1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Copyright (C) Neil Brown 2002 4 * Copyright (C) Christoph Hellwig 2007 5 * 6 * This file contains the code mapping from inodes to NFS file handles, 7 * and for mapping back from file handles to dentries. 8 * 9 * For details on why we do all the strange and hairy things in here 10 * take a look at Documentation/filesystems/nfs/exporting.rst. 11 */ 12 #include <linux/exportfs.h> 13 #include <linux/fs.h> 14 #include <linux/file.h> 15 #include <linux/module.h> 16 #include <linux/mount.h> 17 #include <linux/namei.h> 18 #include <linux/sched.h> 19 #include <linux/cred.h> 20 21 #define dprintk(fmt, args...) pr_debug(fmt, ##args) 22 23 24 static int get_name(const struct path *path, char *name, struct dentry *child); 25 26 27 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir, 28 char *name, struct dentry *child) 29 { 30 const struct export_operations *nop = dir->d_sb->s_export_op; 31 struct path path = {.mnt = mnt, .dentry = dir}; 32 33 if (nop->get_name) 34 return nop->get_name(dir, name, child); 35 else 36 return get_name(&path, name, child); 37 } 38 39 /* 40 * Check if the dentry or any of it's aliases is acceptable. 41 */ 42 static struct dentry * 43 find_acceptable_alias(struct dentry *result, 44 int (*acceptable)(void *context, struct dentry *dentry), 45 void *context) 46 { 47 struct dentry *dentry, *toput = NULL; 48 struct inode *inode; 49 50 if (acceptable(context, result)) 51 return result; 52 53 inode = result->d_inode; 54 spin_lock(&inode->i_lock); 55 hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) { 56 dget(dentry); 57 spin_unlock(&inode->i_lock); 58 if (toput) 59 dput(toput); 60 if (dentry != result && acceptable(context, dentry)) { 61 dput(result); 62 return dentry; 63 } 64 spin_lock(&inode->i_lock); 65 toput = dentry; 66 } 67 spin_unlock(&inode->i_lock); 68 69 if (toput) 70 dput(toput); 71 return NULL; 72 } 73 74 static bool dentry_connected(struct dentry *dentry) 75 { 76 dget(dentry); 77 while (dentry->d_flags & DCACHE_DISCONNECTED) { 78 struct dentry *parent = dget_parent(dentry); 79 80 dput(dentry); 81 if (dentry == parent) { 82 dput(parent); 83 return false; 84 } 85 dentry = parent; 86 } 87 dput(dentry); 88 return true; 89 } 90 91 static void clear_disconnected(struct dentry *dentry) 92 { 93 dget(dentry); 94 while (dentry->d_flags & DCACHE_DISCONNECTED) { 95 struct dentry *parent = dget_parent(dentry); 96 97 WARN_ON_ONCE(IS_ROOT(dentry)); 98 99 spin_lock(&dentry->d_lock); 100 dentry->d_flags &= ~DCACHE_DISCONNECTED; 101 spin_unlock(&dentry->d_lock); 102 103 dput(dentry); 104 dentry = parent; 105 } 106 dput(dentry); 107 } 108 109 /* 110 * Reconnect a directory dentry with its parent. 111 * 112 * This can return a dentry, or NULL, or an error. 113 * 114 * In the first case the returned dentry is the parent of the given 115 * dentry, and may itself need to be reconnected to its parent. 116 * 117 * In the NULL case, a concurrent VFS operation has either renamed or 118 * removed this directory. The concurrent operation has reconnected our 119 * dentry, so we no longer need to. 120 */ 121 static struct dentry *reconnect_one(struct vfsmount *mnt, 122 struct dentry *dentry, char *nbuf) 123 { 124 struct dentry *parent; 125 struct dentry *tmp; 126 int err; 127 128 parent = ERR_PTR(-EACCES); 129 inode_lock(dentry->d_inode); 130 if (mnt->mnt_sb->s_export_op->get_parent) 131 parent = mnt->mnt_sb->s_export_op->get_parent(dentry); 132 inode_unlock(dentry->d_inode); 133 134 if (IS_ERR(parent)) { 135 dprintk("get_parent of %lu failed, err %ld\n", 136 dentry->d_inode->i_ino, PTR_ERR(parent)); 137 return parent; 138 } 139 140 dprintk("%s: find name of %lu in %lu\n", __func__, 141 dentry->d_inode->i_ino, parent->d_inode->i_ino); 142 err = exportfs_get_name(mnt, parent, nbuf, dentry); 143 if (err == -ENOENT) 144 goto out_reconnected; 145 if (err) 146 goto out_err; 147 dprintk("%s: found name: %s\n", __func__, nbuf); 148 tmp = lookup_one_unlocked(mnt_idmap(mnt), nbuf, parent, strlen(nbuf)); 149 if (IS_ERR(tmp)) { 150 dprintk("lookup failed: %ld\n", PTR_ERR(tmp)); 151 err = PTR_ERR(tmp); 152 goto out_err; 153 } 154 if (tmp != dentry) { 155 /* 156 * Somebody has renamed it since exportfs_get_name(); 157 * great, since it could've only been renamed if it 158 * got looked up and thus connected, and it would 159 * remain connected afterwards. We are done. 160 */ 161 dput(tmp); 162 goto out_reconnected; 163 } 164 dput(tmp); 165 if (IS_ROOT(dentry)) { 166 err = -ESTALE; 167 goto out_err; 168 } 169 return parent; 170 171 out_err: 172 dput(parent); 173 return ERR_PTR(err); 174 out_reconnected: 175 dput(parent); 176 /* 177 * Someone must have renamed our entry into another parent, in 178 * which case it has been reconnected by the rename. 179 * 180 * Or someone removed it entirely, in which case filehandle 181 * lookup will succeed but the directory is now IS_DEAD and 182 * subsequent operations on it will fail. 183 * 184 * Alternatively, maybe there was no race at all, and the 185 * filesystem is just corrupt and gave us a parent that doesn't 186 * actually contain any entry pointing to this inode. So, 187 * double check that this worked and return -ESTALE if not: 188 */ 189 if (!dentry_connected(dentry)) 190 return ERR_PTR(-ESTALE); 191 return NULL; 192 } 193 194 /* 195 * Make sure target_dir is fully connected to the dentry tree. 196 * 197 * On successful return, DCACHE_DISCONNECTED will be cleared on 198 * target_dir, and target_dir->d_parent->...->d_parent will reach the 199 * root of the filesystem. 200 * 201 * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected. 202 * But the converse is not true: target_dir may have DCACHE_DISCONNECTED 203 * set but already be connected. In that case we'll verify the 204 * connection to root and then clear the flag. 205 * 206 * Note that target_dir could be removed by a concurrent operation. In 207 * that case reconnect_path may still succeed with target_dir fully 208 * connected, but further operations using the filehandle will fail when 209 * necessary (due to S_DEAD being set on the directory). 210 */ 211 static int 212 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf) 213 { 214 struct dentry *dentry, *parent; 215 216 dentry = dget(target_dir); 217 218 while (dentry->d_flags & DCACHE_DISCONNECTED) { 219 BUG_ON(dentry == mnt->mnt_sb->s_root); 220 221 if (IS_ROOT(dentry)) 222 parent = reconnect_one(mnt, dentry, nbuf); 223 else 224 parent = dget_parent(dentry); 225 226 if (!parent) 227 break; 228 dput(dentry); 229 if (IS_ERR(parent)) 230 return PTR_ERR(parent); 231 dentry = parent; 232 } 233 dput(dentry); 234 clear_disconnected(target_dir); 235 return 0; 236 } 237 238 struct getdents_callback { 239 struct dir_context ctx; 240 char *name; /* name that was found. It already points to a 241 buffer NAME_MAX+1 is size */ 242 u64 ino; /* the inum we are looking for */ 243 int found; /* inode matched? */ 244 int sequence; /* sequence counter */ 245 }; 246 247 /* 248 * A rather strange filldir function to capture 249 * the name matching the specified inode number. 250 */ 251 static bool filldir_one(struct dir_context *ctx, const char *name, int len, 252 loff_t pos, u64 ino, unsigned int d_type) 253 { 254 struct getdents_callback *buf = 255 container_of(ctx, struct getdents_callback, ctx); 256 257 buf->sequence++; 258 if (buf->ino == ino && len <= NAME_MAX && !is_dot_dotdot(name, len)) { 259 memcpy(buf->name, name, len); 260 buf->name[len] = '\0'; 261 buf->found = 1; 262 return false; // no more 263 } 264 return true; 265 } 266 267 /** 268 * get_name - default export_operations->get_name function 269 * @path: the directory in which to find a name 270 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name 271 * @child: the dentry for the child directory. 272 * 273 * calls readdir on the parent until it finds an entry with 274 * the same inode number as the child, and returns that. 275 */ 276 static int get_name(const struct path *path, char *name, struct dentry *child) 277 { 278 const struct cred *cred = current_cred(); 279 struct inode *dir = path->dentry->d_inode; 280 int error; 281 struct file *file; 282 struct kstat stat; 283 struct path child_path = { 284 .mnt = path->mnt, 285 .dentry = child, 286 }; 287 struct getdents_callback buffer = { 288 .ctx.actor = filldir_one, 289 .name = name, 290 }; 291 292 error = -ENOTDIR; 293 if (!dir || !S_ISDIR(dir->i_mode)) 294 goto out; 295 error = -EINVAL; 296 if (!dir->i_fop) 297 goto out; 298 /* 299 * inode->i_ino is unsigned long, kstat->ino is u64, so the 300 * former would be insufficient on 32-bit hosts when the 301 * filesystem supports 64-bit inode numbers. So we need to 302 * actually call ->getattr, not just read i_ino: 303 */ 304 error = vfs_getattr_nosec(&child_path, &stat, 305 STATX_INO, AT_STATX_SYNC_AS_STAT); 306 if (error) 307 return error; 308 buffer.ino = stat.ino; 309 /* 310 * Open the directory ... 311 */ 312 file = dentry_open(path, O_RDONLY, cred); 313 error = PTR_ERR(file); 314 if (IS_ERR(file)) 315 goto out; 316 317 error = -EINVAL; 318 if (!file->f_op->iterate_shared) 319 goto out_close; 320 321 buffer.sequence = 0; 322 while (1) { 323 int old_seq = buffer.sequence; 324 325 error = iterate_dir(file, &buffer.ctx); 326 if (buffer.found) { 327 error = 0; 328 break; 329 } 330 331 if (error < 0) 332 break; 333 334 error = -ENOENT; 335 if (old_seq == buffer.sequence) 336 break; 337 } 338 339 out_close: 340 fput(file); 341 out: 342 return error; 343 } 344 345 #define FILEID_INO64_GEN_LEN 3 346 347 /** 348 * exportfs_encode_ino64_fid - encode non-decodeable 64bit ino file id 349 * @inode: the object to encode 350 * @fid: where to store the file handle fragment 351 * @max_len: maximum length to store there (in 4 byte units) 352 * 353 * This generic function is used to encode a non-decodeable file id for 354 * fanotify for filesystems that do not support NFS export. 355 */ 356 static int exportfs_encode_ino64_fid(struct inode *inode, struct fid *fid, 357 int *max_len) 358 { 359 if (*max_len < FILEID_INO64_GEN_LEN) { 360 *max_len = FILEID_INO64_GEN_LEN; 361 return FILEID_INVALID; 362 } 363 364 fid->i64.ino = inode->i_ino; 365 fid->i64.gen = inode->i_generation; 366 *max_len = FILEID_INO64_GEN_LEN; 367 368 return FILEID_INO64_GEN; 369 } 370 371 /** 372 * exportfs_encode_inode_fh - encode a file handle from inode 373 * @inode: the object to encode 374 * @fid: where to store the file handle fragment 375 * @max_len: maximum length to store there 376 * @parent: parent directory inode, if wanted 377 * @flags: properties of the requested file handle 378 * 379 * Returns an enum fid_type or a negative errno. 380 */ 381 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid, 382 int *max_len, struct inode *parent, int flags) 383 { 384 const struct export_operations *nop = inode->i_sb->s_export_op; 385 386 if (!exportfs_can_encode_fh(nop, flags)) 387 return -EOPNOTSUPP; 388 389 if (!nop && (flags & EXPORT_FH_FID)) 390 return exportfs_encode_ino64_fid(inode, fid, max_len); 391 392 return nop->encode_fh(inode, fid->raw, max_len, parent); 393 } 394 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh); 395 396 /** 397 * exportfs_encode_fh - encode a file handle from dentry 398 * @dentry: the object to encode 399 * @fid: where to store the file handle fragment 400 * @max_len: maximum length to store there 401 * @flags: properties of the requested file handle 402 * 403 * Returns an enum fid_type or a negative errno. 404 */ 405 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, 406 int flags) 407 { 408 int error; 409 struct dentry *p = NULL; 410 struct inode *inode = dentry->d_inode, *parent = NULL; 411 412 if ((flags & EXPORT_FH_CONNECTABLE) && !S_ISDIR(inode->i_mode)) { 413 p = dget_parent(dentry); 414 /* 415 * note that while p might've ceased to be our parent already, 416 * it's still pinned by and still positive. 417 */ 418 parent = p->d_inode; 419 } 420 421 error = exportfs_encode_inode_fh(inode, fid, max_len, parent, flags); 422 dput(p); 423 424 return error; 425 } 426 EXPORT_SYMBOL_GPL(exportfs_encode_fh); 427 428 struct dentry * 429 exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, 430 int fileid_type, unsigned int flags, 431 int (*acceptable)(void *, struct dentry *), 432 void *context) 433 { 434 const struct export_operations *nop = mnt->mnt_sb->s_export_op; 435 struct dentry *result, *alias; 436 char nbuf[NAME_MAX+1]; 437 int err; 438 439 /* 440 * Try to get any dentry for the given file handle from the filesystem. 441 */ 442 if (!exportfs_can_decode_fh(nop)) 443 return ERR_PTR(-ESTALE); 444 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type); 445 if (IS_ERR_OR_NULL(result)) 446 return result; 447 448 if ((flags & EXPORT_FH_DIR_ONLY) && !d_is_dir(result)) { 449 err = -ENOTDIR; 450 goto err_result; 451 } 452 453 /* 454 * If no acceptance criteria was specified by caller, a disconnected 455 * dentry is also accepatable. Callers may use this mode to query if 456 * file handle is stale or to get a reference to an inode without 457 * risking the high overhead caused by directory reconnect. 458 */ 459 if (!acceptable) 460 return result; 461 462 if (d_is_dir(result)) { 463 /* 464 * This request is for a directory. 465 * 466 * On the positive side there is only one dentry for each 467 * directory inode. On the negative side this implies that we 468 * to ensure our dentry is connected all the way up to the 469 * filesystem root. 470 */ 471 if (result->d_flags & DCACHE_DISCONNECTED) { 472 err = reconnect_path(mnt, result, nbuf); 473 if (err) 474 goto err_result; 475 } 476 477 if (!acceptable(context, result)) { 478 err = -EACCES; 479 goto err_result; 480 } 481 482 return result; 483 } else { 484 /* 485 * It's not a directory. Life is a little more complicated. 486 */ 487 struct dentry *target_dir, *nresult; 488 489 /* 490 * See if either the dentry we just got from the filesystem 491 * or any alias for it is acceptable. This is always true 492 * if this filesystem is exported without the subtreecheck 493 * option. If the filesystem is exported with the subtree 494 * check option there's a fair chance we need to look at 495 * the parent directory in the file handle and make sure 496 * it's connected to the filesystem root. 497 */ 498 alias = find_acceptable_alias(result, acceptable, context); 499 if (alias) 500 return alias; 501 502 /* 503 * Try to extract a dentry for the parent directory from the 504 * file handle. If this fails we'll have to give up. 505 */ 506 err = -ESTALE; 507 if (!nop->fh_to_parent) 508 goto err_result; 509 510 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid, 511 fh_len, fileid_type); 512 if (!target_dir) 513 goto err_result; 514 err = PTR_ERR(target_dir); 515 if (IS_ERR(target_dir)) 516 goto err_result; 517 518 /* 519 * And as usual we need to make sure the parent directory is 520 * connected to the filesystem root. The VFS really doesn't 521 * like disconnected directories.. 522 */ 523 err = reconnect_path(mnt, target_dir, nbuf); 524 if (err) { 525 dput(target_dir); 526 goto err_result; 527 } 528 529 /* 530 * Now that we've got both a well-connected parent and a 531 * dentry for the inode we're after, make sure that our 532 * inode is actually connected to the parent. 533 */ 534 err = exportfs_get_name(mnt, target_dir, nbuf, result); 535 if (err) { 536 dput(target_dir); 537 goto err_result; 538 } 539 540 inode_lock(target_dir->d_inode); 541 nresult = lookup_one(mnt_idmap(mnt), nbuf, 542 target_dir, strlen(nbuf)); 543 if (!IS_ERR(nresult)) { 544 if (unlikely(nresult->d_inode != result->d_inode)) { 545 dput(nresult); 546 nresult = ERR_PTR(-ESTALE); 547 } 548 } 549 inode_unlock(target_dir->d_inode); 550 /* 551 * At this point we are done with the parent, but it's pinned 552 * by the child dentry anyway. 553 */ 554 dput(target_dir); 555 556 if (IS_ERR(nresult)) { 557 err = PTR_ERR(nresult); 558 goto err_result; 559 } 560 dput(result); 561 result = nresult; 562 563 /* 564 * And finally make sure the dentry is actually acceptable 565 * to NFSD. 566 */ 567 alias = find_acceptable_alias(result, acceptable, context); 568 if (!alias) { 569 err = -EACCES; 570 goto err_result; 571 } 572 573 return alias; 574 } 575 576 err_result: 577 dput(result); 578 return ERR_PTR(err); 579 } 580 EXPORT_SYMBOL_GPL(exportfs_decode_fh_raw); 581 582 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, 583 int fh_len, int fileid_type, 584 int (*acceptable)(void *, struct dentry *), 585 void *context) 586 { 587 struct dentry *ret; 588 589 ret = exportfs_decode_fh_raw(mnt, fid, fh_len, fileid_type, 0, 590 acceptable, context); 591 if (IS_ERR_OR_NULL(ret)) { 592 if (ret == ERR_PTR(-ENOMEM)) 593 return ret; 594 return ERR_PTR(-ESTALE); 595 } 596 return ret; 597 } 598 EXPORT_SYMBOL_GPL(exportfs_decode_fh); 599 600 MODULE_LICENSE("GPL"); 601