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 const char *ovl_opaque_xattr = "trusted.overlay.opaque";
  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
 108         enum ovl_path_type type = ovl_path_type(dentry);
 109
 110         if (!OVL_TYPE_UPPER(type))
 111                 ovl_path_lower(dentry, path);
 112         else
 113                 ovl_path_upper(dentry, path);
 114
 115         return type;
 116 }
 117
 118 struct dentry *ovl_dentry_upper(struct dentry *dentry)
 119 {
 120         struct ovl_entry *oe = dentry->d_fsdata;
 121
 122         return ovl_upperdentry_dereference(oe);
 123 }
 124
 125 struct dentry *ovl_dentry_lower(struct dentry *dentry)
 126 {
 127         struct ovl_entry *oe = dentry->d_fsdata;
 128
 129         return __ovl_dentry_lower(oe);
 130 }
 131
 132 struct dentry *ovl_dentry_real(struct dentry *dentry)
 133 {
 134         struct ovl_entry *oe = dentry->d_fsdata;
 135         struct dentry *realdentry;
 136
 137         realdentry = ovl_upperdentry_dereference(oe);
 138         if (!realdentry)
 139                 realdentry = __ovl_dentry_lower(oe);
 140
 141         return realdentry;
 142 }
 143
 144 struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
 145 {
 146         struct dentry *realdentry;
 147
 148         realdentry = ovl_upperdentry_dereference(oe);
 149         if (realdentry) {
 150                 *is_upper = true;
 151         } else {
 152                 realdentry = __ovl_dentry_lower(oe);
 153                 *is_upper = false;
 154         }
 155         return realdentry;
 156 }
 157
 158 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
 159 {
 160         struct ovl_entry *oe = dentry->d_fsdata;
 161
 162         return oe->cache;
 163 }
 164
 165 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 166 {
 167         struct ovl_entry *oe = dentry->d_fsdata;
 168
 169         oe->cache = cache;
 170 }
 171
 172 void ovl_path_lower(struct dentry *dentry, struct path *path)
 173 {
 174         struct ovl_entry *oe = dentry->d_fsdata;
 175
 176         *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
 177 }
 178
 179 int ovl_want_write(struct dentry *dentry)
 180 {
 181         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 182         return mnt_want_write(ofs->upper_mnt);
 183 }
 184
 185 void ovl_drop_write(struct dentry *dentry)
 186 {
 187         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 188         mnt_drop_write(ofs->upper_mnt);
 189 }
 190
 191 struct dentry *ovl_workdir(struct dentry *dentry)
 192 {
 193         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 194         return ofs->workdir;
 195 }
 196
 197 bool ovl_dentry_is_opaque(struct dentry *dentry)
 198 {
 199         struct ovl_entry *oe = dentry->d_fsdata;
 200         return oe->opaque;
 201 }
 202
 203 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
 204 {
 205         struct ovl_entry *oe = dentry->d_fsdata;
 206         oe->opaque = opaque;
 207 }
 208
 209 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 210 {
 211         struct ovl_entry *oe = dentry->d_fsdata;
 212
 213         WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
 214         WARN_ON(oe->__upperdentry);
 215         BUG_ON(!upperdentry->d_inode);
 216         /*
 217          * Make sure upperdentry is consistent before making it visible to
 218          * ovl_upperdentry_dereference().
 219          */
 220         smp_wmb();
 221         oe->__upperdentry = upperdentry;
 222 }
 223
 224 void ovl_dentry_version_inc(struct dentry *dentry)
 225 {
 226         struct ovl_entry *oe = dentry->d_fsdata;
 227
 228         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 229         oe->version++;
 230 }
 231
 232 u64 ovl_dentry_version_get(struct dentry *dentry)
 233 {
 234         struct ovl_entry *oe = dentry->d_fsdata;
 235
 236         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 237         return oe->version;
 238 }
 239
 240 bool ovl_is_whiteout(struct dentry *dentry)
 241 {
 242         struct inode *inode = dentry->d_inode;
 243
 244         return inode && IS_WHITEOUT(inode);
 245 }
 246
 247 static bool ovl_is_opaquedir(struct dentry *dentry)
 248 {
 249         int res;
 250         char val;
 251         struct inode *inode = dentry->d_inode;
 252
 253         if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
 254                 return false;
 255
 256         res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
 257         if (res == 1 && val == 'y')
 258                 return true;
 259
 260         return false;
 261 }
 262
 263 static void ovl_dentry_release(struct dentry *dentry)
 264 {
 265         struct ovl_entry *oe = dentry->d_fsdata;
 266
 267         if (oe) {
 268                 unsigned int i;
 269
 270                 dput(oe->__upperdentry);
 271                 for (i = 0; i < oe->numlower; i++)
 272                         dput(oe->lowerstack[i].dentry);
 273                 kfree_rcu(oe, rcu);
 274         }
 275 }
 276
 277 static const struct dentry_operations ovl_dentry_operations = {
 278         .d_release = ovl_dentry_release,
 279 };
 280
 281 static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 282 {
 283         size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
 284         struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
 285
 286         if (oe)
 287                 oe->numlower = numlower;
 288
 289         return oe;
 290 }
 291
 292 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
 293                                              struct qstr *name)
 294 {
 295         struct dentry *dentry;
 296
 297         mutex_lock(&dir->d_inode->i_mutex);
 298         dentry = lookup_one_len(name->name, dir, name->len);
 299         mutex_unlock(&dir->d_inode->i_mutex);
 300
 301         if (IS_ERR(dentry)) {
 302                 if (PTR_ERR(dentry) == -ENOENT)
 303                         dentry = NULL;
 304         } else if (!dentry->d_inode) {
 305                 dput(dentry);
 306                 dentry = NULL;
 307         }
 308         return dentry;
 309 }
 310
 311 /*
 312  * Returns next layer in stack starting from top.
 313  * Returns -1 if this is the last layer.
 314  */
 315 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 316 {
 317         struct ovl_entry *oe = dentry->d_fsdata;
 318
 319         BUG_ON(idx < 0);
 320         if (idx == 0) {
 321                 ovl_path_upper(dentry, path);
 322                 if (path->dentry)
 323                         return oe->numlower ? 1 : -1;
 324                 idx++;
 325         }
 326         BUG_ON(idx > oe->numlower);
 327         *path = oe->lowerstack[idx - 1];
 328
 329         return (idx < oe->numlower) ? idx + 1 : -1;
 330 }
 331
 332 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 333                           unsigned int flags)
 334 {
 335         struct ovl_entry *oe;
 336         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 337         struct path *stack = NULL;
 338         struct dentry *upperdir, *upperdentry = NULL;
 339         unsigned int ctr = 0;
 340         struct inode *inode = NULL;
 341         bool upperopaque = false;
 342         struct dentry *this, *prev = NULL;
 343         unsigned int i;
 344         int err;
 345
 346         upperdir = ovl_upperdentry_dereference(poe);
 347         if (upperdir) {
 348                 this = ovl_lookup_real(upperdir, &dentry->d_name);
 349                 err = PTR_ERR(this);
 350                 if (IS_ERR(this))
 351                         goto out;
 352
 353                 if (this) {
 354                         if (ovl_is_whiteout(this)) {
 355                                 dput(this);
 356                                 this = NULL;
 357                                 upperopaque = true;
 358                         } else if (poe->numlower && ovl_is_opaquedir(this)) {
 359                                 upperopaque = true;
 360                         }
 361                 }
 362                 upperdentry = prev = this;
 363         }
 364
 365         if (!upperopaque && poe->numlower) {
 366                 err = -ENOMEM;
 367                 stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
 368                 if (!stack)
 369                         goto out_put_upper;
 370         }
 371
 372         for (i = 0; !upperopaque && i < poe->numlower; i++) {
 373                 bool opaque = false;
 374                 struct path lowerpath = poe->lowerstack[i];
 375
 376                 opaque = false;
 377                 this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
 378                 err = PTR_ERR(this);
 379                 if (IS_ERR(this)) {
 380                         /*
 381                          * If it's positive, then treat ENAMETOOLONG as ENOENT.
 382                          */
 383                         if (err == -ENAMETOOLONG && (upperdentry || ctr))
 384                                 continue;
 385                         goto out_put;
 386                 }
 387                 if (!this)
 388                         continue;
 389                 if (ovl_is_whiteout(this)) {
 390                         dput(this);
 391                         break;
 392                 }
 393                 /*
 394                  * Only makes sense to check opaque dir if this is not the
 395                  * lowermost layer.
 396                  */
 397                 if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
 398                         opaque = true;
 399                 /*
 400                  * If this is a non-directory then stop here.
 401                  *
 402                  * FIXME: check for opaqueness maybe better done in remove code.
 403                  */
 404                 if (!S_ISDIR(this->d_inode->i_mode)) {
 405                         opaque = true;
 406                 } else if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
 407                                     !S_ISDIR(this->d_inode->i_mode))) {
 408                         if (prev == upperdentry)
 409                                 upperopaque = true;
 410                         dput(this);
 411                         break;
 412                 }
 413                 stack[ctr].dentry = this;
 414                 stack[ctr].mnt = lowerpath.mnt;
 415                 ctr++;
 416                 prev = this;
 417                 if (opaque)
 418                         break;
 419         }
 420
 421         oe = ovl_alloc_entry(ctr);
 422         err = -ENOMEM;
 423         if (!oe)
 424                 goto out_put;
 425
 426         if (upperdentry || ctr) {
 427                 struct dentry *realdentry;
 428
 429                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
 430
 431                 err = -ENOMEM;
 432                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
 433                                       oe);
 434                 if (!inode)
 435                         goto out_free_oe;
 436                 ovl_copyattr(realdentry->d_inode, inode);
 437         }
 438
 439         oe->opaque = upperopaque;
 440         oe->__upperdentry = upperdentry;
 441         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 442         kfree(stack);
 443         dentry->d_fsdata = oe;
 444         d_add(dentry, inode);
 445
 446         return NULL;
 447
 448 out_free_oe:
 449         kfree(oe);
 450 out_put:
 451         for (i = 0; i < ctr; i++)
 452                 dput(stack[i].dentry);
 453         kfree(stack);
 454 out_put_upper:
 455         dput(upperdentry);
 456 out:
 457         return ERR_PTR(err);
 458 }
 459
 460 struct file *ovl_path_open(struct path *path, int flags)
 461 {
 462         return dentry_open(path, flags, current_cred());
 463 }
 464
 465 static void ovl_put_super(struct super_block *sb)
 466 {
 467         struct ovl_fs *ufs = sb->s_fs_info;
 468         unsigned i;
 469
 470         dput(ufs->workdir);
 471         mntput(ufs->upper_mnt);
 472         for (i = 0; i < ufs->numlower; i++)
 473                 mntput(ufs->lower_mnt[i]);
 474
 475         kfree(ufs->config.lowerdir);
 476         kfree(ufs->config.upperdir);
 477         kfree(ufs->config.workdir);
 478         kfree(ufs);
 479 }
 480
 481 /**
 482  * ovl_statfs
 483  * @sb: The overlayfs super block
 484  * @buf: The struct kstatfs to fill in with stats
 485  *
 486  * Get the filesystem statistics.  As writes always target the upper layer
 487  * filesystem pass the statfs to the same filesystem.
 488  */
 489 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 490 {
 491         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 492         struct dentry *root_dentry = dentry->d_sb->s_root;
 493         struct path path;
 494         int err;
 495
 496         ovl_path_upper(root_dentry, &path);
 497
 498         err = vfs_statfs(&path, buf);
 499         if (!err) {
 500                 buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
 501                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
 502         }
 503
 504         return err;
 505 }
 506
 507 /**
 508  * ovl_show_options
 509  *
 510  * Prints the mount options for a given superblock.
 511  * Returns zero; does not fail.
 512  */
 513 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 514 {
 515         struct super_block *sb = dentry->d_sb;
 516         struct ovl_fs *ufs = sb->s_fs_info;
 517
 518         seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
 519         seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
 520         seq_printf(m, ",workdir=%s", ufs->config.workdir);
 521         return 0;
 522 }
 523
 524 static const struct super_operations ovl_super_operations = {
 525         .put_super      = ovl_put_super,
 526         .statfs         = ovl_statfs,
 527         .show_options   = ovl_show_options,
 528 };
 529
 530 enum {
 531         OPT_LOWERDIR,
 532         OPT_UPPERDIR,
 533         OPT_WORKDIR,
 534         OPT_ERR,
 535 };
 536
 537 static const match_table_t ovl_tokens = {
 538         {OPT_LOWERDIR,                  "lowerdir=%s"},
 539         {OPT_UPPERDIR,                  "upperdir=%s"},
 540         {OPT_WORKDIR,                   "workdir=%s"},
 541         {OPT_ERR,                       NULL}
 542 };
 543
 544 static char *ovl_next_opt(char **s)
 545 {
 546         char *sbegin = *s;
 547         char *p;
 548
 549         if (sbegin == NULL)
 550                 return NULL;
 551
 552         for (p = sbegin; *p; p++) {
 553                 if (*p == '\\') {
 554                         p++;
 555                         if (!*p)
 556                                 break;
 557                 } else if (*p == ',') {
 558                         *p = '\0';
 559                         *s = p + 1;
 560                         return sbegin;
 561                 }
 562         }
 563         *s = NULL;
 564         return sbegin;
 565 }
 566
 567 static int ovl_parse_opt(char *opt, struct ovl_config *config)
 568 {
 569         char *p;
 570
 571         while ((p = ovl_next_opt(&opt)) != NULL) {
 572                 int token;
 573                 substring_t args[MAX_OPT_ARGS];
 574
 575                 if (!*p)
 576                         continue;
 577
 578                 token = match_token(p, ovl_tokens, args);
 579                 switch (token) {
 580                 case OPT_UPPERDIR:
 581                         kfree(config->upperdir);
 582                         config->upperdir = match_strdup(&args[0]);
 583                         if (!config->upperdir)
 584                                 return -ENOMEM;
 585                         break;
 586
 587                 case OPT_LOWERDIR:
 588                         kfree(config->lowerdir);
 589                         config->lowerdir = match_strdup(&args[0]);
 590                         if (!config->lowerdir)
 591                                 return -ENOMEM;
 592                         break;
 593
 594                 case OPT_WORKDIR:
 595                         kfree(config->workdir);
 596                         config->workdir = match_strdup(&args[0]);
 597                         if (!config->workdir)
 598                                 return -ENOMEM;
 599                         break;
 600
 601                 default:
 602                         return -EINVAL;
 603                 }
 604         }
 605         return 0;
 606 }
 607
 608 #define OVL_WORKDIR_NAME "work"
 609
 610 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
 611                                          struct dentry *dentry)
 612 {
 613         struct inode *dir = dentry->d_inode;
 614         struct dentry *work;
 615         int err;
 616         bool retried = false;
 617
 618         err = mnt_want_write(mnt);
 619         if (err)
 620                 return ERR_PTR(err);
 621
 622         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 623 retry:
 624         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
 625                               strlen(OVL_WORKDIR_NAME));
 626
 627         if (!IS_ERR(work)) {
 628                 struct kstat stat = {
 629                         .mode = S_IFDIR | 0,
 630                 };
 631
 632                 if (work->d_inode) {
 633                         err = -EEXIST;
 634                         if (retried)
 635                                 goto out_dput;
 636
 637                         retried = true;
 638                         ovl_cleanup(dir, work);
 639                         dput(work);
 640                         goto retry;
 641                 }
 642
 643                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
 644                 if (err)
 645                         goto out_dput;
 646         }
 647 out_unlock:
 648         mutex_unlock(&dir->i_mutex);
 649         mnt_drop_write(mnt);
 650
 651         return work;
 652
 653 out_dput:
 654         dput(work);
 655         work = ERR_PTR(err);
 656         goto out_unlock;
 657 }
 658
 659 static void ovl_unescape(char *s)
 660 {
 661         char *d = s;
 662
 663         for (;; s++, d++) {
 664                 if (*s == '\\')
 665                         s++;
 666                 *d = *s;
 667                 if (!*s)
 668                         break;
 669         }
 670 }
 671
 672 static int ovl_mount_dir(const char *name, struct path *path)
 673 {
 674         int err;
 675         char *tmp = kstrdup(name, GFP_KERNEL);
 676
 677         if (!tmp)
 678                 return -ENOMEM;
 679
 680         ovl_unescape(tmp);
 681         err = kern_path(tmp, LOOKUP_FOLLOW, path);
 682         if (err) {
 683                 pr_err("overlayfs: failed to resolve '%s': %i\n", tmp, err);
 684                 err = -EINVAL;
 685         }
 686         kfree(tmp);
 687         return err;
 688 }
 689
 690 static bool ovl_is_allowed_fs_type(struct dentry *root)
 691 {
 692         const struct dentry_operations *dop = root->d_op;
 693
 694         /*
 695          * We don't support:
 696          *  - automount filesystems
 697          *  - filesystems with revalidate (FIXME for lower layer)
 698          *  - filesystems with case insensitive names
 699          */
 700         if (dop &&
 701             (dop->d_manage || dop->d_automount ||
 702              dop->d_revalidate || dop->d_weak_revalidate ||
 703              dop->d_compare || dop->d_hash)) {
 704                 return false;
 705         }
 706         return true;
 707 }
 708
 709 /* Workdir should not be subdir of upperdir and vice versa */
 710 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 711 {
 712         bool ok = false;
 713
 714         if (workdir != upperdir) {
 715                 ok = (lock_rename(workdir, upperdir) == NULL);
 716                 unlock_rename(workdir, upperdir);
 717         }
 718         return ok;
 719 }
 720
 721 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 722 {
 723         struct path lowerpath;
 724         struct path upperpath;
 725         struct path workpath;
 726         struct inode *root_inode;
 727         struct dentry *root_dentry;
 728         struct ovl_entry *oe;
 729         struct ovl_fs *ufs;
 730         struct kstatfs statfs;
 731         struct vfsmount *mnt;
 732         unsigned int i;
 733         int err;
 734
 735         err = -ENOMEM;
 736         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 737         if (!ufs)
 738                 goto out;
 739
 740         err = ovl_parse_opt((char *) data, &ufs->config);
 741         if (err)
 742                 goto out_free_config;
 743
 744         /* FIXME: workdir is not needed for a R/O mount */
 745         err = -EINVAL;
 746         if (!ufs->config.upperdir || !ufs->config.lowerdir ||
 747             !ufs->config.workdir) {
 748                 pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
 749                 goto out_free_config;
 750         }
 751
 752         err = -ENOMEM;
 753         oe = ovl_alloc_entry(1);
 754         if (oe == NULL)
 755                 goto out_free_config;
 756
 757         err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
 758         if (err)
 759                 goto out_free_oe;
 760
 761         err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
 762         if (err)
 763                 goto out_put_upperpath;
 764
 765         err = ovl_mount_dir(ufs->config.workdir, &workpath);
 766         if (err)
 767                 goto out_put_lowerpath;
 768
 769         err = -EINVAL;
 770         if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
 771             !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
 772             !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
 773                 pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
 774                 goto out_put_workpath;
 775         }
 776
 777         if (upperpath.mnt != workpath.mnt) {
 778                 pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
 779                 goto out_put_workpath;
 780         }
 781         if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
 782                 pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
 783                 goto out_put_workpath;
 784         }
 785
 786         if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
 787                 pr_err("overlayfs: filesystem of upperdir is not supported\n");
 788                 goto out_put_workpath;
 789         }
 790
 791         if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
 792                 pr_err("overlayfs: filesystem of lowerdir is not supported\n");
 793                 goto out_put_workpath;
 794         }
 795
 796         err = vfs_statfs(&lowerpath, &statfs);
 797         if (err) {
 798                 pr_err("overlayfs: statfs failed on lowerpath\n");
 799                 goto out_put_workpath;
 800         }
 801         ufs->lower_namelen = statfs.f_namelen;
 802
 803         sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
 804                                 lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
 805
 806         err = -EINVAL;
 807         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
 808                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
 809                 goto out_put_workpath;
 810         }
 811
 812         ufs->upper_mnt = clone_private_mount(&upperpath);
 813         err = PTR_ERR(ufs->upper_mnt);
 814         if (IS_ERR(ufs->upper_mnt)) {
 815                 pr_err("overlayfs: failed to clone upperpath\n");
 816                 goto out_put_workpath;
 817         }
 818
 819         ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);
 820         if (ufs->lower_mnt == NULL)
 821                 goto out_put_upper_mnt;
 822
 823         mnt = clone_private_mount(&lowerpath);
 824         err = PTR_ERR(mnt);
 825         if (IS_ERR(mnt)) {
 826                 pr_err("overlayfs: failed to clone lowerpath\n");
 827                 goto out_put_lower_mnt;
 828         }
 829         /*
 830          * Make lower_mnt R/O.  That way fchmod/fchown on lower file
 831          * will fail instead of modifying lower fs.
 832          */
 833         mnt->mnt_flags |= MNT_READONLY;
 834
 835         ufs->lower_mnt[0] = mnt;
 836         ufs->numlower = 1;
 837
 838         ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
 839         err = PTR_ERR(ufs->workdir);
 840         if (IS_ERR(ufs->workdir)) {
 841                 pr_err("overlayfs: failed to create directory %s/%s\n",
 842                        ufs->config.workdir, OVL_WORKDIR_NAME);
 843                 goto out_put_lower_mnt;
 844         }
 845
 846         /* If the upper fs is r/o, we mark overlayfs r/o too */
 847         if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
 848                 sb->s_flags |= MS_RDONLY;
 849
 850         sb->s_d_op = &ovl_dentry_operations;
 851
 852         err = -ENOMEM;
 853         root_inode = ovl_new_inode(sb, S_IFDIR, oe);
 854         if (!root_inode)
 855                 goto out_put_workdir;
 856
 857         root_dentry = d_make_root(root_inode);
 858         if (!root_dentry)
 859                 goto out_put_workdir;
 860
 861         mntput(upperpath.mnt);
 862         mntput(lowerpath.mnt);
 863         path_put(&workpath);
 864
 865         oe->__upperdentry = upperpath.dentry;
 866         oe->lowerstack[0].dentry = lowerpath.dentry;
 867         oe->lowerstack[0].mnt = ufs->lower_mnt[0];
 868
 869         root_dentry->d_fsdata = oe;
 870
 871         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
 872         sb->s_op = &ovl_super_operations;
 873         sb->s_root = root_dentry;
 874         sb->s_fs_info = ufs;
 875
 876         return 0;
 877
 878 out_put_workdir:
 879         dput(ufs->workdir);
 880 out_put_lower_mnt:
 881         for (i = 0; i < ufs->numlower; i++)
 882                 mntput(ufs->lower_mnt[i]);
 883         kfree(ufs->lower_mnt);
 884 out_put_upper_mnt:
 885         mntput(ufs->upper_mnt);
 886 out_put_workpath:
 887         path_put(&workpath);
 888 out_put_lowerpath:
 889         path_put(&lowerpath);
 890 out_put_upperpath:
 891         path_put(&upperpath);
 892 out_free_oe:
 893         kfree(oe);
 894 out_free_config:
 895         kfree(ufs->config.lowerdir);
 896         kfree(ufs->config.upperdir);
 897         kfree(ufs->config.workdir);
 898         kfree(ufs);
 899 out:
 900         return err;
 901 }
 902
 903 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
 904                                 const char *dev_name, void *raw_data)
 905 {
 906         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
 907 }
 908
 909 static struct file_system_type ovl_fs_type = {
 910         .owner          = THIS_MODULE,
 911         .name           = "overlay",
 912         .mount          = ovl_mount,
 913         .kill_sb        = kill_anon_super,
 914 };
 915 MODULE_ALIAS_FS("overlay");
 916
 917 static int __init ovl_init(void)
 918 {
 919         return register_filesystem(&ovl_fs_type);
 920 }
 921
 922 static void __exit ovl_exit(void)
 923 {
 924         unregister_filesystem(&ovl_fs_type);
 925 }
 926
 927 module_init(ovl_init);
 928 module_exit(ovl_exit);