linux/fs/exportfs/expfs.c
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   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
  22static int get_name(const struct path *path, char *name, struct dentry *child);
  23
  24
  25static 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 */
  40static struct dentry *
  41find_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 */
  76static struct dentry *
  77find_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 */
  99static int
 100reconnect_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
 215struct 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 */
 227static 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 */
 252static 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
 299out_close:
 300        fput(file);
 301out:
 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 */
 317static 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
 344int 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}
 368EXPORT_SYMBOL_GPL(exportfs_encode_fh);
 369
 370struct 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}
 500EXPORT_SYMBOL_GPL(exportfs_decode_fh);
 501
 502MODULE_LICENSE("GPL");
 503
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