kernel/fs/overlayfs/super.c

   1 /*
   2  *
   3  * Copyright (C) 2011 Novell Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 as published by
   7  * the Free Software Foundation.
   8  */
   9
  10 #include <linux/fs.h>
  11 #include <linux/namei.h>
  12 #include <linux/xattr.h>
  13 #include <linux/security.h>
  14 #include <linux/mount.h>
  15 #include <linux/slab.h>
  16 #include <linux/parser.h>
  17 #include <linux/module.h>
  18 #include <linux/sched.h>
  19 #include <linux/statfs.h>
  20 #include <linux/seq_file.h>
  21 #include "overlayfs.h"
  22
  23 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
  24 MODULE_DESCRIPTION("Overlay filesystem");
  25 MODULE_LICENSE("GPL");
  26
  27 #define OVERLAYFS_SUPER_MAGIC 0x794c7630
  28
  29 struct ovl_config {
  30         char *lowerdir;
  31         char *upperdir;
  32         char *workdir;
  33 };
  34
  35 /* private information held for overlayfs's superblock */
  36 struct ovl_fs {
  37         struct vfsmount *upper_mnt;
  38         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_show_option(m, "lowerdir", ufs->config.lowerdir);
 521         if (ufs->config.upperdir) {
 522                 seq_show_option(m, "upperdir", ufs->config.upperdir);
 523                 seq_show_option(m, "workdir", 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) && (!ufs->upper_mnt || !ufs->workdir))
 533                 return -EROFS;
 534
 535         return 0;
 536 }
 537
 538 static const struct super_operations ovl_super_operations = {
 539         .put_super      = ovl_put_super,
 540         .statfs         = ovl_statfs,
 541         .show_options   = ovl_show_options,
 542         .remount_fs     = ovl_remount,
 543 };
 544
 545 enum {
 546         OPT_LOWERDIR,
 547         OPT_UPPERDIR,
 548         OPT_WORKDIR,
 549         OPT_ERR,
 550 };
 551
 552 static const match_table_t ovl_tokens = {
 553         {OPT_LOWERDIR,                  "lowerdir=%s"},
 554         {OPT_UPPERDIR,                  "upperdir=%s"},
 555         {OPT_WORKDIR,                   "workdir=%s"},
 556         {OPT_ERR,                       NULL}
 557 };
 558
 559 static char *ovl_next_opt(char **s)
 560 {
 561         char *sbegin = *s;
 562         char *p;
 563
 564         if (sbegin == NULL)
 565                 return NULL;
 566
 567         for (p = sbegin; *p; p++) {
 568                 if (*p == '\\') {
 569                         p++;
 570                         if (!*p)
 571                                 break;
 572                 } else if (*p == ',') {
 573                         *p = '\0';
 574                         *s = p + 1;
 575                         return sbegin;
 576                 }
 577         }
 578         *s = NULL;
 579         return sbegin;
 580 }
 581
 582 static int ovl_parse_opt(char *opt, struct ovl_config *config)
 583 {
 584         char *p;
 585
 586         while ((p = ovl_next_opt(&opt)) != NULL) {
 587                 int token;
 588                 substring_t args[MAX_OPT_ARGS];
 589
 590                 if (!*p)
 591                         continue;
 592
 593                 token = match_token(p, ovl_tokens, args);
 594                 switch (token) {
 595                 case OPT_UPPERDIR:
 596                         kfree(config->upperdir);
 597                         config->upperdir = match_strdup(&args[0]);
 598                         if (!config->upperdir)
 599                                 return -ENOMEM;
 600                         break;
 601
 602                 case OPT_LOWERDIR:
 603                         kfree(config->lowerdir);
 604                         config->lowerdir = match_strdup(&args[0]);
 605                         if (!config->lowerdir)
 606                                 return -ENOMEM;
 607                         break;
 608
 609                 case OPT_WORKDIR:
 610                         kfree(config->workdir);
 611                         config->workdir = match_strdup(&args[0]);
 612                         if (!config->workdir)
 613                                 return -ENOMEM;
 614                         break;
 615
 616                 default:
 617                         pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 618                         return -EINVAL;
 619                 }
 620         }
 621
 622         /* Workdir is useless in non-upper mount */
 623         if (!config->upperdir && config->workdir) {
 624                 pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
 625                         config->workdir);
 626                 kfree(config->workdir);
 627                 config->workdir = NULL;
 628         }
 629
 630         return 0;
 631 }
 632
 633 #define OVL_WORKDIR_NAME "work"
 634
 635 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
 636                                          struct dentry *dentry)
 637 {
 638         struct inode *dir = dentry->d_inode;
 639         struct dentry *work;
 640         int err;
 641         bool retried = false;
 642
 643         err = mnt_want_write(mnt);
 644         if (err)
 645                 return ERR_PTR(err);
 646
 647         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 648 retry:
 649         work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
 650                               strlen(OVL_WORKDIR_NAME));
 651
 652         if (!IS_ERR(work)) {
 653                 struct kstat stat = {
 654                         .mode = S_IFDIR | 0,
 655                 };
 656
 657                 if (work->d_inode) {
 658                         err = -EEXIST;
 659                         if (retried)
 660                                 goto out_dput;
 661
 662                         retried = true;
 663                         ovl_cleanup(dir, work);
 664                         dput(work);
 665                         goto retry;
 666                 }
 667
 668                 err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
 669                 if (err)
 670                         goto out_dput;
 671         }
 672 out_unlock:
 673         mutex_unlock(&dir->i_mutex);
 674         mnt_drop_write(mnt);
 675
 676         return work;
 677
 678 out_dput:
 679         dput(work);
 680         work = ERR_PTR(err);
 681         goto out_unlock;
 682 }
 683
 684 static void ovl_unescape(char *s)
 685 {
 686         char *d = s;
 687
 688         for (;; s++, d++) {
 689                 if (*s == '\\')
 690                         s++;
 691                 *d = *s;
 692                 if (!*s)
 693                         break;
 694         }
 695 }
 696
 697 static bool ovl_is_allowed_fs_type(struct dentry *root)
 698 {
 699         const struct dentry_operations *dop = root->d_op;
 700
 701         /*
 702          * We don't support:
 703          *  - automount filesystems
 704          *  - filesystems with revalidate (FIXME for lower layer)
 705          *  - filesystems with case insensitive names
 706          */
 707         if (dop &&
 708             (dop->d_manage || dop->d_automount ||
 709              dop->d_revalidate || dop->d_weak_revalidate ||
 710              dop->d_compare || dop->d_hash)) {
 711                 return false;
 712         }
 713         return true;
 714 }
 715
 716 static int ovl_mount_dir_noesc(const char *name, struct path *path)
 717 {
 718         int err = -EINVAL;
 719
 720         if (!*name) {
 721                 pr_err("overlayfs: empty lowerdir\n");
 722                 goto out;
 723         }
 724         err = kern_path(name, LOOKUP_FOLLOW, path);
 725         if (err) {
 726                 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
 727                 goto out;
 728         }
 729         err = -EINVAL;
 730         if (!ovl_is_allowed_fs_type(path->dentry)) {
 731                 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
 732                 goto out_put;
 733         }
 734         if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
 735                 pr_err("overlayfs: '%s' not a directory\n", name);
 736                 goto out_put;
 737         }
 738         return 0;
 739
 740 out_put:
 741         path_put(path);
 742 out:
 743         return err;
 744 }
 745
 746 static int ovl_mount_dir(const char *name, struct path *path)
 747 {
 748         int err = -ENOMEM;
 749         char *tmp = kstrdup(name, GFP_KERNEL);
 750
 751         if (tmp) {
 752                 ovl_unescape(tmp);
 753                 err = ovl_mount_dir_noesc(tmp, path);
 754                 kfree(tmp);
 755         }
 756         return err;
 757 }
 758
 759 static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
 760                          int *stack_depth)
 761 {
 762         int err;
 763         struct kstatfs statfs;
 764
 765         err = ovl_mount_dir_noesc(name, path);
 766         if (err)
 767                 goto out;
 768
 769         err = vfs_statfs(path, &statfs);
 770         if (err) {
 771                 pr_err("overlayfs: statfs failed on '%s'\n", name);
 772                 goto out_put;
 773         }
 774         *namelen = max(*namelen, statfs.f_namelen);
 775         *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
 776
 777         return 0;
 778
 779 out_put:
 780         path_put(path);
 781 out:
 782         return err;
 783 }
 784
 785 /* Workdir should not be subdir of upperdir and vice versa */
 786 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 787 {
 788         bool ok = false;
 789
 790         if (workdir != upperdir) {
 791                 ok = (lock_rename(workdir, upperdir) == NULL);
 792                 unlock_rename(workdir, upperdir);
 793         }
 794         return ok;
 795 }
 796
 797 static unsigned int ovl_split_lowerdirs(char *str)
 798 {
 799         unsigned int ctr = 1;
 800         char *s, *d;
 801
 802         for (s = d = str;; s++, d++) {
 803                 if (*s == '\\') {
 804                         s++;
 805                 } else if (*s == ':') {
 806                         *d = '\0';
 807                         ctr++;
 808                         continue;
 809                 }
 810                 *d = *s;
 811                 if (!*s)
 812                         break;
 813         }
 814         return ctr;
 815 }
 816
 817 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 818 {
 819         struct path upperpath = { NULL, NULL };
 820         struct path workpath = { NULL, NULL };
 821         struct dentry *root_dentry;
 822         struct ovl_entry *oe;
 823         struct ovl_fs *ufs;
 824         struct path *stack = NULL;
 825         char *lowertmp;
 826         char *lower;
 827         unsigned int numlower;
 828         unsigned int stacklen = 0;
 829         unsigned int i;
 830         int err;
 831
 832         err = -ENOMEM;
 833         ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 834         if (!ufs)
 835                 goto out;
 836
 837         err = ovl_parse_opt((char *) data, &ufs->config);
 838         if (err)
 839                 goto out_free_config;
 840
 841         err = -EINVAL;
 842         if (!ufs->config.lowerdir) {
 843                 pr_err("overlayfs: missing 'lowerdir'\n");
 844                 goto out_free_config;
 845         }
 846
 847         sb->s_stack_depth = 0;
 848         if (ufs->config.upperdir) {
 849                 if (!ufs->config.workdir) {
 850                         pr_err("overlayfs: missing 'workdir'\n");
 851                         goto out_free_config;
 852                 }
 853
 854                 err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
 855                 if (err)
 856                         goto out_free_config;
 857
 858                 /* Upper fs should not be r/o */
 859                 if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
 860                         pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
 861                         err = -EINVAL;
 862                         goto out_put_upperpath;
 863                 }
 864
 865                 err = ovl_mount_dir(ufs->config.workdir, &workpath);
 866                 if (err)
 867                         goto out_put_upperpath;
 868
 869                 err = -EINVAL;
 870                 if (upperpath.mnt != workpath.mnt) {
 871                         pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
 872                         goto out_put_workpath;
 873                 }
 874                 if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
 875                         pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
 876                         goto out_put_workpath;
 877                 }
 878                 sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
 879         }
 880         err = -ENOMEM;
 881         lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
 882         if (!lowertmp)
 883                 goto out_put_workpath;
 884
 885         err = -EINVAL;
 886         stacklen = ovl_split_lowerdirs(lowertmp);
 887         if (stacklen > OVL_MAX_STACK) {
 888                 pr_err("overlayfs: too many lower directries, limit is %d\n",
 889                        OVL_MAX_STACK);
 890                 goto out_free_lowertmp;
 891         } else if (!ufs->config.upperdir && stacklen == 1) {
 892                 pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
 893                 goto out_free_lowertmp;
 894         }
 895
 896         stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
 897         if (!stack)
 898                 goto out_free_lowertmp;
 899
 900         lower = lowertmp;
 901         for (numlower = 0; numlower < stacklen; numlower++) {
 902                 err = ovl_lower_dir(lower, &stack[numlower],
 903                                     &ufs->lower_namelen, &sb->s_stack_depth);
 904                 if (err)
 905                         goto out_put_lowerpath;
 906
 907                 lower = strchr(lower, '\0') + 1;
 908         }
 909
 910         err = -EINVAL;
 911         sb->s_stack_depth++;
 912         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
 913                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
 914                 goto out_put_lowerpath;
 915         }
 916
 917         if (ufs->config.upperdir) {
 918                 ufs->upper_mnt = clone_private_mount(&upperpath);
 919                 err = PTR_ERR(ufs->upper_mnt);
 920                 if (IS_ERR(ufs->upper_mnt)) {
 921                         pr_err("overlayfs: failed to clone upperpath\n");
 922                         goto out_put_lowerpath;
 923                 }
 924
 925                 ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
 926                 err = PTR_ERR(ufs->workdir);
 927                 if (IS_ERR(ufs->workdir)) {
 928                         pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
 929                                 ufs->config.workdir, OVL_WORKDIR_NAME, -err);
 930                         sb->s_flags |= MS_RDONLY;
 931                         ufs->workdir = NULL;
 932                 }
 933         }
 934
 935         err = -ENOMEM;
 936         ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
 937         if (ufs->lower_mnt == NULL)
 938                 goto out_put_workdir;
 939         for (i = 0; i < numlower; i++) {
 940                 struct vfsmount *mnt = clone_private_mount(&stack[i]);
 941
 942                 err = PTR_ERR(mnt);
 943                 if (IS_ERR(mnt)) {
 944                         pr_err("overlayfs: failed to clone lowerpath\n");
 945                         goto out_put_lower_mnt;
 946                 }
 947                 /*
 948                  * Make lower_mnt R/O.  That way fchmod/fchown on lower file
 949                  * will fail instead of modifying lower fs.
 950                  */
 951                 mnt->mnt_flags |= MNT_READONLY;
 952
 953                 ufs->lower_mnt[ufs->numlower] = mnt;
 954                 ufs->numlower++;
 955         }
 956
 957         /* If the upper fs is nonexistent, we mark overlayfs r/o too */
 958         if (!ufs->upper_mnt)
 959                 sb->s_flags |= MS_RDONLY;
 960
 961         sb->s_d_op = &ovl_dentry_operations;
 962
 963         err = -ENOMEM;
 964         oe = ovl_alloc_entry(numlower);
 965         if (!oe)
 966                 goto out_put_lower_mnt;
 967
 968         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
 969         if (!root_dentry)
 970                 goto out_free_oe;
 971
 972         mntput(upperpath.mnt);
 973         for (i = 0; i < numlower; i++)
 974                 mntput(stack[i].mnt);
 975         path_put(&workpath);
 976         kfree(lowertmp);
 977
 978         oe->__upperdentry = upperpath.dentry;
 979         for (i = 0; i < numlower; i++) {
 980                 oe->lowerstack[i].dentry = stack[i].dentry;
 981                 oe->lowerstack[i].mnt = ufs->lower_mnt[i];
 982         }
 983
 984         root_dentry->d_fsdata = oe;
 985
 986         sb->s_magic = OVERLAYFS_SUPER_MAGIC;
 987         sb->s_op = &ovl_super_operations;
 988         sb->s_root = root_dentry;
 989         sb->s_fs_info = ufs;
 990
 991         return 0;
 992
 993 out_free_oe:
 994         kfree(oe);
 995 out_put_lower_mnt:
 996         for (i = 0; i < ufs->numlower; i++)
 997                 mntput(ufs->lower_mnt[i]);
 998         kfree(ufs->lower_mnt);
 999 out_put_workdir:
1000         dput(ufs->workdir);
1001         mntput(ufs->upper_mnt);
1002 out_put_lowerpath:
1003         for (i = 0; i < numlower; i++)
1004                 path_put(&stack[i]);
1005         kfree(stack);
1006 out_free_lowertmp:
1007         kfree(lowertmp);
1008 out_put_workpath:
1009         path_put(&workpath);
1010 out_put_upperpath:
1011         path_put(&upperpath);
1012 out_free_config:
1013         kfree(ufs->config.lowerdir);
1014         kfree(ufs->config.upperdir);
1015         kfree(ufs->config.workdir);
1016         kfree(ufs);
1017 out:
1018         return err;
1019 }
1020
1021 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
1022                                 const char *dev_name, void *raw_data)
1023 {
1024         return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
1025 }
1026
1027 static struct file_system_type ovl_fs_type = {
1028         .owner          = THIS_MODULE,
1029         .name           = "overlay",
1030         .mount          = ovl_mount,
1031         .kill_sb        = kill_anon_super,
1032 };
1033 MODULE_ALIAS_FS("overlay");
1034
1035 static int __init ovl_init(void)
1036 {
1037         return register_filesystem(&ovl_fs_type);
1038 }
1039
1040 static void __exit ovl_exit(void)
1041 {
1042         unregister_filesystem(&ovl_fs_type);
1043 }
1044
1045 module_init(ovl_init);
1046 module_exit(ovl_exit);