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         /* creds of process who forced instantiation of super block */
  46         const struct cred *creator_cred;
  47 };
  48
  49 struct ovl_dir_cache;
  50
  51 /* private information held for every overlayfs dentry */
  52 struct ovl_entry {
  53         struct dentry *__upperdentry;
  54         struct ovl_dir_cache *cache;
  55         union {
  56                 struct {
  57                         u64 version;
  58                         bool opaque;
  59                 };
  60                 struct rcu_head rcu;
  61         };
  62         unsigned numlower;
  63         struct path lowerstack[];
  64 };
  65
  66 #define OVL_MAX_STACK 500
  67
  68 static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
  69 {
  70         return oe->numlower ? oe->lowerstack[0].dentry : NULL;
  71 }
  72
  73 enum ovl_path_type ovl_path_type(struct dentry *dentry)
  74 {
  75         struct ovl_entry *oe = dentry->d_fsdata;
  76         enum ovl_path_type type = 0;
  77
  78         if (oe->__upperdentry) {
  79                 type = __OVL_PATH_UPPER;
  80
  81                 /*
  82                  * Non-dir dentry can hold lower dentry from previous
  83                  * location. Its purity depends only on opaque flag.
  84                  */
  85                 if (oe->numlower && S_ISDIR(dentry->d_inode->i_mode))
  86                         type |= __OVL_PATH_MERGE;
  87                 else if (!oe->opaque)
  88                         type |= __OVL_PATH_PURE;
  89         } else {
  90                 if (oe->numlower > 1)
  91                         type |= __OVL_PATH_MERGE;
  92         }
  93         return type;
  94 }
  95
  96 static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
  97 {
  98         return lockless_dereference(oe->__upperdentry);
  99 }
 100
 101 void ovl_path_upper(struct dentry *dentry, struct path *path)
 102 {
 103         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 104         struct ovl_entry *oe = dentry->d_fsdata;
 105
 106         path->mnt = ofs->upper_mnt;
 107         path->dentry = ovl_upperdentry_dereference(oe);
 108 }
 109
 110 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
 111 {
 112         enum ovl_path_type type = ovl_path_type(dentry);
 113
 114         if (!OVL_TYPE_UPPER(type))
 115                 ovl_path_lower(dentry, path);
 116         else
 117                 ovl_path_upper(dentry, path);
 118
 119         return type;
 120 }
 121
 122 struct dentry *ovl_dentry_upper(struct dentry *dentry)
 123 {
 124         struct ovl_entry *oe = dentry->d_fsdata;
 125
 126         return ovl_upperdentry_dereference(oe);
 127 }
 128
 129 struct dentry *ovl_dentry_lower(struct dentry *dentry)
 130 {
 131         struct ovl_entry *oe = dentry->d_fsdata;
 132
 133         return __ovl_dentry_lower(oe);
 134 }
 135
 136 struct dentry *ovl_dentry_real(struct dentry *dentry)
 137 {
 138         struct ovl_entry *oe = dentry->d_fsdata;
 139         struct dentry *realdentry;
 140
 141         realdentry = ovl_upperdentry_dereference(oe);
 142         if (!realdentry)
 143                 realdentry = __ovl_dentry_lower(oe);
 144
 145         return realdentry;
 146 }
 147
 148 struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
 149 {
 150         struct dentry *realdentry;
 151
 152         realdentry = ovl_upperdentry_dereference(oe);
 153         if (realdentry) {
 154                 *is_upper = true;
 155         } else {
 156                 realdentry = __ovl_dentry_lower(oe);
 157                 *is_upper = false;
 158         }
 159         return realdentry;
 160 }
 161
 162 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
 163 {
 164         struct ovl_entry *oe = dentry->d_fsdata;
 165
 166         return oe->cache;
 167 }
 168
 169 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 170 {
 171         struct ovl_entry *oe = dentry->d_fsdata;
 172
 173         oe->cache = cache;
 174 }
 175
 176 void ovl_path_lower(struct dentry *dentry, struct path *path)
 177 {
 178         struct ovl_entry *oe = dentry->d_fsdata;
 179
 180         *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
 181 }
 182
 183 int ovl_want_write(struct dentry *dentry)
 184 {
 185         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 186         return mnt_want_write(ofs->upper_mnt);
 187 }
 188
 189 void ovl_drop_write(struct dentry *dentry)
 190 {
 191         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 192         mnt_drop_write(ofs->upper_mnt);
 193 }
 194
 195 struct dentry *ovl_workdir(struct dentry *dentry)
 196 {
 197         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 198         return ofs->workdir;
 199 }
 200
 201 bool ovl_dentry_is_opaque(struct dentry *dentry)
 202 {
 203         struct ovl_entry *oe = dentry->d_fsdata;
 204         return oe->opaque;
 205 }
 206
 207 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
 208 {
 209         struct ovl_entry *oe = dentry->d_fsdata;
 210         oe->opaque = opaque;
 211 }
 212
 213 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 214 {
 215         struct ovl_entry *oe = dentry->d_fsdata;
 216
 217         WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
 218         WARN_ON(oe->__upperdentry);
 219         BUG_ON(!upperdentry->d_inode);
 220         /*
 221          * Make sure upperdentry is consistent before making it visible to
 222          * ovl_upperdentry_dereference().
 223          */
 224         smp_wmb();
 225         oe->__upperdentry = upperdentry;
 226 }
 227
 228 void ovl_dentry_version_inc(struct dentry *dentry)
 229 {
 230         struct ovl_entry *oe = dentry->d_fsdata;
 231
 232         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 233         oe->version++;
 234 }
 235
 236 u64 ovl_dentry_version_get(struct dentry *dentry)
 237 {
 238         struct ovl_entry *oe = dentry->d_fsdata;
 239
 240         WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 241         return oe->version;
 242 }
 243
 244 bool ovl_is_whiteout(struct dentry *dentry)
 245 {
 246         struct inode *inode = dentry->d_inode;
 247
 248         return inode && IS_WHITEOUT(inode);
 249 }
 250
 251 const struct cred *ovl_override_creds(struct super_block *sb)
 252 {
 253         struct ovl_fs *ofs = sb->s_fs_info;
 254
 255         return override_creds(ofs->creator_cred);
 256 }
 257
 258 static bool ovl_is_opaquedir(struct dentry *dentry)
 259 {
 260         int res;
 261         char val;
 262         struct inode *inode = dentry->d_inode;
 263
 264         if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
 265                 return false;
 266
 267         res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
 268         if (res == 1 && val == 'y')
 269                 return true;
 270
 271         return false;
 272 }
 273
 274 static void ovl_dentry_release(struct dentry *dentry)
 275 {
 276         struct ovl_entry *oe = dentry->d_fsdata;
 277
 278         if (oe) {
 279                 unsigned int i;
 280
 281                 dput(oe->__upperdentry);
 282                 for (i = 0; i < oe->numlower; i++)
 283                         dput(oe->lowerstack[i].dentry);
 284                 kfree_rcu(oe, rcu);
 285         }
 286 }
 287
 288 static struct dentry *ovl_d_real(struct dentry *dentry, struct inode *inode)
 289 {
 290         struct dentry *real;
 291
 292         if (d_is_dir(dentry)) {
 293                 if (!inode || inode == d_inode(dentry))
 294                         return dentry;
 295                 goto bug;
 296         }
 297
 298         real = ovl_dentry_upper(dentry);
 299         if (real && (!inode || inode == d_inode(real)))
 300                 return real;
 301
 302         real = ovl_dentry_lower(dentry);
 303         if (!real)
 304                 goto bug;
 305
 306         if (!inode || inode == d_inode(real))
 307                 return real;
 308
 309         /* Handle recursion */
 310         if (real->d_flags & DCACHE_OP_REAL)
 311                 return real->d_op->d_real(real, inode);
 312
 313 bug:
 314         WARN(1, "ovl_d_real(%pd4, %s:%lu\n): real dentry not found\n", dentry,
 315              inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
 316         return dentry;
 317 }
 318
 319 static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
 320 {
 321         struct ovl_entry *oe = dentry->d_fsdata;
 322         unsigned int i;
 323         int ret = 1;
 324
 325         for (i = 0; i < oe->numlower; i++) {
 326                 struct dentry *d = oe->lowerstack[i].dentry;
 327
 328                 if (d->d_flags & DCACHE_OP_REVALIDATE) {
 329                         ret = d->d_op->d_revalidate(d, flags);
 330                         if (ret < 0)
 331                                 return ret;
 332                         if (!ret) {
 333                                 if (!(flags & LOOKUP_RCU))
 334                                         d_invalidate(d);
 335                                 return -ESTALE;
 336                         }
 337                 }
 338         }
 339         return 1;
 340 }
 341
 342 static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 343 {
 344         struct ovl_entry *oe = dentry->d_fsdata;
 345         unsigned int i;
 346         int ret = 1;
 347
 348         for (i = 0; i < oe->numlower; i++) {
 349                 struct dentry *d = oe->lowerstack[i].dentry;
 350
 351                 if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
 352                         ret = d->d_op->d_weak_revalidate(d, flags);
 353                         if (ret <= 0)
 354                                 break;
 355                 }
 356         }
 357         return ret;
 358 }
 359
 360 static const struct dentry_operations ovl_dentry_operations = {
 361         .d_release = ovl_dentry_release,
 362         .d_select_inode = ovl_d_select_inode,
 363         .d_real = ovl_d_real,
 364 };
 365
 366 static const struct dentry_operations ovl_reval_dentry_operations = {
 367         .d_release = ovl_dentry_release,
 368         .d_select_inode = ovl_d_select_inode,
 369         .d_real = ovl_d_real,
 370         .d_revalidate = ovl_dentry_revalidate,
 371         .d_weak_revalidate = ovl_dentry_weak_revalidate,
 372 };
 373
 374 static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 375 {
 376         size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
 377         struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
 378
 379         if (oe)
 380                 oe->numlower = numlower;
 381
 382         return oe;
 383 }
 384
 385 static bool ovl_dentry_remote(struct dentry *dentry)
 386 {
 387         return dentry->d_flags &
 388                 (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE |
 389                  DCACHE_OP_REAL);
 390 }
 391
 392 static bool ovl_dentry_weird(struct dentry *dentry)
 393 {
 394         return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
 395                                   DCACHE_MANAGE_TRANSIT |
 396                                   DCACHE_OP_HASH |
 397                                   DCACHE_OP_COMPARE);
 398 }
 399
 400 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
 401                                              struct qstr *name)
 402 {
 403         struct dentry *dentry;
 404
 405         mutex_lock(&dir->d_inode->i_mutex);
 406         dentry = lookup_one_len(name->name, dir, name->len);
 407         mutex_unlock(&dir->d_inode->i_mutex);
 408
 409         if (IS_ERR(dentry)) {
 410                 if (PTR_ERR(dentry) == -ENOENT)
 411                         dentry = NULL;
 412         } else if (!dentry->d_inode) {
 413                 dput(dentry);
 414                 dentry = NULL;
 415         } else if (ovl_dentry_weird(dentry)) {
 416                 dput(dentry);
 417                 /* Don't support traversing automounts and other weirdness */
 418                 dentry = ERR_PTR(-EREMOTE);
 419         }
 420         return dentry;
 421 }
 422
 423 /*
 424  * Returns next layer in stack starting from top.
 425  * Returns -1 if this is the last layer.
 426  */
 427 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 428 {
 429         struct ovl_entry *oe = dentry->d_fsdata;
 430
 431         BUG_ON(idx < 0);
 432         if (idx == 0) {
 433                 ovl_path_upper(dentry, path);
 434                 if (path->dentry)
 435                         return oe->numlower ? 1 : -1;
 436                 idx++;
 437         }
 438         BUG_ON(idx > oe->numlower);
 439         *path = oe->lowerstack[idx - 1];
 440
 441         return (idx < oe->numlower) ? idx + 1 : -1;
 442 }
 443
 444 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 445                           unsigned int flags)
 446 {
 447         struct ovl_entry *oe;
 448         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 449         struct path *stack = NULL;
 450         struct dentry *upperdir, *upperdentry = NULL;
 451         unsigned int ctr = 0;
 452         struct inode *inode = NULL;
 453         bool upperopaque = false;
 454         struct dentry *this, *prev = NULL;
 455         unsigned int i;
 456         int err;
 457
 458         upperdir = ovl_upperdentry_dereference(poe);
 459         if (upperdir) {
 460                 this = ovl_lookup_real(upperdir, &dentry->d_name);
 461                 err = PTR_ERR(this);
 462                 if (IS_ERR(this))
 463                         goto out;
 464
 465                 if (this) {
 466                         if (unlikely(ovl_dentry_remote(this))) {
 467                                 dput(this);
 468                                 err = -EREMOTE;
 469                                 goto out;
 470                         }
 471                         if (ovl_is_whiteout(this)) {
 472                                 dput(this);
 473                                 this = NULL;
 474                                 upperopaque = true;
 475                         } else if (poe->numlower && ovl_is_opaquedir(this)) {
 476                                 upperopaque = true;
 477                         }
 478                 }
 479                 upperdentry = prev = this;
 480         }
 481
 482         if (!upperopaque && poe->numlower) {
 483                 err = -ENOMEM;
 484                 stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
 485                 if (!stack)
 486                         goto out_put_upper;
 487         }
 488
 489         for (i = 0; !upperopaque && i < poe->numlower; i++) {
 490                 bool opaque = false;
 491                 struct path lowerpath = poe->lowerstack[i];
 492
 493                 this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
 494                 err = PTR_ERR(this);
 495                 if (IS_ERR(this)) {
 496                         /*
 497                          * If it's positive, then treat ENAMETOOLONG as ENOENT.
 498                          */
 499                         if (err == -ENAMETOOLONG && (upperdentry || ctr))
 500                                 continue;
 501                         goto out_put;
 502                 }
 503                 if (!this)
 504                         continue;
 505                 if (ovl_is_whiteout(this)) {
 506                         dput(this);
 507                         break;
 508                 }
 509                 /*
 510                  * Only makes sense to check opaque dir if this is not the
 511                  * lowermost layer.
 512                  */
 513                 if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
 514                         opaque = true;
 515
 516                 if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
 517                              !S_ISDIR(this->d_inode->i_mode))) {
 518                         /*
 519                          * FIXME: check for upper-opaqueness maybe better done
 520                          * in remove code.
 521                          */
 522                         if (prev == upperdentry)
 523                                 upperopaque = true;
 524                         dput(this);
 525                         break;
 526                 }
 527                 /*
 528                  * If this is a non-directory then stop here.
 529                  */
 530                 if (!S_ISDIR(this->d_inode->i_mode))
 531                         opaque = true;
 532
 533                 stack[ctr].dentry = this;
 534                 stack[ctr].mnt = lowerpath.mnt;
 535                 ctr++;
 536                 prev = this;
 537                 if (opaque)
 538                         break;
 539         }
 540
 541         oe = ovl_alloc_entry(ctr);
 542         err = -ENOMEM;
 543         if (!oe)
 544                 goto out_put;
 545
 546         if (upperdentry || ctr) {
 547                 struct dentry *realdentry;
 548
 549                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
 550
 551                 err = -ENOMEM;
 552                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
 553                                       oe);
 554                 if (!inode)
 555                         goto out_free_oe;
 556                 ovl_copyattr(realdentry->d_inode, inode);
 557         }
 558
 559         oe->opaque = upperopaque;
 560         oe->__upperdentry = upperdentry;
 561         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 562         kfree(stack);
 563         dentry->d_fsdata = oe;
 564         d_add(dentry, inode);
 565
 566         return NULL;
 567
 568 out_free_oe:
 569         kfree(oe);
 570 out_put:
 571         for (i = 0; i < ctr; i++)
 572                 dput(stack[i].dentry);
 573         kfree(stack);
 574 out_put_upper:
 575         dput(upperdentry);
 576 out:
 577         return ERR_PTR(err);
 578 }
 579
 580 struct file *ovl_path_open(struct path *path, int flags)
 581 {
 582         return dentry_open(path, flags, current_cred());
 583 }
 584
 585 static void ovl_put_super(struct super_block *sb)
 586 {
 587         struct ovl_fs *ufs = sb->s_fs_info;
 588         unsigned i;
 589
 590         dput(ufs->workdir);
 591         mntput(ufs->upper_mnt);
 592         for (i = 0; i < ufs->numlower; i++)
 593                 mntput(ufs->lower_mnt[i]);
 594         kfree(ufs->lower_mnt);
 595
 596         kfree(ufs->config.lowerdir);
 597         kfree(ufs->config.upperdir);
 598         kfree(ufs->config.workdir);
 599         put_cred(ufs->creator_cred);
 600         kfree(ufs);
 601 }
 602
 603 /**
 604  * ovl_statfs
 605  * @sb: The overlayfs super block
 606  * @buf: The struct kstatfs to fill in with stats
 607  *
 608  * Get the filesystem statistics.  As writes always target the upper layer
 609  * filesystem pass the statfs to the upper filesystem (if it exists)
 610  */
 611 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 612 {
 613         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 614         struct dentry *root_dentry = dentry->d_sb->s_root;
 615         struct path path;
 616         int err;
 617
 618         ovl_path_real(root_dentry, &path);
 619
 620         err = vfs_statfs(&path, buf);
 621         if (!err) {
 622                 buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
 623                 buf->f_type = OVERLAYFS_SUPER_MAGIC;
 624         }
 625
 626         return err;
 627 }
 628
 629 /**
 630  * ovl_show_options
 631  *
 632  * Prints the mount options for a given superblock.
 633  * Returns zero; does not fail.
 634  */
 635 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 636 {
 637         struct super_block *sb = dentry->d_sb;
 638         struct ovl_fs *ufs = sb->s_fs_info;
 639
 640         seq_show_option(m, "lowerdir", ufs->config.lowerdir);
 641         if (ufs->config.upperdir) {
 642                 seq_show_option(m, "upperdir", ufs->config.upperdir);
 643                 seq_show_option(m, "workdir", ufs->config.workdir);
 644         }
 645         return 0;
 646 }
 647
 648 static int ovl_remount(struct super_block *sb, int *flags, char *data)
 649 {
 650         struct ovl_fs *ufs = sb->s_fs_info;
 651
 652         if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
 653                 return -EROFS;
 654
 655         return 0;
 656 }
 657
 658 static const struct super_operations ovl_super_operations = {
 659         .put_super      = ovl_put_super,
 660         .statfs         = ovl_statfs,
 661         .show_options   = ovl_show_options,
 662         .remount_fs     = ovl_remount,
 663 };
 664
 665 enum {
 666         OPT_LOWERDIR,
 667         OPT_UPPERDIR,
 668         OPT_WORKDIR,
 669         OPT_ERR,
 670 };
 671
 672 static const match_table_t ovl_tokens = {
 673         {OPT_LOWERDIR,                  "lowerdir=%s"},
 674         {OPT_UPPERDIR,                  "upperdir=%s"},
 675         {OPT_WORKDIR,                   "workdir=%s"},
 676         {OPT_ERR,                       NULL}
 677 };
 678
 679 static char *ovl_next_opt(char **s)
 680 {
 681         char *sbegin = *s;
 682         char *p;
 683
 684         if (sbegin == NULL)
 685                 return NULL;
 686
 687         for (p = sbegin; *p; p++) {
 688                 if (*p == '\\') {
 689                         p++;
 690                         if (!*p)
 691                                 break;
 692                 } else if (*p == ',') {
 693                         *p = '\0';
 694                         *s = p + 1;
 695                         return sbegin;
 696                 }
 697         }
 698         *s = NULL;
 699         return sbegin;
 700 }
 701
 702 static int ovl_parse_opt(char *opt, struct ovl_config *config)
 703 {
 704         char *p;
 705
 706         while ((p = ovl_next_opt(&opt)) != NULL) {
 707                 int token;
 708                 substring_t args[MAX_OPT_ARGS];
 709
 710                 if (!*p)
 711                         continue;
 712
 713                 token = match_token(p, ovl_tokens, args);
 714                 switch (token) {
 715                 case OPT_UPPERDIR:
 716                         kfree(config->upperdir);
 717                         config->upperdir = match_strdup(&args[0]);
 718                         if (!config->upperdir)
 719                                 return -ENOMEM;
 720                         break;
 721
 722                 case OPT_LOWERDIR:
 723                         kfree(config->lowerdir);
 724                         config->lowerdir = match_strdup(&args[0]);
 725                         if (!config->lowerdir)
 726                                 return -ENOMEM;
 727                         break;
 728
 729                 case OPT_WORKDIR:
 730                         kfree(config->workdir);
 731                         config->workdir = match_strdup(&args[0]);
 732                         if (!config->workdir)
 733                                 return -ENOMEM;
 734                         break;
 735
 736                 default:
 737                         pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 738                         return -EINVAL;
 739                 }
 740         }
 741
 742         /* Workdir is useless in non-upper mount */
 743         if (!config->upperdir && config->workdir) {
 744                 pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
 745                         config->workdir);
 746                 kfree(config->workdir);
 747                 config->workdir = NULL;
 748         }
 749
 750         return 0;
 751 }
 752
 753 #define OVL_WORKDIR_NAME "work"
 754
 755 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
 756                                          struct dentry *dentry)
 757 {
 758         struct inode *dir = dentry->d_inode;
 759         struct dentry *work;
 760         int err;
 761         bool retried = false;
 762
 763         err = mnt_want_write(mnt);
 764         if (err)
 765                 return ERR_PTR(err);
 766
 767         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 768 retry:
 769         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
 770                               strlen(OVL_WORKDIR_NAME));
 771
 772         if (!IS_ERR(work)) {
 773                 struct kstat stat = {
 774                         .mode = S_IFDIR | 0,
 775                 };
 776                 struct iattr attr = {
 777                         .ia_valid = ATTR_MODE,
 778                         .ia_mode = stat.mode,
 779                 };
 780
 781                 if (work->d_inode) {
 782                         err = -EEXIST;
 783                         if (retried)
 784                                 goto out_dput;
 785
 786                         retried = true;
 787                         ovl_workdir_cleanup(dir, mnt, work, 0);
 788                         dput(work);
 789                         goto retry;
 790                 }
 791
 792                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
 793                 if (err)
 794                         goto out_dput;
 795
 796                 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
 797                 if (err && err != -ENODATA && err != -EOPNOTSUPP)
 798                         goto out_dput;
 799
 800                 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
 801                 if (err && err != -ENODATA && err != -EOPNOTSUPP)
 802                         goto out_dput;
 803
 804                 /* Clear any inherited mode bits */
 805                 inode_lock(work->d_inode);
 806                 err = notify_change(work, &attr, NULL);
 807                 inode_unlock(work->d_inode);
 808                 if (err)
 809                         goto out_dput;
 810         }
 811 out_unlock:
 812         mutex_unlock(&dir->i_mutex);
 813         mnt_drop_write(mnt);
 814
 815         return work;
 816
 817 out_dput:
 818         dput(work);
 819         work = ERR_PTR(err);
 820         goto out_unlock;
 821 }
 822
 823 static void ovl_unescape(char *s)
 824 {
 825         char *d = s;
 826
 827         for (;; s++, d++) {
 828                 if (*s == '\\')
 829                         s++;
 830                 *d = *s;
 831                 if (!*s)
 832                         break;
 833         }
 834 }
 835
 836 static int ovl_mount_dir_noesc(const char *name, struct path *path)
 837 {
 838         int err = -EINVAL;
 839
 840         if (!*name) {
 841                 pr_err("overlayfs: empty lowerdir\n");
 842                 goto out;
 843         }
 844         err = kern_path(name, LOOKUP_FOLLOW, path);
 845         if (err) {
 846                 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
 847                 goto out;
 848         }
 849         err = -EINVAL;
 850         if (ovl_dentry_weird(path->dentry)) {
 851                 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
 852                 goto out_put;
 853         }
 854         if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
 855                 pr_err("overlayfs: '%s' not a directory\n", name);
 856                 goto out_put;
 857         }
 858         return 0;
 859
 860 out_put:
 861         path_put(path);
 862 out:
 863         return err;
 864 }
 865
 866 static int ovl_mount_dir(const char *name, struct path *path)
 867 {
 868         int err = -ENOMEM;
 869         char *tmp = kstrdup(name, GFP_KERNEL);
 870
 871         if (tmp) {
 872                 ovl_unescape(tmp);
 873                 err = ovl_mount_dir_noesc(tmp, path);
 874
 875                 if (!err)
 876                         if (ovl_dentry_remote(path->dentry)) {
 877                                 pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
 878                                        tmp);
 879                                 path_put(path);
 880                                 err = -EINVAL;
 881                         }
 882                 kfree(tmp);
 883         }
 884         return err;
 885 }
 886
 887 static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
 888                          int *stack_depth, bool *remote)
 889 {
 890         int err;
 891         struct kstatfs statfs;
 892
 893         err = ovl_mount_dir_noesc(name, path);
 894         if (err)
 895                 goto out;
 896
 897         err = vfs_statfs(path, &statfs);
 898         if (err) {
 899                 pr_err("overlayfs: statfs failed on '%s'\n", name);
 900                 goto out_put;
 901         }
 902         *namelen = max(*namelen, statfs.f_namelen);
 903         *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
 904
 905         if (ovl_dentry_remote(path->dentry))
 906                 *remote = true;
 907
 908         return 0;
 909
 910 out_put:
 911         path_put(path);
 912 out:
 913         return err;
 914 }
 915
 916 /* Workdir should not be subdir of upperdir and vice versa */
 917 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 918 {
 919         bool ok = false;
 920
 921         if (workdir != upperdir) {
 922                 ok = (lock_rename(workdir, upperdir) == NULL);
 923                 unlock_rename(workdir, upperdir);
 924         }
 925         return ok;
 926 }
 927
 928 static unsigned int ovl_split_lowerdirs(char *str)
 929 {
 930         unsigned int ctr = 1;
 931         char *s, *d;
 932
 933         for (s = d = str;; s++, d++) {
 934                 if (*s == '\\') {
 935                         s++;
 936                 } else if (*s == ':') {
 937                         *d = '\0';
 938                         ctr++;
 939                         continue;
 940                 }
 941                 *d = *s;
 942                 if (!*s)
 943                         break;
 944         }
 945         return ctr;
 946 }
 947
 948 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 949 {
 950         struct path upperpath = { NULL, NULL };
 951         struct path workpath = { NULL, NULL };
 952         struct dentry *root_dentry;
 953         struct ovl_entry *oe;
 954         struct ovl_fs *ufs;
 955         struct path *stack = NULL;
 956         char *lowertmp;
 957         char *lower;
 958         unsigned int numlower;
 959         unsigned int stacklen = 0;
 960         unsigned int i;
 961         bool remote = false;
 962         int err;
 963
 964         err = -ENOMEM;
 965         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 966         if (!ufs)
 967                 goto out;
 968
 969         err = ovl_parse_opt((char *) data, &ufs->config);
 970         if (err)
 971                 goto out_free_config;
 972
 973         err = -EINVAL;
 974         if (!ufs->config.lowerdir) {
 975                 pr_err("overlayfs: missing 'lowerdir'\n");
 976                 goto out_free_config;
 977         }
 978
 979         sb->s_stack_depth = 0;
 980         sb->s_maxbytes = MAX_LFS_FILESIZE;
 981         if (ufs->config.upperdir) {
 982                 if (!ufs->config.workdir) {
 983                         pr_err("overlayfs: missing 'workdir'\n");
 984                         goto out_free_config;
 985                 }
 986
 987                 err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
 988                 if (err)
 989                         goto out_free_config;
 990
 991                 /* Upper fs should not be r/o */
 992                 if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
 993                         pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
 994                         err = -EINVAL;
 995                         goto out_put_upperpath;
 996                 }
 997
 998                 err = ovl_mount_dir(ufs->config.workdir, &workpath);
 999                 if (err)
1000                         goto out_put_upperpath;
1001
1002                 err = -EINVAL;
1003                 if (upperpath.mnt != workpath.mnt) {
1004                         pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
1005                         goto out_put_workpath;
1006                 }
1007                 if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
1008                         pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
1009                         goto out_put_workpath;
1010                 }
1011                 sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
1012         }
1013         err = -ENOMEM;
1014         lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
1015         if (!lowertmp)
1016                 goto out_put_workpath;
1017
1018         err = -EINVAL;
1019         stacklen = ovl_split_lowerdirs(lowertmp);
1020         if (stacklen > OVL_MAX_STACK) {
1021                 pr_err("overlayfs: too many lower directries, limit is %d\n",
1022                        OVL_MAX_STACK);
1023                 goto out_free_lowertmp;
1024         } else if (!ufs->config.upperdir && stacklen == 1) {
1025                 pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
1026                 goto out_free_lowertmp;
1027         }
1028
1029         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
1030         if (!stack)
1031                 goto out_free_lowertmp;
1032
1033         lower = lowertmp;
1034         for (numlower = 0; numlower < stacklen; numlower++) {
1035                 err = ovl_lower_dir(lower, &stack[numlower],
1036                                     &ufs->lower_namelen, &sb->s_stack_depth,
1037                                     &remote);
1038                 if (err)
1039                         goto out_put_lowerpath;
1040
1041                 lower = strchr(lower, '\0') + 1;
1042         }
1043
1044         err = -EINVAL;
1045         sb->s_stack_depth++;
1046         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
1047                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
1048                 goto out_put_lowerpath;
1049         }
1050
1051         if (ufs->config.upperdir) {
1052                 ufs->upper_mnt = clone_private_mount(&upperpath);
1053                 err = PTR_ERR(ufs->upper_mnt);
1054                 if (IS_ERR(ufs->upper_mnt)) {
1055                         pr_err("overlayfs: failed to clone upperpath\n");
1056                         goto out_put_lowerpath;
1057                 }
1058
1059                 ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
1060                 err = PTR_ERR(ufs->workdir);
1061                 if (IS_ERR(ufs->workdir)) {
1062                         pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
1063                                 ufs->config.workdir, OVL_WORKDIR_NAME, -err);
1064                         sb->s_flags |= MS_RDONLY;
1065                         ufs->workdir = NULL;
1066                 }
1067
1068                 /*
1069                  * Upper should support d_type, else whiteouts are visible.
1070                  * Given workdir and upper are on same fs, we can do
1071                  * iterate_dir() on workdir. This check requires successful
1072                  * creation of workdir in previous step.
1073                  */
1074                 if (ufs->workdir) {
1075                         err = ovl_check_d_type_supported(&workpath);
1076                         if (err < 0)
1077                                 goto out_put_workdir;
1078
1079                         /*
1080                          * We allowed this configuration and don't want to
1081                          * break users over kernel upgrade. So warn instead
1082                          * of erroring out.
1083                          */
1084                         if (!err)
1085                                 pr_warn("overlayfs: upper fs needs to support d_type.\n");
1086                 }
1087         }
1088
1089         err = -ENOMEM;
1090         ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
1091         if (ufs->lower_mnt == NULL)
1092                 goto out_put_workdir;
1093         for (i = 0; i < numlower; i++) {
1094                 struct vfsmount *mnt = clone_private_mount(&stack[i]);
1095
1096                 err = PTR_ERR(mnt);
1097                 if (IS_ERR(mnt)) {
1098                         pr_err("overlayfs: failed to clone lowerpath\n");
1099                         goto out_put_lower_mnt;
1100                 }
1101                 /*
1102                  * Make lower_mnt R/O.  That way fchmod/fchown on lower file
1103                  * will fail instead of modifying lower fs.
1104                  */
1105                 mnt->mnt_flags |= MNT_READONLY;
1106
1107                 ufs->lower_mnt[ufs->numlower] = mnt;
1108                 ufs->numlower++;
1109         }
1110
1111         /* If the upper fs is nonexistent, we mark overlayfs r/o too */
1112         if (!ufs->upper_mnt)
1113                 sb->s_flags |= MS_RDONLY;
1114
1115         if (remote)
1116                 sb->s_d_op = &ovl_reval_dentry_operations;
1117         else
1118                 sb->s_d_op = &ovl_dentry_operations;
1119
1120         ufs->creator_cred = prepare_creds();
1121         if (!ufs->creator_cred)
1122                 goto out_put_lower_mnt;
1123
1124         err = -ENOMEM;
1125         oe = ovl_alloc_entry(numlower);
1126         if (!oe)
1127                 goto out_put_cred;
1128
1129         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
1130         if (!root_dentry)
1131                 goto out_free_oe;
1132
1133         mntput(upperpath.mnt);
1134         for (i = 0; i < numlower; i++)
1135                 mntput(stack[i].mnt);
1136         path_put(&workpath);
1137         kfree(lowertmp);
1138
1139         oe->__upperdentry = upperpath.dentry;
1140         for (i = 0; i < numlower; i++) {
1141                 oe->lowerstack[i].dentry = stack[i].dentry;
1142                 oe->lowerstack[i].mnt = ufs->lower_mnt[i];
1143         }
1144         kfree(stack);
1145
1146         root_dentry->d_fsdata = oe;
1147
1148         ovl_copyattr(ovl_dentry_real(root_dentry)->d_inode,
1149                      root_dentry->d_inode);
1150
1151         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
1152         sb->s_op = &ovl_super_operations;
1153         sb->s_root = root_dentry;
1154         sb->s_fs_info = ufs;
1155
1156         return 0;
1157
1158 out_free_oe:
1159         kfree(oe);
1160 out_put_cred:
1161         put_cred(ufs->creator_cred);
1162 out_put_lower_mnt:
1163         for (i = 0; i < ufs->numlower; i++)
1164                 mntput(ufs->lower_mnt[i]);
1165         kfree(ufs->lower_mnt);
1166 out_put_workdir:
1167         dput(ufs->workdir);
1168         mntput(ufs->upper_mnt);
1169 out_put_lowerpath:
1170         for (i = 0; i < numlower; i++)
1171                 path_put(&stack[i]);
1172         kfree(stack);
1173 out_free_lowertmp:
1174         kfree(lowertmp);
1175 out_put_workpath:
1176         path_put(&workpath);
1177 out_put_upperpath:
1178         path_put(&upperpath);
1179 out_free_config:
1180         kfree(ufs->config.lowerdir);
1181         kfree(ufs->config.upperdir);
1182         kfree(ufs->config.workdir);
1183         kfree(ufs);
1184 out:
1185         return err;
1186 }
1187
1188 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
1189                                 const char *dev_name, void *raw_data)
1190 {
1191         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
1192 }
1193
1194 static struct file_system_type ovl_fs_type = {
1195         .owner          = THIS_MODULE,
1196         .name           = "overlay",
1197         .mount          = ovl_mount,
1198         .kill_sb        = kill_anon_super,
1199 };
1200 MODULE_ALIAS_FS("overlay");
1201
1202 static int __init ovl_init(void)
1203 {
1204         return register_filesystem(&ovl_fs_type);
1205 }
1206
1207 static void __exit ovl_exit(void)
1208 {
1209         unregister_filesystem(&ovl_fs_type);
1210 }
1211
1212 module_init(ovl_init);
1213 module_exit(ovl_exit);