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

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

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