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         struct vfsmount *lower_mnt;
  39         struct dentry *workdir;
  40         long lower_namelen;
  41         /* pathnames of lower and upper dirs, for show_options */
  42         struct ovl_config config;
  43 };
  44
  45 struct ovl_dir_cache;
  46
  47 /* private information held for every overlayfs dentry */
  48 struct ovl_entry {
  49         struct dentry *__upperdentry;
  50         struct dentry *lowerdentry;
  51         struct ovl_dir_cache *cache;
  52         union {
  53                 struct {
  54                         u64 version;
  55                         bool opaque;
  56                 };
  57                 struct rcu_head rcu;
  58         };
  59 };
  60
  61 const char *ovl_opaque_xattr = "trusted.overlay.opaque";
  62
  63
  64 enum ovl_path_type ovl_path_type(struct dentry *dentry)
  65 {
  66         struct ovl_entry *oe = dentry->d_fsdata;
  67
  68         if (oe->__upperdentry) {
  69                 if (oe->lowerdentry) {
  70                         if (S_ISDIR(dentry->d_inode->i_mode))
  71                                 return OVL_PATH_MERGE;
  72                         else
  73                                 return OVL_PATH_UPPER;
  74                 } else {
  75                         if (oe->opaque)
  76                                 return OVL_PATH_UPPER;
  77                         else
  78                                 return OVL_PATH_PURE_UPPER;
  79                 }
  80         } else {
  81                 return OVL_PATH_LOWER;
  82         }
  83 }
  84
  85 static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
  86 {
  87         return lockless_dereference(oe->__upperdentry);
  88 }
  89
  90 void ovl_path_upper(struct dentry *dentry, struct path *path)
  91 {
  92         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
  93         struct ovl_entry *oe = dentry->d_fsdata;
  94
  95         path->mnt = ofs->upper_mnt;
  96         path->dentry = ovl_upperdentry_dereference(oe);
  97 }
  98
  99 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
 100 {
 101
 102         enum ovl_path_type type = ovl_path_type(dentry);
 103
 104         if (type == OVL_PATH_LOWER)
 105                 ovl_path_lower(dentry, path);
 106         else
 107                 ovl_path_upper(dentry, path);
 108
 109         return type;
 110 }
 111
 112 struct dentry *ovl_dentry_upper(struct dentry *dentry)
 113 {
 114         struct ovl_entry *oe = dentry->d_fsdata;
 115
 116         return ovl_upperdentry_dereference(oe);
 117 }
 118
 119 struct dentry *ovl_dentry_lower(struct dentry *dentry)
 120 {
 121         struct ovl_entry *oe = dentry->d_fsdata;
 122
 123         return oe->lowerdentry;
 124 }
 125
 126 struct dentry *ovl_dentry_real(struct dentry *dentry)
 127 {
 128         struct ovl_entry *oe = dentry->d_fsdata;
 129         struct dentry *realdentry;
 130
 131         realdentry = ovl_upperdentry_dereference(oe);
 132         if (!realdentry)
 133                 realdentry = oe->lowerdentry;
 134
 135         return realdentry;
 136 }
 137
 138 struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
 139 {
 140         struct dentry *realdentry;
 141
 142         realdentry = ovl_upperdentry_dereference(oe);
 143         if (realdentry) {
 144                 *is_upper = true;
 145         } else {
 146                 realdentry = oe->lowerdentry;
 147                 *is_upper = false;
 148         }
 149         return realdentry;
 150 }
 151
 152 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
 153 {
 154         struct ovl_entry *oe = dentry->d_fsdata;
 155
 156         return oe->cache;
 157 }
 158
 159 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 160 {
 161         struct ovl_entry *oe = dentry->d_fsdata;
 162
 163         oe->cache = cache;
 164 }
 165
 166 void ovl_path_lower(struct dentry *dentry, struct path *path)
 167 {
 168         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 169         struct ovl_entry *oe = dentry->d_fsdata;
 170
 171         path->mnt = ofs->lower_mnt;
 172         path->dentry = oe->lowerdentry;
 173 }
 174
 175 int ovl_want_write(struct dentry *dentry)
 176 {
 177         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 178         return mnt_want_write(ofs->upper_mnt);
 179 }
 180
 181 void ovl_drop_write(struct dentry *dentry)
 182 {
 183         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 184         mnt_drop_write(ofs->upper_mnt);
 185 }
 186
 187 struct dentry *ovl_workdir(struct dentry *dentry)
 188 {
 189         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 190         return ofs->workdir;
 191 }
 192
 193 bool ovl_dentry_is_opaque(struct dentry *dentry)
 194 {
 195         struct ovl_entry *oe = dentry->d_fsdata;
 196         return oe->opaque;
 197 }
 198
 199 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
 200 {
 201         struct ovl_entry *oe = dentry->d_fsdata;
 202         oe->opaque = opaque;
 203 }
 204
 205 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 206 {
 207         struct ovl_entry *oe = dentry->d_fsdata;
 208
 209         WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
 210         WARN_ON(oe->__upperdentry);
 211         BUG_ON(!upperdentry->d_inode);
 212         /*
 213          * Make sure upperdentry is consistent before making it visible to
 214          * ovl_upperdentry_dereference().
 215          */
 216         smp_wmb();
 217         oe->__upperdentry = upperdentry;
 218 }
 219
 220 void ovl_dentry_version_inc(struct dentry *dentry)
 221 {
 222         struct ovl_entry *oe = dentry->d_fsdata;
 223
 224         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 225         oe->version++;
 226 }
 227
 228 u64 ovl_dentry_version_get(struct dentry *dentry)
 229 {
 230         struct ovl_entry *oe = dentry->d_fsdata;
 231
 232         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 233         return oe->version;
 234 }
 235
 236 bool ovl_is_whiteout(struct dentry *dentry)
 237 {
 238         struct inode *inode = dentry->d_inode;
 239
 240         return inode && IS_WHITEOUT(inode);
 241 }
 242
 243 static bool ovl_is_opaquedir(struct dentry *dentry)
 244 {
 245         int res;
 246         char val;
 247         struct inode *inode = dentry->d_inode;
 248
 249         if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
 250                 return false;
 251
 252         res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
 253         if (res == 1 && val == 'y')
 254                 return true;
 255
 256         return false;
 257 }
 258
 259 static void ovl_dentry_release(struct dentry *dentry)
 260 {
 261         struct ovl_entry *oe = dentry->d_fsdata;
 262
 263         if (oe) {
 264                 dput(oe->__upperdentry);
 265                 dput(oe->lowerdentry);
 266                 kfree_rcu(oe, rcu);
 267         }
 268 }
 269
 270 static const struct dentry_operations ovl_dentry_operations = {
 271         .d_release = ovl_dentry_release,
 272 };
 273
 274 static struct ovl_entry *ovl_alloc_entry(void)
 275 {
 276         return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
 277 }
 278
 279 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
 280                                              struct qstr *name)
 281 {
 282         struct dentry *dentry;
 283
 284         mutex_lock(&dir->d_inode->i_mutex);
 285         dentry = lookup_one_len(name->name, dir, name->len);
 286         mutex_unlock(&dir->d_inode->i_mutex);
 287
 288         if (IS_ERR(dentry)) {
 289                 if (PTR_ERR(dentry) == -ENOENT)
 290                         dentry = NULL;
 291         } else if (!dentry->d_inode) {
 292                 dput(dentry);
 293                 dentry = NULL;
 294         }
 295         return dentry;
 296 }
 297
 298 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 299                           unsigned int flags)
 300 {
 301         struct ovl_entry *oe;
 302         struct dentry *upperdir;
 303         struct dentry *lowerdir;
 304         struct dentry *upperdentry = NULL;
 305         struct dentry *lowerdentry = NULL;
 306         struct inode *inode = NULL;
 307         int err;
 308
 309         err = -ENOMEM;
 310         oe = ovl_alloc_entry();
 311         if (!oe)
 312                 goto out;
 313
 314         upperdir = ovl_dentry_upper(dentry->d_parent);
 315         lowerdir = ovl_dentry_lower(dentry->d_parent);
 316
 317         if (upperdir) {
 318                 upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
 319                 err = PTR_ERR(upperdentry);
 320                 if (IS_ERR(upperdentry))
 321                         goto out_put_dir;
 322
 323                 if (lowerdir && upperdentry) {
 324                         if (ovl_is_whiteout(upperdentry)) {
 325                                 dput(upperdentry);
 326                                 upperdentry = NULL;
 327                                 oe->opaque = true;
 328                         } else if (ovl_is_opaquedir(upperdentry)) {
 329                                 oe->opaque = true;
 330                         }
 331                 }
 332         }
 333         if (lowerdir && !oe->opaque) {
 334                 lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
 335                 err = PTR_ERR(lowerdentry);
 336                 if (IS_ERR(lowerdentry))
 337                         goto out_dput_upper;
 338         }
 339
 340         if (lowerdentry && upperdentry &&
 341             (!S_ISDIR(upperdentry->d_inode->i_mode) ||
 342              !S_ISDIR(lowerdentry->d_inode->i_mode))) {
 343                 dput(lowerdentry);
 344                 lowerdentry = NULL;
 345                 oe->opaque = true;
 346         }
 347
 348         if (lowerdentry || upperdentry) {
 349                 struct dentry *realdentry;
 350
 351                 realdentry = upperdentry ? upperdentry : lowerdentry;
 352                 err = -ENOMEM;
 353                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
 354                                       oe);
 355                 if (!inode)
 356                         goto out_dput;
 357                 ovl_copyattr(realdentry->d_inode, inode);
 358         }
 359
 360         oe->__upperdentry = upperdentry;
 361         oe->lowerdentry = lowerdentry;
 362
 363         dentry->d_fsdata = oe;
 364         d_add(dentry, inode);
 365
 366         return NULL;
 367
 368 out_dput:
 369         dput(lowerdentry);
 370 out_dput_upper:
 371         dput(upperdentry);
 372 out_put_dir:
 373         kfree(oe);
 374 out:
 375         return ERR_PTR(err);
 376 }
 377
 378 struct file *ovl_path_open(struct path *path, int flags)
 379 {
 380         return dentry_open(path, flags, current_cred());
 381 }
 382
 383 static void ovl_put_super(struct super_block *sb)
 384 {
 385         struct ovl_fs *ufs = sb->s_fs_info;
 386
 387         dput(ufs->workdir);
 388         mntput(ufs->upper_mnt);
 389         mntput(ufs->lower_mnt);
 390
 391         kfree(ufs->config.lowerdir);
 392         kfree(ufs->config.upperdir);
 393         kfree(ufs->config.workdir);
 394         kfree(ufs);
 395 }
 396
 397 /**
 398  * ovl_statfs
 399  * @sb: The overlayfs super block
 400  * @buf: The struct kstatfs to fill in with stats
 401  *
 402  * Get the filesystem statistics.  As writes always target the upper layer
 403  * filesystem pass the statfs to the same filesystem.
 404  */
 405 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 406 {
 407         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 408         struct dentry *root_dentry = dentry->d_sb->s_root;
 409         struct path path;
 410         int err;
 411
 412         ovl_path_upper(root_dentry, &path);
 413
 414         err = vfs_statfs(&path, buf);
 415         if (!err) {
 416                 buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
 417                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
 418         }
 419
 420         return err;
 421 }
 422
 423 /**
 424  * ovl_show_options
 425  *
 426  * Prints the mount options for a given superblock.
 427  * Returns zero; does not fail.
 428  */
 429 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 430 {
 431         struct super_block *sb = dentry->d_sb;
 432         struct ovl_fs *ufs = sb->s_fs_info;
 433
 434         seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
 435         seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
 436         seq_printf(m, ",workdir=%s", ufs->config.workdir);
 437         return 0;
 438 }
 439
 440 static const struct super_operations ovl_super_operations = {
 441         .put_super      = ovl_put_super,
 442         .statfs         = ovl_statfs,
 443         .show_options   = ovl_show_options,
 444 };
 445
 446 enum {
 447         OPT_LOWERDIR,
 448         OPT_UPPERDIR,
 449         OPT_WORKDIR,
 450         OPT_ERR,
 451 };
 452
 453 static const match_table_t ovl_tokens = {
 454         {OPT_LOWERDIR,                  "lowerdir=%s"},
 455         {OPT_UPPERDIR,                  "upperdir=%s"},
 456         {OPT_WORKDIR,                   "workdir=%s"},
 457         {OPT_ERR,                       NULL}
 458 };
 459
 460 static char *ovl_next_opt(char **s)
 461 {
 462         char *sbegin = *s;
 463         char *p;
 464
 465         if (sbegin == NULL)
 466                 return NULL;
 467
 468         for (p = sbegin; *p; p++) {
 469                 if (*p == '\\') {
 470                         p++;
 471                         if (!*p)
 472                                 break;
 473                 } else if (*p == ',') {
 474                         *p = '\0';
 475                         *s = p + 1;
 476                         return sbegin;
 477                 }
 478         }
 479         *s = NULL;
 480         return sbegin;
 481 }
 482
 483 static int ovl_parse_opt(char *opt, struct ovl_config *config)
 484 {
 485         char *p;
 486
 487         while ((p = ovl_next_opt(&opt)) != NULL) {
 488                 int token;
 489                 substring_t args[MAX_OPT_ARGS];
 490
 491                 if (!*p)
 492                         continue;
 493
 494                 token = match_token(p, ovl_tokens, args);
 495                 switch (token) {
 496                 case OPT_UPPERDIR:
 497                         kfree(config->upperdir);
 498                         config->upperdir = match_strdup(&args[0]);
 499                         if (!config->upperdir)
 500                                 return -ENOMEM;
 501                         break;
 502
 503                 case OPT_LOWERDIR:
 504                         kfree(config->lowerdir);
 505                         config->lowerdir = match_strdup(&args[0]);
 506                         if (!config->lowerdir)
 507                                 return -ENOMEM;
 508                         break;
 509
 510                 case OPT_WORKDIR:
 511                         kfree(config->workdir);
 512                         config->workdir = match_strdup(&args[0]);
 513                         if (!config->workdir)
 514                                 return -ENOMEM;
 515                         break;
 516
 517                 default:
 518                         return -EINVAL;
 519                 }
 520         }
 521         return 0;
 522 }
 523
 524 #define OVL_WORKDIR_NAME "work"
 525
 526 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
 527                                          struct dentry *dentry)
 528 {
 529         struct inode *dir = dentry->d_inode;
 530         struct dentry *work;
 531         int err;
 532         bool retried = false;
 533
 534         err = mnt_want_write(mnt);
 535         if (err)
 536                 return ERR_PTR(err);
 537
 538         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 539 retry:
 540         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
 541                               strlen(OVL_WORKDIR_NAME));
 542
 543         if (!IS_ERR(work)) {
 544                 struct kstat stat = {
 545                         .mode = S_IFDIR | 0,
 546                 };
 547
 548                 if (work->d_inode) {
 549                         err = -EEXIST;
 550                         if (retried)
 551                                 goto out_dput;
 552
 553                         retried = true;
 554                         ovl_cleanup(dir, work);
 555                         dput(work);
 556                         goto retry;
 557                 }
 558
 559                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
 560                 if (err)
 561                         goto out_dput;
 562         }
 563 out_unlock:
 564         mutex_unlock(&dir->i_mutex);
 565         mnt_drop_write(mnt);
 566
 567         return work;
 568
 569 out_dput:
 570         dput(work);
 571         work = ERR_PTR(err);
 572         goto out_unlock;
 573 }
 574
 575 static void ovl_unescape(char *s)
 576 {
 577         char *d = s;
 578
 579         for (;; s++, d++) {
 580                 if (*s == '\\')
 581                         s++;
 582                 *d = *s;
 583                 if (!*s)
 584                         break;
 585         }
 586 }
 587
 588 static int ovl_mount_dir(const char *name, struct path *path)
 589 {
 590         int err;
 591         char *tmp = kstrdup(name, GFP_KERNEL);
 592
 593         if (!tmp)
 594                 return -ENOMEM;
 595
 596         ovl_unescape(tmp);
 597         err = kern_path(tmp, LOOKUP_FOLLOW, path);
 598         if (err) {
 599                 pr_err("overlayfs: failed to resolve '%s': %i\n", tmp, err);
 600                 err = -EINVAL;
 601         }
 602         kfree(tmp);
 603         return err;
 604 }
 605
 606 static bool ovl_is_allowed_fs_type(struct dentry *root)
 607 {
 608         const struct dentry_operations *dop = root->d_op;
 609
 610         /*
 611          * We don't support:
 612          *  - automount filesystems
 613          *  - filesystems with revalidate (FIXME for lower layer)
 614          *  - filesystems with case insensitive names
 615          */
 616         if (dop &&
 617             (dop->d_manage || dop->d_automount ||
 618              dop->d_revalidate || dop->d_weak_revalidate ||
 619              dop->d_compare || dop->d_hash)) {
 620                 return false;
 621         }
 622         return true;
 623 }
 624
 625 /* Workdir should not be subdir of upperdir and vice versa */
 626 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 627 {
 628         bool ok = false;
 629
 630         if (workdir != upperdir) {
 631                 ok = (lock_rename(workdir, upperdir) == NULL);
 632                 unlock_rename(workdir, upperdir);
 633         }
 634         return ok;
 635 }
 636
 637 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 638 {
 639         struct path lowerpath;
 640         struct path upperpath;
 641         struct path workpath;
 642         struct inode *root_inode;
 643         struct dentry *root_dentry;
 644         struct ovl_entry *oe;
 645         struct ovl_fs *ufs;
 646         struct kstatfs statfs;
 647         int err;
 648
 649         err = -ENOMEM;
 650         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 651         if (!ufs)
 652                 goto out;
 653
 654         err = ovl_parse_opt((char *) data, &ufs->config);
 655         if (err)
 656                 goto out_free_config;
 657
 658         /* FIXME: workdir is not needed for a R/O mount */
 659         err = -EINVAL;
 660         if (!ufs->config.upperdir || !ufs->config.lowerdir ||
 661             !ufs->config.workdir) {
 662                 pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
 663                 goto out_free_config;
 664         }
 665
 666         err = -ENOMEM;
 667         oe = ovl_alloc_entry();
 668         if (oe == NULL)
 669                 goto out_free_config;
 670
 671         err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
 672         if (err)
 673                 goto out_free_oe;
 674
 675         err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
 676         if (err)
 677                 goto out_put_upperpath;
 678
 679         err = ovl_mount_dir(ufs->config.workdir, &workpath);
 680         if (err)
 681                 goto out_put_lowerpath;
 682
 683         err = -EINVAL;
 684         if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
 685             !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
 686             !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
 687                 pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
 688                 goto out_put_workpath;
 689         }
 690
 691         if (upperpath.mnt != workpath.mnt) {
 692                 pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
 693                 goto out_put_workpath;
 694         }
 695         if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
 696                 pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
 697                 goto out_put_workpath;
 698         }
 699
 700         if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
 701                 pr_err("overlayfs: filesystem of upperdir is not supported\n");
 702                 goto out_put_workpath;
 703         }
 704
 705         if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
 706                 pr_err("overlayfs: filesystem of lowerdir is not supported\n");
 707                 goto out_put_workpath;
 708         }
 709
 710         err = vfs_statfs(&lowerpath, &statfs);
 711         if (err) {
 712                 pr_err("overlayfs: statfs failed on lowerpath\n");
 713                 goto out_put_workpath;
 714         }
 715         ufs->lower_namelen = statfs.f_namelen;
 716
 717         sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
 718                                 lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
 719
 720         err = -EINVAL;
 721         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
 722                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
 723                 goto out_put_workpath;
 724         }
 725
 726         ufs->upper_mnt = clone_private_mount(&upperpath);
 727         err = PTR_ERR(ufs->upper_mnt);
 728         if (IS_ERR(ufs->upper_mnt)) {
 729                 pr_err("overlayfs: failed to clone upperpath\n");
 730                 goto out_put_workpath;
 731         }
 732
 733         ufs->lower_mnt = clone_private_mount(&lowerpath);
 734         err = PTR_ERR(ufs->lower_mnt);
 735         if (IS_ERR(ufs->lower_mnt)) {
 736                 pr_err("overlayfs: failed to clone lowerpath\n");
 737                 goto out_put_upper_mnt;
 738         }
 739
 740         ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
 741         err = PTR_ERR(ufs->workdir);
 742         if (IS_ERR(ufs->workdir)) {
 743                 pr_err("overlayfs: failed to create directory %s/%s\n",
 744                        ufs->config.workdir, OVL_WORKDIR_NAME);
 745                 goto out_put_lower_mnt;
 746         }
 747
 748         /*
 749          * Make lower_mnt R/O.  That way fchmod/fchown on lower file
 750          * will fail instead of modifying lower fs.
 751          */
 752         ufs->lower_mnt->mnt_flags |= MNT_READONLY;
 753
 754         /* If the upper fs is r/o, we mark overlayfs r/o too */
 755         if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
 756                 sb->s_flags |= MS_RDONLY;
 757
 758         sb->s_d_op = &ovl_dentry_operations;
 759
 760         err = -ENOMEM;
 761         root_inode = ovl_new_inode(sb, S_IFDIR, oe);
 762         if (!root_inode)
 763                 goto out_put_workdir;
 764
 765         root_dentry = d_make_root(root_inode);
 766         if (!root_dentry)
 767                 goto out_put_workdir;
 768
 769         mntput(upperpath.mnt);
 770         mntput(lowerpath.mnt);
 771         path_put(&workpath);
 772
 773         oe->__upperdentry = upperpath.dentry;
 774         oe->lowerdentry = lowerpath.dentry;
 775
 776         root_dentry->d_fsdata = oe;
 777
 778         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
 779         sb->s_op = &ovl_super_operations;
 780         sb->s_root = root_dentry;
 781         sb->s_fs_info = ufs;
 782
 783         return 0;
 784
 785 out_put_workdir:
 786         dput(ufs->workdir);
 787 out_put_lower_mnt:
 788         mntput(ufs->lower_mnt);
 789 out_put_upper_mnt:
 790         mntput(ufs->upper_mnt);
 791 out_put_workpath:
 792         path_put(&workpath);
 793 out_put_lowerpath:
 794         path_put(&lowerpath);
 795 out_put_upperpath:
 796         path_put(&upperpath);
 797 out_free_oe:
 798         kfree(oe);
 799 out_free_config:
 800         kfree(ufs->config.lowerdir);
 801         kfree(ufs->config.upperdir);
 802         kfree(ufs->config.workdir);
 803         kfree(ufs);
 804 out:
 805         return err;
 806 }
 807
 808 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
 809                                 const char *dev_name, void *raw_data)
 810 {
 811         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
 812 }
 813
 814 static struct file_system_type ovl_fs_type = {
 815         .owner          = THIS_MODULE,
 816         .name           = "overlay",
 817         .mount          = ovl_mount,
 818         .kill_sb        = kill_anon_super,
 819 };
 820 MODULE_ALIAS_FS("overlay");
 821
 822 static int __init ovl_init(void)
 823 {
 824         return register_filesystem(&ovl_fs_type);
 825 }
 826
 827 static void __exit ovl_exit(void)
 828 {
 829         unregister_filesystem(&ovl_fs_type);
 830 }
 831
 832 module_init(ovl_init);
 833 module_exit(ovl_exit);