| 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 | inode_lock(parent->d_inode); |
| 147 | tmp = lookup_one_len(nbuf, parent, strlen(nbuf)); |
| 148 | inode_unlock(parent->d_inode); |
| 149 | if (IS_ERR(tmp)) { |
| 150 | dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp)); |
| 151 | goto out_err; |
| 152 | } |
| 153 | if (tmp != dentry) { |
| 154 | dput(tmp); |
| 155 | goto out_reconnected; |
| 156 | } |
| 157 | dput(tmp); |
| 158 | if (IS_ROOT(dentry)) { |
| 159 | err = -ESTALE; |
| 160 | goto out_err; |
| 161 | } |
| 162 | return parent; |
| 163 | |
| 164 | out_err: |
| 165 | dput(parent); |
| 166 | return ERR_PTR(err); |
| 167 | out_reconnected: |
| 168 | dput(parent); |
| 169 | /* |
| 170 | * Someone must have renamed our entry into another parent, in |
| 171 | * which case it has been reconnected by the rename. |
| 172 | * |
| 173 | * Or someone removed it entirely, in which case filehandle |
| 174 | * lookup will succeed but the directory is now IS_DEAD and |
| 175 | * subsequent operations on it will fail. |
| 176 | * |
| 177 | * Alternatively, maybe there was no race at all, and the |
| 178 | * filesystem is just corrupt and gave us a parent that doesn't |
| 179 | * actually contain any entry pointing to this inode. So, |
| 180 | * double check that this worked and return -ESTALE if not: |
| 181 | */ |
| 182 | if (!dentry_connected(dentry)) |
| 183 | return ERR_PTR(-ESTALE); |
| 184 | return NULL; |
| 185 | } |
| 186 | |
| 187 | /* |
| 188 | * Make sure target_dir is fully connected to the dentry tree. |
| 189 | * |
| 190 | * On successful return, DCACHE_DISCONNECTED will be cleared on |
| 191 | * target_dir, and target_dir->d_parent->...->d_parent will reach the |
| 192 | * root of the filesystem. |
| 193 | * |
| 194 | * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected. |
| 195 | * But the converse is not true: target_dir may have DCACHE_DISCONNECTED |
| 196 | * set but already be connected. In that case we'll verify the |
| 197 | * connection to root and then clear the flag. |
| 198 | * |
| 199 | * Note that target_dir could be removed by a concurrent operation. In |
| 200 | * that case reconnect_path may still succeed with target_dir fully |
| 201 | * connected, but further operations using the filehandle will fail when |
| 202 | * necessary (due to S_DEAD being set on the directory). |
| 203 | */ |
| 204 | static int |
| 205 | reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf) |
| 206 | { |
| 207 | struct dentry *dentry, *parent; |
| 208 | |
| 209 | dentry = dget(target_dir); |
| 210 | |
| 211 | while (dentry->d_flags & DCACHE_DISCONNECTED) { |
| 212 | BUG_ON(dentry == mnt->mnt_sb->s_root); |
| 213 | |
| 214 | if (IS_ROOT(dentry)) |
| 215 | parent = reconnect_one(mnt, dentry, nbuf); |
| 216 | else |
| 217 | parent = dget_parent(dentry); |
| 218 | |
| 219 | if (!parent) |
| 220 | break; |
| 221 | dput(dentry); |
| 222 | if (IS_ERR(parent)) |
| 223 | return PTR_ERR(parent); |
| 224 | dentry = parent; |
| 225 | } |
| 226 | dput(dentry); |
| 227 | clear_disconnected(target_dir); |
| 228 | return 0; |
| 229 | } |
| 230 | |
| 231 | struct getdents_callback { |
| 232 | struct dir_context ctx; |
| 233 | char *name; /* name that was found. It already points to a |
| 234 | buffer NAME_MAX+1 is size */ |
| 235 | u64 ino; /* the inum we are looking for */ |
| 236 | int found; /* inode matched? */ |
| 237 | int sequence; /* sequence counter */ |
| 238 | }; |
| 239 | |
| 240 | /* |
| 241 | * A rather strange filldir function to capture |
| 242 | * the name matching the specified inode number. |
| 243 | */ |
| 244 | static int filldir_one(struct dir_context *ctx, const char *name, int len, |
| 245 | loff_t pos, u64 ino, unsigned int d_type) |
| 246 | { |
| 247 | struct getdents_callback *buf = |
| 248 | container_of(ctx, struct getdents_callback, ctx); |
| 249 | int result = 0; |
| 250 | |
| 251 | buf->sequence++; |
| 252 | if (buf->ino == ino && len <= NAME_MAX) { |
| 253 | memcpy(buf->name, name, len); |
| 254 | buf->name[len] = '\0'; |
| 255 | buf->found = 1; |
| 256 | result = -1; |
| 257 | } |
| 258 | return result; |
| 259 | } |
| 260 | |
| 261 | /** |
| 262 | * get_name - default export_operations->get_name function |
| 263 | * @path: the directory in which to find a name |
| 264 | * @name: a pointer to a %NAME_MAX+1 char buffer to store the name |
| 265 | * @child: the dentry for the child directory. |
| 266 | * |
| 267 | * calls readdir on the parent until it finds an entry with |
| 268 | * the same inode number as the child, and returns that. |
| 269 | */ |
| 270 | static int get_name(const struct path *path, char *name, struct dentry *child) |
| 271 | { |
| 272 | const struct cred *cred = current_cred(); |
| 273 | struct inode *dir = path->dentry->d_inode; |
| 274 | int error; |
| 275 | struct file *file; |
| 276 | struct kstat stat; |
| 277 | struct path child_path = { |
| 278 | .mnt = path->mnt, |
| 279 | .dentry = child, |
| 280 | }; |
| 281 | struct getdents_callback buffer = { |
| 282 | .ctx.actor = filldir_one, |
| 283 | .name = name, |
| 284 | }; |
| 285 | |
| 286 | error = -ENOTDIR; |
| 287 | if (!dir || !S_ISDIR(dir->i_mode)) |
| 288 | goto out; |
| 289 | error = -EINVAL; |
| 290 | if (!dir->i_fop) |
| 291 | goto out; |
| 292 | /* |
| 293 | * inode->i_ino is unsigned long, kstat->ino is u64, so the |
| 294 | * former would be insufficient on 32-bit hosts when the |
| 295 | * filesystem supports 64-bit inode numbers. So we need to |
| 296 | * actually call ->getattr, not just read i_ino: |
| 297 | */ |
| 298 | error = vfs_getattr_nosec(&child_path, &stat); |
| 299 | if (error) |
| 300 | return error; |
| 301 | buffer.ino = stat.ino; |
| 302 | /* |
| 303 | * Open the directory ... |
| 304 | */ |
| 305 | file = dentry_open(path, O_RDONLY, cred); |
| 306 | error = PTR_ERR(file); |
| 307 | if (IS_ERR(file)) |
| 308 | goto out; |
| 309 | |
| 310 | error = -EINVAL; |
| 311 | if (!file->f_op->iterate) |
| 312 | goto out_close; |
| 313 | |
| 314 | buffer.sequence = 0; |
| 315 | while (1) { |
| 316 | int old_seq = buffer.sequence; |
| 317 | |
| 318 | error = iterate_dir(file, &buffer.ctx); |
| 319 | if (buffer.found) { |
| 320 | error = 0; |
| 321 | break; |
| 322 | } |
| 323 | |
| 324 | if (error < 0) |
| 325 | break; |
| 326 | |
| 327 | error = -ENOENT; |
| 328 | if (old_seq == buffer.sequence) |
| 329 | break; |
| 330 | } |
| 331 | |
| 332 | out_close: |
| 333 | fput(file); |
| 334 | out: |
| 335 | return error; |
| 336 | } |
| 337 | |
| 338 | /** |
| 339 | * export_encode_fh - default export_operations->encode_fh function |
| 340 | * @inode: the object to encode |
| 341 | * @fid: where to store the file handle fragment |
| 342 | * @max_len: maximum length to store there |
| 343 | * @parent: parent directory inode, if wanted |
| 344 | * |
| 345 | * This default encode_fh function assumes that the 32 inode number |
| 346 | * is suitable for locating an inode, and that the generation number |
| 347 | * can be used to check that it is still valid. It places them in the |
| 348 | * filehandle fragment where export_decode_fh expects to find them. |
| 349 | */ |
| 350 | static int export_encode_fh(struct inode *inode, struct fid *fid, |
| 351 | int *max_len, struct inode *parent) |
| 352 | { |
| 353 | int len = *max_len; |
| 354 | int type = FILEID_INO32_GEN; |
| 355 | |
| 356 | if (parent && (len < 4)) { |
| 357 | *max_len = 4; |
| 358 | return FILEID_INVALID; |
| 359 | } else if (len < 2) { |
| 360 | *max_len = 2; |
| 361 | return FILEID_INVALID; |
| 362 | } |
| 363 | |
| 364 | len = 2; |
| 365 | fid->i32.ino = inode->i_ino; |
| 366 | fid->i32.gen = inode->i_generation; |
| 367 | if (parent) { |
| 368 | fid->i32.parent_ino = parent->i_ino; |
| 369 | fid->i32.parent_gen = parent->i_generation; |
| 370 | len = 4; |
| 371 | type = FILEID_INO32_GEN_PARENT; |
| 372 | } |
| 373 | *max_len = len; |
| 374 | return type; |
| 375 | } |
| 376 | |
| 377 | int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid, |
| 378 | int *max_len, struct inode *parent) |
| 379 | { |
| 380 | const struct export_operations *nop = inode->i_sb->s_export_op; |
| 381 | |
| 382 | if (nop && nop->encode_fh) |
| 383 | return nop->encode_fh(inode, fid->raw, max_len, parent); |
| 384 | |
| 385 | return export_encode_fh(inode, fid, max_len, parent); |
| 386 | } |
| 387 | EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh); |
| 388 | |
| 389 | int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, |
| 390 | int connectable) |
| 391 | { |
| 392 | int error; |
| 393 | struct dentry *p = NULL; |
| 394 | struct inode *inode = dentry->d_inode, *parent = NULL; |
| 395 | |
| 396 | if (connectable && !S_ISDIR(inode->i_mode)) { |
| 397 | p = dget_parent(dentry); |
| 398 | /* |
| 399 | * note that while p might've ceased to be our parent already, |
| 400 | * it's still pinned by and still positive. |
| 401 | */ |
| 402 | parent = p->d_inode; |
| 403 | } |
| 404 | |
| 405 | error = exportfs_encode_inode_fh(inode, fid, max_len, parent); |
| 406 | dput(p); |
| 407 | |
| 408 | return error; |
| 409 | } |
| 410 | EXPORT_SYMBOL_GPL(exportfs_encode_fh); |
| 411 | |
| 412 | struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, |
| 413 | int fh_len, int fileid_type, |
| 414 | int (*acceptable)(void *, struct dentry *), void *context) |
| 415 | { |
| 416 | const struct export_operations *nop = mnt->mnt_sb->s_export_op; |
| 417 | struct dentry *result, *alias; |
| 418 | char nbuf[NAME_MAX+1]; |
| 419 | int err; |
| 420 | |
| 421 | /* |
| 422 | * Try to get any dentry for the given file handle from the filesystem. |
| 423 | */ |
| 424 | if (!nop || !nop->fh_to_dentry) |
| 425 | return ERR_PTR(-ESTALE); |
| 426 | result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type); |
| 427 | if (!result) |
| 428 | result = ERR_PTR(-ESTALE); |
| 429 | if (IS_ERR(result)) |
| 430 | return result; |
| 431 | |
| 432 | if (d_is_dir(result)) { |
| 433 | /* |
| 434 | * This request is for a directory. |
| 435 | * |
| 436 | * On the positive side there is only one dentry for each |
| 437 | * directory inode. On the negative side this implies that we |
| 438 | * to ensure our dentry is connected all the way up to the |
| 439 | * filesystem root. |
| 440 | */ |
| 441 | if (result->d_flags & DCACHE_DISCONNECTED) { |
| 442 | err = reconnect_path(mnt, result, nbuf); |
| 443 | if (err) |
| 444 | goto err_result; |
| 445 | } |
| 446 | |
| 447 | if (!acceptable(context, result)) { |
| 448 | err = -EACCES; |
| 449 | goto err_result; |
| 450 | } |
| 451 | |
| 452 | return result; |
| 453 | } else { |
| 454 | /* |
| 455 | * It's not a directory. Life is a little more complicated. |
| 456 | */ |
| 457 | struct dentry *target_dir, *nresult; |
| 458 | |
| 459 | /* |
| 460 | * See if either the dentry we just got from the filesystem |
| 461 | * or any alias for it is acceptable. This is always true |
| 462 | * if this filesystem is exported without the subtreecheck |
| 463 | * option. If the filesystem is exported with the subtree |
| 464 | * check option there's a fair chance we need to look at |
| 465 | * the parent directory in the file handle and make sure |
| 466 | * it's connected to the filesystem root. |
| 467 | */ |
| 468 | alias = find_acceptable_alias(result, acceptable, context); |
| 469 | if (alias) |
| 470 | return alias; |
| 471 | |
| 472 | /* |
| 473 | * Try to extract a dentry for the parent directory from the |
| 474 | * file handle. If this fails we'll have to give up. |
| 475 | */ |
| 476 | err = -ESTALE; |
| 477 | if (!nop->fh_to_parent) |
| 478 | goto err_result; |
| 479 | |
| 480 | target_dir = nop->fh_to_parent(mnt->mnt_sb, fid, |
| 481 | fh_len, fileid_type); |
| 482 | if (!target_dir) |
| 483 | goto err_result; |
| 484 | err = PTR_ERR(target_dir); |
| 485 | if (IS_ERR(target_dir)) |
| 486 | goto err_result; |
| 487 | |
| 488 | /* |
| 489 | * And as usual we need to make sure the parent directory is |
| 490 | * connected to the filesystem root. The VFS really doesn't |
| 491 | * like disconnected directories.. |
| 492 | */ |
| 493 | err = reconnect_path(mnt, target_dir, nbuf); |
| 494 | if (err) { |
| 495 | dput(target_dir); |
| 496 | goto err_result; |
| 497 | } |
| 498 | |
| 499 | /* |
| 500 | * Now that we've got both a well-connected parent and a |
| 501 | * dentry for the inode we're after, make sure that our |
| 502 | * inode is actually connected to the parent. |
| 503 | */ |
| 504 | err = exportfs_get_name(mnt, target_dir, nbuf, result); |
| 505 | if (!err) { |
| 506 | inode_lock(target_dir->d_inode); |
| 507 | nresult = lookup_one_len(nbuf, target_dir, |
| 508 | strlen(nbuf)); |
| 509 | inode_unlock(target_dir->d_inode); |
| 510 | if (!IS_ERR(nresult)) { |
| 511 | if (nresult->d_inode) { |
| 512 | dput(result); |
| 513 | result = nresult; |
| 514 | } else |
| 515 | dput(nresult); |
| 516 | } |
| 517 | } |
| 518 | |
| 519 | /* |
| 520 | * At this point we are done with the parent, but it's pinned |
| 521 | * by the child dentry anyway. |
| 522 | */ |
| 523 | dput(target_dir); |
| 524 | |
| 525 | /* |
| 526 | * And finally make sure the dentry is actually acceptable |
| 527 | * to NFSD. |
| 528 | */ |
| 529 | alias = find_acceptable_alias(result, acceptable, context); |
| 530 | if (!alias) { |
| 531 | err = -EACCES; |
| 532 | goto err_result; |
| 533 | } |
| 534 | |
| 535 | return alias; |
| 536 | } |
| 537 | |
| 538 | err_result: |
| 539 | dput(result); |
| 540 | return ERR_PTR(err); |
| 541 | } |
| 542 | EXPORT_SYMBOL_GPL(exportfs_decode_fh); |
| 543 | |
| 544 | MODULE_LICENSE("GPL"); |