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 <uapi/linux/magic.h>
  11 #include <linux/fs.h>
  12 #include <linux/namei.h>
  13 #include <linux/xattr.h>
  14 #include <linux/mount.h>
  15 #include <linux/parser.h>
  16 #include <linux/module.h>
  17 #include <linux/statfs.h>
  18 #include <linux/seq_file.h>
  19 #include <linux/posix_acl_xattr.h>
  20 #include "overlayfs.h"
  21
  22 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
  23 MODULE_DESCRIPTION("Overlay filesystem");
  24 MODULE_LICENSE("GPL");
  25
  26
  27 struct ovl_dir_cache;
  28
  29 #define OVL_MAX_STACK 500
  30
  31 static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
  32 module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
  33 MODULE_PARM_DESC(ovl_redirect_dir_def,
  34                  "Default to on or off for the redirect_dir feature");
  35
  36 static bool ovl_redirect_always_follow =
  37         IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW);
  38 module_param_named(redirect_always_follow, ovl_redirect_always_follow,
  39                    bool, 0644);
  40 MODULE_PARM_DESC(ovl_redirect_always_follow,
  41                  "Follow redirects even if redirect_dir feature is turned off");
  42
  43 static bool ovl_index_def = IS_ENABLED(CONFIG_OVERLAY_FS_INDEX);
  44 module_param_named(index, ovl_index_def, bool, 0644);
  45 MODULE_PARM_DESC(ovl_index_def,
  46                  "Default to on or off for the inodes index feature");
  47
  48 static void ovl_entry_stack_free(struct ovl_entry *oe)
  49 {
  50         unsigned int i;
  51
  52         for (i = 0; i < oe->numlower; i++)
  53                 dput(oe->lowerstack[i].dentry);
  54 }
  55
  56 static void ovl_dentry_release(struct dentry *dentry)
  57 {
  58         struct ovl_entry *oe = dentry->d_fsdata;
  59
  60         if (oe) {
  61                 ovl_entry_stack_free(oe);
  62                 kfree_rcu(oe, rcu);
  63         }
  64 }
  65
  66 static int ovl_check_append_only(struct inode *inode, int flag)
  67 {
  68         /*
  69          * This test was moot in vfs may_open() because overlay inode does
  70          * not have the S_APPEND flag, so re-check on real upper inode
  71          */
  72         if (IS_APPEND(inode)) {
  73                 if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
  74                         return -EPERM;
  75                 if (flag & O_TRUNC)
  76                         return -EPERM;
  77         }
  78
  79         return 0;
  80 }
  81
  82 static struct dentry *ovl_d_real(struct dentry *dentry,
  83                                  const struct inode *inode,
  84                                  unsigned int open_flags, unsigned int flags)
  85 {
  86         struct dentry *real;
  87         int err;
  88
  89         if (flags & D_REAL_UPPER)
  90                 return ovl_dentry_upper(dentry);
  91
  92         if (!d_is_reg(dentry)) {
  93                 if (!inode || inode == d_inode(dentry))
  94                         return dentry;
  95                 goto bug;
  96         }
  97
  98         if (open_flags) {
  99                 err = ovl_open_maybe_copy_up(dentry, open_flags);
 100                 if (err)
 101                         return ERR_PTR(err);
 102         }
 103
 104         real = ovl_dentry_upper(dentry);
 105         if (real && (!inode || inode == d_inode(real))) {
 106                 if (!inode) {
 107                         err = ovl_check_append_only(d_inode(real), open_flags);
 108                         if (err)
 109                                 return ERR_PTR(err);
 110                 }
 111                 return real;
 112         }
 113
 114         real = ovl_dentry_lower(dentry);
 115         if (!real)
 116                 goto bug;
 117
 118         /* Handle recursion */
 119         real = d_real(real, inode, open_flags, 0);
 120
 121         if (!inode || inode == d_inode(real))
 122                 return real;
 123 bug:
 124         WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
 125              inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
 126         return dentry;
 127 }
 128
 129 static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
 130 {
 131         struct ovl_entry *oe = dentry->d_fsdata;
 132         unsigned int i;
 133         int ret = 1;
 134
 135         for (i = 0; i < oe->numlower; i++) {
 136                 struct dentry *d = oe->lowerstack[i].dentry;
 137
 138                 if (d->d_flags & DCACHE_OP_REVALIDATE) {
 139                         ret = d->d_op->d_revalidate(d, flags);
 140                         if (ret < 0)
 141                                 return ret;
 142                         if (!ret) {
 143                                 if (!(flags & LOOKUP_RCU))
 144                                         d_invalidate(d);
 145                                 return -ESTALE;
 146                         }
 147                 }
 148         }
 149         return 1;
 150 }
 151
 152 static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 153 {
 154         struct ovl_entry *oe = dentry->d_fsdata;
 155         unsigned int i;
 156         int ret = 1;
 157
 158         for (i = 0; i < oe->numlower; i++) {
 159                 struct dentry *d = oe->lowerstack[i].dentry;
 160
 161                 if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
 162                         ret = d->d_op->d_weak_revalidate(d, flags);
 163                         if (ret <= 0)
 164                                 break;
 165                 }
 166         }
 167         return ret;
 168 }
 169
 170 static const struct dentry_operations ovl_dentry_operations = {
 171         .d_release = ovl_dentry_release,
 172         .d_real = ovl_d_real,
 173 };
 174
 175 static const struct dentry_operations ovl_reval_dentry_operations = {
 176         .d_release = ovl_dentry_release,
 177         .d_real = ovl_d_real,
 178         .d_revalidate = ovl_dentry_revalidate,
 179         .d_weak_revalidate = ovl_dentry_weak_revalidate,
 180 };
 181
 182 static struct kmem_cache *ovl_inode_cachep;
 183
 184 static struct inode *ovl_alloc_inode(struct super_block *sb)
 185 {
 186         struct ovl_inode *oi = kmem_cache_alloc(ovl_inode_cachep, GFP_KERNEL);
 187
 188         if (!oi)
 189                 return NULL;
 190
 191         oi->cache = NULL;
 192         oi->redirect = NULL;
 193         oi->version = 0;
 194         oi->flags = 0;
 195         oi->__upperdentry = NULL;
 196         oi->lower = NULL;
 197         mutex_init(&oi->lock);
 198
 199         return &oi->vfs_inode;
 200 }
 201
 202 static void ovl_i_callback(struct rcu_head *head)
 203 {
 204         struct inode *inode = container_of(head, struct inode, i_rcu);
 205
 206         kmem_cache_free(ovl_inode_cachep, OVL_I(inode));
 207 }
 208
 209 static void ovl_destroy_inode(struct inode *inode)
 210 {
 211         struct ovl_inode *oi = OVL_I(inode);
 212
 213         dput(oi->__upperdentry);
 214         iput(oi->lower);
 215         kfree(oi->redirect);
 216         ovl_dir_cache_free(inode);
 217         mutex_destroy(&oi->lock);
 218
 219         call_rcu(&inode->i_rcu, ovl_i_callback);
 220 }
 221
 222 static void ovl_free_fs(struct ovl_fs *ofs)
 223 {
 224         unsigned i;
 225
 226         dput(ofs->indexdir);
 227         dput(ofs->workdir);
 228         if (ofs->workdir_locked)
 229                 ovl_inuse_unlock(ofs->workbasedir);
 230         dput(ofs->workbasedir);
 231         if (ofs->upperdir_locked)
 232                 ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
 233         mntput(ofs->upper_mnt);
 234         for (i = 0; i < ofs->numlower; i++) {
 235                 mntput(ofs->lower_layers[i].mnt);
 236                 free_anon_bdev(ofs->lower_layers[i].pseudo_dev);
 237         }
 238         kfree(ofs->lower_layers);
 239
 240         kfree(ofs->config.lowerdir);
 241         kfree(ofs->config.upperdir);
 242         kfree(ofs->config.workdir);
 243         kfree(ofs->config.redirect_mode);
 244         if (ofs->creator_cred)
 245                 put_cred(ofs->creator_cred);
 246         kfree(ofs);
 247 }
 248
 249 static void ovl_put_super(struct super_block *sb)
 250 {
 251         struct ovl_fs *ofs = sb->s_fs_info;
 252
 253         ovl_free_fs(ofs);
 254 }
 255
 256 /* Sync real dirty inodes in upper filesystem (if it exists) */
 257 static int ovl_sync_fs(struct super_block *sb, int wait)
 258 {
 259         struct ovl_fs *ofs = sb->s_fs_info;
 260         struct super_block *upper_sb;
 261         int ret;
 262
 263         if (!ofs->upper_mnt)
 264                 return 0;
 265
 266         /*
 267          * If this is a sync(2) call or an emergency sync, all the super blocks
 268          * will be iterated, including upper_sb, so no need to do anything.
 269          *
 270          * If this is a syncfs(2) call, then we do need to call
 271          * sync_filesystem() on upper_sb, but enough if we do it when being
 272          * called with wait == 1.
 273          */
 274         if (!wait)
 275                 return 0;
 276
 277         upper_sb = ofs->upper_mnt->mnt_sb;
 278
 279         down_read(&upper_sb->s_umount);
 280         ret = sync_filesystem(upper_sb);
 281         up_read(&upper_sb->s_umount);
 282
 283         return ret;
 284 }
 285
 286 /**
 287  * ovl_statfs
 288  * @sb: The overlayfs super block
 289  * @buf: The struct kstatfs to fill in with stats
 290  *
 291  * Get the filesystem statistics.  As writes always target the upper layer
 292  * filesystem pass the statfs to the upper filesystem (if it exists)
 293  */
 294 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 295 {
 296         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 297         struct dentry *root_dentry = dentry->d_sb->s_root;
 298         struct path path;
 299         int err;
 300
 301         ovl_path_real(root_dentry, &path);
 302
 303         err = vfs_statfs(&path, buf);
 304         if (!err) {
 305                 buf->f_namelen = ofs->namelen;
 306                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
 307         }
 308
 309         return err;
 310 }
 311
 312 /* Will this overlay be forced to mount/remount ro? */
 313 static bool ovl_force_readonly(struct ovl_fs *ofs)
 314 {
 315         return (!ofs->upper_mnt || !ofs->workdir);
 316 }
 317
 318 static const char *ovl_redirect_mode_def(void)
 319 {
 320         return ovl_redirect_dir_def ? "on" : "off";
 321 }
 322
 323 /**
 324  * ovl_show_options
 325  *
 326  * Prints the mount options for a given superblock.
 327  * Returns zero; does not fail.
 328  */
 329 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 330 {
 331         struct super_block *sb = dentry->d_sb;
 332         struct ovl_fs *ofs = sb->s_fs_info;
 333
 334         seq_show_option(m, "lowerdir", ofs->config.lowerdir);
 335         if (ofs->config.upperdir) {
 336                 seq_show_option(m, "upperdir", ofs->config.upperdir);
 337                 seq_show_option(m, "workdir", ofs->config.workdir);
 338         }
 339         if (ofs->config.default_permissions)
 340                 seq_puts(m, ",default_permissions");
 341         if (strcmp(ofs->config.redirect_mode, ovl_redirect_mode_def()) != 0)
 342                 seq_printf(m, ",redirect_dir=%s", ofs->config.redirect_mode);
 343         if (ofs->config.index != ovl_index_def)
 344                 seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
 345         return 0;
 346 }
 347
 348 static int ovl_remount(struct super_block *sb, int *flags, char *data)
 349 {
 350         struct ovl_fs *ofs = sb->s_fs_info;
 351
 352         if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
 353                 return -EROFS;
 354
 355         return 0;
 356 }
 357
 358 static const struct super_operations ovl_super_operations = {
 359         .alloc_inode    = ovl_alloc_inode,
 360         .destroy_inode  = ovl_destroy_inode,
 361         .drop_inode     = generic_delete_inode,
 362         .put_super      = ovl_put_super,
 363         .sync_fs        = ovl_sync_fs,
 364         .statfs         = ovl_statfs,
 365         .show_options   = ovl_show_options,
 366         .remount_fs     = ovl_remount,
 367 };
 368
 369 enum {
 370         OPT_LOWERDIR,
 371         OPT_UPPERDIR,
 372         OPT_WORKDIR,
 373         OPT_DEFAULT_PERMISSIONS,
 374         OPT_REDIRECT_DIR,
 375         OPT_INDEX_ON,
 376         OPT_INDEX_OFF,
 377         OPT_ERR,
 378 };
 379
 380 static const match_table_t ovl_tokens = {
 381         {OPT_LOWERDIR,                  "lowerdir=%s"},
 382         {OPT_UPPERDIR,                  "upperdir=%s"},
 383         {OPT_WORKDIR,                   "workdir=%s"},
 384         {OPT_DEFAULT_PERMISSIONS,       "default_permissions"},
 385         {OPT_REDIRECT_DIR,              "redirect_dir=%s"},
 386         {OPT_INDEX_ON,                  "index=on"},
 387         {OPT_INDEX_OFF,                 "index=off"},
 388         {OPT_ERR,                       NULL}
 389 };
 390
 391 static char *ovl_next_opt(char **s)
 392 {
 393         char *sbegin = *s;
 394         char *p;
 395
 396         if (sbegin == NULL)
 397                 return NULL;
 398
 399         for (p = sbegin; *p; p++) {
 400                 if (*p == '\\') {
 401                         p++;
 402                         if (!*p)
 403                                 break;
 404                 } else if (*p == ',') {
 405                         *p = '\0';
 406                         *s = p + 1;
 407                         return sbegin;
 408                 }
 409         }
 410         *s = NULL;
 411         return sbegin;
 412 }
 413
 414 static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
 415 {
 416         if (strcmp(mode, "on") == 0) {
 417                 config->redirect_dir = true;
 418                 /*
 419                  * Does not make sense to have redirect creation without
 420                  * redirect following.
 421                  */
 422                 config->redirect_follow = true;
 423         } else if (strcmp(mode, "follow") == 0) {
 424                 config->redirect_follow = true;
 425         } else if (strcmp(mode, "off") == 0) {
 426                 if (ovl_redirect_always_follow)
 427                         config->redirect_follow = true;
 428         } else if (strcmp(mode, "nofollow") != 0) {
 429                 pr_err("overlayfs: bad mount option \"redirect_dir=%s\"\n",
 430                        mode);
 431                 return -EINVAL;
 432         }
 433
 434         return 0;
 435 }
 436
 437 static int ovl_parse_opt(char *opt, struct ovl_config *config)
 438 {
 439         char *p;
 440
 441         config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
 442         if (!config->redirect_mode)
 443                 return -ENOMEM;
 444
 445         while ((p = ovl_next_opt(&opt)) != NULL) {
 446                 int token;
 447                 substring_t args[MAX_OPT_ARGS];
 448
 449                 if (!*p)
 450                         continue;
 451
 452                 token = match_token(p, ovl_tokens, args);
 453                 switch (token) {
 454                 case OPT_UPPERDIR:
 455                         kfree(config->upperdir);
 456                         config->upperdir = match_strdup(&args[0]);
 457                         if (!config->upperdir)
 458                                 return -ENOMEM;
 459                         break;
 460
 461                 case OPT_LOWERDIR:
 462                         kfree(config->lowerdir);
 463                         config->lowerdir = match_strdup(&args[0]);
 464                         if (!config->lowerdir)
 465                                 return -ENOMEM;
 466                         break;
 467
 468                 case OPT_WORKDIR:
 469                         kfree(config->workdir);
 470                         config->workdir = match_strdup(&args[0]);
 471                         if (!config->workdir)
 472                                 return -ENOMEM;
 473                         break;
 474
 475                 case OPT_DEFAULT_PERMISSIONS:
 476                         config->default_permissions = true;
 477                         break;
 478
 479                 case OPT_REDIRECT_DIR:
 480                         kfree(config->redirect_mode);
 481                         config->redirect_mode = match_strdup(&args[0]);
 482                         if (!config->redirect_mode)
 483                                 return -ENOMEM;
 484                         break;
 485
 486                 case OPT_INDEX_ON:
 487                         config->index = true;
 488                         break;
 489
 490                 case OPT_INDEX_OFF:
 491                         config->index = false;
 492                         break;
 493
 494                 default:
 495                         pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 496                         return -EINVAL;
 497                 }
 498         }
 499
 500         /* Workdir is useless in non-upper mount */
 501         if (!config->upperdir && config->workdir) {
 502                 pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
 503                         config->workdir);
 504                 kfree(config->workdir);
 505                 config->workdir = NULL;
 506         }
 507
 508         return ovl_parse_redirect_mode(config, config->redirect_mode);
 509 }
 510
 511 #define OVL_WORKDIR_NAME "work"
 512 #define OVL_INDEXDIR_NAME "index"
 513
 514 static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
 515                                          const char *name, bool persist)
 516 {
 517         struct inode *dir =  ofs->workbasedir->d_inode;
 518         struct vfsmount *mnt = ofs->upper_mnt;
 519         struct dentry *work;
 520         int err;
 521         bool retried = false;
 522         bool locked = false;
 523
 524         inode_lock_nested(dir, I_MUTEX_PARENT);
 525         locked = true;
 526
 527 retry:
 528         work = lookup_one_len(name, ofs->workbasedir, strlen(name));
 529
 530         if (!IS_ERR(work)) {
 531                 struct iattr attr = {
 532                         .ia_valid = ATTR_MODE,
 533                         .ia_mode = S_IFDIR | 0,
 534                 };
 535
 536                 if (work->d_inode) {
 537                         err = -EEXIST;
 538                         if (retried)
 539                                 goto out_dput;
 540
 541                         if (persist)
 542                                 goto out_unlock;
 543
 544                         retried = true;
 545                         ovl_workdir_cleanup(dir, mnt, work, 0);
 546                         dput(work);
 547                         goto retry;
 548                 }
 549
 550                 err = ovl_create_real(dir, work,
 551                                       &(struct cattr){.mode = S_IFDIR | 0},
 552                                       NULL, true);
 553                 if (err)
 554                         goto out_dput;
 555
 556                 /*
 557                  * Try to remove POSIX ACL xattrs from workdir.  We are good if:
 558                  *
 559                  * a) success (there was a POSIX ACL xattr and was removed)
 560                  * b) -ENODATA (there was no POSIX ACL xattr)
 561                  * c) -EOPNOTSUPP (POSIX ACL xattrs are not supported)
 562                  *
 563                  * There are various other error values that could effectively
 564                  * mean that the xattr doesn't exist (e.g. -ERANGE is returned
 565                  * if the xattr name is too long), but the set of filesystems
 566                  * allowed as upper are limited to "normal" ones, where checking
 567                  * for the above two errors is sufficient.
 568                  */
 569                 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
 570                 if (err && err != -ENODATA && err != -EOPNOTSUPP)
 571                         goto out_dput;
 572
 573                 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
 574                 if (err && err != -ENODATA && err != -EOPNOTSUPP)
 575                         goto out_dput;
 576
 577                 /* Clear any inherited mode bits */
 578                 inode_lock(work->d_inode);
 579                 err = notify_change(work, &attr, NULL);
 580                 inode_unlock(work->d_inode);
 581                 if (err)
 582                         goto out_dput;
 583         } else {
 584                 err = PTR_ERR(work);
 585                 goto out_err;
 586         }
 587 out_unlock:
 588         if (locked)
 589                 inode_unlock(dir);
 590
 591         return work;
 592
 593 out_dput:
 594         dput(work);
 595 out_err:
 596         pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
 597                 ofs->config.workdir, name, -err);
 598         work = NULL;
 599         goto out_unlock;
 600 }
 601
 602 static void ovl_unescape(char *s)
 603 {
 604         char *d = s;
 605
 606         for (;; s++, d++) {
 607                 if (*s == '\\')
 608                         s++;
 609                 *d = *s;
 610                 if (!*s)
 611                         break;
 612         }
 613 }
 614
 615 static int ovl_mount_dir_noesc(const char *name, struct path *path)
 616 {
 617         int err = -EINVAL;
 618
 619         if (!*name) {
 620                 pr_err("overlayfs: empty lowerdir\n");
 621                 goto out;
 622         }
 623         err = kern_path(name, LOOKUP_FOLLOW, path);
 624         if (err) {
 625                 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
 626                 goto out;
 627         }
 628         err = -EINVAL;
 629         if (ovl_dentry_weird(path->dentry)) {
 630                 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
 631                 goto out_put;
 632         }
 633         if (!d_is_dir(path->dentry)) {
 634                 pr_err("overlayfs: '%s' not a directory\n", name);
 635                 goto out_put;
 636         }
 637         return 0;
 638
 639 out_put:
 640         path_put_init(path);
 641 out:
 642         return err;
 643 }
 644
 645 static int ovl_mount_dir(const char *name, struct path *path)
 646 {
 647         int err = -ENOMEM;
 648         char *tmp = kstrdup(name, GFP_KERNEL);
 649
 650         if (tmp) {
 651                 ovl_unescape(tmp);
 652                 err = ovl_mount_dir_noesc(tmp, path);
 653
 654                 if (!err)
 655                         if (ovl_dentry_remote(path->dentry)) {
 656                                 pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
 657                                        tmp);
 658                                 path_put_init(path);
 659                                 err = -EINVAL;
 660                         }
 661                 kfree(tmp);
 662         }
 663         return err;
 664 }
 665
 666 static int ovl_check_namelen(struct path *path, struct ovl_fs *ofs,
 667                              const char *name)
 668 {
 669         struct kstatfs statfs;
 670         int err = vfs_statfs(path, &statfs);
 671
 672         if (err)
 673                 pr_err("overlayfs: statfs failed on '%s'\n", name);
 674         else
 675                 ofs->namelen = max(ofs->namelen, statfs.f_namelen);
 676
 677         return err;
 678 }
 679
 680 static int ovl_lower_dir(const char *name, struct path *path,
 681                          struct ovl_fs *ofs, int *stack_depth, bool *remote)
 682 {
 683         int err;
 684
 685         err = ovl_mount_dir_noesc(name, path);
 686         if (err)
 687                 goto out;
 688
 689         err = ovl_check_namelen(path, ofs, name);
 690         if (err)
 691                 goto out_put;
 692
 693         *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
 694
 695         if (ovl_dentry_remote(path->dentry))
 696                 *remote = true;
 697
 698         /*
 699          * The inodes index feature needs to encode and decode file
 700          * handles, so it requires that all layers support them.
 701          */
 702         if (ofs->config.index && ofs->config.upperdir &&
 703             !ovl_can_decode_fh(path->dentry->d_sb)) {
 704                 ofs->config.index = false;
 705                 pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
 706         }
 707
 708         return 0;
 709
 710 out_put:
 711         path_put_init(path);
 712 out:
 713         return err;
 714 }
 715
 716 /* Workdir should not be subdir of upperdir and vice versa */
 717 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 718 {
 719         bool ok = false;
 720
 721         if (workdir != upperdir) {
 722                 ok = (lock_rename(workdir, upperdir) == NULL);
 723                 unlock_rename(workdir, upperdir);
 724         }
 725         return ok;
 726 }
 727
 728 static unsigned int ovl_split_lowerdirs(char *str)
 729 {
 730         unsigned int ctr = 1;
 731         char *s, *d;
 732
 733         for (s = d = str;; s++, d++) {
 734                 if (*s == '\\') {
 735                         s++;
 736                 } else if (*s == ':') {
 737                         *d = '\0';
 738                         ctr++;
 739                         continue;
 740                 }
 741                 *d = *s;
 742                 if (!*s)
 743                         break;
 744         }
 745         return ctr;
 746 }
 747
 748 static int __maybe_unused
 749 ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
 750                         struct dentry *dentry, struct inode *inode,
 751                         const char *name, void *buffer, size_t size)
 752 {
 753         return ovl_xattr_get(dentry, inode, handler->name, buffer, size);
 754 }
 755
 756 static int __maybe_unused
 757 ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
 758                         struct dentry *dentry, struct inode *inode,
 759                         const char *name, const void *value,
 760                         size_t size, int flags)
 761 {
 762         struct dentry *workdir = ovl_workdir(dentry);
 763         struct inode *realinode = ovl_inode_real(inode);
 764         struct posix_acl *acl = NULL;
 765         int err;
 766
 767         /* Check that everything is OK before copy-up */
 768         if (value) {
 769                 acl = posix_acl_from_xattr(&init_user_ns, value, size);
 770                 if (IS_ERR(acl))
 771                         return PTR_ERR(acl);
 772         }
 773         err = -EOPNOTSUPP;
 774         if (!IS_POSIXACL(d_inode(workdir)))
 775                 goto out_acl_release;
 776         if (!realinode->i_op->set_acl)
 777                 goto out_acl_release;
 778         if (handler->flags == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode)) {
 779                 err = acl ? -EACCES : 0;
 780                 goto out_acl_release;
 781         }
 782         err = -EPERM;
 783         if (!inode_owner_or_capable(inode))
 784                 goto out_acl_release;
 785
 786         posix_acl_release(acl);
 787
 788         /*
 789          * Check if sgid bit needs to be cleared (actual setacl operation will
 790          * be done with mounter's capabilities and so that won't do it for us).
 791          */
 792         if (unlikely(inode->i_mode & S_ISGID) &&
 793             handler->flags == ACL_TYPE_ACCESS &&
 794             !in_group_p(inode->i_gid) &&
 795             !capable_wrt_inode_uidgid(inode, CAP_FSETID)) {
 796                 struct iattr iattr = { .ia_valid = ATTR_KILL_SGID };
 797
 798                 err = ovl_setattr(dentry, &iattr);
 799                 if (err)
 800                         return err;
 801         }
 802
 803         err = ovl_xattr_set(dentry, inode, handler->name, value, size, flags);
 804         if (!err)
 805                 ovl_copyattr(ovl_inode_real(inode), inode);
 806
 807         return err;
 808
 809 out_acl_release:
 810         posix_acl_release(acl);
 811         return err;
 812 }
 813
 814 static int ovl_own_xattr_get(const struct xattr_handler *handler,
 815                              struct dentry *dentry, struct inode *inode,
 816                              const char *name, void *buffer, size_t size)
 817 {
 818         return -EOPNOTSUPP;
 819 }
 820
 821 static int ovl_own_xattr_set(const struct xattr_handler *handler,
 822                              struct dentry *dentry, struct inode *inode,
 823                              const char *name, const void *value,
 824                              size_t size, int flags)
 825 {
 826         return -EOPNOTSUPP;
 827 }
 828
 829 static int ovl_other_xattr_get(const struct xattr_handler *handler,
 830                                struct dentry *dentry, struct inode *inode,
 831                                const char *name, void *buffer, size_t size)
 832 {
 833         return ovl_xattr_get(dentry, inode, name, buffer, size);
 834 }
 835
 836 static int ovl_other_xattr_set(const struct xattr_handler *handler,
 837                                struct dentry *dentry, struct inode *inode,
 838                                const char *name, const void *value,
 839                                size_t size, int flags)
 840 {
 841         return ovl_xattr_set(dentry, inode, name, value, size, flags);
 842 }
 843
 844 static const struct xattr_handler __maybe_unused
 845 ovl_posix_acl_access_xattr_handler = {
 846         .name = XATTR_NAME_POSIX_ACL_ACCESS,
 847         .flags = ACL_TYPE_ACCESS,
 848         .get = ovl_posix_acl_xattr_get,
 849         .set = ovl_posix_acl_xattr_set,
 850 };
 851
 852 static const struct xattr_handler __maybe_unused
 853 ovl_posix_acl_default_xattr_handler = {
 854         .name = XATTR_NAME_POSIX_ACL_DEFAULT,
 855         .flags = ACL_TYPE_DEFAULT,
 856         .get = ovl_posix_acl_xattr_get,
 857         .set = ovl_posix_acl_xattr_set,
 858 };
 859
 860 static const struct xattr_handler ovl_own_xattr_handler = {
 861         .prefix = OVL_XATTR_PREFIX,
 862         .get = ovl_own_xattr_get,
 863         .set = ovl_own_xattr_set,
 864 };
 865
 866 static const struct xattr_handler ovl_other_xattr_handler = {
 867         .prefix = "", /* catch all */
 868         .get = ovl_other_xattr_get,
 869         .set = ovl_other_xattr_set,
 870 };
 871
 872 static const struct xattr_handler *ovl_xattr_handlers[] = {
 873 #ifdef CONFIG_FS_POSIX_ACL
 874         &ovl_posix_acl_access_xattr_handler,
 875         &ovl_posix_acl_default_xattr_handler,
 876 #endif
 877         &ovl_own_xattr_handler,
 878         &ovl_other_xattr_handler,
 879         NULL
 880 };
 881
 882 static int ovl_get_upper(struct ovl_fs *ofs, struct path *upperpath)
 883 {
 884         struct vfsmount *upper_mnt;
 885         int err;
 886
 887         err = ovl_mount_dir(ofs->config.upperdir, upperpath);
 888         if (err)
 889                 goto out;
 890
 891         /* Upper fs should not be r/o */
 892         if (sb_rdonly(upperpath->mnt->mnt_sb)) {
 893                 pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
 894                 err = -EINVAL;
 895                 goto out;
 896         }
 897
 898         err = ovl_check_namelen(upperpath, ofs, ofs->config.upperdir);
 899         if (err)
 900                 goto out;
 901
 902         err = -EBUSY;
 903         if (ovl_inuse_trylock(upperpath->dentry)) {
 904                 ofs->upperdir_locked = true;
 905         } else if (ofs->config.index) {
 906                 pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
 907                 goto out;
 908         } else {
 909                 pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
 910         }
 911
 912         upper_mnt = clone_private_mount(upperpath);
 913         err = PTR_ERR(upper_mnt);
 914         if (IS_ERR(upper_mnt)) {
 915                 pr_err("overlayfs: failed to clone upperpath\n");
 916                 goto out;
 917         }
 918
 919         /* Don't inherit atime flags */
 920         upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);
 921         ofs->upper_mnt = upper_mnt;
 922         err = 0;
 923 out:
 924         return err;
 925 }
 926
 927 static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
 928 {
 929         struct vfsmount *mnt = ofs->upper_mnt;
 930         struct dentry *temp;
 931         int err;
 932
 933         err = mnt_want_write(mnt);
 934         if (err)
 935                 return err;
 936
 937         ofs->workdir = ovl_workdir_create(ofs, OVL_WORKDIR_NAME, false);
 938         if (!ofs->workdir)
 939                 goto out;
 940
 941         /*
 942          * Upper should support d_type, else whiteouts are visible.  Given
 943          * workdir and upper are on same fs, we can do iterate_dir() on
 944          * workdir. This check requires successful creation of workdir in
 945          * previous step.
 946          */
 947         err = ovl_check_d_type_supported(workpath);
 948         if (err < 0)
 949                 goto out;
 950
 951         /*
 952          * We allowed this configuration and don't want to break users over
 953          * kernel upgrade. So warn instead of erroring out.
 954          */
 955         if (!err)
 956                 pr_warn("overlayfs: upper fs needs to support d_type.\n");
 957
 958         /* Check if upper/work fs supports O_TMPFILE */
 959         temp = ovl_do_tmpfile(ofs->workdir, S_IFREG | 0);
 960         ofs->tmpfile = !IS_ERR(temp);
 961         if (ofs->tmpfile)
 962                 dput(temp);
 963         else
 964                 pr_warn("overlayfs: upper fs does not support tmpfile.\n");
 965
 966         /*
 967          * Check if upper/work fs supports trusted.overlay.* xattr
 968          */
 969         err = ovl_do_setxattr(ofs->workdir, OVL_XATTR_OPAQUE, "0", 1, 0);
 970         if (err) {
 971                 ofs->noxattr = true;
 972                 ofs->config.index = false;
 973                 pr_warn("overlayfs: upper fs does not support xattr, falling back to index=off.\n");
 974                 err = 0;
 975         } else {
 976                 vfs_removexattr(ofs->workdir, OVL_XATTR_OPAQUE);
 977         }
 978
 979         /* Check if upper/work fs supports file handles */
 980         if (ofs->config.index &&
 981             !ovl_can_decode_fh(ofs->workdir->d_sb)) {
 982                 ofs->config.index = false;
 983                 pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
 984         }
 985
 986 out:
 987         mnt_drop_write(mnt);
 988         return err;
 989 }
 990
 991 static int ovl_get_workdir(struct ovl_fs *ofs, struct path *upperpath)
 992 {
 993         int err;
 994         struct path workpath = { };
 995
 996         err = ovl_mount_dir(ofs->config.workdir, &workpath);
 997         if (err)
 998                 goto out;
 999
1000         err = -EINVAL;
1001         if (upperpath->mnt != workpath.mnt) {
1002                 pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
1003                 goto out;
1004         }
1005         if (!ovl_workdir_ok(workpath.dentry, upperpath->dentry)) {
1006                 pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
1007                 goto out;
1008         }
1009
1010         err = -EBUSY;
1011         if (ovl_inuse_trylock(workpath.dentry)) {
1012                 ofs->workdir_locked = true;
1013         } else if (ofs->config.index) {
1014                 pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
1015                 goto out;
1016         } else {
1017                 pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
1018         }
1019
1020         ofs->workbasedir = dget(workpath.dentry);
1021         err = ovl_make_workdir(ofs, &workpath);
1022         if (err)
1023                 goto out;
1024
1025         err = 0;
1026 out:
1027         path_put(&workpath);
1028
1029         return err;
1030 }
1031
1032 static int ovl_get_indexdir(struct ovl_fs *ofs, struct ovl_entry *oe,
1033                             struct path *upperpath)
1034 {
1035         struct vfsmount *mnt = ofs->upper_mnt;
1036         int err;
1037
1038         err = mnt_want_write(mnt);
1039         if (err)
1040                 return err;
1041
1042         /* Verify lower root is upper root origin */
1043         err = ovl_verify_origin(upperpath->dentry, oe->lowerstack[0].dentry,
1044                                 false, true);
1045         if (err) {
1046                 pr_err("overlayfs: failed to verify upper root origin\n");
1047                 goto out;
1048         }
1049
1050         ofs->indexdir = ovl_workdir_create(ofs, OVL_INDEXDIR_NAME, true);
1051         if (ofs->indexdir) {
1052                 /* Verify upper root is index dir origin */
1053                 err = ovl_verify_origin(ofs->indexdir, upperpath->dentry,
1054                                         true, true);
1055                 if (err)
1056                         pr_err("overlayfs: failed to verify index dir origin\n");
1057
1058                 /* Cleanup bad/stale/orphan index entries */
1059                 if (!err)
1060                         err = ovl_indexdir_cleanup(ofs->indexdir,
1061                                                    ofs->upper_mnt,
1062                                                    oe->lowerstack,
1063                                                    oe->numlower);
1064         }
1065         if (err || !ofs->indexdir)
1066                 pr_warn("overlayfs: try deleting index dir or mounting with '-o index=off' to disable inodes index.\n");
1067
1068 out:
1069         mnt_drop_write(mnt);
1070         return err;
1071 }
1072
1073 static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
1074                                 unsigned int numlower)
1075 {
1076         int err;
1077         unsigned int i;
1078
1079         err = -ENOMEM;
1080         ofs->lower_layers = kcalloc(numlower, sizeof(struct ovl_layer),
1081                                     GFP_KERNEL);
1082         if (ofs->lower_layers == NULL)
1083                 goto out;
1084         for (i = 0; i < numlower; i++) {
1085                 struct vfsmount *mnt;
1086                 dev_t dev;
1087
1088                 err = get_anon_bdev(&dev);
1089                 if (err) {
1090                         pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
1091                         goto out;
1092                 }
1093
1094                 mnt = clone_private_mount(&stack[i]);
1095                 err = PTR_ERR(mnt);
1096                 if (IS_ERR(mnt)) {
1097                         pr_err("overlayfs: failed to clone lowerpath\n");
1098                         free_anon_bdev(dev);
1099                         goto out;
1100                 }
1101                 /*
1102                  * Make lower layers R/O.  That way fchmod/fchown on lower file
1103                  * will fail instead of modifying lower fs.
1104                  */
1105                 mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
1106
1107                 ofs->lower_layers[ofs->numlower].mnt = mnt;
1108                 ofs->lower_layers[ofs->numlower].pseudo_dev = dev;
1109                 ofs->numlower++;
1110
1111                 /* Check if all lower layers are on same sb */
1112                 if (i == 0)
1113                         ofs->same_sb = mnt->mnt_sb;
1114                 else if (ofs->same_sb != mnt->mnt_sb)
1115                         ofs->same_sb = NULL;
1116         }
1117         err = 0;
1118 out:
1119         return err;
1120 }
1121
1122 static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
1123                                             struct ovl_fs *ofs)
1124 {
1125         int err;
1126         char *lowertmp, *lower;
1127         struct path *stack = NULL;
1128         unsigned int stacklen, numlower = 0, i;
1129         bool remote = false;
1130         struct ovl_entry *oe;
1131
1132         err = -ENOMEM;
1133         lowertmp = kstrdup(ofs->config.lowerdir, GFP_KERNEL);
1134         if (!lowertmp)
1135                 goto out_err;
1136
1137         err = -EINVAL;
1138         stacklen = ovl_split_lowerdirs(lowertmp);
1139         if (stacklen > OVL_MAX_STACK) {
1140                 pr_err("overlayfs: too many lower directories, limit is %d\n",
1141                        OVL_MAX_STACK);
1142                 goto out_err;
1143         } else if (!ofs->config.upperdir && stacklen == 1) {
1144                 pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
1145                 goto out_err;
1146         }
1147
1148         err = -ENOMEM;
1149         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
1150         if (!stack)
1151                 goto out_err;
1152
1153         err = -EINVAL;
1154         lower = lowertmp;
1155         for (numlower = 0; numlower < stacklen; numlower++) {
1156                 err = ovl_lower_dir(lower, &stack[numlower], ofs,
1157                                     &sb->s_stack_depth, &remote);
1158                 if (err)
1159                         goto out_err;
1160
1161                 lower = strchr(lower, '\0') + 1;
1162         }
1163
1164         err = -EINVAL;
1165         sb->s_stack_depth++;
1166         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
1167                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
1168                 goto out_err;
1169         }
1170
1171         err = ovl_get_lower_layers(ofs, stack, numlower);
1172         if (err)
1173                 goto out_err;
1174
1175         err = -ENOMEM;
1176         oe = ovl_alloc_entry(numlower);
1177         if (!oe)
1178                 goto out_err;
1179
1180         for (i = 0; i < numlower; i++) {
1181                 oe->lowerstack[i].dentry = dget(stack[i].dentry);
1182                 oe->lowerstack[i].layer = &ofs->lower_layers[i];
1183         }
1184
1185         if (remote)
1186                 sb->s_d_op = &ovl_reval_dentry_operations;
1187         else
1188                 sb->s_d_op = &ovl_dentry_operations;
1189
1190 out:
1191         for (i = 0; i < numlower; i++)
1192                 path_put(&stack[i]);
1193         kfree(stack);
1194         kfree(lowertmp);
1195
1196         return oe;
1197
1198 out_err:
1199         oe = ERR_PTR(err);
1200         goto out;
1201 }
1202
1203 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
1204 {
1205         struct path upperpath = { };
1206         struct dentry *root_dentry;
1207         struct ovl_entry *oe;
1208         struct ovl_fs *ofs;
1209         struct cred *cred;
1210         int err;
1211
1212         err = -ENOMEM;
1213         ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
1214         if (!ofs)
1215                 goto out;
1216
1217         ofs->creator_cred = cred = prepare_creds();
1218         if (!cred)
1219                 goto out_err;
1220
1221         ofs->config.index = ovl_index_def;
1222         err = ovl_parse_opt((char *) data, &ofs->config);
1223         if (err)
1224                 goto out_err;
1225
1226         err = -EINVAL;
1227         if (!ofs->config.lowerdir) {
1228                 if (!silent)
1229                         pr_err("overlayfs: missing 'lowerdir'\n");
1230                 goto out_err;
1231         }
1232
1233         sb->s_stack_depth = 0;
1234         sb->s_maxbytes = MAX_LFS_FILESIZE;
1235         if (ofs->config.upperdir) {
1236                 if (!ofs->config.workdir) {
1237                         pr_err("overlayfs: missing 'workdir'\n");
1238                         goto out_err;
1239                 }
1240
1241                 err = ovl_get_upper(ofs, &upperpath);
1242                 if (err)
1243                         goto out_err;
1244
1245                 err = ovl_get_workdir(ofs, &upperpath);
1246                 if (err)
1247                         goto out_err;
1248
1249                 if (!ofs->workdir)
1250                         sb->s_flags |= SB_RDONLY;
1251
1252                 sb->s_stack_depth = ofs->upper_mnt->mnt_sb->s_stack_depth;
1253                 sb->s_time_gran = ofs->upper_mnt->mnt_sb->s_time_gran;
1254
1255         }
1256         oe = ovl_get_lowerstack(sb, ofs);
1257         err = PTR_ERR(oe);
1258         if (IS_ERR(oe))
1259                 goto out_err;
1260
1261         /* If the upper fs is nonexistent, we mark overlayfs r/o too */
1262         if (!ofs->upper_mnt)
1263                 sb->s_flags |= SB_RDONLY;
1264         else if (ofs->upper_mnt->mnt_sb != ofs->same_sb)
1265                 ofs->same_sb = NULL;
1266
1267         if (!(ovl_force_readonly(ofs)) && ofs->config.index) {
1268                 err = ovl_get_indexdir(ofs, oe, &upperpath);
1269                 if (err)
1270                         goto out_free_oe;
1271
1272                 /* Force r/o mount with no index dir */
1273                 if (!ofs->indexdir) {
1274                         dput(ofs->workdir);
1275                         ofs->workdir = NULL;
1276                         sb->s_flags |= SB_RDONLY;
1277                 }
1278
1279         }
1280
1281         /* Show index=off in /proc/mounts for forced r/o mount */
1282         if (!ofs->indexdir)
1283                 ofs->config.index = false;
1284
1285         /* Never override disk quota limits or use reserved space */
1286         cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
1287
1288         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
1289         sb->s_op = &ovl_super_operations;
1290         sb->s_xattr = ovl_xattr_handlers;
1291         sb->s_fs_info = ofs;
1292         sb->s_flags |= SB_POSIXACL | SB_NOREMOTELOCK;
1293
1294         err = -ENOMEM;
1295         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
1296         if (!root_dentry)
1297                 goto out_free_oe;
1298
1299         mntput(upperpath.mnt);
1300         if (upperpath.dentry) {
1301                 oe->has_upper = true;
1302                 if (ovl_is_impuredir(upperpath.dentry))
1303                         ovl_set_flag(OVL_IMPURE, d_inode(root_dentry));
1304         }
1305
1306         root_dentry->d_fsdata = oe;
1307
1308         /* Root is always merge -> can have whiteouts */
1309         ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
1310         ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
1311                        ovl_dentry_lower(root_dentry));
1312
1313         sb->s_root = root_dentry;
1314
1315         return 0;
1316
1317 out_free_oe:
1318         ovl_entry_stack_free(oe);
1319         kfree(oe);
1320 out_err:
1321         path_put(&upperpath);
1322         ovl_free_fs(ofs);
1323 out:
1324         return err;
1325 }
1326
1327 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
1328                                 const char *dev_name, void *raw_data)
1329 {
1330         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
1331 }
1332
1333 static struct file_system_type ovl_fs_type = {
1334         .owner          = THIS_MODULE,
1335         .name           = "overlay",
1336         .mount          = ovl_mount,
1337         .kill_sb        = kill_anon_super,
1338 };
1339 MODULE_ALIAS_FS("overlay");
1340
1341 static void ovl_inode_init_once(void *foo)
1342 {
1343         struct ovl_inode *oi = foo;
1344
1345         inode_init_once(&oi->vfs_inode);
1346 }
1347
1348 static int __init ovl_init(void)
1349 {
1350         int err;
1351
1352         ovl_inode_cachep = kmem_cache_create("ovl_inode",
1353                                              sizeof(struct ovl_inode), 0,
1354                                              (SLAB_RECLAIM_ACCOUNT|
1355                                               SLAB_MEM_SPREAD|SLAB_ACCOUNT),
1356                                              ovl_inode_init_once);
1357         if (ovl_inode_cachep == NULL)
1358                 return -ENOMEM;
1359
1360         err = register_filesystem(&ovl_fs_type);
1361         if (err)
1362                 kmem_cache_destroy(ovl_inode_cachep);
1363
1364         return err;
1365 }
1366
1367 static void __exit ovl_exit(void)
1368 {
1369         unregister_filesystem(&ovl_fs_type);
1370
1371         /*
1372          * Make sure all delayed rcu free inodes are flushed before we
1373          * destroy cache.
1374          */
1375         rcu_barrier();
1376         kmem_cache_destroy(ovl_inode_cachep);
1377
1378 }
1379
1380 module_init(ovl_init);
1381 module_exit(ovl_exit);