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