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TOMOYO Linux Cross Reference
Linux/fs/overlayfs/export.c

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

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