fs/overlayfs/readdir.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/slab.h>
  12 #include <linux/namei.h>
  13 #include <linux/file.h>
  14 #include <linux/xattr.h>
  15 #include <linux/rbtree.h>
  16 #include <linux/security.h>
  17 #include <linux/cred.h>
  18 #include "overlayfs.h"
  19
  20 struct ovl_cache_entry {
  21         unsigned int len;
  22         unsigned int type;
  23         u64 ino;
  24         struct list_head l_node;
  25         struct rb_node node;
  26         struct ovl_cache_entry *next_maybe_whiteout;
  27         bool is_whiteout;
  28         char name[];
  29 };
  30
  31 struct ovl_dir_cache {
  32         long refcount;
  33         u64 version;
  34         struct list_head entries;
  35 };
  36
  37 struct ovl_readdir_data {
  38         struct dir_context ctx;
  39         bool is_lowest;
  40         struct rb_root root;
  41         struct list_head *list;
  42         struct list_head middle;
  43         struct ovl_cache_entry *first_maybe_whiteout;
  44         int count;
  45         int err;
  46         bool d_type_supported;
  47 };
  48
  49 struct ovl_dir_file {
  50         bool is_real;
  51         bool is_upper;
  52         struct ovl_dir_cache *cache;
  53         struct list_head *cursor;
  54         struct file *realfile;
  55         struct file *upperfile;
  56 };
  57
  58 static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
  59 {
  60         return container_of(n, struct ovl_cache_entry, node);
  61 }
  62
  63 static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
  64                                                     const char *name, int len)
  65 {
  66         struct rb_node *node = root->rb_node;
  67         int cmp;
  68
  69         while (node) {
  70                 struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
  71
  72                 cmp = strncmp(name, p->name, len);
  73                 if (cmp > 0)
  74                         node = p->node.rb_right;
  75                 else if (cmp < 0 || len < p->len)
  76                         node = p->node.rb_left;
  77                 else
  78                         return p;
  79         }
  80
  81         return NULL;
  82 }
  83
  84 static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
  85                                                    const char *name, int len,
  86                                                    u64 ino, unsigned int d_type)
  87 {
  88         struct ovl_cache_entry *p;
  89         size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);
  90
  91         p = kmalloc(size, GFP_KERNEL);
  92         if (!p)
  93                 return NULL;
  94
  95         memcpy(p->name, name, len);
  96         p->name[len] = '\0';
  97         p->len = len;
  98         p->type = d_type;
  99         p->ino = ino;
 100         p->is_whiteout = false;
 101
 102         if (d_type == DT_CHR) {
 103                 p->next_maybe_whiteout = rdd->first_maybe_whiteout;
 104                 rdd->first_maybe_whiteout = p;
 105         }
 106         return p;
 107 }
 108
 109 static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
 110                                   const char *name, int len, u64 ino,
 111                                   unsigned int d_type)
 112 {
 113         struct rb_node **newp = &rdd->root.rb_node;
 114         struct rb_node *parent = NULL;
 115         struct ovl_cache_entry *p;
 116
 117         while (*newp) {
 118                 int cmp;
 119                 struct ovl_cache_entry *tmp;
 120
 121                 parent = *newp;
 122                 tmp = ovl_cache_entry_from_node(*newp);
 123                 cmp = strncmp(name, tmp->name, len);
 124                 if (cmp > 0)
 125                         newp = &tmp->node.rb_right;
 126                 else if (cmp < 0 || len < tmp->len)
 127                         newp = &tmp->node.rb_left;
 128                 else
 129                         return 0;
 130         }
 131
 132         p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
 133         if (p == NULL)
 134                 return -ENOMEM;
 135
 136         list_add_tail(&p->l_node, rdd->list);
 137         rb_link_node(&p->node, parent, newp);
 138         rb_insert_color(&p->node, &rdd->root);
 139
 140         return 0;
 141 }
 142
 143 static int ovl_fill_lowest(struct ovl_readdir_data *rdd,
 144                            const char *name, int namelen,
 145                            loff_t offset, u64 ino, unsigned int d_type)
 146 {
 147         struct ovl_cache_entry *p;
 148
 149         p = ovl_cache_entry_find(&rdd->root, name, namelen);
 150         if (p) {
 151                 list_move_tail(&p->l_node, &rdd->middle);
 152         } else {
 153                 p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
 154                 if (p == NULL)
 155                         rdd->err = -ENOMEM;
 156                 else
 157                         list_add_tail(&p->l_node, &rdd->middle);
 158         }
 159
 160         return rdd->err;
 161 }
 162
 163 void ovl_cache_free(struct list_head *list)
 164 {
 165         struct ovl_cache_entry *p;
 166         struct ovl_cache_entry *n;
 167
 168         list_for_each_entry_safe(p, n, list, l_node)
 169                 kfree(p);
 170
 171         INIT_LIST_HEAD(list);
 172 }
 173
 174 static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
 175 {
 176         struct ovl_dir_cache *cache = od->cache;
 177
 178         WARN_ON(cache->refcount <= 0);
 179         cache->refcount--;
 180         if (!cache->refcount) {
 181                 if (ovl_dir_cache(dentry) == cache)
 182                         ovl_set_dir_cache(dentry, NULL);
 183
 184                 ovl_cache_free(&cache->entries);
 185                 kfree(cache);
 186         }
 187 }
 188
 189 static int ovl_fill_merge(struct dir_context *ctx, const char *name,
 190                           int namelen, loff_t offset, u64 ino,
 191                           unsigned int d_type)
 192 {
 193         struct ovl_readdir_data *rdd =
 194                 container_of(ctx, struct ovl_readdir_data, ctx);
 195
 196         rdd->count++;
 197         if (!rdd->is_lowest)
 198                 return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
 199         else
 200                 return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
 201 }
 202
 203 static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
 204 {
 205         int err;
 206         struct ovl_cache_entry *p;
 207         struct dentry *dentry;
 208         const struct cred *old_cred;
 209         struct cred *override_cred;
 210
 211         override_cred = prepare_creds();
 212         if (!override_cred)
 213                 return -ENOMEM;
 214
 215         /*
 216          * CAP_DAC_OVERRIDE for lookup
 217          */
 218         cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
 219         old_cred = override_creds(override_cred);
 220
 221         inode_lock(dir->d_inode);
 222         err = 0;
 223         // XXX: err = mutex_lock_killable(&dir->d_inode->i_mutex);
 224         if (!err) {
 225                 while (rdd->first_maybe_whiteout) {
 226                         p = rdd->first_maybe_whiteout;
 227                         rdd->first_maybe_whiteout = p->next_maybe_whiteout;
 228                         dentry = lookup_one_len(p->name, dir, p->len);
 229                         if (!IS_ERR(dentry)) {
 230                                 p->is_whiteout = ovl_is_whiteout(dentry);
 231                                 dput(dentry);
 232                         }
 233                 }
 234                 inode_unlock(dir->d_inode);
 235         }
 236         revert_creds(old_cred);
 237         put_cred(override_cred);
 238
 239         return err;
 240 }
 241
 242 static inline int ovl_dir_read(struct path *realpath,
 243                                struct ovl_readdir_data *rdd)
 244 {
 245         struct file *realfile;
 246         int err;
 247
 248         realfile = ovl_path_open(realpath, O_RDONLY | O_DIRECTORY);
 249         if (IS_ERR(realfile))
 250                 return PTR_ERR(realfile);
 251
 252         rdd->first_maybe_whiteout = NULL;
 253         rdd->ctx.pos = 0;
 254         do {
 255                 rdd->count = 0;
 256                 rdd->err = 0;
 257                 err = iterate_dir(realfile, &rdd->ctx);
 258                 if (err >= 0)
 259                         err = rdd->err;
 260         } while (!err && rdd->count);
 261
 262         if (!err && rdd->first_maybe_whiteout)
 263                 err = ovl_check_whiteouts(realpath->dentry, rdd);
 264
 265         fput(realfile);
 266
 267         return err;
 268 }
 269
 270 static void ovl_dir_reset(struct file *file)
 271 {
 272         struct ovl_dir_file *od = file->private_data;
 273         struct ovl_dir_cache *cache = od->cache;
 274         struct dentry *dentry = file->f_path.dentry;
 275         enum ovl_path_type type = ovl_path_type(dentry);
 276
 277         if (cache && ovl_dentry_version_get(dentry) != cache->version) {
 278                 ovl_cache_put(od, dentry);
 279                 od->cache = NULL;
 280                 od->cursor = NULL;
 281         }
 282         WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
 283         if (od->is_real && OVL_TYPE_MERGE(type))
 284                 od->is_real = false;
 285 }
 286
 287 static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
 288 {
 289         int err;
 290         struct path realpath;
 291         struct ovl_readdir_data rdd = {
 292                 .ctx.actor = ovl_fill_merge,
 293                 .list = list,
 294                 .root = RB_ROOT,
 295                 .is_lowest = false,
 296         };
 297         int idx, next;
 298
 299         for (idx = 0; idx != -1; idx = next) {
 300                 next = ovl_path_next(idx, dentry, &realpath);
 301
 302                 if (next != -1) {
 303                         err = ovl_dir_read(&realpath, &rdd);
 304                         if (err)
 305                                 break;
 306                 } else {
 307                         /*
 308                          * Insert lowest layer entries before upper ones, this
 309                          * allows offsets to be reasonably constant
 310                          */
 311                         list_add(&rdd.middle, rdd.list);
 312                         rdd.is_lowest = true;
 313                         err = ovl_dir_read(&realpath, &rdd);
 314                         list_del(&rdd.middle);
 315                 }
 316         }
 317         return err;
 318 }
 319
 320 static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
 321 {
 322         struct list_head *p;
 323         loff_t off = 0;
 324
 325         list_for_each(p, &od->cache->entries) {
 326                 if (off >= pos)
 327                         break;
 328                 off++;
 329         }
 330         /* Cursor is safe since the cache is stable */
 331         od->cursor = p;
 332 }
 333
 334 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
 335 {
 336         int res;
 337         struct ovl_dir_cache *cache;
 338
 339         cache = ovl_dir_cache(dentry);
 340         if (cache && ovl_dentry_version_get(dentry) == cache->version) {
 341                 cache->refcount++;
 342                 return cache;
 343         }
 344         ovl_set_dir_cache(dentry, NULL);
 345
 346         cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
 347         if (!cache)
 348                 return ERR_PTR(-ENOMEM);
 349
 350         cache->refcount = 1;
 351         INIT_LIST_HEAD(&cache->entries);
 352
 353         res = ovl_dir_read_merged(dentry, &cache->entries);
 354         if (res) {
 355                 ovl_cache_free(&cache->entries);
 356                 kfree(cache);
 357                 return ERR_PTR(res);
 358         }
 359
 360         cache->version = ovl_dentry_version_get(dentry);
 361         ovl_set_dir_cache(dentry, cache);
 362
 363         return cache;
 364 }
 365
 366 static int ovl_iterate(struct file *file, struct dir_context *ctx)
 367 {
 368         struct ovl_dir_file *od = file->private_data;
 369         struct dentry *dentry = file->f_path.dentry;
 370         struct ovl_cache_entry *p;
 371
 372         if (!ctx->pos)
 373                 ovl_dir_reset(file);
 374
 375         if (od->is_real)
 376                 return iterate_dir(od->realfile, ctx);
 377
 378         if (!od->cache) {
 379                 struct ovl_dir_cache *cache;
 380
 381                 cache = ovl_cache_get(dentry);
 382                 if (IS_ERR(cache))
 383                         return PTR_ERR(cache);
 384
 385                 od->cache = cache;
 386                 ovl_seek_cursor(od, ctx->pos);
 387         }
 388
 389         while (od->cursor != &od->cache->entries) {
 390                 p = list_entry(od->cursor, struct ovl_cache_entry, l_node);
 391                 if (!p->is_whiteout)
 392                         if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
 393                                 break;
 394                 od->cursor = p->l_node.next;
 395                 ctx->pos++;
 396         }
 397         return 0;
 398 }
 399
 400 static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
 401 {
 402         loff_t res;
 403         struct ovl_dir_file *od = file->private_data;
 404
 405         inode_lock(file_inode(file));
 406         if (!file->f_pos)
 407                 ovl_dir_reset(file);
 408
 409         if (od->is_real) {
 410                 res = vfs_llseek(od->realfile, offset, origin);
 411                 file->f_pos = od->realfile->f_pos;
 412         } else {
 413                 res = -EINVAL;
 414
 415                 switch (origin) {
 416                 case SEEK_CUR:
 417                         offset += file->f_pos;
 418                         break;
 419                 case SEEK_SET:
 420                         break;
 421                 default:
 422                         goto out_unlock;
 423                 }
 424                 if (offset < 0)
 425                         goto out_unlock;
 426
 427                 if (offset != file->f_pos) {
 428                         file->f_pos = offset;
 429                         if (od->cache)
 430                                 ovl_seek_cursor(od, offset);
 431                 }
 432                 res = offset;
 433         }
 434 out_unlock:
 435         inode_unlock(file_inode(file));
 436
 437         return res;
 438 }
 439
 440 static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
 441                          int datasync)
 442 {
 443         struct ovl_dir_file *od = file->private_data;
 444         struct dentry *dentry = file->f_path.dentry;
 445         struct file *realfile = od->realfile;
 446
 447         /*
 448          * Need to check if we started out being a lower dir, but got copied up
 449          */
 450         if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
 451                 struct inode *inode = file_inode(file);
 452
 453                 realfile = lockless_dereference(od->upperfile);
 454                 if (!realfile) {
 455                         struct path upperpath;
 456
 457                         ovl_path_upper(dentry, &upperpath);
 458                         realfile = ovl_path_open(&upperpath, O_RDONLY);
 459                         smp_mb__before_spinlock();
 460                         inode_lock(inode);
 461                         if (!od->upperfile) {
 462                                 if (IS_ERR(realfile)) {
 463                                         inode_unlock(inode);
 464                                         return PTR_ERR(realfile);
 465                                 }
 466                                 od->upperfile = realfile;
 467                         } else {
 468                                 /* somebody has beaten us to it */
 469                                 if (!IS_ERR(realfile))
 470                                         fput(realfile);
 471                                 realfile = od->upperfile;
 472                         }
 473                         inode_unlock(inode);
 474                 }
 475         }
 476
 477         return vfs_fsync_range(realfile, start, end, datasync);
 478 }
 479
 480 static int ovl_dir_release(struct inode *inode, struct file *file)
 481 {
 482         struct ovl_dir_file *od = file->private_data;
 483
 484         if (od->cache) {
 485                 inode_lock(inode);
 486                 ovl_cache_put(od, file->f_path.dentry);
 487                 inode_unlock(inode);
 488         }
 489         fput(od->realfile);
 490         if (od->upperfile)
 491                 fput(od->upperfile);
 492         kfree(od);
 493
 494         return 0;
 495 }
 496
 497 static int ovl_dir_open(struct inode *inode, struct file *file)
 498 {
 499         struct path realpath;
 500         struct file *realfile;
 501         struct ovl_dir_file *od;
 502         enum ovl_path_type type;
 503
 504         od = kzalloc(sizeof(struct ovl_dir_file), GFP_KERNEL);
 505         if (!od)
 506                 return -ENOMEM;
 507
 508         type = ovl_path_real(file->f_path.dentry, &realpath);
 509         realfile = ovl_path_open(&realpath, file->f_flags);
 510         if (IS_ERR(realfile)) {
 511                 kfree(od);
 512                 return PTR_ERR(realfile);
 513         }
 514         od->realfile = realfile;
 515         od->is_real = !OVL_TYPE_MERGE(type);
 516         od->is_upper = OVL_TYPE_UPPER(type);
 517         file->private_data = od;
 518
 519         return 0;
 520 }
 521
 522 const struct file_operations ovl_dir_operations = {
 523         .read           = generic_read_dir,
 524         .open           = ovl_dir_open,
 525         .iterate        = ovl_iterate,
 526         .llseek         = ovl_dir_llseek,
 527         .fsync          = ovl_dir_fsync,
 528         .release        = ovl_dir_release,
 529 };
 530
 531 int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
 532 {
 533         int err;
 534         struct ovl_cache_entry *p;
 535
 536         err = ovl_dir_read_merged(dentry, list);
 537         if (err)
 538                 return err;
 539
 540         err = 0;
 541
 542         list_for_each_entry(p, list, l_node) {
 543                 if (p->is_whiteout)
 544                         continue;
 545
 546                 if (p->name[0] == '.') {
 547                         if (p->len == 1)
 548                                 continue;
 549                         if (p->len == 2 && p->name[1] == '.')
 550                                 continue;
 551                 }
 552                 err = -ENOTEMPTY;
 553                 break;
 554         }
 555
 556         return err;
 557 }
 558
 559 void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
 560 {
 561         struct ovl_cache_entry *p;
 562
 563         inode_lock_nested(upper->d_inode, I_MUTEX_CHILD);
 564         list_for_each_entry(p, list, l_node) {
 565                 struct dentry *dentry;
 566
 567                 if (!p->is_whiteout)
 568                         continue;
 569
 570                 dentry = lookup_one_len(p->name, upper, p->len);
 571                 if (IS_ERR(dentry)) {
 572                         pr_err("overlayfs: lookup '%s/%.*s' failed (%i)\n",
 573                                upper->d_name.name, p->len, p->name,
 574                                (int) PTR_ERR(dentry));
 575                         continue;
 576                 }
 577                 if (dentry->d_inode)
 578                         ovl_cleanup(upper->d_inode, dentry);
 579                 dput(dentry);
 580         }
 581         inode_unlock(upper->d_inode);
 582 }
 583
 584 static int ovl_check_d_type(struct dir_context *ctx, const char *name,
 585                           int namelen, loff_t offset, u64 ino,
 586                           unsigned int d_type)
 587 {
 588         struct ovl_readdir_data *rdd =
 589                 container_of(ctx, struct ovl_readdir_data, ctx);
 590
 591         /* Even if d_type is not supported, DT_DIR is returned for . and .. */
 592         if (!strncmp(name, ".", namelen) || !strncmp(name, "..", namelen))
 593                 return 0;
 594
 595         if (d_type != DT_UNKNOWN)
 596                 rdd->d_type_supported = true;
 597
 598         return 0;
 599 }
 600
 601 /*
 602  * Returns 1 if d_type is supported, 0 not supported/unknown. Negative values
 603  * if error is encountered.
 604  */
 605 int ovl_check_d_type_supported(struct path *realpath)
 606 {
 607         int err;
 608         struct ovl_readdir_data rdd = {
 609                 .ctx.actor = ovl_check_d_type,
 610                 .d_type_supported = false,
 611         };
 612
 613         err = ovl_dir_read(realpath, &rdd);
 614         if (err)
 615                 return err;
 616
 617         return rdd.d_type_supported;
 618 }