xref: /openbmc/linux/fs/overlayfs/export.c (revision 407e7517)
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 /*
23  * We only need to encode origin if there is a chance that the same object was
24  * encoded pre copy up and then we need to stay consistent with the same
25  * encoding also after copy up. If non-pure upper is not indexed, then it was
26  * copied up before NFS export was enabled. In that case we don't need to worry
27  * about staying consistent with pre copy up encoding and we encode an upper
28  * file handle. Overlay root dentry is a private case of non-indexed upper.
29  *
30  * The following table summarizes the different file handle encodings used for
31  * different overlay object types:
32  *
33  *  Object type		| Encoding
34  * --------------------------------
35  *  Pure upper		| U
36  *  Non-indexed upper	| U
37  *  Indexed upper	| L (*)
38  *  Non-upper		| L (*)
39  *
40  * U = upper file handle
41  * L = lower file handle
42  *
43  * (*) Connecting an overlay dir from real lower dentry is not always
44  * possible when there are redirects in lower layers. To mitigate this case,
45  * we copy up the lower dir first and then encode an upper dir file handle.
46  */
47 static bool ovl_should_encode_origin(struct dentry *dentry)
48 {
49 	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
50 
51 	if (!ovl_dentry_lower(dentry))
52 		return false;
53 
54 	/*
55 	 * Decoding a merge dir, whose origin's parent is under a redirected
56 	 * lower dir is not always possible. As a simple aproximation, we do
57 	 * not encode lower dir file handles when overlay has multiple lower
58 	 * layers and origin is below the topmost lower layer.
59 	 *
60 	 * TODO: copy up only the parent that is under redirected lower.
61 	 */
62 	if (d_is_dir(dentry) && ofs->upper_mnt &&
63 	    OVL_E(dentry)->lowerstack[0].layer->idx > 1)
64 		return false;
65 
66 	/* Decoding a non-indexed upper from origin is not implemented */
67 	if (ovl_dentry_upper(dentry) &&
68 	    !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
69 		return false;
70 
71 	return true;
72 }
73 
74 static int ovl_encode_maybe_copy_up(struct dentry *dentry)
75 {
76 	int err;
77 
78 	if (ovl_dentry_upper(dentry))
79 		return 0;
80 
81 	err = ovl_want_write(dentry);
82 	if (err)
83 		return err;
84 
85 	err = ovl_copy_up(dentry);
86 
87 	ovl_drop_write(dentry);
88 	return err;
89 }
90 
91 static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
92 {
93 	struct dentry *origin = ovl_dentry_lower(dentry);
94 	struct ovl_fh *fh = NULL;
95 	int err;
96 
97 	/*
98 	 * If we should not encode a lower dir file handle, copy up and encode
99 	 * an upper dir file handle.
100 	 */
101 	if (!ovl_should_encode_origin(dentry)) {
102 		err = ovl_encode_maybe_copy_up(dentry);
103 		if (err)
104 			goto fail;
105 
106 		origin = NULL;
107 	}
108 
109 	/* Encode an upper or origin file handle */
110 	fh = ovl_encode_fh(origin ?: ovl_dentry_upper(dentry), !origin);
111 	err = PTR_ERR(fh);
112 	if (IS_ERR(fh))
113 		goto fail;
114 
115 	err = -EOVERFLOW;
116 	if (fh->len > buflen)
117 		goto fail;
118 
119 	memcpy(buf, (char *)fh, fh->len);
120 	err = fh->len;
121 
122 out:
123 	kfree(fh);
124 	return err;
125 
126 fail:
127 	pr_warn_ratelimited("overlayfs: failed to encode file handle (%pd2, err=%i, buflen=%d, len=%d, type=%d)\n",
128 			    dentry, err, buflen, fh ? (int)fh->len : 0,
129 			    fh ? fh->type : 0);
130 	goto out;
131 }
132 
133 static int ovl_dentry_to_fh(struct dentry *dentry, u32 *fid, int *max_len)
134 {
135 	int res, len = *max_len << 2;
136 
137 	res = ovl_d_to_fh(dentry, (char *)fid, len);
138 	if (res <= 0)
139 		return FILEID_INVALID;
140 
141 	len = res;
142 
143 	/* Round up to dwords */
144 	*max_len = (len + 3) >> 2;
145 	return OVL_FILEID;
146 }
147 
148 static int ovl_encode_inode_fh(struct inode *inode, u32 *fid, int *max_len,
149 			       struct inode *parent)
150 {
151 	struct dentry *dentry;
152 	int type;
153 
154 	/* TODO: encode connectable file handles */
155 	if (parent)
156 		return FILEID_INVALID;
157 
158 	dentry = d_find_any_alias(inode);
159 	if (WARN_ON(!dentry))
160 		return FILEID_INVALID;
161 
162 	type = ovl_dentry_to_fh(dentry, fid, max_len);
163 
164 	dput(dentry);
165 	return type;
166 }
167 
168 /*
169  * Find or instantiate an overlay dentry from real dentries and index.
170  */
171 static struct dentry *ovl_obtain_alias(struct super_block *sb,
172 				       struct dentry *upper_alias,
173 				       struct ovl_path *lowerpath,
174 				       struct dentry *index)
175 {
176 	struct dentry *lower = lowerpath ? lowerpath->dentry : NULL;
177 	struct dentry *upper = upper_alias ?: index;
178 	struct dentry *dentry;
179 	struct inode *inode;
180 	struct ovl_entry *oe;
181 
182 	/* We get overlay directory dentries with ovl_lookup_real() */
183 	if (d_is_dir(upper ?: lower))
184 		return ERR_PTR(-EIO);
185 
186 	inode = ovl_get_inode(sb, dget(upper), lower, index, !!lower);
187 	if (IS_ERR(inode)) {
188 		dput(upper);
189 		return ERR_CAST(inode);
190 	}
191 
192 	if (index)
193 		ovl_set_flag(OVL_INDEX, inode);
194 
195 	dentry = d_find_any_alias(inode);
196 	if (!dentry) {
197 		dentry = d_alloc_anon(inode->i_sb);
198 		if (!dentry)
199 			goto nomem;
200 		oe = ovl_alloc_entry(lower ? 1 : 0);
201 		if (!oe)
202 			goto nomem;
203 
204 		if (lower) {
205 			oe->lowerstack->dentry = dget(lower);
206 			oe->lowerstack->layer = lowerpath->layer;
207 		}
208 		dentry->d_fsdata = oe;
209 		if (upper_alias)
210 			ovl_dentry_set_upper_alias(dentry);
211 	}
212 
213 	return d_instantiate_anon(dentry, inode);
214 
215 nomem:
216 	iput(inode);
217 	dput(dentry);
218 	return ERR_PTR(-ENOMEM);
219 }
220 
221 /* Get the upper or lower dentry in stach whose on layer @idx */
222 static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx)
223 {
224 	struct ovl_entry *oe = dentry->d_fsdata;
225 	int i;
226 
227 	if (!idx)
228 		return ovl_dentry_upper(dentry);
229 
230 	for (i = 0; i < oe->numlower; i++) {
231 		if (oe->lowerstack[i].layer->idx == idx)
232 			return oe->lowerstack[i].dentry;
233 	}
234 
235 	return NULL;
236 }
237 
238 /*
239  * Lookup a child overlay dentry to get a connected overlay dentry whose real
240  * dentry is @real. If @real is on upper layer, we lookup a child overlay
241  * dentry with the same name as the real dentry. Otherwise, we need to consult
242  * index for lookup.
243  */
244 static struct dentry *ovl_lookup_real_one(struct dentry *connected,
245 					  struct dentry *real,
246 					  struct ovl_layer *layer)
247 {
248 	struct inode *dir = d_inode(connected);
249 	struct dentry *this, *parent = NULL;
250 	struct name_snapshot name;
251 	int err;
252 
253 	/*
254 	 * Lookup child overlay dentry by real name. The dir mutex protects us
255 	 * from racing with overlay rename. If the overlay dentry that is above
256 	 * real has already been moved to a parent that is not under the
257 	 * connected overlay dir, we return -ECHILD and restart the lookup of
258 	 * connected real path from the top.
259 	 */
260 	inode_lock_nested(dir, I_MUTEX_PARENT);
261 	err = -ECHILD;
262 	parent = dget_parent(real);
263 	if (ovl_dentry_real_at(connected, layer->idx) != parent)
264 		goto fail;
265 
266 	/*
267 	 * We also need to take a snapshot of real dentry name to protect us
268 	 * from racing with underlying layer rename. In this case, we don't
269 	 * care about returning ESTALE, only from dereferencing a free name
270 	 * pointer because we hold no lock on the real dentry.
271 	 */
272 	take_dentry_name_snapshot(&name, real);
273 	this = lookup_one_len(name.name, connected, strlen(name.name));
274 	err = PTR_ERR(this);
275 	if (IS_ERR(this)) {
276 		goto fail;
277 	} else if (!this || !this->d_inode) {
278 		dput(this);
279 		err = -ENOENT;
280 		goto fail;
281 	} else if (ovl_dentry_real_at(this, layer->idx) != real) {
282 		dput(this);
283 		err = -ESTALE;
284 		goto fail;
285 	}
286 
287 out:
288 	release_dentry_name_snapshot(&name);
289 	dput(parent);
290 	inode_unlock(dir);
291 	return this;
292 
293 fail:
294 	pr_warn_ratelimited("overlayfs: failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
295 			    real, layer->idx, connected, err);
296 	this = ERR_PTR(err);
297 	goto out;
298 }
299 
300 static struct dentry *ovl_lookup_real(struct super_block *sb,
301 				      struct dentry *real,
302 				      struct ovl_layer *layer);
303 
304 /*
305  * Lookup an indexed or hashed overlay dentry by real inode.
306  */
307 static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
308 					    struct dentry *real,
309 					    struct ovl_layer *layer)
310 {
311 	struct ovl_fs *ofs = sb->s_fs_info;
312 	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
313 	struct dentry *index = NULL;
314 	struct dentry *this = NULL;
315 	struct inode *inode;
316 
317 	/*
318 	 * Decoding upper dir from index is expensive, so first try to lookup
319 	 * overlay dentry in inode/dcache.
320 	 */
321 	inode = ovl_lookup_inode(sb, real, !layer->idx);
322 	if (IS_ERR(inode))
323 		return ERR_CAST(inode);
324 	if (inode) {
325 		this = d_find_any_alias(inode);
326 		iput(inode);
327 	}
328 
329 	/*
330 	 * For decoded lower dir file handle, lookup index by origin to check
331 	 * if lower dir was copied up and and/or removed.
332 	 */
333 	if (!this && layer->idx && ofs->indexdir && !WARN_ON(!d_is_dir(real))) {
334 		index = ovl_lookup_index(ofs, NULL, real, false);
335 		if (IS_ERR(index))
336 			return index;
337 	}
338 
339 	/* Get connected upper overlay dir from index */
340 	if (index) {
341 		struct dentry *upper = ovl_index_upper(ofs, index);
342 
343 		dput(index);
344 		if (IS_ERR_OR_NULL(upper))
345 			return upper;
346 
347 		/*
348 		 * ovl_lookup_real() in lower layer may call recursively once to
349 		 * ovl_lookup_real() in upper layer. The first level call walks
350 		 * back lower parents to the topmost indexed parent. The second
351 		 * recursive call walks back from indexed upper to the topmost
352 		 * connected/hashed upper parent (or up to root).
353 		 */
354 		this = ovl_lookup_real(sb, upper, &upper_layer);
355 		dput(upper);
356 	}
357 
358 	if (!this)
359 		return NULL;
360 
361 	if (WARN_ON(ovl_dentry_real_at(this, layer->idx) != real)) {
362 		dput(this);
363 		this = ERR_PTR(-EIO);
364 	}
365 
366 	return this;
367 }
368 
369 /*
370  * Lookup an indexed or hashed overlay dentry, whose real dentry is an
371  * ancestor of @real.
372  */
373 static struct dentry *ovl_lookup_real_ancestor(struct super_block *sb,
374 					       struct dentry *real,
375 					       struct ovl_layer *layer)
376 {
377 	struct dentry *next, *parent = NULL;
378 	struct dentry *ancestor = ERR_PTR(-EIO);
379 
380 	if (real == layer->mnt->mnt_root)
381 		return dget(sb->s_root);
382 
383 	/* Find the topmost indexed or hashed ancestor */
384 	next = dget(real);
385 	for (;;) {
386 		parent = dget_parent(next);
387 
388 		/*
389 		 * Lookup a matching overlay dentry in inode/dentry
390 		 * cache or in index by real inode.
391 		 */
392 		ancestor = ovl_lookup_real_inode(sb, next, layer);
393 		if (ancestor)
394 			break;
395 
396 		if (parent == layer->mnt->mnt_root) {
397 			ancestor = dget(sb->s_root);
398 			break;
399 		}
400 
401 		/*
402 		 * If @real has been moved out of the layer root directory,
403 		 * we will eventully hit the real fs root. This cannot happen
404 		 * by legit overlay rename, so we return error in that case.
405 		 */
406 		if (parent == next) {
407 			ancestor = ERR_PTR(-EXDEV);
408 			break;
409 		}
410 
411 		dput(next);
412 		next = parent;
413 	}
414 
415 	dput(parent);
416 	dput(next);
417 
418 	return ancestor;
419 }
420 
421 /*
422  * Lookup a connected overlay dentry whose real dentry is @real.
423  * If @real is on upper layer, we lookup a child overlay dentry with the same
424  * path the real dentry. Otherwise, we need to consult index for lookup.
425  */
426 static struct dentry *ovl_lookup_real(struct super_block *sb,
427 				      struct dentry *real,
428 				      struct ovl_layer *layer)
429 {
430 	struct dentry *connected;
431 	int err = 0;
432 
433 	connected = ovl_lookup_real_ancestor(sb, real, layer);
434 	if (IS_ERR(connected))
435 		return connected;
436 
437 	while (!err) {
438 		struct dentry *next, *this;
439 		struct dentry *parent = NULL;
440 		struct dentry *real_connected = ovl_dentry_real_at(connected,
441 								   layer->idx);
442 
443 		if (real_connected == real)
444 			break;
445 
446 		/* Find the topmost dentry not yet connected */
447 		next = dget(real);
448 		for (;;) {
449 			parent = dget_parent(next);
450 
451 			if (parent == real_connected)
452 				break;
453 
454 			/*
455 			 * If real has been moved out of 'real_connected',
456 			 * we will not find 'real_connected' and hit the layer
457 			 * root. In that case, we need to restart connecting.
458 			 * This game can go on forever in the worst case. We
459 			 * may want to consider taking s_vfs_rename_mutex if
460 			 * this happens more than once.
461 			 */
462 			if (parent == layer->mnt->mnt_root) {
463 				dput(connected);
464 				connected = dget(sb->s_root);
465 				break;
466 			}
467 
468 			/*
469 			 * If real file has been moved out of the layer root
470 			 * directory, we will eventully hit the real fs root.
471 			 * This cannot happen by legit overlay rename, so we
472 			 * return error in that case.
473 			 */
474 			if (parent == next) {
475 				err = -EXDEV;
476 				break;
477 			}
478 
479 			dput(next);
480 			next = parent;
481 		}
482 
483 		if (!err) {
484 			this = ovl_lookup_real_one(connected, next, layer);
485 			if (IS_ERR(this))
486 				err = PTR_ERR(this);
487 
488 			/*
489 			 * Lookup of child in overlay can fail when racing with
490 			 * overlay rename of child away from 'connected' parent.
491 			 * In this case, we need to restart the lookup from the
492 			 * top, because we cannot trust that 'real_connected' is
493 			 * still an ancestor of 'real'. There is a good chance
494 			 * that the renamed overlay ancestor is now in cache, so
495 			 * ovl_lookup_real_ancestor() will find it and we can
496 			 * continue to connect exactly from where lookup failed.
497 			 */
498 			if (err == -ECHILD) {
499 				this = ovl_lookup_real_ancestor(sb, real,
500 								layer);
501 				err = IS_ERR(this) ? PTR_ERR(this) : 0;
502 			}
503 			if (!err) {
504 				dput(connected);
505 				connected = this;
506 			}
507 		}
508 
509 		dput(parent);
510 		dput(next);
511 	}
512 
513 	if (err)
514 		goto fail;
515 
516 	return connected;
517 
518 fail:
519 	pr_warn_ratelimited("overlayfs: failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
520 			    real, layer->idx, connected, err);
521 	dput(connected);
522 	return ERR_PTR(err);
523 }
524 
525 /*
526  * Get an overlay dentry from upper/lower real dentries and index.
527  */
528 static struct dentry *ovl_get_dentry(struct super_block *sb,
529 				     struct dentry *upper,
530 				     struct ovl_path *lowerpath,
531 				     struct dentry *index)
532 {
533 	struct ovl_fs *ofs = sb->s_fs_info;
534 	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
535 	struct ovl_layer *layer = upper ? &upper_layer : lowerpath->layer;
536 	struct dentry *real = upper ?: (index ?: lowerpath->dentry);
537 
538 	/*
539 	 * Obtain a disconnected overlay dentry from a non-dir real dentry
540 	 * and index.
541 	 */
542 	if (!d_is_dir(real))
543 		return ovl_obtain_alias(sb, upper, lowerpath, index);
544 
545 	/* Removed empty directory? */
546 	if ((real->d_flags & DCACHE_DISCONNECTED) || d_unhashed(real))
547 		return ERR_PTR(-ENOENT);
548 
549 	/*
550 	 * If real dentry is connected and hashed, get a connected overlay
551 	 * dentry whose real dentry is @real.
552 	 */
553 	return ovl_lookup_real(sb, real, layer);
554 }
555 
556 static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
557 					struct ovl_fh *fh)
558 {
559 	struct ovl_fs *ofs = sb->s_fs_info;
560 	struct dentry *dentry;
561 	struct dentry *upper;
562 
563 	if (!ofs->upper_mnt)
564 		return ERR_PTR(-EACCES);
565 
566 	upper = ovl_decode_fh(fh, ofs->upper_mnt);
567 	if (IS_ERR_OR_NULL(upper))
568 		return upper;
569 
570 	dentry = ovl_get_dentry(sb, upper, NULL, NULL);
571 	dput(upper);
572 
573 	return dentry;
574 }
575 
576 static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
577 					struct ovl_fh *fh)
578 {
579 	struct ovl_fs *ofs = sb->s_fs_info;
580 	struct ovl_path origin = { };
581 	struct ovl_path *stack = &origin;
582 	struct dentry *dentry = NULL;
583 	struct dentry *index = NULL;
584 	struct inode *inode = NULL;
585 	bool is_deleted = false;
586 	int err;
587 
588 	/* First lookup indexed upper by fh */
589 	if (ofs->indexdir) {
590 		index = ovl_get_index_fh(ofs, fh);
591 		err = PTR_ERR(index);
592 		if (IS_ERR(index)) {
593 			if (err != -ESTALE)
594 				return ERR_PTR(err);
595 
596 			/* Found a whiteout index - treat as deleted inode */
597 			is_deleted = true;
598 			index = NULL;
599 		}
600 	}
601 
602 	/* Then try to get upper dir by index */
603 	if (index && d_is_dir(index)) {
604 		struct dentry *upper = ovl_index_upper(ofs, index);
605 
606 		err = PTR_ERR(upper);
607 		if (IS_ERR_OR_NULL(upper))
608 			goto out_err;
609 
610 		dentry = ovl_get_dentry(sb, upper, NULL, NULL);
611 		dput(upper);
612 		goto out;
613 	}
614 
615 	/* Then lookup origin by fh */
616 	err = ovl_check_origin_fh(ofs, fh, NULL, &stack);
617 	if (err) {
618 		goto out_err;
619 	} else if (index) {
620 		err = ovl_verify_origin(index, origin.dentry, false);
621 		if (err)
622 			goto out_err;
623 	} else if (is_deleted) {
624 		/* Lookup deleted non-dir by origin inode */
625 		if (!d_is_dir(origin.dentry))
626 			inode = ovl_lookup_inode(sb, origin.dentry, false);
627 		err = -ESTALE;
628 		if (!inode || atomic_read(&inode->i_count) == 1)
629 			goto out_err;
630 
631 		/* Deleted but still open? */
632 		index = dget(ovl_i_dentry_upper(inode));
633 	}
634 
635 	dentry = ovl_get_dentry(sb, NULL, &origin, index);
636 
637 out:
638 	dput(origin.dentry);
639 	dput(index);
640 	iput(inode);
641 	return dentry;
642 
643 out_err:
644 	dentry = ERR_PTR(err);
645 	goto out;
646 }
647 
648 static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
649 				       int fh_len, int fh_type)
650 {
651 	struct dentry *dentry = NULL;
652 	struct ovl_fh *fh = (struct ovl_fh *) fid;
653 	int len = fh_len << 2;
654 	unsigned int flags = 0;
655 	int err;
656 
657 	err = -EINVAL;
658 	if (fh_type != OVL_FILEID)
659 		goto out_err;
660 
661 	err = ovl_check_fh_len(fh, len);
662 	if (err)
663 		goto out_err;
664 
665 	flags = fh->flags;
666 	dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ?
667 		 ovl_upper_fh_to_d(sb, fh) :
668 		 ovl_lower_fh_to_d(sb, fh);
669 	err = PTR_ERR(dentry);
670 	if (IS_ERR(dentry) && err != -ESTALE)
671 		goto out_err;
672 
673 	return dentry;
674 
675 out_err:
676 	pr_warn_ratelimited("overlayfs: failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
677 			    len, fh_type, flags, err);
678 	return ERR_PTR(err);
679 }
680 
681 static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid,
682 				       int fh_len, int fh_type)
683 {
684 	pr_warn_ratelimited("overlayfs: connectable file handles not supported; use 'no_subtree_check' exportfs option.\n");
685 	return ERR_PTR(-EACCES);
686 }
687 
688 static int ovl_get_name(struct dentry *parent, char *name,
689 			struct dentry *child)
690 {
691 	/*
692 	 * ovl_fh_to_dentry() returns connected dir overlay dentries and
693 	 * ovl_fh_to_parent() is not implemented, so we should not get here.
694 	 */
695 	WARN_ON_ONCE(1);
696 	return -EIO;
697 }
698 
699 static struct dentry *ovl_get_parent(struct dentry *dentry)
700 {
701 	/*
702 	 * ovl_fh_to_dentry() returns connected dir overlay dentries, so we
703 	 * should not get here.
704 	 */
705 	WARN_ON_ONCE(1);
706 	return ERR_PTR(-EIO);
707 }
708 
709 const struct export_operations ovl_export_operations = {
710 	.encode_fh	= ovl_encode_inode_fh,
711 	.fh_to_dentry	= ovl_fh_to_dentry,
712 	.fh_to_parent	= ovl_fh_to_parent,
713 	.get_name	= ovl_get_name,
714 	.get_parent	= ovl_get_parent,
715 };
716