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

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  1 /*
  2  *
  3  * Copyright (C) 2011 Novell Inc.
  4  *
  5  * This program is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 as published by
  7  * the Free Software Foundation.
  8  */
  9 
 10 #include <linux/fs.h>
 11 #include <linux/namei.h>
 12 #include <linux/xattr.h>
 13 #include <linux/security.h>
 14 #include <linux/mount.h>
 15 #include <linux/slab.h>
 16 #include <linux/parser.h>
 17 #include <linux/module.h>
 18 #include <linux/sched.h>
 19 #include <linux/statfs.h>
 20 #include <linux/seq_file.h>
 21 #include "overlayfs.h"
 22 
 23 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
 24 MODULE_DESCRIPTION("Overlay filesystem");
 25 MODULE_LICENSE("GPL");
 26 
 27 #define OVERLAYFS_SUPER_MAGIC 0x794c7630
 28 
 29 struct ovl_config {
 30         char *lowerdir;
 31         char *upperdir;
 32         char *workdir;
 33 };
 34 
 35 /* private information held for overlayfs's superblock */
 36 struct ovl_fs {
 37         struct vfsmount *upper_mnt;
 38         unsigned numlower;
 39         struct vfsmount **lower_mnt;
 40         struct dentry *workdir;
 41         long lower_namelen;
 42         /* pathnames of lower and upper dirs, for show_options */
 43         struct ovl_config config;
 44 };
 45 
 46 struct ovl_dir_cache;
 47 
 48 /* private information held for every overlayfs dentry */
 49 struct ovl_entry {
 50         struct dentry *__upperdentry;
 51         struct ovl_dir_cache *cache;
 52         union {
 53                 struct {
 54                         u64 version;
 55                         bool opaque;
 56                 };
 57                 struct rcu_head rcu;
 58         };
 59         unsigned numlower;
 60         struct path lowerstack[];
 61 };
 62 
 63 #define OVL_MAX_STACK 500
 64 
 65 static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
 66 {
 67         return oe->numlower ? oe->lowerstack[0].dentry : NULL;
 68 }
 69 
 70 enum ovl_path_type ovl_path_type(struct dentry *dentry)
 71 {
 72         struct ovl_entry *oe = dentry->d_fsdata;
 73         enum ovl_path_type type = 0;
 74 
 75         if (oe->__upperdentry) {
 76                 type = __OVL_PATH_UPPER;
 77 
 78                 if (oe->numlower) {
 79                         if (S_ISDIR(dentry->d_inode->i_mode))
 80                                 type |= __OVL_PATH_MERGE;
 81                 } else if (!oe->opaque) {
 82                         type |= __OVL_PATH_PURE;
 83                 }
 84         } else {
 85                 if (oe->numlower > 1)
 86                         type |= __OVL_PATH_MERGE;
 87         }
 88         return type;
 89 }
 90 
 91 static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
 92 {
 93         return lockless_dereference(oe->__upperdentry);
 94 }
 95 
 96 void ovl_path_upper(struct dentry *dentry, struct path *path)
 97 {
 98         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 99         struct ovl_entry *oe = dentry->d_fsdata;
100 
101         path->mnt = ofs->upper_mnt;
102         path->dentry = ovl_upperdentry_dereference(oe);
103 }
104 
105 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
106 {
107         enum ovl_path_type type = ovl_path_type(dentry);
108 
109         if (!OVL_TYPE_UPPER(type))
110                 ovl_path_lower(dentry, path);
111         else
112                 ovl_path_upper(dentry, path);
113 
114         return type;
115 }
116 
117 struct dentry *ovl_dentry_upper(struct dentry *dentry)
118 {
119         struct ovl_entry *oe = dentry->d_fsdata;
120 
121         return ovl_upperdentry_dereference(oe);
122 }
123 
124 struct dentry *ovl_dentry_lower(struct dentry *dentry)
125 {
126         struct ovl_entry *oe = dentry->d_fsdata;
127 
128         return __ovl_dentry_lower(oe);
129 }
130 
131 struct dentry *ovl_dentry_real(struct dentry *dentry)
132 {
133         struct ovl_entry *oe = dentry->d_fsdata;
134         struct dentry *realdentry;
135 
136         realdentry = ovl_upperdentry_dereference(oe);
137         if (!realdentry)
138                 realdentry = __ovl_dentry_lower(oe);
139 
140         return realdentry;
141 }
142 
143 struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
144 {
145         struct dentry *realdentry;
146 
147         realdentry = ovl_upperdentry_dereference(oe);
148         if (realdentry) {
149                 *is_upper = true;
150         } else {
151                 realdentry = __ovl_dentry_lower(oe);
152                 *is_upper = false;
153         }
154         return realdentry;
155 }
156 
157 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
158 {
159         struct ovl_entry *oe = dentry->d_fsdata;
160 
161         return oe->cache;
162 }
163 
164 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
165 {
166         struct ovl_entry *oe = dentry->d_fsdata;
167 
168         oe->cache = cache;
169 }
170 
171 void ovl_path_lower(struct dentry *dentry, struct path *path)
172 {
173         struct ovl_entry *oe = dentry->d_fsdata;
174 
175         *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
176 }
177 
178 int ovl_want_write(struct dentry *dentry)
179 {
180         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
181         return mnt_want_write(ofs->upper_mnt);
182 }
183 
184 void ovl_drop_write(struct dentry *dentry)
185 {
186         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
187         mnt_drop_write(ofs->upper_mnt);
188 }
189 
190 struct dentry *ovl_workdir(struct dentry *dentry)
191 {
192         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
193         return ofs->workdir;
194 }
195 
196 bool ovl_dentry_is_opaque(struct dentry *dentry)
197 {
198         struct ovl_entry *oe = dentry->d_fsdata;
199         return oe->opaque;
200 }
201 
202 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
203 {
204         struct ovl_entry *oe = dentry->d_fsdata;
205         oe->opaque = opaque;
206 }
207 
208 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
209 {
210         struct ovl_entry *oe = dentry->d_fsdata;
211 
212         WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
213         WARN_ON(oe->__upperdentry);
214         BUG_ON(!upperdentry->d_inode);
215         /*
216          * Make sure upperdentry is consistent before making it visible to
217          * ovl_upperdentry_dereference().
218          */
219         smp_wmb();
220         oe->__upperdentry = upperdentry;
221 }
222 
223 void ovl_dentry_version_inc(struct dentry *dentry)
224 {
225         struct ovl_entry *oe = dentry->d_fsdata;
226 
227         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
228         oe->version++;
229 }
230 
231 u64 ovl_dentry_version_get(struct dentry *dentry)
232 {
233         struct ovl_entry *oe = dentry->d_fsdata;
234 
235         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
236         return oe->version;
237 }
238 
239 bool ovl_is_whiteout(struct dentry *dentry)
240 {
241         struct inode *inode = dentry->d_inode;
242 
243         return inode && IS_WHITEOUT(inode);
244 }
245 
246 static bool ovl_is_opaquedir(struct dentry *dentry)
247 {
248         int res;
249         char val;
250         struct inode *inode = dentry->d_inode;
251 
252         if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
253                 return false;
254 
255         res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
256         if (res == 1 && val == 'y')
257                 return true;
258 
259         return false;
260 }
261 
262 static void ovl_dentry_release(struct dentry *dentry)
263 {
264         struct ovl_entry *oe = dentry->d_fsdata;
265 
266         if (oe) {
267                 unsigned int i;
268 
269                 dput(oe->__upperdentry);
270                 for (i = 0; i < oe->numlower; i++)
271                         dput(oe->lowerstack[i].dentry);
272                 kfree_rcu(oe, rcu);
273         }
274 }
275 
276 static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
277 {
278         struct ovl_entry *oe = dentry->d_fsdata;
279         unsigned int i;
280         int ret = 1;
281 
282         for (i = 0; i < oe->numlower; i++) {
283                 struct dentry *d = oe->lowerstack[i].dentry;
284 
285                 if (d->d_flags & DCACHE_OP_REVALIDATE) {
286                         ret = d->d_op->d_revalidate(d, flags);
287                         if (ret < 0)
288                                 return ret;
289                         if (!ret) {
290                                 if (!(flags & LOOKUP_RCU))
291                                         d_invalidate(d);
292                                 return -ESTALE;
293                         }
294                 }
295         }
296         return 1;
297 }
298 
299 static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
300 {
301         struct ovl_entry *oe = dentry->d_fsdata;
302         unsigned int i;
303         int ret = 1;
304 
305         for (i = 0; i < oe->numlower; i++) {
306                 struct dentry *d = oe->lowerstack[i].dentry;
307 
308                 if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
309                         ret = d->d_op->d_weak_revalidate(d, flags);
310                         if (ret <= 0)
311                                 break;
312                 }
313         }
314         return ret;
315 }
316 
317 static const struct dentry_operations ovl_dentry_operations = {
318         .d_release = ovl_dentry_release,
319         .d_select_inode = ovl_d_select_inode,
320 };
321 
322 static const struct dentry_operations ovl_reval_dentry_operations = {
323         .d_release = ovl_dentry_release,
324         .d_revalidate = ovl_dentry_revalidate,
325         .d_weak_revalidate = ovl_dentry_weak_revalidate,
326 };
327 
328 static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
329 {
330         size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
331         struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
332 
333         if (oe)
334                 oe->numlower = numlower;
335 
336         return oe;
337 }
338 
339 static bool ovl_dentry_remote(struct dentry *dentry)
340 {
341         return dentry->d_flags &
342                 (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
343 }
344 
345 static bool ovl_dentry_weird(struct dentry *dentry)
346 {
347         return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
348                                   DCACHE_MANAGE_TRANSIT |
349                                   DCACHE_OP_HASH |
350                                   DCACHE_OP_COMPARE);
351 }
352 
353 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
354                                              struct qstr *name)
355 {
356         struct dentry *dentry;
357 
358         mutex_lock(&dir->d_inode->i_mutex);
359         dentry = lookup_one_len(name->name, dir, name->len);
360         mutex_unlock(&dir->d_inode->i_mutex);
361 
362         if (IS_ERR(dentry)) {
363                 if (PTR_ERR(dentry) == -ENOENT)
364                         dentry = NULL;
365         } else if (!dentry->d_inode) {
366                 dput(dentry);
367                 dentry = NULL;
368         } else if (ovl_dentry_weird(dentry)) {
369                 dput(dentry);
370                 /* Don't support traversing automounts and other weirdness */
371                 dentry = ERR_PTR(-EREMOTE);
372         }
373         return dentry;
374 }
375 
376 /*
377  * Returns next layer in stack starting from top.
378  * Returns -1 if this is the last layer.
379  */
380 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
381 {
382         struct ovl_entry *oe = dentry->d_fsdata;
383 
384         BUG_ON(idx < 0);
385         if (idx == 0) {
386                 ovl_path_upper(dentry, path);
387                 if (path->dentry)
388                         return oe->numlower ? 1 : -1;
389                 idx++;
390         }
391         BUG_ON(idx > oe->numlower);
392         *path = oe->lowerstack[idx - 1];
393 
394         return (idx < oe->numlower) ? idx + 1 : -1;
395 }
396 
397 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
398                           unsigned int flags)
399 {
400         struct ovl_entry *oe;
401         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
402         struct path *stack = NULL;
403         struct dentry *upperdir, *upperdentry = NULL;
404         unsigned int ctr = 0;
405         struct inode *inode = NULL;
406         bool upperopaque = false;
407         struct dentry *this, *prev = NULL;
408         unsigned int i;
409         int err;
410 
411         upperdir = ovl_upperdentry_dereference(poe);
412         if (upperdir) {
413                 this = ovl_lookup_real(upperdir, &dentry->d_name);
414                 err = PTR_ERR(this);
415                 if (IS_ERR(this))
416                         goto out;
417 
418                 if (this) {
419                         if (unlikely(ovl_dentry_remote(this))) {
420                                 dput(this);
421                                 err = -EREMOTE;
422                                 goto out;
423                         }
424                         if (ovl_is_whiteout(this)) {
425                                 dput(this);
426                                 this = NULL;
427                                 upperopaque = true;
428                         } else if (poe->numlower && ovl_is_opaquedir(this)) {
429                                 upperopaque = true;
430                         }
431                 }
432                 upperdentry = prev = this;
433         }
434 
435         if (!upperopaque && poe->numlower) {
436                 err = -ENOMEM;
437                 stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
438                 if (!stack)
439                         goto out_put_upper;
440         }
441 
442         for (i = 0; !upperopaque && i < poe->numlower; i++) {
443                 bool opaque = false;
444                 struct path lowerpath = poe->lowerstack[i];
445 
446                 this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
447                 err = PTR_ERR(this);
448                 if (IS_ERR(this)) {
449                         /*
450                          * If it's positive, then treat ENAMETOOLONG as ENOENT.
451                          */
452                         if (err == -ENAMETOOLONG && (upperdentry || ctr))
453                                 continue;
454                         goto out_put;
455                 }
456                 if (!this)
457                         continue;
458                 if (ovl_is_whiteout(this)) {
459                         dput(this);
460                         break;
461                 }
462                 /*
463                  * Only makes sense to check opaque dir if this is not the
464                  * lowermost layer.
465                  */
466                 if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
467                         opaque = true;
468 
469                 if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
470                              !S_ISDIR(this->d_inode->i_mode))) {
471                         /*
472                          * FIXME: check for upper-opaqueness maybe better done
473                          * in remove code.
474                          */
475                         if (prev == upperdentry)
476                                 upperopaque = true;
477                         dput(this);
478                         break;
479                 }
480                 /*
481                  * If this is a non-directory then stop here.
482                  */
483                 if (!S_ISDIR(this->d_inode->i_mode))
484                         opaque = true;
485 
486                 stack[ctr].dentry = this;
487                 stack[ctr].mnt = lowerpath.mnt;
488                 ctr++;
489                 prev = this;
490                 if (opaque)
491                         break;
492         }
493 
494         oe = ovl_alloc_entry(ctr);
495         err = -ENOMEM;
496         if (!oe)
497                 goto out_put;
498 
499         if (upperdentry || ctr) {
500                 struct dentry *realdentry;
501 
502                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
503 
504                 err = -ENOMEM;
505                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
506                                       oe);
507                 if (!inode)
508                         goto out_free_oe;
509                 ovl_copyattr(realdentry->d_inode, inode);
510         }
511 
512         oe->opaque = upperopaque;
513         oe->__upperdentry = upperdentry;
514         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
515         kfree(stack);
516         dentry->d_fsdata = oe;
517         d_add(dentry, inode);
518 
519         return NULL;
520 
521 out_free_oe:
522         kfree(oe);
523 out_put:
524         for (i = 0; i < ctr; i++)
525                 dput(stack[i].dentry);
526         kfree(stack);
527 out_put_upper:
528         dput(upperdentry);
529 out:
530         return ERR_PTR(err);
531 }
532 
533 struct file *ovl_path_open(struct path *path, int flags)
534 {
535         return dentry_open(path, flags, current_cred());
536 }
537 
538 static void ovl_put_super(struct super_block *sb)
539 {
540         struct ovl_fs *ufs = sb->s_fs_info;
541         unsigned i;
542 
543         dput(ufs->workdir);
544         mntput(ufs->upper_mnt);
545         for (i = 0; i < ufs->numlower; i++)
546                 mntput(ufs->lower_mnt[i]);
547         kfree(ufs->lower_mnt);
548 
549         kfree(ufs->config.lowerdir);
550         kfree(ufs->config.upperdir);
551         kfree(ufs->config.workdir);
552         kfree(ufs);
553 }
554 
555 /**
556  * ovl_statfs
557  * @sb: The overlayfs super block
558  * @buf: The struct kstatfs to fill in with stats
559  *
560  * Get the filesystem statistics.  As writes always target the upper layer
561  * filesystem pass the statfs to the upper filesystem (if it exists)
562  */
563 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
564 {
565         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
566         struct dentry *root_dentry = dentry->d_sb->s_root;
567         struct path path;
568         int err;
569 
570         ovl_path_real(root_dentry, &path);
571 
572         err = vfs_statfs(&path, buf);
573         if (!err) {
574                 buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
575                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
576         }
577 
578         return err;
579 }
580 
581 /**
582  * ovl_show_options
583  *
584  * Prints the mount options for a given superblock.
585  * Returns zero; does not fail.
586  */
587 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
588 {
589         struct super_block *sb = dentry->d_sb;
590         struct ovl_fs *ufs = sb->s_fs_info;
591 
592         seq_show_option(m, "lowerdir", ufs->config.lowerdir);
593         if (ufs->config.upperdir) {
594                 seq_show_option(m, "upperdir", ufs->config.upperdir);
595                 seq_show_option(m, "workdir", ufs->config.workdir);
596         }
597         return 0;
598 }
599 
600 static int ovl_remount(struct super_block *sb, int *flags, char *data)
601 {
602         struct ovl_fs *ufs = sb->s_fs_info;
603 
604         if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
605                 return -EROFS;
606 
607         return 0;
608 }
609 
610 static const struct super_operations ovl_super_operations = {
611         .put_super      = ovl_put_super,
612         .statfs         = ovl_statfs,
613         .show_options   = ovl_show_options,
614         .remount_fs     = ovl_remount,
615 };
616 
617 enum {
618         OPT_LOWERDIR,
619         OPT_UPPERDIR,
620         OPT_WORKDIR,
621         OPT_ERR,
622 };
623 
624 static const match_table_t ovl_tokens = {
625         {OPT_LOWERDIR,                  "lowerdir=%s"},
626         {OPT_UPPERDIR,                  "upperdir=%s"},
627         {OPT_WORKDIR,                   "workdir=%s"},
628         {OPT_ERR,                       NULL}
629 };
630 
631 static char *ovl_next_opt(char **s)
632 {
633         char *sbegin = *s;
634         char *p;
635 
636         if (sbegin == NULL)
637                 return NULL;
638 
639         for (p = sbegin; *p; p++) {
640                 if (*p == '\\') {
641                         p++;
642                         if (!*p)
643                                 break;
644                 } else if (*p == ',') {
645                         *p = '\0';
646                         *s = p + 1;
647                         return sbegin;
648                 }
649         }
650         *s = NULL;
651         return sbegin;
652 }
653 
654 static int ovl_parse_opt(char *opt, struct ovl_config *config)
655 {
656         char *p;
657 
658         while ((p = ovl_next_opt(&opt)) != NULL) {
659                 int token;
660                 substring_t args[MAX_OPT_ARGS];
661 
662                 if (!*p)
663                         continue;
664 
665                 token = match_token(p, ovl_tokens, args);
666                 switch (token) {
667                 case OPT_UPPERDIR:
668                         kfree(config->upperdir);
669                         config->upperdir = match_strdup(&args[0]);
670                         if (!config->upperdir)
671                                 return -ENOMEM;
672                         break;
673 
674                 case OPT_LOWERDIR:
675                         kfree(config->lowerdir);
676                         config->lowerdir = match_strdup(&args[0]);
677                         if (!config->lowerdir)
678                                 return -ENOMEM;
679                         break;
680 
681                 case OPT_WORKDIR:
682                         kfree(config->workdir);
683                         config->workdir = match_strdup(&args[0]);
684                         if (!config->workdir)
685                                 return -ENOMEM;
686                         break;
687 
688                 default:
689                         pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
690                         return -EINVAL;
691                 }
692         }
693 
694         /* Workdir is useless in non-upper mount */
695         if (!config->upperdir && config->workdir) {
696                 pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
697                         config->workdir);
698                 kfree(config->workdir);
699                 config->workdir = NULL;
700         }
701 
702         return 0;
703 }
704 
705 #define OVL_WORKDIR_NAME "work"
706 
707 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
708                                          struct dentry *dentry)
709 {
710         struct inode *dir = dentry->d_inode;
711         struct dentry *work;
712         int err;
713         bool retried = false;
714 
715         err = mnt_want_write(mnt);
716         if (err)
717                 return ERR_PTR(err);
718 
719         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
720 retry:
721         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
722                               strlen(OVL_WORKDIR_NAME));
723 
724         if (!IS_ERR(work)) {
725                 struct kstat stat = {
726                         .mode = S_IFDIR | 0,
727                 };
728 
729                 if (work->d_inode) {
730                         err = -EEXIST;
731                         if (retried)
732                                 goto out_dput;
733 
734                         retried = true;
735                         ovl_cleanup(dir, work);
736                         dput(work);
737                         goto retry;
738                 }
739 
740                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
741                 if (err)
742                         goto out_dput;
743         }
744 out_unlock:
745         mutex_unlock(&dir->i_mutex);
746         mnt_drop_write(mnt);
747 
748         return work;
749 
750 out_dput:
751         dput(work);
752         work = ERR_PTR(err);
753         goto out_unlock;
754 }
755 
756 static void ovl_unescape(char *s)
757 {
758         char *d = s;
759 
760         for (;; s++, d++) {
761                 if (*s == '\\')
762                         s++;
763                 *d = *s;
764                 if (!*s)
765                         break;
766         }
767 }
768 
769 static int ovl_mount_dir_noesc(const char *name, struct path *path)
770 {
771         int err = -EINVAL;
772 
773         if (!*name) {
774                 pr_err("overlayfs: empty lowerdir\n");
775                 goto out;
776         }
777         err = kern_path(name, LOOKUP_FOLLOW, path);
778         if (err) {
779                 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
780                 goto out;
781         }
782         err = -EINVAL;
783         if (ovl_dentry_weird(path->dentry)) {
784                 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
785                 goto out_put;
786         }
787         if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
788                 pr_err("overlayfs: '%s' not a directory\n", name);
789                 goto out_put;
790         }
791         return 0;
792 
793 out_put:
794         path_put(path);
795 out:
796         return err;
797 }
798 
799 static int ovl_mount_dir(const char *name, struct path *path)
800 {
801         int err = -ENOMEM;
802         char *tmp = kstrdup(name, GFP_KERNEL);
803 
804         if (tmp) {
805                 ovl_unescape(tmp);
806                 err = ovl_mount_dir_noesc(tmp, path);
807 
808                 if (!err)
809                         if (ovl_dentry_remote(path->dentry)) {
810                                 pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
811                                        tmp);
812                                 path_put(path);
813                                 err = -EINVAL;
814                         }
815                 kfree(tmp);
816         }
817         return err;
818 }
819 
820 static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
821                          int *stack_depth, bool *remote)
822 {
823         int err;
824         struct kstatfs statfs;
825 
826         err = ovl_mount_dir_noesc(name, path);
827         if (err)
828                 goto out;
829 
830         err = vfs_statfs(path, &statfs);
831         if (err) {
832                 pr_err("overlayfs: statfs failed on '%s'\n", name);
833                 goto out_put;
834         }
835         *namelen = max(*namelen, statfs.f_namelen);
836         *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
837 
838         if (ovl_dentry_remote(path->dentry))
839                 *remote = true;
840 
841         return 0;
842 
843 out_put:
844         path_put(path);
845 out:
846         return err;
847 }
848 
849 /* Workdir should not be subdir of upperdir and vice versa */
850 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
851 {
852         bool ok = false;
853 
854         if (workdir != upperdir) {
855                 ok = (lock_rename(workdir, upperdir) == NULL);
856                 unlock_rename(workdir, upperdir);
857         }
858         return ok;
859 }
860 
861 static unsigned int ovl_split_lowerdirs(char *str)
862 {
863         unsigned int ctr = 1;
864         char *s, *d;
865 
866         for (s = d = str;; s++, d++) {
867                 if (*s == '\\') {
868                         s++;
869                 } else if (*s == ':') {
870                         *d = '\0';
871                         ctr++;
872                         continue;
873                 }
874                 *d = *s;
875                 if (!*s)
876                         break;
877         }
878         return ctr;
879 }
880 
881 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
882 {
883         struct path upperpath = { NULL, NULL };
884         struct path workpath = { NULL, NULL };
885         struct dentry *root_dentry;
886         struct ovl_entry *oe;
887         struct ovl_fs *ufs;
888         struct path *stack = NULL;
889         char *lowertmp;
890         char *lower;
891         unsigned int numlower;
892         unsigned int stacklen = 0;
893         unsigned int i;
894         bool remote = false;
895         int err;
896 
897         err = -ENOMEM;
898         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
899         if (!ufs)
900                 goto out;
901 
902         err = ovl_parse_opt((char *) data, &ufs->config);
903         if (err)
904                 goto out_free_config;
905 
906         err = -EINVAL;
907         if (!ufs->config.lowerdir) {
908                 pr_err("overlayfs: missing 'lowerdir'\n");
909                 goto out_free_config;
910         }
911 
912         sb->s_stack_depth = 0;
913         if (ufs->config.upperdir) {
914                 if (!ufs->config.workdir) {
915                         pr_err("overlayfs: missing 'workdir'\n");
916                         goto out_free_config;
917                 }
918 
919                 err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
920                 if (err)
921                         goto out_free_config;
922 
923                 /* Upper fs should not be r/o */
924                 if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
925                         pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
926                         err = -EINVAL;
927                         goto out_put_upperpath;
928                 }
929 
930                 err = ovl_mount_dir(ufs->config.workdir, &workpath);
931                 if (err)
932                         goto out_put_upperpath;
933 
934                 err = -EINVAL;
935                 if (upperpath.mnt != workpath.mnt) {
936                         pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
937                         goto out_put_workpath;
938                 }
939                 if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
940                         pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
941                         goto out_put_workpath;
942                 }
943                 sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
944         }
945         err = -ENOMEM;
946         lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
947         if (!lowertmp)
948                 goto out_put_workpath;
949 
950         err = -EINVAL;
951         stacklen = ovl_split_lowerdirs(lowertmp);
952         if (stacklen > OVL_MAX_STACK) {
953                 pr_err("overlayfs: too many lower directries, limit is %d\n",
954                        OVL_MAX_STACK);
955                 goto out_free_lowertmp;
956         } else if (!ufs->config.upperdir && stacklen == 1) {
957                 pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
958                 goto out_free_lowertmp;
959         }
960 
961         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
962         if (!stack)
963                 goto out_free_lowertmp;
964 
965         lower = lowertmp;
966         for (numlower = 0; numlower < stacklen; numlower++) {
967                 err = ovl_lower_dir(lower, &stack[numlower],
968                                     &ufs->lower_namelen, &sb->s_stack_depth,
969                                     &remote);
970                 if (err)
971                         goto out_put_lowerpath;
972 
973                 lower = strchr(lower, '\0') + 1;
974         }
975 
976         err = -EINVAL;
977         sb->s_stack_depth++;
978         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
979                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
980                 goto out_put_lowerpath;
981         }
982 
983         if (ufs->config.upperdir) {
984                 ufs->upper_mnt = clone_private_mount(&upperpath);
985                 err = PTR_ERR(ufs->upper_mnt);
986                 if (IS_ERR(ufs->upper_mnt)) {
987                         pr_err("overlayfs: failed to clone upperpath\n");
988                         goto out_put_lowerpath;
989                 }
990 
991                 ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
992                 err = PTR_ERR(ufs->workdir);
993                 if (IS_ERR(ufs->workdir)) {
994                         pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
995                                 ufs->config.workdir, OVL_WORKDIR_NAME, -err);
996                         sb->s_flags |= MS_RDONLY;
997                         ufs->workdir = NULL;
998                 }
999         }
1000 
1001         err = -ENOMEM;
1002         ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
1003         if (ufs->lower_mnt == NULL)
1004                 goto out_put_workdir;
1005         for (i = 0; i < numlower; i++) {
1006                 struct vfsmount *mnt = clone_private_mount(&stack[i]);
1007 
1008                 err = PTR_ERR(mnt);
1009                 if (IS_ERR(mnt)) {
1010                         pr_err("overlayfs: failed to clone lowerpath\n");
1011                         goto out_put_lower_mnt;
1012                 }
1013                 /*
1014                  * Make lower_mnt R/O.  That way fchmod/fchown on lower file
1015                  * will fail instead of modifying lower fs.
1016                  */
1017                 mnt->mnt_flags |= MNT_READONLY;
1018 
1019                 ufs->lower_mnt[ufs->numlower] = mnt;
1020                 ufs->numlower++;
1021         }
1022 
1023         /* If the upper fs is nonexistent, we mark overlayfs r/o too */
1024         if (!ufs->upper_mnt)
1025                 sb->s_flags |= MS_RDONLY;
1026 
1027         if (remote)
1028                 sb->s_d_op = &ovl_reval_dentry_operations;
1029         else
1030                 sb->s_d_op = &ovl_dentry_operations;
1031 
1032         err = -ENOMEM;
1033         oe = ovl_alloc_entry(numlower);
1034         if (!oe)
1035                 goto out_put_lower_mnt;
1036 
1037         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
1038         if (!root_dentry)
1039                 goto out_free_oe;
1040 
1041         mntput(upperpath.mnt);
1042         for (i = 0; i < numlower; i++)
1043                 mntput(stack[i].mnt);
1044         path_put(&workpath);
1045         kfree(lowertmp);
1046 
1047         oe->__upperdentry = upperpath.dentry;
1048         for (i = 0; i < numlower; i++) {
1049                 oe->lowerstack[i].dentry = stack[i].dentry;
1050                 oe->lowerstack[i].mnt = ufs->lower_mnt[i];
1051         }
1052         kfree(stack);
1053 
1054         root_dentry->d_fsdata = oe;
1055 
1056         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
1057         sb->s_op = &ovl_super_operations;
1058         sb->s_root = root_dentry;
1059         sb->s_fs_info = ufs;
1060 
1061         return 0;
1062 
1063 out_free_oe:
1064         kfree(oe);
1065 out_put_lower_mnt:
1066         for (i = 0; i < ufs->numlower; i++)
1067                 mntput(ufs->lower_mnt[i]);
1068         kfree(ufs->lower_mnt);
1069 out_put_workdir:
1070         dput(ufs->workdir);
1071         mntput(ufs->upper_mnt);
1072 out_put_lowerpath:
1073         for (i = 0; i < numlower; i++)
1074                 path_put(&stack[i]);
1075         kfree(stack);
1076 out_free_lowertmp:
1077         kfree(lowertmp);
1078 out_put_workpath:
1079         path_put(&workpath);
1080 out_put_upperpath:
1081         path_put(&upperpath);
1082 out_free_config:
1083         kfree(ufs->config.lowerdir);
1084         kfree(ufs->config.upperdir);
1085         kfree(ufs->config.workdir);
1086         kfree(ufs);
1087 out:
1088         return err;
1089 }
1090 
1091 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
1092                                 const char *dev_name, void *raw_data)
1093 {
1094         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
1095 }
1096 
1097 static struct file_system_type ovl_fs_type = {
1098         .owner          = THIS_MODULE,
1099         .name           = "overlay",
1100         .mount          = ovl_mount,
1101         .kill_sb        = kill_anon_super,
1102 };
1103 MODULE_ALIAS_FS("overlay");
1104 
1105 static int __init ovl_init(void)
1106 {
1107         return register_filesystem(&ovl_fs_type);
1108 }
1109 
1110 static void __exit ovl_exit(void)
1111 {
1112         unregister_filesystem(&ovl_fs_type);
1113 }
1114 
1115 module_init(ovl_init);
1116 module_exit(ovl_exit);
1117 

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