(ptr: inode)) {
314 ovl_free_entry(oe);
315 dput(upper);
316 return ERR_CAST(ptr: inode);
317 }
318
319 if (upper)
320 ovl_set_flag(flag: OVL_UPPERDATA, inode);
321
322 return d_obtain_alias(inode);
323}
324
325/* Get the upper or lower dentry in stack whose on layer @idx */
326static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx)
327{
328 struct ovl_entry *oe = OVL_E(dentry);
329 struct ovl_path *lowerstack = ovl_lowerstack(oe);
330 int i;
331
332 if (!idx)
333 return ovl_dentry_upper(dentry);
334
335 for (i = 0; i < ovl_numlower(oe); i++) {
336 if (lowerstack[i].layer->idx == idx)
337 return lowerstack[i].dentry;
338 }
339
340 return NULL;
341}
342
343/*
344 * Lookup a child overlay dentry to get a connected overlay dentry whose real
345 * dentry is @real. If @real is on upper layer, we lookup a child overlay
346 * dentry with the same name as the real dentry. Otherwise, we need to consult
347 * index for lookup.
348 */
349static struct dentry *ovl_lookup_real_one(struct dentry *connected,
350 struct dentry *real,
351 const struct ovl_layer *layer)
352{
353 struct inode *dir = d_inode(dentry: connected);
354 struct dentry *this, *parent = NULL;
355 struct name_snapshot name;
356 int err;
357
358 /*
359 * Lookup child overlay dentry by real name. The dir mutex protects us
360 * from racing with overlay rename. If the overlay dentry that is above
361 * real has already been moved to a parent that is not under the
362 * connected overlay dir, we return -ECHILD and restart the lookup of
363 * connected real path from the top.
364 */
365 inode_lock_nested(inode: dir, subclass: I_MUTEX_PARENT);
366 err = -ECHILD;
367 parent = dget_parent(dentry: real);
368 if (ovl_dentry_real_at(dentry: connected, idx: layer->idx) != parent)
369 goto fail;
370
371 /*
372 * We also need to take a snapshot of real dentry name to protect us
373 * from racing with underlying layer rename. In this case, we don't
374 * care about returning ESTALE, only from dereferencing a free name
375 * pointer because we hold no lock on the real dentry.
376 */
377 take_dentry_name_snapshot(&name, real);
378 /*
379 * No idmap handling here: it's an internal lookup. Could skip
380 * permission checking altogether, but for now just use non-idmap
381 * transformed ids.
382 */
383 this = lookup_one_len(name.name.name, connected, name.name.len);
384 release_dentry_name_snapshot(&name);
385 err = PTR_ERR(ptr: this);
386 if (IS_ERR(ptr: this)) {
387 goto fail;
388 } else if (!this || !this->d_inode) {
389 dput(this);
390 err = -ENOENT;
391 goto fail;
392 } else if (ovl_dentry_real_at(dentry: this, idx: layer->idx) != real) {
393 dput(this);
394 err = -ESTALE;
395 goto fail;
396 }
397
398out:
399 dput(parent);
400 inode_unlock(inode: dir);
401 return this;
402
403fail:
404 pr_warn_ratelimited("failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
405 real, layer->idx, connected, err);
406 this = ERR_PTR(error: err);
407 goto out;
408}
409
410static struct dentry *ovl_lookup_real(struct super_block *sb,
411 struct dentry *real,
412 const struct ovl_layer *layer);
413
414/*
415 * Lookup an indexed or hashed overlay dentry by real inode.
416 */
417static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
418 struct dentry *real,
419 const struct ovl_layer *layer)
420{
421 struct ovl_fs *ofs = OVL_FS(sb);
422 struct dentry *index = NULL;
423 struct dentry *this = NULL;
424 struct inode *inode;
425
426 /*
427 * Decoding upper dir from index is expensive, so first try to lookup
428 * overlay dentry in inode/dcache.
429 */
430 inode = ovl_lookup_inode(sb, real, is_upper: !layer->idx);
431 if (IS_ERR(ptr: inode))
432 return ERR_CAST(ptr: inode);
433 if (inode) {
434 this = d_find_any_alias(inode);
435 iput(inode);
436 }
437
438 /*
439 * For decoded lower dir file handle, lookup index by origin to check
440 * if lower dir was copied up and and/or removed.
441 */
442 if (!this && layer->idx && ovl_indexdir(sb) && !WARN_ON(!d_is_dir(real))) {
443 index = ovl_lookup_index(ofs, NULL, origin: real, verify: false);
444 if (IS_ERR(ptr: index))
445 return index;
446 }
447
448 /* Get connected upper overlay dir from index */
449 if (index) {
450 struct dentry *upper = ovl_index_upper(ofs, index, connected: true);
451
452 dput(index);
453 if (IS_ERR_OR_NULL(ptr: upper))
454 return upper;
455
456 /*
457 * ovl_lookup_real() in lower layer may call recursively once to
458 * ovl_lookup_real() in upper layer. The first level call walks
459 * back lower parents to the topmost indexed parent. The second
460 * recursive call walks back from indexed upper to the topmost
461 * connected/hashed upper parent (or up to root).
462 */
463 this = ovl_lookup_real(sb, real: upper, layer: &ofs->layers[0]);
464 dput(upper);
465 }
466
467 if (IS_ERR_OR_NULL(ptr: this))
468 return this;
469
470 if (ovl_dentry_real_at(dentry: this, idx: layer->idx) != real) {
471 dput(this);
472 this = ERR_PTR(error: -EIO);
473 }
474
475 return this;
476}
477
478/*
479 * Lookup an indexed or hashed overlay dentry, whose real dentry is an
480 * ancestor of @real.
481 */
482static struct dentry *ovl_lookup_real_ancestor(struct super_block *sb,
483 struct dentry *real,
484 const struct ovl_layer *layer)
485{
486 struct dentry *next, *parent = NULL;
487 struct dentry *ancestor = ERR_PTR(error: -EIO);
488
489 if (real == layer->mnt->mnt_root)
490 return dget(dentry: sb->s_root);
491
492 /* Find the topmost indexed or hashed ancestor */
493 next = dget(dentry: real);
494 for (;;) {
495 parent = dget_parent(dentry: next);
496
497 /*
498 * Lookup a matching overlay dentry in inode/dentry
499 * cache or in index by real inode.
500 */
501 ancestor = ovl_lookup_real_inode(sb, real: next, layer);
502 if (ancestor)
503 break;
504
505 if (parent == layer->mnt->mnt_root) {
506 ancestor = dget(dentry: sb->s_root);
507 break;
508 }
509
510 /*
511 * If @real has been moved out of the layer root directory,
512 * we will eventully hit the real fs root. This cannot happen
513 * by legit overlay rename, so we return error in that case.
514 */
515 if (parent == next) {
516 ancestor = ERR_PTR(error: -EXDEV);
517 break;
518 }
519
520 dput(next);
521 next = parent;
522 }
523
524 dput(parent);
525 dput(next);
526
527 return ancestor;
528}
529
530/*
531 * Lookup a connected overlay dentry whose real dentry is @real.
532 * If @real is on upper layer, we lookup a child overlay dentry with the same
533 * path the real dentry. Otherwise, we need to consult index for lookup.
534 */
535static struct dentry *ovl_lookup_real(struct super_block *sb,
536 struct dentry *real,
537 const struct ovl_layer *layer)
538{
539 struct dentry *connected;
540 int err = 0;
541
542 connected = ovl_lookup_real_ancestor(sb, real, layer);
543 if (IS_ERR(ptr: connected))
544 return connected;
545
546 while (!err) {
547 struct dentry *next, *this;
548 struct dentry *parent = NULL;
549 struct dentry *real_connected = ovl_dentry_real_at(dentry: connected,
550 idx: layer->idx);
551
552 if (real_connected == real)
553 break;
554
555 /* Find the topmost dentry not yet connected */
556 next = dget(dentry: real);
557 for (;;) {
558 parent = dget_parent(dentry: next);
559
560 if (parent == real_connected)
561 break;
562
563 /*
564 * If real has been moved out of 'real_connected',
565 * we will not find 'real_connected' and hit the layer
566 * root. In that case, we need to restart connecting.
567 * This game can go on forever in the worst case. We
568 * may want to consider taking s_vfs_rename_mutex if
569 * this happens more than once.
570 */
571 if (parent == layer->mnt->mnt_root) {
572 dput(connected);
573 connected = dget(dentry: sb->s_root);
574 break;
575 }
576
577 /*
578 * If real file has been moved out of the layer root
579 * directory, we will eventully hit the real fs root.
580 * This cannot happen by legit overlay rename, so we
581 * return error in that case.
582 */
583 if (parent == next) {
584 err = -EXDEV;
585 break;
586 }
587
588 dput(next);
589 next = parent;
590 }
591
592 if (!err) {
593 this = ovl_lookup_real_one(connected, real: next, layer);
594 if (IS_ERR(ptr: this))
595 err = PTR_ERR(ptr: this);
596
597 /*
598 * Lookup of child in overlay can fail when racing with
599 * overlay rename of child away from 'connected' parent.
600 * In this case, we need to restart the lookup from the
601 * top, because we cannot trust that 'real_connected' is
602 * still an ancestor of 'real'. There is a good chance
603 * that the renamed overlay ancestor is now in cache, so
604 * ovl_lookup_real_ancestor() will find it and we can
605 * continue to connect exactly from where lookup failed.
606 */
607 if (err == -ECHILD) {
608 this = ovl_lookup_real_ancestor(sb, real,
609 layer);
610 err = PTR_ERR_OR_ZERO(ptr: this);
611 }
612 if (!err) {
613 dput(connected);
614 connected = this;
615 }
616 }
617
618 dput(parent);
619 dput(next);
620 }
621
622 if (err)
623 goto fail;
624
625 return connected;
626
627fail:
628 pr_warn_ratelimited("failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
629 real, layer->idx, connected, err);
630 dput(connected);
631 return ERR_PTR(error: err);
632}
633
634/*
635 * Get an overlay dentry from upper/lower real dentries and index.
636 */
637static struct dentry *ovl_get_dentry(struct super_block *sb,
638 struct dentry *upper,
639 struct ovl_path *lowerpath,
640 struct dentry *index)
641{
642 struct ovl_fs *ofs = OVL_FS(sb);
643 const struct ovl_layer *layer = upper ? &ofs->layers[0] : lowerpath->layer;
644 struct dentry *real = upper ?: (index ?: lowerpath->dentry);
645
646 /*
647 * Obtain a disconnected overlay dentry from a non-dir real dentry
648 * and index.
649 */
650 if (!d_is_dir(dentry: real))
651 return ovl_obtain_alias(sb, upper_alias: upper, lowerpath, index);
652
653 /* Removed empty directory? */
654 if ((real->d_flags & DCACHE_DISCONNECTED) || d_unhashed(dentry: real))
655 return ERR_PTR(error: -ENOENT);
656
657 /*
658 * If real dentry is connected and hashed, get a connected overlay
659 * dentry whose real dentry is @real.
660 */
661 return ovl_lookup_real(sb, real, layer);
662}
663
664static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
665 struct ovl_fh *fh)
666{
667 struct ovl_fs *ofs = OVL_FS(sb);
668 struct dentry *dentry;
669 struct dentry *upper;
670
671 if (!ovl_upper_mnt(ofs))
672 return ERR_PTR(error: -EACCES);
673
674 upper = ovl_decode_real_fh(ofs, fh, mnt: ovl_upper_mnt(ofs), connected: true);
675 if (IS_ERR_OR_NULL(ptr: upper))
676 return upper;
677
678 dentry = ovl_get_dentry(sb, upper, NULL, NULL);
679 dput(upper);
680
681 return dentry;
682}
683
684static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
685 struct ovl_fh *fh)
686{
687 struct ovl_fs *ofs = OVL_FS(sb);
688 struct ovl_path origin = { };
689 struct ovl_path *stack = &origin;
690 struct dentry *dentry = NULL;
691 struct dentry *index = NULL;
692 struct inode *inode;
693 int err;
694
695 /* First lookup overlay inode in inode cache by origin fh */
696 err = ovl_check_origin_fh(ofs, fh, connected: false, NULL, stackp: &stack);
697 if (err)
698 return ERR_PTR(error: err);
699
700 if (!d_is_dir(dentry: origin.dentry) ||
701 !(origin.dentry->d_flags & DCACHE_DISCONNECTED)) {
702 inode = ovl_lookup_inode(sb, real: origin.dentry, is_upper: false);
703 err = PTR_ERR(ptr: inode);
704 if (IS_ERR(ptr: inode))
705 goto out_err;
706 if (inode) {
707 dentry = d_find_any_alias(inode);
708 iput(inode);
709 if (dentry)
710 goto out;
711 }
712 }
713
714 /* Then lookup indexed upper/whiteout by origin fh */
715 if (ovl_indexdir(sb)) {
716 index = ovl_get_index_fh(ofs, fh);
717 err = PTR_ERR(ptr: index);
718 if (IS_ERR(ptr: index)) {
719 index = NULL;
720 goto out_err;
721 }
722 }
723
724 /* Then try to get a connected upper dir by index */
725 if (index && d_is_dir(dentry: index)) {
726 struct dentry *upper = ovl_index_upper(ofs, index, connected: true);
727
728 err = PTR_ERR(ptr: upper);
729 if (IS_ERR_OR_NULL(ptr: upper))
730 goto out_err;
731
732 dentry = ovl_get_dentry(sb, upper, NULL, NULL);
733 dput(upper);
734 goto out;
735 }
736
737 /* Find origin.dentry again with ovl_acceptable() layer check */
738 if (d_is_dir(dentry: origin.dentry)) {
739 dput(origin.dentry);
740 origin.dentry = NULL;
741 err = ovl_check_origin_fh(ofs, fh, connected: true, NULL, stackp: &stack);
742 if (err)
743 goto out_err;
744 }
745 if (index) {
746 err = ovl_verify_origin(ofs, upper: index, origin: origin.dentry, set: false);
747 if (err)
748 goto out_err;
749 }
750
751 /* Get a connected non-upper dir or disconnected non-dir */
752 dentry = ovl_get_dentry(sb, NULL, lowerpath: &origin, index);
753
754out:
755 dput(origin.dentry);
756 dput(index);
757 return dentry;
758
759out_err:
760 dentry = ERR_PTR(error: err);
761 goto out;
762}
763
764static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
765{
766 struct ovl_fh *fh;
767
768 /* If on-wire inner fid is aligned - nothing to do */
769 if (fh_type == OVL_FILEID_V1)
770 return (struct ovl_fh *)fid;
771
772 if (fh_type != OVL_FILEID_V0)
773 return ERR_PTR(error: -EINVAL);
774
775 if (buflen <= OVL_FH_WIRE_OFFSET)
776 return ERR_PTR(error: -EINVAL);
777
778 fh = kzalloc(size: buflen, GFP_KERNEL);
779 if (!fh)
780 return ERR_PTR(error: -ENOMEM);
781
782 /* Copy unaligned inner fh into aligned buffer */
783 memcpy(fh->buf, fid, buflen - OVL_FH_WIRE_OFFSET);
784 return fh;
785}
786
787static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
788 int fh_len, int fh_type)
789{
790 struct dentry *dentry = NULL;
791 struct ovl_fh *fh = NULL;
792 int len = fh_len << 2;
793 unsigned int flags = 0;
794 int err;
795
796 fh = ovl_fid_to_fh(fid, buflen: len, fh_type);
797 err = PTR_ERR(ptr: fh);
798 if (IS_ERR(ptr: fh))
799 goto out_err;
800
801 err = ovl_check_fh_len(fh, fh_len: len);
802 if (err)
803 goto out_err;
804
805 flags = fh->fb.flags;
806 dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ?
807 ovl_upper_fh_to_d(sb, fh) :
808 ovl_lower_fh_to_d(sb, fh);
809 err = PTR_ERR(ptr: dentry);
810 if (IS_ERR(ptr: dentry) && err != -ESTALE)
811 goto out_err;
812
813out:
814 /* We may have needed to re-align OVL_FILEID_V0 */
815 if (!IS_ERR_OR_NULL(ptr: fh) && fh != (void *)fid)
816 kfree(objp: fh);
817
818 return dentry;
819
820out_err:
821 pr_warn_ratelimited("failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
822 fh_len, fh_type, flags, err);
823 dentry = ERR_PTR(error: err);
824 goto out;
825}
826
827static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid,
828 int fh_len, int fh_type)
829{
830 pr_warn_ratelimited("connectable file handles not supported; use 'no_subtree_check' exportfs option.\n");
831 return ERR_PTR(error: -EACCES);
832}
833
834static int ovl_get_name(struct dentry *parent, char *name,
835 struct dentry *child)
836{
837 /*
838 * ovl_fh_to_dentry() returns connected dir overlay dentries and
839 * ovl_fh_to_parent() is not implemented, so we should not get here.
840 */
841 WARN_ON_ONCE(1);
842 return -EIO;
843}
844
845static struct dentry *ovl_get_parent(struct dentry *dentry)
846{
847 /*
848 * ovl_fh_to_dentry() returns connected dir overlay dentries, so we
849 * should not get here.
850 */
851 WARN_ON_ONCE(1);
852 return ERR_PTR(error: -EIO);
853}
854
855const struct export_operations ovl_export_operations = {
856 .encode_fh = ovl_encode_fh,
857 .fh_to_dentry = ovl_fh_to_dentry,
858 .fh_to_parent = ovl_fh_to_parent,
859 .get_name = ovl_get_name,
860 .get_parent = ovl_get_parent,
861};
862
863/* encode_fh() encodes non-decodable file handles with nfs_export=off */
864const struct export_operations ovl_export_fid_operations = {
865 .encode_fh = ovl_encode_fh,
866};
867

source code of linux/fs/overlayfs/export.c