fs/exportfs/expfs.c

   1 /*
   2  * Copyright (C) Neil Brown 2002
   3  * Copyright (C) Christoph Hellwig 2007
   4  *
   5  * This file contains the code mapping from inodes to NFS file handles,
   6  * and for mapping back from file handles to dentries.
   7  *
   8  * For details on why we do all the strange and hairy things in here
   9  * take a look at Documentation/filesystems/nfs/Exporting.
  10  */
  11 #include <linux/exportfs.h>
  12 #include <linux/fs.h>
  13 #include <linux/file.h>
  14 #include <linux/module.h>
  15 #include <linux/mount.h>
  16 #include <linux/namei.h>
  17 #include <linux/sched.h>
  18
  19 #define dprintk(fmt, args...) do{}while(0)
  20
  21
  22 static int get_name(const struct path *path, char *name, struct dentry *child);
  23
  24
  25 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
  26                 char *name, struct dentry *child)
  27 {
  28         const struct export_operations *nop = dir->d_sb->s_export_op;
  29         struct path path = {.mnt = mnt, .dentry = dir};
  30
  31         if (nop->get_name)
  32                 return nop->get_name(dir, name, child);
  33         else
  34                 return get_name(&path, name, child);
  35 }
  36
  37 /*
  38  * Check if the dentry or any of it's aliases is acceptable.
  39  */
  40 static struct dentry *
  41 find_acceptable_alias(struct dentry *result,
  42                 int (*acceptable)(void *context, struct dentry *dentry),
  43                 void *context)
  44 {
  45         struct dentry *dentry, *toput = NULL;
  46         struct inode *inode;
  47
  48         if (acceptable(context, result))
  49                 return result;
  50
  51         inode = result->d_inode;
  52         spin_lock(&inode->i_lock);
  53         hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
  54                 dget(dentry);
  55                 spin_unlock(&inode->i_lock);
  56                 if (toput)
  57                         dput(toput);
  58                 if (dentry != result && acceptable(context, dentry)) {
  59                         dput(result);
  60                         return dentry;
  61                 }
  62                 spin_lock(&inode->i_lock);
  63                 toput = dentry;
  64         }
  65         spin_unlock(&inode->i_lock);
  66
  67         if (toput)
  68                 dput(toput);
  69         return NULL;
  70 }
  71
  72 static bool dentry_connected(struct dentry *dentry)
  73 {
  74         dget(dentry);
  75         while (dentry->d_flags & DCACHE_DISCONNECTED) {
  76                 struct dentry *parent = dget_parent(dentry);
  77
  78                 dput(dentry);
  79                 if (IS_ROOT(dentry)) {
  80                         dput(parent);
  81                         return false;
  82                 }
  83                 dentry = parent;
  84         }
  85         dput(dentry);
  86         return true;
  87 }
  88
  89 static void clear_disconnected(struct dentry *dentry)
  90 {
  91         dget(dentry);
  92         while (dentry->d_flags & DCACHE_DISCONNECTED) {
  93                 struct dentry *parent = dget_parent(dentry);
  94
  95                 WARN_ON_ONCE(IS_ROOT(dentry));
  96
  97                 spin_lock(&dentry->d_lock);
  98                 dentry->d_flags &= ~DCACHE_DISCONNECTED;
  99                 spin_unlock(&dentry->d_lock);
 100
 101                 dput(dentry);
 102                 dentry = parent;
 103         }
 104         dput(dentry);
 105 }
 106
 107 /*
 108  * Reconnect a directory dentry with its parent.
 109  *
 110  * This can return a dentry, or NULL, or an error.
 111  *
 112  * In the first case the returned dentry is the parent of the given
 113  * dentry, and may itself need to be reconnected to its parent.
 114  *
 115  * In the NULL case, a concurrent VFS operation has either renamed or
 116  * removed this directory.  The concurrent operation has reconnected our
 117  * dentry, so we no longer need to.
 118  */
 119 static struct dentry *reconnect_one(struct vfsmount *mnt,
 120                 struct dentry *dentry, char *nbuf)
 121 {
 122         struct dentry *parent;
 123         struct dentry *tmp;
 124         int err;
 125
 126         parent = ERR_PTR(-EACCES);
 127         inode_lock(dentry->d_inode);
 128         if (mnt->mnt_sb->s_export_op->get_parent)
 129                 parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
 130         inode_unlock(dentry->d_inode);
 131
 132         if (IS_ERR(parent)) {
 133                 dprintk("%s: get_parent of %ld failed, err %d\n",
 134                         __func__, dentry->d_inode->i_ino, PTR_ERR(parent));
 135                 return parent;
 136         }
 137
 138         dprintk("%s: find name of %lu in %lu\n", __func__,
 139                 dentry->d_inode->i_ino, parent->d_inode->i_ino);
 140         err = exportfs_get_name(mnt, parent, nbuf, dentry);
 141         if (err == -ENOENT)
 142                 goto out_reconnected;
 143         if (err)
 144                 goto out_err;
 145         dprintk("%s: found name: %s\n", __func__, nbuf);
 146         tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
 147         if (IS_ERR(tmp)) {
 148                 dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
 149                 goto out_err;
 150         }
 151         if (tmp != dentry) {
 152                 /*
 153                  * Somebody has renamed it since exportfs_get_name();
 154                  * great, since it could've only been renamed if it
 155                  * got looked up and thus connected, and it would
 156                  * remain connected afterwards.  We are done.
 157                  */
 158                 dput(tmp);
 159                 goto out_reconnected;
 160         }
 161         dput(tmp);
 162         if (IS_ROOT(dentry)) {
 163                 err = -ESTALE;
 164                 goto out_err;
 165         }
 166         return parent;
 167
 168 out_err:
 169         dput(parent);
 170         return ERR_PTR(err);
 171 out_reconnected:
 172         dput(parent);
 173         /*
 174          * Someone must have renamed our entry into another parent, in
 175          * which case it has been reconnected by the rename.
 176          *
 177          * Or someone removed it entirely, in which case filehandle
 178          * lookup will succeed but the directory is now IS_DEAD and
 179          * subsequent operations on it will fail.
 180          *
 181          * Alternatively, maybe there was no race at all, and the
 182          * filesystem is just corrupt and gave us a parent that doesn't
 183          * actually contain any entry pointing to this inode.  So,
 184          * double check that this worked and return -ESTALE if not:
 185          */
 186         if (!dentry_connected(dentry))
 187                 return ERR_PTR(-ESTALE);
 188         return NULL;
 189 }
 190
 191 /*
 192  * Make sure target_dir is fully connected to the dentry tree.
 193  *
 194  * On successful return, DCACHE_DISCONNECTED will be cleared on
 195  * target_dir, and target_dir->d_parent->...->d_parent will reach the
 196  * root of the filesystem.
 197  *
 198  * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
 199  * But the converse is not true: target_dir may have DCACHE_DISCONNECTED
 200  * set but already be connected.  In that case we'll verify the
 201  * connection to root and then clear the flag.
 202  *
 203  * Note that target_dir could be removed by a concurrent operation.  In
 204  * that case reconnect_path may still succeed with target_dir fully
 205  * connected, but further operations using the filehandle will fail when
 206  * necessary (due to S_DEAD being set on the directory).
 207  */
 208 static int
 209 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
 210 {
 211         struct dentry *dentry, *parent;
 212
 213         dentry = dget(target_dir);
 214
 215         while (dentry->d_flags & DCACHE_DISCONNECTED) {
 216                 BUG_ON(dentry == mnt->mnt_sb->s_root);
 217
 218                 if (IS_ROOT(dentry))
 219                         parent = reconnect_one(mnt, dentry, nbuf);
 220                 else
 221                         parent = dget_parent(dentry);
 222
 223                 if (!parent)
 224                         break;
 225                 dput(dentry);
 226                 if (IS_ERR(parent))
 227                         return PTR_ERR(parent);
 228                 dentry = parent;
 229         }
 230         dput(dentry);
 231         clear_disconnected(target_dir);
 232         return 0;
 233 }
 234
 235 struct getdents_callback {
 236         struct dir_context ctx;
 237         char *name;             /* name that was found. It already points to a
 238                                    buffer NAME_MAX+1 is size */
 239         u64 ino;                /* the inum we are looking for */
 240         int found;              /* inode matched? */
 241         int sequence;           /* sequence counter */
 242 };
 243
 244 /*
 245  * A rather strange filldir function to capture
 246  * the name matching the specified inode number.
 247  */
 248 static int filldir_one(struct dir_context *ctx, const char *name, int len,
 249                         loff_t pos, u64 ino, unsigned int d_type)
 250 {
 251         struct getdents_callback *buf =
 252                 container_of(ctx, struct getdents_callback, ctx);
 253         int result = 0;
 254
 255         buf->sequence++;
 256         if (buf->ino == ino && len <= NAME_MAX) {
 257                 memcpy(buf->name, name, len);
 258                 buf->name[len] = '\0';
 259                 buf->found = 1;
 260                 result = -1;
 261         }
 262         return result;
 263 }
 264
 265 /**
 266  * get_name - default export_operations->get_name function
 267  * @path:   the directory in which to find a name
 268  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 269  * @child:  the dentry for the child directory.
 270  *
 271  * calls readdir on the parent until it finds an entry with
 272  * the same inode number as the child, and returns that.
 273  */
 274 static int get_name(const struct path *path, char *name, struct dentry *child)
 275 {
 276         const struct cred *cred = current_cred();
 277         struct inode *dir = path->dentry->d_inode;
 278         int error;
 279         struct file *file;
 280         struct kstat stat;
 281         struct path child_path = {
 282                 .mnt = path->mnt,
 283                 .dentry = child,
 284         };
 285         struct getdents_callback buffer = {
 286                 .ctx.actor = filldir_one,
 287                 .name = name,
 288         };
 289
 290         error = -ENOTDIR;
 291         if (!dir || !S_ISDIR(dir->i_mode))
 292                 goto out;
 293         error = -EINVAL;
 294         if (!dir->i_fop)
 295                 goto out;
 296         /*
 297          * inode->i_ino is unsigned long, kstat->ino is u64, so the
 298          * former would be insufficient on 32-bit hosts when the
 299          * filesystem supports 64-bit inode numbers.  So we need to
 300          * actually call ->getattr, not just read i_ino:
 301          */
 302         error = vfs_getattr_nosec(&child_path, &stat);
 303         if (error)
 304                 return error;
 305         buffer.ino = stat.ino;
 306         /*
 307          * Open the directory ...
 308          */
 309         file = dentry_open(path, O_RDONLY, cred);
 310         error = PTR_ERR(file);
 311         if (IS_ERR(file))
 312                 goto out;
 313
 314         error = -EINVAL;
 315         if (!file->f_op->iterate && !file->f_op->iterate_shared)
 316                 goto out_close;
 317
 318         buffer.sequence = 0;
 319         while (1) {
 320                 int old_seq = buffer.sequence;
 321
 322                 error = iterate_dir(file, &buffer.ctx);
 323                 if (buffer.found) {
 324                         error = 0;
 325                         break;
 326                 }
 327
 328                 if (error < 0)
 329                         break;
 330
 331                 error = -ENOENT;
 332                 if (old_seq == buffer.sequence)
 333                         break;
 334         }
 335
 336 out_close:
 337         fput(file);
 338 out:
 339         return error;
 340 }
 341
 342 /**
 343  * export_encode_fh - default export_operations->encode_fh function
 344  * @inode:   the object to encode
 345  * @fid:     where to store the file handle fragment
 346  * @max_len: maximum length to store there
 347  * @parent:  parent directory inode, if wanted
 348  *
 349  * This default encode_fh function assumes that the 32 inode number
 350  * is suitable for locating an inode, and that the generation number
 351  * can be used to check that it is still valid.  It places them in the
 352  * filehandle fragment where export_decode_fh expects to find them.
 353  */
 354 static int export_encode_fh(struct inode *inode, struct fid *fid,
 355                 int *max_len, struct inode *parent)
 356 {
 357         int len = *max_len;
 358         int type = FILEID_INO32_GEN;
 359
 360         if (parent && (len < 4)) {
 361                 *max_len = 4;
 362                 return FILEID_INVALID;
 363         } else if (len < 2) {
 364                 *max_len = 2;
 365                 return FILEID_INVALID;
 366         }
 367
 368         len = 2;
 369         fid->i32.ino = inode->i_ino;
 370         fid->i32.gen = inode->i_generation;
 371         if (parent) {
 372                 fid->i32.parent_ino = parent->i_ino;
 373                 fid->i32.parent_gen = parent->i_generation;
 374                 len = 4;
 375                 type = FILEID_INO32_GEN_PARENT;
 376         }
 377         *max_len = len;
 378         return type;
 379 }
 380
 381 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
 382                              int *max_len, struct inode *parent)
 383 {
 384         const struct export_operations *nop = inode->i_sb->s_export_op;
 385
 386         if (nop && nop->encode_fh)
 387                 return nop->encode_fh(inode, fid->raw, max_len, parent);
 388
 389         return export_encode_fh(inode, fid, max_len, parent);
 390 }
 391 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
 392
 393 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
 394                 int connectable)
 395 {
 396         int error;
 397         struct dentry *p = NULL;
 398         struct inode *inode = dentry->d_inode, *parent = NULL;
 399
 400         if (connectable && !S_ISDIR(inode->i_mode)) {
 401                 p = dget_parent(dentry);
 402                 /*
 403                  * note that while p might've ceased to be our parent already,
 404                  * it's still pinned by and still positive.
 405                  */
 406                 parent = p->d_inode;
 407         }
 408
 409         error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
 410         dput(p);
 411
 412         return error;
 413 }
 414 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
 415
 416 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
 417                 int fh_len, int fileid_type,
 418                 int (*acceptable)(void *, struct dentry *), void *context)
 419 {
 420         const struct export_operations *nop = mnt->mnt_sb->s_export_op;
 421         struct dentry *result, *alias;
 422         char nbuf[NAME_MAX+1];
 423         int err;
 424
 425         /*
 426          * Try to get any dentry for the given file handle from the filesystem.
 427          */
 428         if (!nop || !nop->fh_to_dentry)
 429                 return ERR_PTR(-ESTALE);
 430         result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
 431         if (PTR_ERR(result) == -ENOMEM)
 432                 return ERR_CAST(result);
 433         if (IS_ERR_OR_NULL(result))
 434                 return ERR_PTR(-ESTALE);
 435
 436         if (d_is_dir(result)) {
 437                 /*
 438                  * This request is for a directory.
 439                  *
 440                  * On the positive side there is only one dentry for each
 441                  * directory inode.  On the negative side this implies that we
 442                  * to ensure our dentry is connected all the way up to the
 443                  * filesystem root.
 444                  */
 445                 if (result->d_flags & DCACHE_DISCONNECTED) {
 446                         err = reconnect_path(mnt, result, nbuf);
 447                         if (err)
 448                                 goto err_result;
 449                 }
 450
 451                 if (!acceptable(context, result)) {
 452                         err = -EACCES;
 453                         goto err_result;
 454                 }
 455
 456                 return result;
 457         } else {
 458                 /*
 459                  * It's not a directory.  Life is a little more complicated.
 460                  */
 461                 struct dentry *target_dir, *nresult;
 462
 463                 /*
 464                  * See if either the dentry we just got from the filesystem
 465                  * or any alias for it is acceptable.  This is always true
 466                  * if this filesystem is exported without the subtreecheck
 467                  * option.  If the filesystem is exported with the subtree
 468                  * check option there's a fair chance we need to look at
 469                  * the parent directory in the file handle and make sure
 470                  * it's connected to the filesystem root.
 471                  */
 472                 alias = find_acceptable_alias(result, acceptable, context);
 473                 if (alias)
 474                         return alias;
 475
 476                 /*
 477                  * Try to extract a dentry for the parent directory from the
 478                  * file handle.  If this fails we'll have to give up.
 479                  */
 480                 err = -ESTALE;
 481                 if (!nop->fh_to_parent)
 482                         goto err_result;
 483
 484                 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
 485                                 fh_len, fileid_type);
 486                 if (!target_dir)
 487                         goto err_result;
 488                 err = PTR_ERR(target_dir);
 489                 if (IS_ERR(target_dir))
 490                         goto err_result;
 491
 492                 /*
 493                  * And as usual we need to make sure the parent directory is
 494                  * connected to the filesystem root.  The VFS really doesn't
 495                  * like disconnected directories..
 496                  */
 497                 err = reconnect_path(mnt, target_dir, nbuf);
 498                 if (err) {
 499                         dput(target_dir);
 500                         goto err_result;
 501                 }
 502
 503                 /*
 504                  * Now that we've got both a well-connected parent and a
 505                  * dentry for the inode we're after, make sure that our
 506                  * inode is actually connected to the parent.
 507                  */
 508                 err = exportfs_get_name(mnt, target_dir, nbuf, result);
 509                 if (!err) {
 510                         inode_lock(target_dir->d_inode);
 511                         nresult = lookup_one_len(nbuf, target_dir,
 512                                                  strlen(nbuf));
 513                         inode_unlock(target_dir->d_inode);
 514                         if (!IS_ERR(nresult)) {
 515                                 if (nresult->d_inode) {
 516                                         dput(result);
 517                                         result = nresult;
 518                                 } else
 519                                         dput(nresult);
 520                         }
 521                 }
 522
 523                 /*
 524                  * At this point we are done with the parent, but it's pinned
 525                  * by the child dentry anyway.
 526                  */
 527                 dput(target_dir);
 528
 529                 /*
 530                  * And finally make sure the dentry is actually acceptable
 531                  * to NFSD.
 532                  */
 533                 alias = find_acceptable_alias(result, acceptable, context);
 534                 if (!alias) {
 535                         err = -EACCES;
 536                         goto err_result;
 537                 }
 538
 539                 return alias;
 540         }
 541
 542  err_result:
 543         dput(result);
 544         if (err != -ENOMEM)
 545                 err = -ESTALE;
 546         return ERR_PTR(err);
 547 }
 548 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
 549
 550 MODULE_LICENSE("GPL");