xref: /openbmc/linux/fs/overlayfs/namei.c (revision e7253313)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2011 Novell Inc.
4  * Copyright (C) 2016 Red Hat, Inc.
5  */
6 
7 #include <linux/fs.h>
8 #include <linux/cred.h>
9 #include <linux/ctype.h>
10 #include <linux/namei.h>
11 #include <linux/xattr.h>
12 #include <linux/ratelimit.h>
13 #include <linux/mount.h>
14 #include <linux/exportfs.h>
15 #include "overlayfs.h"
16 
17 struct ovl_lookup_data {
18 	struct super_block *sb;
19 	struct qstr name;
20 	bool is_dir;
21 	bool opaque;
22 	bool stop;
23 	bool last;
24 	char *redirect;
25 	bool metacopy;
26 };
27 
28 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
29 			      size_t prelen, const char *post)
30 {
31 	int res;
32 	char *buf;
33 
34 	buf = ovl_get_redirect_xattr(dentry, prelen + strlen(post));
35 	if (IS_ERR_OR_NULL(buf))
36 		return PTR_ERR(buf);
37 
38 	if (buf[0] == '/') {
39 		/*
40 		 * One of the ancestor path elements in an absolute path
41 		 * lookup in ovl_lookup_layer() could have been opaque and
42 		 * that will stop further lookup in lower layers (d->stop=true)
43 		 * But we have found an absolute redirect in decendant path
44 		 * element and that should force continue lookup in lower
45 		 * layers (reset d->stop).
46 		 */
47 		d->stop = false;
48 	} else {
49 		res = strlen(buf) + 1;
50 		memmove(buf + prelen, buf, res);
51 		memcpy(buf, d->name.name, prelen);
52 	}
53 
54 	strcat(buf, post);
55 	kfree(d->redirect);
56 	d->redirect = buf;
57 	d->name.name = d->redirect;
58 	d->name.len = strlen(d->redirect);
59 
60 	return 0;
61 }
62 
63 static int ovl_acceptable(void *ctx, struct dentry *dentry)
64 {
65 	/*
66 	 * A non-dir origin may be disconnected, which is fine, because
67 	 * we only need it for its unique inode number.
68 	 */
69 	if (!d_is_dir(dentry))
70 		return 1;
71 
72 	/* Don't decode a deleted empty directory */
73 	if (d_unhashed(dentry))
74 		return 0;
75 
76 	/* Check if directory belongs to the layer we are decoding from */
77 	return is_subdir(dentry, ((struct vfsmount *)ctx)->mnt_root);
78 }
79 
80 /*
81  * Check validity of an overlay file handle buffer.
82  *
83  * Return 0 for a valid file handle.
84  * Return -ENODATA for "origin unknown".
85  * Return <0 for an invalid file handle.
86  */
87 int ovl_check_fb_len(struct ovl_fb *fb, int fb_len)
88 {
89 	if (fb_len < sizeof(struct ovl_fb) || fb_len < fb->len)
90 		return -EINVAL;
91 
92 	if (fb->magic != OVL_FH_MAGIC)
93 		return -EINVAL;
94 
95 	/* Treat larger version and unknown flags as "origin unknown" */
96 	if (fb->version > OVL_FH_VERSION || fb->flags & ~OVL_FH_FLAG_ALL)
97 		return -ENODATA;
98 
99 	/* Treat endianness mismatch as "origin unknown" */
100 	if (!(fb->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
101 	    (fb->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
102 		return -ENODATA;
103 
104 	return 0;
105 }
106 
107 static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
108 {
109 	int res, err;
110 	struct ovl_fh *fh = NULL;
111 
112 	res = vfs_getxattr(dentry, name, NULL, 0);
113 	if (res < 0) {
114 		if (res == -ENODATA || res == -EOPNOTSUPP)
115 			return NULL;
116 		goto fail;
117 	}
118 	/* Zero size value means "copied up but origin unknown" */
119 	if (res == 0)
120 		return NULL;
121 
122 	fh = kzalloc(res + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
123 	if (!fh)
124 		return ERR_PTR(-ENOMEM);
125 
126 	res = vfs_getxattr(dentry, name, fh->buf, res);
127 	if (res < 0)
128 		goto fail;
129 
130 	err = ovl_check_fb_len(&fh->fb, res);
131 	if (err < 0) {
132 		if (err == -ENODATA)
133 			goto out;
134 		goto invalid;
135 	}
136 
137 	return fh;
138 
139 out:
140 	kfree(fh);
141 	return NULL;
142 
143 fail:
144 	pr_warn_ratelimited("overlayfs: failed to get origin (%i)\n", res);
145 	goto out;
146 invalid:
147 	pr_warn_ratelimited("overlayfs: invalid origin (%*phN)\n", res, fh);
148 	goto out;
149 }
150 
151 struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
152 				  bool connected)
153 {
154 	struct dentry *real;
155 	int bytes;
156 
157 	/*
158 	 * Make sure that the stored uuid matches the uuid of the lower
159 	 * layer where file handle will be decoded.
160 	 */
161 	if (!uuid_equal(&fh->fb.uuid, &mnt->mnt_sb->s_uuid))
162 		return NULL;
163 
164 	bytes = (fh->fb.len - offsetof(struct ovl_fb, fid));
165 	real = exportfs_decode_fh(mnt, (struct fid *)fh->fb.fid,
166 				  bytes >> 2, (int)fh->fb.type,
167 				  connected ? ovl_acceptable : NULL, mnt);
168 	if (IS_ERR(real)) {
169 		/*
170 		 * Treat stale file handle to lower file as "origin unknown".
171 		 * upper file handle could become stale when upper file is
172 		 * unlinked and this information is needed to handle stale
173 		 * index entries correctly.
174 		 */
175 		if (real == ERR_PTR(-ESTALE) &&
176 		    !(fh->fb.flags & OVL_FH_FLAG_PATH_UPPER))
177 			real = NULL;
178 		return real;
179 	}
180 
181 	if (ovl_dentry_weird(real)) {
182 		dput(real);
183 		return NULL;
184 	}
185 
186 	return real;
187 }
188 
189 static bool ovl_is_opaquedir(struct dentry *dentry)
190 {
191 	return ovl_check_dir_xattr(dentry, OVL_XATTR_OPAQUE);
192 }
193 
194 static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
195 			     const char *name, unsigned int namelen,
196 			     size_t prelen, const char *post,
197 			     struct dentry **ret)
198 {
199 	struct dentry *this;
200 	int err;
201 	bool last_element = !post[0];
202 
203 	this = lookup_positive_unlocked(name, base, namelen);
204 	if (IS_ERR(this)) {
205 		err = PTR_ERR(this);
206 		this = NULL;
207 		if (err == -ENOENT || err == -ENAMETOOLONG)
208 			goto out;
209 		goto out_err;
210 	}
211 
212 	if (ovl_dentry_weird(this)) {
213 		/* Don't support traversing automounts and other weirdness */
214 		err = -EREMOTE;
215 		goto out_err;
216 	}
217 	if (ovl_is_whiteout(this)) {
218 		d->stop = d->opaque = true;
219 		goto put_and_out;
220 	}
221 	/*
222 	 * This dentry should be a regular file if previous layer lookup
223 	 * found a metacopy dentry.
224 	 */
225 	if (last_element && d->metacopy && !d_is_reg(this)) {
226 		d->stop = true;
227 		goto put_and_out;
228 	}
229 	if (!d_can_lookup(this)) {
230 		if (d->is_dir || !last_element) {
231 			d->stop = true;
232 			goto put_and_out;
233 		}
234 		err = ovl_check_metacopy_xattr(this);
235 		if (err < 0)
236 			goto out_err;
237 
238 		d->metacopy = err;
239 		d->stop = !d->metacopy;
240 		if (!d->metacopy || d->last)
241 			goto out;
242 	} else {
243 		if (ovl_lookup_trap_inode(d->sb, this)) {
244 			/* Caught in a trap of overlapping layers */
245 			err = -ELOOP;
246 			goto out_err;
247 		}
248 
249 		if (last_element)
250 			d->is_dir = true;
251 		if (d->last)
252 			goto out;
253 
254 		if (ovl_is_opaquedir(this)) {
255 			d->stop = true;
256 			if (last_element)
257 				d->opaque = true;
258 			goto out;
259 		}
260 	}
261 	err = ovl_check_redirect(this, d, prelen, post);
262 	if (err)
263 		goto out_err;
264 out:
265 	*ret = this;
266 	return 0;
267 
268 put_and_out:
269 	dput(this);
270 	this = NULL;
271 	goto out;
272 
273 out_err:
274 	dput(this);
275 	return err;
276 }
277 
278 static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
279 			    struct dentry **ret)
280 {
281 	/* Counting down from the end, since the prefix can change */
282 	size_t rem = d->name.len - 1;
283 	struct dentry *dentry = NULL;
284 	int err;
285 
286 	if (d->name.name[0] != '/')
287 		return ovl_lookup_single(base, d, d->name.name, d->name.len,
288 					 0, "", ret);
289 
290 	while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
291 		const char *s = d->name.name + d->name.len - rem;
292 		const char *next = strchrnul(s, '/');
293 		size_t thislen = next - s;
294 		bool end = !next[0];
295 
296 		/* Verify we did not go off the rails */
297 		if (WARN_ON(s[-1] != '/'))
298 			return -EIO;
299 
300 		err = ovl_lookup_single(base, d, s, thislen,
301 					d->name.len - rem, next, &base);
302 		dput(dentry);
303 		if (err)
304 			return err;
305 		dentry = base;
306 		if (end)
307 			break;
308 
309 		rem -= thislen + 1;
310 
311 		if (WARN_ON(rem >= d->name.len))
312 			return -EIO;
313 	}
314 	*ret = dentry;
315 	return 0;
316 }
317 
318 
319 int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
320 			struct dentry *upperdentry, struct ovl_path **stackp)
321 {
322 	struct dentry *origin = NULL;
323 	int i;
324 
325 	for (i = 0; i < ofs->numlower; i++) {
326 		/*
327 		 * If lower fs uuid is not unique among lower fs we cannot match
328 		 * fh->uuid to layer.
329 		 */
330 		if (ofs->lower_layers[i].fsid &&
331 		    ofs->lower_layers[i].fs->bad_uuid)
332 			continue;
333 
334 		origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
335 					    connected);
336 		if (origin)
337 			break;
338 	}
339 
340 	if (!origin)
341 		return -ESTALE;
342 	else if (IS_ERR(origin))
343 		return PTR_ERR(origin);
344 
345 	if (upperdentry && !ovl_is_whiteout(upperdentry) &&
346 	    ((d_inode(origin)->i_mode ^ d_inode(upperdentry)->i_mode) & S_IFMT))
347 		goto invalid;
348 
349 	if (!*stackp)
350 		*stackp = kmalloc(sizeof(struct ovl_path), GFP_KERNEL);
351 	if (!*stackp) {
352 		dput(origin);
353 		return -ENOMEM;
354 	}
355 	**stackp = (struct ovl_path){
356 		.dentry = origin,
357 		.layer = &ofs->lower_layers[i]
358 	};
359 
360 	return 0;
361 
362 invalid:
363 	pr_warn_ratelimited("overlayfs: invalid origin (%pd2, ftype=%x, origin ftype=%x).\n",
364 			    upperdentry, d_inode(upperdentry)->i_mode & S_IFMT,
365 			    d_inode(origin)->i_mode & S_IFMT);
366 	dput(origin);
367 	return -EIO;
368 }
369 
370 static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
371 			    struct ovl_path **stackp, unsigned int *ctrp)
372 {
373 	struct ovl_fh *fh = ovl_get_fh(upperdentry, OVL_XATTR_ORIGIN);
374 	int err;
375 
376 	if (IS_ERR_OR_NULL(fh))
377 		return PTR_ERR(fh);
378 
379 	err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
380 	kfree(fh);
381 
382 	if (err) {
383 		if (err == -ESTALE)
384 			return 0;
385 		return err;
386 	}
387 
388 	if (WARN_ON(*ctrp))
389 		return -EIO;
390 
391 	*ctrp = 1;
392 	return 0;
393 }
394 
395 /*
396  * Verify that @fh matches the file handle stored in xattr @name.
397  * Return 0 on match, -ESTALE on mismatch, < 0 on error.
398  */
399 static int ovl_verify_fh(struct dentry *dentry, const char *name,
400 			 const struct ovl_fh *fh)
401 {
402 	struct ovl_fh *ofh = ovl_get_fh(dentry, name);
403 	int err = 0;
404 
405 	if (!ofh)
406 		return -ENODATA;
407 
408 	if (IS_ERR(ofh))
409 		return PTR_ERR(ofh);
410 
411 	if (fh->fb.len != ofh->fb.len || memcmp(&fh->fb, &ofh->fb, fh->fb.len))
412 		err = -ESTALE;
413 
414 	kfree(ofh);
415 	return err;
416 }
417 
418 /*
419  * Verify that @real dentry matches the file handle stored in xattr @name.
420  *
421  * If @set is true and there is no stored file handle, encode @real and store
422  * file handle in xattr @name.
423  *
424  * Return 0 on match, -ESTALE on mismatch, -ENODATA on no xattr, < 0 on error.
425  */
426 int ovl_verify_set_fh(struct dentry *dentry, const char *name,
427 		      struct dentry *real, bool is_upper, bool set)
428 {
429 	struct inode *inode;
430 	struct ovl_fh *fh;
431 	int err;
432 
433 	fh = ovl_encode_real_fh(real, is_upper);
434 	err = PTR_ERR(fh);
435 	if (IS_ERR(fh)) {
436 		fh = NULL;
437 		goto fail;
438 	}
439 
440 	err = ovl_verify_fh(dentry, name, fh);
441 	if (set && err == -ENODATA)
442 		err = ovl_do_setxattr(dentry, name, fh->buf, fh->fb.len, 0);
443 	if (err)
444 		goto fail;
445 
446 out:
447 	kfree(fh);
448 	return err;
449 
450 fail:
451 	inode = d_inode(real);
452 	pr_warn_ratelimited("overlayfs: failed to verify %s (%pd2, ino=%lu, err=%i)\n",
453 			    is_upper ? "upper" : "origin", real,
454 			    inode ? inode->i_ino : 0, err);
455 	goto out;
456 }
457 
458 /* Get upper dentry from index */
459 struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index)
460 {
461 	struct ovl_fh *fh;
462 	struct dentry *upper;
463 
464 	if (!d_is_dir(index))
465 		return dget(index);
466 
467 	fh = ovl_get_fh(index, OVL_XATTR_UPPER);
468 	if (IS_ERR_OR_NULL(fh))
469 		return ERR_CAST(fh);
470 
471 	upper = ovl_decode_real_fh(fh, ofs->upper_mnt, true);
472 	kfree(fh);
473 
474 	if (IS_ERR_OR_NULL(upper))
475 		return upper ?: ERR_PTR(-ESTALE);
476 
477 	if (!d_is_dir(upper)) {
478 		pr_warn_ratelimited("overlayfs: invalid index upper (%pd2, upper=%pd2).\n",
479 				    index, upper);
480 		dput(upper);
481 		return ERR_PTR(-EIO);
482 	}
483 
484 	return upper;
485 }
486 
487 /* Is this a leftover from create/whiteout of directory index entry? */
488 static bool ovl_is_temp_index(struct dentry *index)
489 {
490 	return index->d_name.name[0] == '#';
491 }
492 
493 /*
494  * Verify that an index entry name matches the origin file handle stored in
495  * OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
496  * Return 0 on match, -ESTALE on mismatch or stale origin, < 0 on error.
497  */
498 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
499 {
500 	struct ovl_fh *fh = NULL;
501 	size_t len;
502 	struct ovl_path origin = { };
503 	struct ovl_path *stack = &origin;
504 	struct dentry *upper = NULL;
505 	int err;
506 
507 	if (!d_inode(index))
508 		return 0;
509 
510 	/* Cleanup leftover from index create/cleanup attempt */
511 	err = -ESTALE;
512 	if (ovl_is_temp_index(index))
513 		goto fail;
514 
515 	err = -EINVAL;
516 	if (index->d_name.len < sizeof(struct ovl_fb)*2)
517 		goto fail;
518 
519 	err = -ENOMEM;
520 	len = index->d_name.len / 2;
521 	fh = kzalloc(len + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
522 	if (!fh)
523 		goto fail;
524 
525 	err = -EINVAL;
526 	if (hex2bin(fh->buf, index->d_name.name, len))
527 		goto fail;
528 
529 	err = ovl_check_fb_len(&fh->fb, len);
530 	if (err)
531 		goto fail;
532 
533 	/*
534 	 * Whiteout index entries are used as an indication that an exported
535 	 * overlay file handle should be treated as stale (i.e. after unlink
536 	 * of the overlay inode). These entries contain no origin xattr.
537 	 */
538 	if (ovl_is_whiteout(index))
539 		goto out;
540 
541 	/*
542 	 * Verifying directory index entries are not stale is expensive, so
543 	 * only verify stale dir index if NFS export is enabled.
544 	 */
545 	if (d_is_dir(index) && !ofs->config.nfs_export)
546 		goto out;
547 
548 	/*
549 	 * Directory index entries should have 'upper' xattr pointing to the
550 	 * real upper dir. Non-dir index entries are hardlinks to the upper
551 	 * real inode. For non-dir index, we can read the copy up origin xattr
552 	 * directly from the index dentry, but for dir index we first need to
553 	 * decode the upper directory.
554 	 */
555 	upper = ovl_index_upper(ofs, index);
556 	if (IS_ERR_OR_NULL(upper)) {
557 		err = PTR_ERR(upper);
558 		/*
559 		 * Directory index entries with no 'upper' xattr need to be
560 		 * removed. When dir index entry has a stale 'upper' xattr,
561 		 * we assume that upper dir was removed and we treat the dir
562 		 * index as orphan entry that needs to be whited out.
563 		 */
564 		if (err == -ESTALE)
565 			goto orphan;
566 		else if (!err)
567 			err = -ESTALE;
568 		goto fail;
569 	}
570 
571 	err = ovl_verify_fh(upper, OVL_XATTR_ORIGIN, fh);
572 	dput(upper);
573 	if (err)
574 		goto fail;
575 
576 	/* Check if non-dir index is orphan and don't warn before cleaning it */
577 	if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
578 		err = ovl_check_origin_fh(ofs, fh, false, index, &stack);
579 		if (err)
580 			goto fail;
581 
582 		if (ovl_get_nlink(origin.dentry, index, 0) == 0)
583 			goto orphan;
584 	}
585 
586 out:
587 	dput(origin.dentry);
588 	kfree(fh);
589 	return err;
590 
591 fail:
592 	pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, ftype=%x, err=%i)\n",
593 			    index, d_inode(index)->i_mode & S_IFMT, err);
594 	goto out;
595 
596 orphan:
597 	pr_warn_ratelimited("overlayfs: orphan index entry (%pd2, ftype=%x, nlink=%u)\n",
598 			    index, d_inode(index)->i_mode & S_IFMT,
599 			    d_inode(index)->i_nlink);
600 	err = -ENOENT;
601 	goto out;
602 }
603 
604 static int ovl_get_index_name_fh(struct ovl_fh *fh, struct qstr *name)
605 {
606 	char *n, *s;
607 
608 	n = kcalloc(fh->fb.len, 2, GFP_KERNEL);
609 	if (!n)
610 		return -ENOMEM;
611 
612 	s  = bin2hex(n, fh->buf, fh->fb.len);
613 	*name = (struct qstr) QSTR_INIT(n, s - n);
614 
615 	return 0;
616 
617 }
618 
619 /*
620  * Lookup in indexdir for the index entry of a lower real inode or a copy up
621  * origin inode. The index entry name is the hex representation of the lower
622  * inode file handle.
623  *
624  * If the index dentry in negative, then either no lower aliases have been
625  * copied up yet, or aliases have been copied up in older kernels and are
626  * not indexed.
627  *
628  * If the index dentry for a copy up origin inode is positive, but points
629  * to an inode different than the upper inode, then either the upper inode
630  * has been copied up and not indexed or it was indexed, but since then
631  * index dir was cleared. Either way, that index cannot be used to indentify
632  * the overlay inode.
633  */
634 int ovl_get_index_name(struct dentry *origin, struct qstr *name)
635 {
636 	struct ovl_fh *fh;
637 	int err;
638 
639 	fh = ovl_encode_real_fh(origin, false);
640 	if (IS_ERR(fh))
641 		return PTR_ERR(fh);
642 
643 	err = ovl_get_index_name_fh(fh, name);
644 
645 	kfree(fh);
646 	return err;
647 }
648 
649 /* Lookup index by file handle for NFS export */
650 struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
651 {
652 	struct dentry *index;
653 	struct qstr name;
654 	int err;
655 
656 	err = ovl_get_index_name_fh(fh, &name);
657 	if (err)
658 		return ERR_PTR(err);
659 
660 	index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len);
661 	kfree(name.name);
662 	if (IS_ERR(index)) {
663 		if (PTR_ERR(index) == -ENOENT)
664 			index = NULL;
665 		return index;
666 	}
667 
668 	if (ovl_is_whiteout(index))
669 		err = -ESTALE;
670 	else if (ovl_dentry_weird(index))
671 		err = -EIO;
672 	else
673 		return index;
674 
675 	dput(index);
676 	return ERR_PTR(err);
677 }
678 
679 struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
680 				struct dentry *origin, bool verify)
681 {
682 	struct dentry *index;
683 	struct inode *inode;
684 	struct qstr name;
685 	bool is_dir = d_is_dir(origin);
686 	int err;
687 
688 	err = ovl_get_index_name(origin, &name);
689 	if (err)
690 		return ERR_PTR(err);
691 
692 	index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len);
693 	if (IS_ERR(index)) {
694 		err = PTR_ERR(index);
695 		if (err == -ENOENT) {
696 			index = NULL;
697 			goto out;
698 		}
699 		pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%.*s, err=%i);\n"
700 				    "overlayfs: mount with '-o index=off' to disable inodes index.\n",
701 				    d_inode(origin)->i_ino, name.len, name.name,
702 				    err);
703 		goto out;
704 	}
705 
706 	inode = d_inode(index);
707 	if (ovl_is_whiteout(index) && !verify) {
708 		/*
709 		 * When index lookup is called with !verify for decoding an
710 		 * overlay file handle, a whiteout index implies that decode
711 		 * should treat file handle as stale and no need to print a
712 		 * warning about it.
713 		 */
714 		dput(index);
715 		index = ERR_PTR(-ESTALE);
716 		goto out;
717 	} else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
718 		   ((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
719 		/*
720 		 * Index should always be of the same file type as origin
721 		 * except for the case of a whiteout index. A whiteout
722 		 * index should only exist if all lower aliases have been
723 		 * unlinked, which means that finding a lower origin on lookup
724 		 * whose index is a whiteout should be treated as an error.
725 		 */
726 		pr_warn_ratelimited("overlayfs: bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
727 				    index, d_inode(index)->i_mode & S_IFMT,
728 				    d_inode(origin)->i_mode & S_IFMT);
729 		goto fail;
730 	} else if (is_dir && verify) {
731 		if (!upper) {
732 			pr_warn_ratelimited("overlayfs: suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
733 					    origin, index);
734 			goto fail;
735 		}
736 
737 		/* Verify that dir index 'upper' xattr points to upper dir */
738 		err = ovl_verify_upper(index, upper, false);
739 		if (err) {
740 			if (err == -ESTALE) {
741 				pr_warn_ratelimited("overlayfs: suspected multiply redirected dir found (upper=%pd2, origin=%pd2, index=%pd2).\n",
742 						    upper, origin, index);
743 			}
744 			goto fail;
745 		}
746 	} else if (upper && d_inode(upper) != inode) {
747 		goto out_dput;
748 	}
749 out:
750 	kfree(name.name);
751 	return index;
752 
753 out_dput:
754 	dput(index);
755 	index = NULL;
756 	goto out;
757 
758 fail:
759 	dput(index);
760 	index = ERR_PTR(-EIO);
761 	goto out;
762 }
763 
764 /*
765  * Returns next layer in stack starting from top.
766  * Returns -1 if this is the last layer.
767  */
768 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
769 {
770 	struct ovl_entry *oe = dentry->d_fsdata;
771 
772 	BUG_ON(idx < 0);
773 	if (idx == 0) {
774 		ovl_path_upper(dentry, path);
775 		if (path->dentry)
776 			return oe->numlower ? 1 : -1;
777 		idx++;
778 	}
779 	BUG_ON(idx > oe->numlower);
780 	path->dentry = oe->lowerstack[idx - 1].dentry;
781 	path->mnt = oe->lowerstack[idx - 1].layer->mnt;
782 
783 	return (idx < oe->numlower) ? idx + 1 : -1;
784 }
785 
786 /* Fix missing 'origin' xattr */
787 static int ovl_fix_origin(struct dentry *dentry, struct dentry *lower,
788 			  struct dentry *upper)
789 {
790 	int err;
791 
792 	if (ovl_check_origin_xattr(upper))
793 		return 0;
794 
795 	err = ovl_want_write(dentry);
796 	if (err)
797 		return err;
798 
799 	err = ovl_set_origin(dentry, lower, upper);
800 	if (!err)
801 		err = ovl_set_impure(dentry->d_parent, upper->d_parent);
802 
803 	ovl_drop_write(dentry);
804 	return err;
805 }
806 
807 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
808 			  unsigned int flags)
809 {
810 	struct ovl_entry *oe;
811 	const struct cred *old_cred;
812 	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
813 	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
814 	struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
815 	struct ovl_path *stack = NULL, *origin_path = NULL;
816 	struct dentry *upperdir, *upperdentry = NULL;
817 	struct dentry *origin = NULL;
818 	struct dentry *index = NULL;
819 	unsigned int ctr = 0;
820 	struct inode *inode = NULL;
821 	bool upperopaque = false;
822 	char *upperredirect = NULL;
823 	struct dentry *this;
824 	unsigned int i;
825 	int err;
826 	bool metacopy = false;
827 	struct ovl_lookup_data d = {
828 		.sb = dentry->d_sb,
829 		.name = dentry->d_name,
830 		.is_dir = false,
831 		.opaque = false,
832 		.stop = false,
833 		.last = ofs->config.redirect_follow ? false : !poe->numlower,
834 		.redirect = NULL,
835 		.metacopy = false,
836 	};
837 
838 	if (dentry->d_name.len > ofs->namelen)
839 		return ERR_PTR(-ENAMETOOLONG);
840 
841 	old_cred = ovl_override_creds(dentry->d_sb);
842 	upperdir = ovl_dentry_upper(dentry->d_parent);
843 	if (upperdir) {
844 		err = ovl_lookup_layer(upperdir, &d, &upperdentry);
845 		if (err)
846 			goto out;
847 
848 		if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
849 			dput(upperdentry);
850 			err = -EREMOTE;
851 			goto out;
852 		}
853 		if (upperdentry && !d.is_dir) {
854 			unsigned int origin_ctr = 0;
855 
856 			/*
857 			 * Lookup copy up origin by decoding origin file handle.
858 			 * We may get a disconnected dentry, which is fine,
859 			 * because we only need to hold the origin inode in
860 			 * cache and use its inode number.  We may even get a
861 			 * connected dentry, that is not under any of the lower
862 			 * layers root.  That is also fine for using it's inode
863 			 * number - it's the same as if we held a reference
864 			 * to a dentry in lower layer that was moved under us.
865 			 */
866 			err = ovl_check_origin(ofs, upperdentry, &origin_path,
867 					       &origin_ctr);
868 			if (err)
869 				goto out_put_upper;
870 
871 			if (d.metacopy)
872 				metacopy = true;
873 		}
874 
875 		if (d.redirect) {
876 			err = -ENOMEM;
877 			upperredirect = kstrdup(d.redirect, GFP_KERNEL);
878 			if (!upperredirect)
879 				goto out_put_upper;
880 			if (d.redirect[0] == '/')
881 				poe = roe;
882 		}
883 		upperopaque = d.opaque;
884 	}
885 
886 	if (!d.stop && poe->numlower) {
887 		err = -ENOMEM;
888 		stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
889 				GFP_KERNEL);
890 		if (!stack)
891 			goto out_put_upper;
892 	}
893 
894 	for (i = 0; !d.stop && i < poe->numlower; i++) {
895 		struct ovl_path lower = poe->lowerstack[i];
896 
897 		if (!ofs->config.redirect_follow)
898 			d.last = i == poe->numlower - 1;
899 		else
900 			d.last = lower.layer->idx == roe->numlower;
901 
902 		err = ovl_lookup_layer(lower.dentry, &d, &this);
903 		if (err)
904 			goto out_put;
905 
906 		if (!this)
907 			continue;
908 
909 		/*
910 		 * If no origin fh is stored in upper of a merge dir, store fh
911 		 * of lower dir and set upper parent "impure".
912 		 */
913 		if (upperdentry && !ctr && !ofs->noxattr && d.is_dir) {
914 			err = ovl_fix_origin(dentry, this, upperdentry);
915 			if (err) {
916 				dput(this);
917 				goto out_put;
918 			}
919 		}
920 
921 		/*
922 		 * When "verify_lower" feature is enabled, do not merge with a
923 		 * lower dir that does not match a stored origin xattr. In any
924 		 * case, only verified origin is used for index lookup.
925 		 *
926 		 * For non-dir dentry, if index=on, then ensure origin
927 		 * matches the dentry found using path based lookup,
928 		 * otherwise error out.
929 		 */
930 		if (upperdentry && !ctr &&
931 		    ((d.is_dir && ovl_verify_lower(dentry->d_sb)) ||
932 		     (!d.is_dir && ofs->config.index && origin_path))) {
933 			err = ovl_verify_origin(upperdentry, this, false);
934 			if (err) {
935 				dput(this);
936 				if (d.is_dir)
937 					break;
938 				goto out_put;
939 			}
940 			origin = this;
941 		}
942 
943 		if (d.metacopy)
944 			metacopy = true;
945 		/*
946 		 * Do not store intermediate metacopy dentries in chain,
947 		 * except top most lower metacopy dentry
948 		 */
949 		if (d.metacopy && ctr) {
950 			dput(this);
951 			continue;
952 		}
953 
954 		stack[ctr].dentry = this;
955 		stack[ctr].layer = lower.layer;
956 		ctr++;
957 
958 		/*
959 		 * Following redirects can have security consequences: it's like
960 		 * a symlink into the lower layer without the permission checks.
961 		 * This is only a problem if the upper layer is untrusted (e.g
962 		 * comes from an USB drive).  This can allow a non-readable file
963 		 * or directory to become readable.
964 		 *
965 		 * Only following redirects when redirects are enabled disables
966 		 * this attack vector when not necessary.
967 		 */
968 		err = -EPERM;
969 		if (d.redirect && !ofs->config.redirect_follow) {
970 			pr_warn_ratelimited("overlayfs: refusing to follow redirect for (%pd2)\n",
971 					    dentry);
972 			goto out_put;
973 		}
974 
975 		if (d.stop)
976 			break;
977 
978 		if (d.redirect && d.redirect[0] == '/' && poe != roe) {
979 			poe = roe;
980 			/* Find the current layer on the root dentry */
981 			i = lower.layer->idx - 1;
982 		}
983 	}
984 
985 	if (metacopy) {
986 		/*
987 		 * Found a metacopy dentry but did not find corresponding
988 		 * data dentry
989 		 */
990 		if (d.metacopy) {
991 			err = -EIO;
992 			goto out_put;
993 		}
994 
995 		err = -EPERM;
996 		if (!ofs->config.metacopy) {
997 			pr_warn_ratelimited("overlay: refusing to follow metacopy origin for (%pd2)\n",
998 					    dentry);
999 			goto out_put;
1000 		}
1001 	} else if (!d.is_dir && upperdentry && !ctr && origin_path) {
1002 		if (WARN_ON(stack != NULL)) {
1003 			err = -EIO;
1004 			goto out_put;
1005 		}
1006 		stack = origin_path;
1007 		ctr = 1;
1008 		origin_path = NULL;
1009 	}
1010 
1011 	/*
1012 	 * Lookup index by lower inode and verify it matches upper inode.
1013 	 * We only trust dir index if we verified that lower dir matches
1014 	 * origin, otherwise dir index entries may be inconsistent and we
1015 	 * ignore them.
1016 	 *
1017 	 * For non-dir upper metacopy dentry, we already set "origin" if we
1018 	 * verified that lower matched upper origin. If upper origin was
1019 	 * not present (because lower layer did not support fh encode/decode),
1020 	 * or indexing is not enabled, do not set "origin" and skip looking up
1021 	 * index. This case should be handled in same way as a non-dir upper
1022 	 * without ORIGIN is handled.
1023 	 *
1024 	 * Always lookup index of non-dir non-metacopy and non-upper.
1025 	 */
1026 	if (ctr && (!upperdentry || (!d.is_dir && !metacopy)))
1027 		origin = stack[0].dentry;
1028 
1029 	if (origin && ovl_indexdir(dentry->d_sb) &&
1030 	    (!d.is_dir || ovl_index_all(dentry->d_sb))) {
1031 		index = ovl_lookup_index(ofs, upperdentry, origin, true);
1032 		if (IS_ERR(index)) {
1033 			err = PTR_ERR(index);
1034 			index = NULL;
1035 			goto out_put;
1036 		}
1037 	}
1038 
1039 	oe = ovl_alloc_entry(ctr);
1040 	err = -ENOMEM;
1041 	if (!oe)
1042 		goto out_put;
1043 
1044 	memcpy(oe->lowerstack, stack, sizeof(struct ovl_path) * ctr);
1045 	dentry->d_fsdata = oe;
1046 
1047 	if (upperopaque)
1048 		ovl_dentry_set_opaque(dentry);
1049 
1050 	if (upperdentry)
1051 		ovl_dentry_set_upper_alias(dentry);
1052 	else if (index) {
1053 		upperdentry = dget(index);
1054 		upperredirect = ovl_get_redirect_xattr(upperdentry, 0);
1055 		if (IS_ERR(upperredirect)) {
1056 			err = PTR_ERR(upperredirect);
1057 			upperredirect = NULL;
1058 			goto out_free_oe;
1059 		}
1060 	}
1061 
1062 	if (upperdentry || ctr) {
1063 		struct ovl_inode_params oip = {
1064 			.upperdentry = upperdentry,
1065 			.lowerpath = stack,
1066 			.index = index,
1067 			.numlower = ctr,
1068 			.redirect = upperredirect,
1069 			.lowerdata = (ctr > 1 && !d.is_dir) ?
1070 				      stack[ctr - 1].dentry : NULL,
1071 		};
1072 
1073 		inode = ovl_get_inode(dentry->d_sb, &oip);
1074 		err = PTR_ERR(inode);
1075 		if (IS_ERR(inode))
1076 			goto out_free_oe;
1077 	}
1078 
1079 	revert_creds(old_cred);
1080 	if (origin_path) {
1081 		dput(origin_path->dentry);
1082 		kfree(origin_path);
1083 	}
1084 	dput(index);
1085 	kfree(stack);
1086 	kfree(d.redirect);
1087 	return d_splice_alias(inode, dentry);
1088 
1089 out_free_oe:
1090 	dentry->d_fsdata = NULL;
1091 	kfree(oe);
1092 out_put:
1093 	dput(index);
1094 	for (i = 0; i < ctr; i++)
1095 		dput(stack[i].dentry);
1096 	kfree(stack);
1097 out_put_upper:
1098 	if (origin_path) {
1099 		dput(origin_path->dentry);
1100 		kfree(origin_path);
1101 	}
1102 	dput(upperdentry);
1103 	kfree(upperredirect);
1104 out:
1105 	kfree(d.redirect);
1106 	revert_creds(old_cred);
1107 	return ERR_PTR(err);
1108 }
1109 
1110 bool ovl_lower_positive(struct dentry *dentry)
1111 {
1112 	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
1113 	const struct qstr *name = &dentry->d_name;
1114 	const struct cred *old_cred;
1115 	unsigned int i;
1116 	bool positive = false;
1117 	bool done = false;
1118 
1119 	/*
1120 	 * If dentry is negative, then lower is positive iff this is a
1121 	 * whiteout.
1122 	 */
1123 	if (!dentry->d_inode)
1124 		return ovl_dentry_is_opaque(dentry);
1125 
1126 	/* Negative upper -> positive lower */
1127 	if (!ovl_dentry_upper(dentry))
1128 		return true;
1129 
1130 	old_cred = ovl_override_creds(dentry->d_sb);
1131 	/* Positive upper -> have to look up lower to see whether it exists */
1132 	for (i = 0; !done && !positive && i < poe->numlower; i++) {
1133 		struct dentry *this;
1134 		struct dentry *lowerdir = poe->lowerstack[i].dentry;
1135 
1136 		this = lookup_positive_unlocked(name->name, lowerdir,
1137 					       name->len);
1138 		if (IS_ERR(this)) {
1139 			switch (PTR_ERR(this)) {
1140 			case -ENOENT:
1141 			case -ENAMETOOLONG:
1142 				break;
1143 
1144 			default:
1145 				/*
1146 				 * Assume something is there, we just couldn't
1147 				 * access it.
1148 				 */
1149 				positive = true;
1150 				break;
1151 			}
1152 		} else {
1153 			positive = !ovl_is_whiteout(this);
1154 			done = true;
1155 			dput(this);
1156 		}
1157 	}
1158 	revert_creds(old_cred);
1159 
1160 	return positive;
1161 }
1162