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         struct hlist_node *p;
  48
  49         if (acceptable(context, result))
  50                 return result;
  51
  52         inode = result->d_inode;
  53         spin_lock(&inode->i_lock);
  54         hlist_for_each_entry(dentry, p, &inode->i_dentry, d_alias) {
  55                 dget(dentry);
  56                 spin_unlock(&inode->i_lock);
  57                 if (toput)
  58                         dput(toput);
  59                 if (dentry != result && acceptable(context, dentry)) {
  60                         dput(result);
  61                         return dentry;
  62                 }
  63                 spin_lock(&inode->i_lock);
  64                 toput = dentry;
  65         }
  66         spin_unlock(&inode->i_lock);
  67
  68         if (toput)
  69                 dput(toput);
  70         return NULL;
  71 }
  72
  73 /*
  74  * Find root of a disconnected subtree and return a reference to it.
  75  */
  76 static struct dentry *
  77 find_disconnected_root(struct dentry *dentry)
  78 {
  79         dget(dentry);
  80         while (!IS_ROOT(dentry)) {
  81                 struct dentry *parent = dget_parent(dentry);
  82
  83                 if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
  84                         dput(parent);
  85                         break;
  86                 }
  87
  88                 dput(dentry);
  89                 dentry = parent;
  90         }
  91         return dentry;
  92 }
  93
  94 /*
  95  * Make sure target_dir is fully connected to the dentry tree.
  96  *
  97  * It may already be, as the flag isn't always updated when connection happens.
  98  */
  99 static int
 100 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
 101 {
 102         int noprogress = 0;
 103         int err = -ESTALE;
 104
 105         /*
 106          * It is possible that a confused file system might not let us complete
 107          * the path to the root.  For example, if get_parent returns a directory
 108          * in which we cannot find a name for the child.  While this implies a
 109          * very sick filesystem we don't want it to cause knfsd to spin.  Hence
 110          * the noprogress counter.  If we go through the loop 10 times (2 is
 111          * probably enough) without getting anywhere, we just give up
 112          */
 113         while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
 114                 struct dentry *pd = find_disconnected_root(target_dir);
 115
 116                 if (!IS_ROOT(pd)) {
 117                         /* must have found a connected parent - great */
 118                         spin_lock(&pd->d_lock);
 119                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 120                         spin_unlock(&pd->d_lock);
 121                         noprogress = 0;
 122                 } else if (pd == mnt->mnt_sb->s_root) {
 123                         printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
 124                         spin_lock(&pd->d_lock);
 125                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 126                         spin_unlock(&pd->d_lock);
 127                         noprogress = 0;
 128                 } else {
 129                         /*
 130                          * We have hit the top of a disconnected path, try to
 131                          * find parent and connect.
 132                          *
 133                          * Racing with some other process renaming a directory
 134                          * isn't much of a problem here.  If someone renames
 135                          * the directory, it will end up properly connected,
 136                          * which is what we want
 137                          *
 138                          * Getting the parent can't be supported generically,
 139                          * the locking is too icky.
 140                          *
 141                          * Instead we just return EACCES.  If server reboots
 142                          * or inodes get flushed, you lose
 143                          */
 144                         struct dentry *ppd = ERR_PTR(-EACCES);
 145                         struct dentry *npd;
 146
 147                         mutex_lock(&pd->d_inode->i_mutex);
 148                         if (mnt->mnt_sb->s_export_op->get_parent)
 149                                 ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
 150                         mutex_unlock(&pd->d_inode->i_mutex);
 151
 152                         if (IS_ERR(ppd)) {
 153                                 err = PTR_ERR(ppd);
 154                                 dprintk("%s: get_parent of %ld failed, err %d\n",
 155                                         __func__, pd->d_inode->i_ino, err);
 156                                 dput(pd);
 157                                 break;
 158                         }
 159
 160                         dprintk("%s: find name of %lu in %lu\n", __func__,
 161                                 pd->d_inode->i_ino, ppd->d_inode->i_ino);
 162                         err = exportfs_get_name(mnt, ppd, nbuf, pd);
 163                         if (err) {
 164                                 dput(ppd);
 165                                 dput(pd);
 166                                 if (err == -ENOENT)
 167                                         /* some race between get_parent and
 168                                          * get_name?  just try again
 169                                          */
 170                                         continue;
 171                                 break;
 172                         }
 173                         dprintk("%s: found name: %s\n", __func__, nbuf);
 174                         mutex_lock(&ppd->d_inode->i_mutex);
 175                         npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
 176                         mutex_unlock(&ppd->d_inode->i_mutex);
 177                         if (IS_ERR(npd)) {
 178                                 err = PTR_ERR(npd);
 179                                 dprintk("%s: lookup failed: %d\n",
 180                                         __func__, err);
 181                                 dput(ppd);
 182                                 dput(pd);
 183                                 break;
 184                         }
 185                         /* we didn't really want npd, we really wanted
 186                          * a side-effect of the lookup.
 187                          * hopefully, npd == pd, though it isn't really
 188                          * a problem if it isn't
 189                          */
 190                         if (npd == pd)
 191                                 noprogress = 0;
 192                         else
 193                                 printk("%s: npd != pd\n", __func__);
 194                         dput(npd);
 195                         dput(ppd);
 196                         if (IS_ROOT(pd)) {
 197                                 /* something went wrong, we have to give up */
 198                                 dput(pd);
 199                                 break;
 200                         }
 201                 }
 202                 dput(pd);
 203         }
 204
 205         if (target_dir->d_flags & DCACHE_DISCONNECTED) {
 206                 /* something went wrong - oh-well */
 207                 if (!err)
 208                         err = -ESTALE;
 209                 return err;
 210         }
 211
 212         return 0;
 213 }
 214
 215 struct getdents_callback {
 216         char *name;             /* name that was found. It already points to a
 217                                    buffer NAME_MAX+1 is size */
 218         unsigned long ino;      /* the inum we are looking for */
 219         int found;              /* inode matched? */
 220         int sequence;           /* sequence counter */
 221 };
 222
 223 /*
 224  * A rather strange filldir function to capture
 225  * the name matching the specified inode number.
 226  */
 227 static int filldir_one(void * __buf, const char * name, int len,
 228                         loff_t pos, u64 ino, unsigned int d_type)
 229 {
 230         struct getdents_callback *buf = __buf;
 231         int result = 0;
 232
 233         buf->sequence++;
 234         if (buf->ino == ino) {
 235                 memcpy(buf->name, name, len);
 236                 buf->name[len] = '\0';
 237                 buf->found = 1;
 238                 result = -1;
 239         }
 240         return result;
 241 }
 242
 243 /**
 244  * get_name - default export_operations->get_name function
 245  * @dentry: the directory in which to find a name
 246  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 247  * @child:  the dentry for the child directory.
 248  *
 249  * calls readdir on the parent until it finds an entry with
 250  * the same inode number as the child, and returns that.
 251  */
 252 static int get_name(const struct path *path, char *name, struct dentry *child)
 253 {
 254         const struct cred *cred = current_cred();
 255         struct inode *dir = path->dentry->d_inode;
 256         int error;
 257         struct file *file;
 258         struct getdents_callback buffer;
 259
 260         error = -ENOTDIR;
 261         if (!dir || !S_ISDIR(dir->i_mode))
 262                 goto out;
 263         error = -EINVAL;
 264         if (!dir->i_fop)
 265                 goto out;
 266         /*
 267          * Open the directory ...
 268          */
 269         file = dentry_open(path, O_RDONLY, cred);
 270         error = PTR_ERR(file);
 271         if (IS_ERR(file))
 272                 goto out;
 273
 274         error = -EINVAL;
 275         if (!file->f_op->readdir)
 276                 goto out_close;
 277
 278         buffer.name = name;
 279         buffer.ino = child->d_inode->i_ino;
 280         buffer.found = 0;
 281         buffer.sequence = 0;
 282         while (1) {
 283                 int old_seq = buffer.sequence;
 284
 285                 error = vfs_readdir(file, filldir_one, &buffer);
 286                 if (buffer.found) {
 287                         error = 0;
 288                         break;
 289                 }
 290
 291                 if (error < 0)
 292                         break;
 293
 294                 error = -ENOENT;
 295                 if (old_seq == buffer.sequence)
 296                         break;
 297         }
 298
 299 out_close:
 300         fput(file);
 301 out:
 302         return error;
 303 }
 304
 305 /**
 306  * export_encode_fh - default export_operations->encode_fh function
 307  * @inode:   the object to encode
 308  * @fh:      where to store the file handle fragment
 309  * @max_len: maximum length to store there
 310  * @parent:  parent directory inode, if wanted
 311  *
 312  * This default encode_fh function assumes that the 32 inode number
 313  * is suitable for locating an inode, and that the generation number
 314  * can be used to check that it is still valid.  It places them in the
 315  * filehandle fragment where export_decode_fh expects to find them.
 316  */
 317 static int export_encode_fh(struct inode *inode, struct fid *fid,
 318                 int *max_len, struct inode *parent)
 319 {
 320         int len = *max_len;
 321         int type = FILEID_INO32_GEN;
 322
 323         if (parent && (len < 4)) {
 324                 *max_len = 4;
 325                 return 255;
 326         } else if (len < 2) {
 327                 *max_len = 2;
 328                 return 255;
 329         }
 330
 331         len = 2;
 332         fid->i32.ino = inode->i_ino;
 333         fid->i32.gen = inode->i_generation;
 334         if (parent) {
 335                 fid->i32.parent_ino = parent->i_ino;
 336                 fid->i32.parent_gen = parent->i_generation;
 337                 len = 4;
 338                 type = FILEID_INO32_GEN_PARENT;
 339         }
 340         *max_len = len;
 341         return type;
 342 }
 343
 344 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
 345                 int connectable)
 346 {
 347         const struct export_operations *nop = dentry->d_sb->s_export_op;
 348         int error;
 349         struct dentry *p = NULL;
 350         struct inode *inode = dentry->d_inode, *parent = NULL;
 351
 352         if (connectable && !S_ISDIR(inode->i_mode)) {
 353                 p = dget_parent(dentry);
 354                 /*
 355                  * note that while p might've ceased to be our parent already,
 356                  * it's still pinned by and still positive.
 357                  */
 358                 parent = p->d_inode;
 359         }
 360         if (nop->encode_fh)
 361                 error = nop->encode_fh(inode, fid->raw, max_len, parent);
 362         else
 363                 error = export_encode_fh(inode, fid, max_len, parent);
 364         dput(p);
 365
 366         return error;
 367 }
 368 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
 369
 370 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
 371                 int fh_len, int fileid_type,
 372                 int (*acceptable)(void *, struct dentry *), void *context)
 373 {
 374         const struct export_operations *nop = mnt->mnt_sb->s_export_op;
 375         struct dentry *result, *alias;
 376         char nbuf[NAME_MAX+1];
 377         int err;
 378
 379         /*
 380          * Try to get any dentry for the given file handle from the filesystem.
 381          */
 382         if (!nop || !nop->fh_to_dentry)
 383                 return ERR_PTR(-ESTALE);
 384         result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
 385         if (!result)
 386                 result = ERR_PTR(-ESTALE);
 387         if (IS_ERR(result))
 388                 return result;
 389
 390         if (S_ISDIR(result->d_inode->i_mode)) {
 391                 /*
 392                  * This request is for a directory.
 393                  *
 394                  * On the positive side there is only one dentry for each
 395                  * directory inode.  On the negative side this implies that we
 396                  * to ensure our dentry is connected all the way up to the
 397                  * filesystem root.
 398                  */
 399                 if (result->d_flags & DCACHE_DISCONNECTED) {
 400                         err = reconnect_path(mnt, result, nbuf);
 401                         if (err)
 402                                 goto err_result;
 403                 }
 404
 405                 if (!acceptable(context, result)) {
 406                         err = -EACCES;
 407                         goto err_result;
 408                 }
 409
 410                 return result;
 411         } else {
 412                 /*
 413                  * It's not a directory.  Life is a little more complicated.
 414                  */
 415                 struct dentry *target_dir, *nresult;
 416
 417                 /*
 418                  * See if either the dentry we just got from the filesystem
 419                  * or any alias for it is acceptable.  This is always true
 420                  * if this filesystem is exported without the subtreecheck
 421                  * option.  If the filesystem is exported with the subtree
 422                  * check option there's a fair chance we need to look at
 423                  * the parent directory in the file handle and make sure
 424                  * it's connected to the filesystem root.
 425                  */
 426                 alias = find_acceptable_alias(result, acceptable, context);
 427                 if (alias)
 428                         return alias;
 429
 430                 /*
 431                  * Try to extract a dentry for the parent directory from the
 432                  * file handle.  If this fails we'll have to give up.
 433                  */
 434                 err = -ESTALE;
 435                 if (!nop->fh_to_parent)
 436                         goto err_result;
 437
 438                 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
 439                                 fh_len, fileid_type);
 440                 if (!target_dir)
 441                         goto err_result;
 442                 err = PTR_ERR(target_dir);
 443                 if (IS_ERR(target_dir))
 444                         goto err_result;
 445
 446                 /*
 447                  * And as usual we need to make sure the parent directory is
 448                  * connected to the filesystem root.  The VFS really doesn't
 449                  * like disconnected directories..
 450                  */
 451                 err = reconnect_path(mnt, target_dir, nbuf);
 452                 if (err) {
 453                         dput(target_dir);
 454                         goto err_result;
 455                 }
 456
 457                 /*
 458                  * Now that we've got both a well-connected parent and a
 459                  * dentry for the inode we're after, make sure that our
 460                  * inode is actually connected to the parent.
 461                  */
 462                 err = exportfs_get_name(mnt, target_dir, nbuf, result);
 463                 if (!err) {
 464                         mutex_lock(&target_dir->d_inode->i_mutex);
 465                         nresult = lookup_one_len(nbuf, target_dir,
 466                                                  strlen(nbuf));
 467                         mutex_unlock(&target_dir->d_inode->i_mutex);
 468                         if (!IS_ERR(nresult)) {
 469                                 if (nresult->d_inode) {
 470                                         dput(result);
 471                                         result = nresult;
 472                                 } else
 473                                         dput(nresult);
 474                         }
 475                 }
 476
 477                 /*
 478                  * At this point we are done with the parent, but it's pinned
 479                  * by the child dentry anyway.
 480                  */
 481                 dput(target_dir);
 482
 483                 /*
 484                  * And finally make sure the dentry is actually acceptable
 485                  * to NFSD.
 486                  */
 487                 alias = find_acceptable_alias(result, acceptable, context);
 488                 if (!alias) {
 489                         err = -EACCES;
 490                         goto err_result;
 491                 }
 492
 493                 return alias;
 494         }
 495
 496  err_result:
 497         dput(result);
 498         return ERR_PTR(err);
 499 }
 500 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
 501
 502 MODULE_LICENSE("GPL");