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