ab3c8cb8e52d2ffaaffd9940f578a2b2d2790dca
[sfrench/cifs-2.6.git] / fs / overlayfs / super.c
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 const struct dentry_operations ovl_dentry_operations = {
277         .d_release = ovl_dentry_release,
278 };
279
280 static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
281 {
282         size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
283         struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
284
285         if (oe)
286                 oe->numlower = numlower;
287
288         return oe;
289 }
290
291 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
292                                              struct qstr *name)
293 {
294         struct dentry *dentry;
295
296         mutex_lock(&dir->d_inode->i_mutex);
297         dentry = lookup_one_len(name->name, dir, name->len);
298         mutex_unlock(&dir->d_inode->i_mutex);
299
300         if (IS_ERR(dentry)) {
301                 if (PTR_ERR(dentry) == -ENOENT)
302                         dentry = NULL;
303         } else if (!dentry->d_inode) {
304                 dput(dentry);
305                 dentry = NULL;
306         }
307         return dentry;
308 }
309
310 /*
311  * Returns next layer in stack starting from top.
312  * Returns -1 if this is the last layer.
313  */
314 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
315 {
316         struct ovl_entry *oe = dentry->d_fsdata;
317
318         BUG_ON(idx < 0);
319         if (idx == 0) {
320                 ovl_path_upper(dentry, path);
321                 if (path->dentry)
322                         return oe->numlower ? 1 : -1;
323                 idx++;
324         }
325         BUG_ON(idx > oe->numlower);
326         *path = oe->lowerstack[idx - 1];
327
328         return (idx < oe->numlower) ? idx + 1 : -1;
329 }
330
331 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
332                           unsigned int flags)
333 {
334         struct ovl_entry *oe;
335         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
336         struct path *stack = NULL;
337         struct dentry *upperdir, *upperdentry = NULL;
338         unsigned int ctr = 0;
339         struct inode *inode = NULL;
340         bool upperopaque = false;
341         struct dentry *this, *prev = NULL;
342         unsigned int i;
343         int err;
344
345         upperdir = ovl_upperdentry_dereference(poe);
346         if (upperdir) {
347                 this = ovl_lookup_real(upperdir, &dentry->d_name);
348                 err = PTR_ERR(this);
349                 if (IS_ERR(this))
350                         goto out;
351
352                 if (this) {
353                         if (ovl_is_whiteout(this)) {
354                                 dput(this);
355                                 this = NULL;
356                                 upperopaque = true;
357                         } else if (poe->numlower && ovl_is_opaquedir(this)) {
358                                 upperopaque = true;
359                         }
360                 }
361                 upperdentry = prev = this;
362         }
363
364         if (!upperopaque && poe->numlower) {
365                 err = -ENOMEM;
366                 stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
367                 if (!stack)
368                         goto out_put_upper;
369         }
370
371         for (i = 0; !upperopaque && i < poe->numlower; i++) {
372                 bool opaque = false;
373                 struct path lowerpath = poe->lowerstack[i];
374
375                 this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
376                 err = PTR_ERR(this);
377                 if (IS_ERR(this)) {
378                         /*
379                          * If it's positive, then treat ENAMETOOLONG as ENOENT.
380                          */
381                         if (err == -ENAMETOOLONG && (upperdentry || ctr))
382                                 continue;
383                         goto out_put;
384                 }
385                 if (!this)
386                         continue;
387                 if (ovl_is_whiteout(this)) {
388                         dput(this);
389                         break;
390                 }
391                 /*
392                  * Only makes sense to check opaque dir if this is not the
393                  * lowermost layer.
394                  */
395                 if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
396                         opaque = true;
397
398                 if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
399                              !S_ISDIR(this->d_inode->i_mode))) {
400                         /*
401                          * FIXME: check for upper-opaqueness maybe better done
402                          * in remove code.
403                          */
404                         if (prev == upperdentry)
405                                 upperopaque = true;
406                         dput(this);
407                         break;
408                 }
409                 /*
410                  * If this is a non-directory then stop here.
411                  */
412                 if (!S_ISDIR(this->d_inode->i_mode))
413                         opaque = true;
414
415                 stack[ctr].dentry = this;
416                 stack[ctr].mnt = lowerpath.mnt;
417                 ctr++;
418                 prev = this;
419                 if (opaque)
420                         break;
421         }
422
423         oe = ovl_alloc_entry(ctr);
424         err = -ENOMEM;
425         if (!oe)
426                 goto out_put;
427
428         if (upperdentry || ctr) {
429                 struct dentry *realdentry;
430
431                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
432
433                 err = -ENOMEM;
434                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
435                                       oe);
436                 if (!inode)
437                         goto out_free_oe;
438                 ovl_copyattr(realdentry->d_inode, inode);
439         }
440
441         oe->opaque = upperopaque;
442         oe->__upperdentry = upperdentry;
443         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
444         kfree(stack);
445         dentry->d_fsdata = oe;
446         d_add(dentry, inode);
447
448         return NULL;
449
450 out_free_oe:
451         kfree(oe);
452 out_put:
453         for (i = 0; i < ctr; i++)
454                 dput(stack[i].dentry);
455         kfree(stack);
456 out_put_upper:
457         dput(upperdentry);
458 out:
459         return ERR_PTR(err);
460 }
461
462 struct file *ovl_path_open(struct path *path, int flags)
463 {
464         return dentry_open(path, flags, current_cred());
465 }
466
467 static void ovl_put_super(struct super_block *sb)
468 {
469         struct ovl_fs *ufs = sb->s_fs_info;
470         unsigned i;
471
472         dput(ufs->workdir);
473         mntput(ufs->upper_mnt);
474         for (i = 0; i < ufs->numlower; i++)
475                 mntput(ufs->lower_mnt[i]);
476
477         kfree(ufs->config.lowerdir);
478         kfree(ufs->config.upperdir);
479         kfree(ufs->config.workdir);
480         kfree(ufs);
481 }
482
483 /**
484  * ovl_statfs
485  * @sb: The overlayfs super block
486  * @buf: The struct kstatfs to fill in with stats
487  *
488  * Get the filesystem statistics.  As writes always target the upper layer
489  * filesystem pass the statfs to the upper filesystem (if it exists)
490  */
491 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
492 {
493         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
494         struct dentry *root_dentry = dentry->d_sb->s_root;
495         struct path path;
496         int err;
497
498         ovl_path_real(root_dentry, &path);
499
500         err = vfs_statfs(&path, buf);
501         if (!err) {
502                 buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
503                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
504         }
505
506         return err;
507 }
508
509 /**
510  * ovl_show_options
511  *
512  * Prints the mount options for a given superblock.
513  * Returns zero; does not fail.
514  */
515 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
516 {
517         struct super_block *sb = dentry->d_sb;
518         struct ovl_fs *ufs = sb->s_fs_info;
519
520         seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
521         if (ufs->config.upperdir) {
522                 seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
523                 seq_printf(m, ",workdir=%s", ufs->config.workdir);
524         }
525         return 0;
526 }
527
528 static int ovl_remount(struct super_block *sb, int *flags, char *data)
529 {
530         struct ovl_fs *ufs = sb->s_fs_info;
531
532         if (!(*flags & MS_RDONLY) &&
533             (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)))
534                 return -EROFS;
535
536         return 0;
537 }
538
539 static const struct super_operations ovl_super_operations = {
540         .put_super      = ovl_put_super,
541         .statfs         = ovl_statfs,
542         .show_options   = ovl_show_options,
543         .remount_fs     = ovl_remount,
544 };
545
546 enum {
547         OPT_LOWERDIR,
548         OPT_UPPERDIR,
549         OPT_WORKDIR,
550         OPT_ERR,
551 };
552
553 static const match_table_t ovl_tokens = {
554         {OPT_LOWERDIR,                  "lowerdir=%s"},
555         {OPT_UPPERDIR,                  "upperdir=%s"},
556         {OPT_WORKDIR,                   "workdir=%s"},
557         {OPT_ERR,                       NULL}
558 };
559
560 static char *ovl_next_opt(char **s)
561 {
562         char *sbegin = *s;
563         char *p;
564
565         if (sbegin == NULL)
566                 return NULL;
567
568         for (p = sbegin; *p; p++) {
569                 if (*p == '\\') {
570                         p++;
571                         if (!*p)
572                                 break;
573                 } else if (*p == ',') {
574                         *p = '\0';
575                         *s = p + 1;
576                         return sbegin;
577                 }
578         }
579         *s = NULL;
580         return sbegin;
581 }
582
583 static int ovl_parse_opt(char *opt, struct ovl_config *config)
584 {
585         char *p;
586
587         while ((p = ovl_next_opt(&opt)) != NULL) {
588                 int token;
589                 substring_t args[MAX_OPT_ARGS];
590
591                 if (!*p)
592                         continue;
593
594                 token = match_token(p, ovl_tokens, args);
595                 switch (token) {
596                 case OPT_UPPERDIR:
597                         kfree(config->upperdir);
598                         config->upperdir = match_strdup(&args[0]);
599                         if (!config->upperdir)
600                                 return -ENOMEM;
601                         break;
602
603                 case OPT_LOWERDIR:
604                         kfree(config->lowerdir);
605                         config->lowerdir = match_strdup(&args[0]);
606                         if (!config->lowerdir)
607                                 return -ENOMEM;
608                         break;
609
610                 case OPT_WORKDIR:
611                         kfree(config->workdir);
612                         config->workdir = match_strdup(&args[0]);
613                         if (!config->workdir)
614                                 return -ENOMEM;
615                         break;
616
617                 default:
618                         pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
619                         return -EINVAL;
620                 }
621         }
622         return 0;
623 }
624
625 #define OVL_WORKDIR_NAME "work"
626
627 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
628                                          struct dentry *dentry)
629 {
630         struct inode *dir = dentry->d_inode;
631         struct dentry *work;
632         int err;
633         bool retried = false;
634
635         err = mnt_want_write(mnt);
636         if (err)
637                 return ERR_PTR(err);
638
639         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
640 retry:
641         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
642                               strlen(OVL_WORKDIR_NAME));
643
644         if (!IS_ERR(work)) {
645                 struct kstat stat = {
646                         .mode = S_IFDIR | 0,
647                 };
648
649                 if (work->d_inode) {
650                         err = -EEXIST;
651                         if (retried)
652                                 goto out_dput;
653
654                         retried = true;
655                         ovl_cleanup(dir, work);
656                         dput(work);
657                         goto retry;
658                 }
659
660                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
661                 if (err)
662                         goto out_dput;
663         }
664 out_unlock:
665         mutex_unlock(&dir->i_mutex);
666         mnt_drop_write(mnt);
667
668         return work;
669
670 out_dput:
671         dput(work);
672         work = ERR_PTR(err);
673         goto out_unlock;
674 }
675
676 static void ovl_unescape(char *s)
677 {
678         char *d = s;
679
680         for (;; s++, d++) {
681                 if (*s == '\\')
682                         s++;
683                 *d = *s;
684                 if (!*s)
685                         break;
686         }
687 }
688
689 static bool ovl_is_allowed_fs_type(struct dentry *root)
690 {
691         const struct dentry_operations *dop = root->d_op;
692
693         /*
694          * We don't support:
695          *  - automount filesystems
696          *  - filesystems with revalidate (FIXME for lower layer)
697          *  - filesystems with case insensitive names
698          */
699         if (dop &&
700             (dop->d_manage || dop->d_automount ||
701              dop->d_revalidate || dop->d_weak_revalidate ||
702              dop->d_compare || dop->d_hash)) {
703                 return false;
704         }
705         return true;
706 }
707
708 static int ovl_mount_dir_noesc(const char *name, struct path *path)
709 {
710         int err = -EINVAL;
711
712         if (!*name) {
713                 pr_err("overlayfs: empty lowerdir\n");
714                 goto out;
715         }
716         err = kern_path(name, LOOKUP_FOLLOW, path);
717         if (err) {
718                 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
719                 goto out;
720         }
721         err = -EINVAL;
722         if (!ovl_is_allowed_fs_type(path->dentry)) {
723                 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
724                 goto out_put;
725         }
726         if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
727                 pr_err("overlayfs: '%s' not a directory\n", name);
728                 goto out_put;
729         }
730         return 0;
731
732 out_put:
733         path_put(path);
734 out:
735         return err;
736 }
737
738 static int ovl_mount_dir(const char *name, struct path *path)
739 {
740         int err = -ENOMEM;
741         char *tmp = kstrdup(name, GFP_KERNEL);
742
743         if (tmp) {
744                 ovl_unescape(tmp);
745                 err = ovl_mount_dir_noesc(tmp, path);
746                 kfree(tmp);
747         }
748         return err;
749 }
750
751 static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
752                          int *stack_depth)
753 {
754         int err;
755         struct kstatfs statfs;
756
757         err = ovl_mount_dir_noesc(name, path);
758         if (err)
759                 goto out;
760
761         err = vfs_statfs(path, &statfs);
762         if (err) {
763                 pr_err("overlayfs: statfs failed on '%s'\n", name);
764                 goto out_put;
765         }
766         *namelen = max(*namelen, statfs.f_namelen);
767         *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
768
769         return 0;
770
771 out_put:
772         path_put(path);
773 out:
774         return err;
775 }
776
777 /* Workdir should not be subdir of upperdir and vice versa */
778 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
779 {
780         bool ok = false;
781
782         if (workdir != upperdir) {
783                 ok = (lock_rename(workdir, upperdir) == NULL);
784                 unlock_rename(workdir, upperdir);
785         }
786         return ok;
787 }
788
789 static unsigned int ovl_split_lowerdirs(char *str)
790 {
791         unsigned int ctr = 1;
792         char *s, *d;
793
794         for (s = d = str;; s++, d++) {
795                 if (*s == '\\') {
796                         s++;
797                 } else if (*s == ':') {
798                         *d = '\0';
799                         ctr++;
800                         continue;
801                 }
802                 *d = *s;
803                 if (!*s)
804                         break;
805         }
806         return ctr;
807 }
808
809 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
810 {
811         struct path upperpath = { NULL, NULL };
812         struct path workpath = { NULL, NULL };
813         struct dentry *root_dentry;
814         struct ovl_entry *oe;
815         struct ovl_fs *ufs;
816         struct path *stack = NULL;
817         char *lowertmp;
818         char *lower;
819         unsigned int numlower;
820         unsigned int stacklen = 0;
821         unsigned int i;
822         int err;
823
824         err = -ENOMEM;
825         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
826         if (!ufs)
827                 goto out;
828
829         err = ovl_parse_opt((char *) data, &ufs->config);
830         if (err)
831                 goto out_free_config;
832
833         err = -EINVAL;
834         if (!ufs->config.lowerdir) {
835                 pr_err("overlayfs: missing 'lowerdir'\n");
836                 goto out_free_config;
837         }
838
839         sb->s_stack_depth = 0;
840         if (ufs->config.upperdir) {
841                 /* FIXME: workdir is not needed for a R/O mount */
842                 if (!ufs->config.workdir) {
843                         pr_err("overlayfs: missing 'workdir'\n");
844                         goto out_free_config;
845                 }
846
847                 err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
848                 if (err)
849                         goto out_free_config;
850
851                 err = ovl_mount_dir(ufs->config.workdir, &workpath);
852                 if (err)
853                         goto out_put_upperpath;
854
855                 err = -EINVAL;
856                 if (upperpath.mnt != workpath.mnt) {
857                         pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
858                         goto out_put_workpath;
859                 }
860                 if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
861                         pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
862                         goto out_put_workpath;
863                 }
864                 sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
865         }
866         err = -ENOMEM;
867         lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
868         if (!lowertmp)
869                 goto out_put_workpath;
870
871         err = -EINVAL;
872         stacklen = ovl_split_lowerdirs(lowertmp);
873         if (stacklen > OVL_MAX_STACK)
874                 goto out_free_lowertmp;
875
876         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
877         if (!stack)
878                 goto out_free_lowertmp;
879
880         lower = lowertmp;
881         for (numlower = 0; numlower < stacklen; numlower++) {
882                 err = ovl_lower_dir(lower, &stack[numlower],
883                                     &ufs->lower_namelen, &sb->s_stack_depth);
884                 if (err)
885                         goto out_put_lowerpath;
886
887                 lower = strchr(lower, '\0') + 1;
888         }
889
890         err = -EINVAL;
891         sb->s_stack_depth++;
892         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
893                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
894                 goto out_put_lowerpath;
895         }
896
897         if (ufs->config.upperdir) {
898                 ufs->upper_mnt = clone_private_mount(&upperpath);
899                 err = PTR_ERR(ufs->upper_mnt);
900                 if (IS_ERR(ufs->upper_mnt)) {
901                         pr_err("overlayfs: failed to clone upperpath\n");
902                         goto out_put_lowerpath;
903                 }
904
905                 ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
906                 err = PTR_ERR(ufs->workdir);
907                 if (IS_ERR(ufs->workdir)) {
908                         pr_err("overlayfs: failed to create directory %s/%s\n",
909                                ufs->config.workdir, OVL_WORKDIR_NAME);
910                         goto out_put_upper_mnt;
911                 }
912         }
913
914         err = -ENOMEM;
915         ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
916         if (ufs->lower_mnt == NULL)
917                 goto out_put_workdir;
918         for (i = 0; i < numlower; i++) {
919                 struct vfsmount *mnt = clone_private_mount(&stack[i]);
920
921                 err = PTR_ERR(mnt);
922                 if (IS_ERR(mnt)) {
923                         pr_err("overlayfs: failed to clone lowerpath\n");
924                         goto out_put_lower_mnt;
925                 }
926                 /*
927                  * Make lower_mnt R/O.  That way fchmod/fchown on lower file
928                  * will fail instead of modifying lower fs.
929                  */
930                 mnt->mnt_flags |= MNT_READONLY;
931
932                 ufs->lower_mnt[ufs->numlower] = mnt;
933                 ufs->numlower++;
934         }
935
936         /* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
937         if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
938                 sb->s_flags |= MS_RDONLY;
939
940         sb->s_d_op = &ovl_dentry_operations;
941
942         err = -ENOMEM;
943         oe = ovl_alloc_entry(numlower);
944         if (!oe)
945                 goto out_put_lower_mnt;
946
947         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
948         if (!root_dentry)
949                 goto out_free_oe;
950
951         mntput(upperpath.mnt);
952         for (i = 0; i < numlower; i++)
953                 mntput(stack[i].mnt);
954         path_put(&workpath);
955         kfree(lowertmp);
956
957         oe->__upperdentry = upperpath.dentry;
958         for (i = 0; i < numlower; i++) {
959                 oe->lowerstack[i].dentry = stack[i].dentry;
960                 oe->lowerstack[i].mnt = ufs->lower_mnt[i];
961         }
962
963         root_dentry->d_fsdata = oe;
964
965         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
966         sb->s_op = &ovl_super_operations;
967         sb->s_root = root_dentry;
968         sb->s_fs_info = ufs;
969
970         return 0;
971
972 out_free_oe:
973         kfree(oe);
974 out_put_lower_mnt:
975         for (i = 0; i < ufs->numlower; i++)
976                 mntput(ufs->lower_mnt[i]);
977         kfree(ufs->lower_mnt);
978 out_put_workdir:
979         dput(ufs->workdir);
980 out_put_upper_mnt:
981         mntput(ufs->upper_mnt);
982 out_put_lowerpath:
983         for (i = 0; i < numlower; i++)
984                 path_put(&stack[i]);
985         kfree(stack);
986 out_free_lowertmp:
987         kfree(lowertmp);
988 out_put_workpath:
989         path_put(&workpath);
990 out_put_upperpath:
991         path_put(&upperpath);
992 out_free_config:
993         kfree(ufs->config.lowerdir);
994         kfree(ufs->config.upperdir);
995         kfree(ufs->config.workdir);
996         kfree(ufs);
997 out:
998         return err;
999 }
1000
1001 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
1002                                 const char *dev_name, void *raw_data)
1003 {
1004         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
1005 }
1006
1007 static struct file_system_type ovl_fs_type = {
1008         .owner          = THIS_MODULE,
1009         .name           = "overlay",
1010         .mount          = ovl_mount,
1011         .kill_sb        = kill_anon_super,
1012 };
1013 MODULE_ALIAS_FS("overlay");
1014
1015 static int __init ovl_init(void)
1016 {
1017         return register_filesystem(&ovl_fs_type);
1018 }
1019
1020 static void __exit ovl_exit(void)
1021 {
1022         unregister_filesystem(&ovl_fs_type);
1023 }
1024
1025 module_init(ovl_init);
1026 module_exit(ovl_exit);