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