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...) do{}while(0) 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("%s: get_parent of %ld failed, err %d\n", 136 __func__, 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_user_ns(mnt), nbuf, parent, strlen(nbuf)); 149 if (IS_ERR(tmp)) { 150 dprintk("%s: lookup failed: %d\n", __func__, 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) { 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 && !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 /** 346 * export_encode_fh - default export_operations->encode_fh function 347 * @inode: the object to encode 348 * @fid: where to store the file handle fragment 349 * @max_len: maximum length to store there 350 * @parent: parent directory inode, if wanted 351 * 352 * This default encode_fh function assumes that the 32 inode number 353 * is suitable for locating an inode, and that the generation number 354 * can be used to check that it is still valid. It places them in the 355 * filehandle fragment where export_decode_fh expects to find them. 356 */ 357 static int export_encode_fh(struct inode *inode, struct fid *fid, 358 int *max_len, struct inode *parent) 359 { 360 int len = *max_len; 361 int type = FILEID_INO32_GEN; 362 363 if (parent && (len < 4)) { 364 *max_len = 4; 365 return FILEID_INVALID; 366 } else if (len < 2) { 367 *max_len = 2; 368 return FILEID_INVALID; 369 } 370 371 len = 2; 372 fid->i32.ino = inode->i_ino; 373 fid->i32.gen = inode->i_generation; 374 if (parent) { 375 fid->i32.parent_ino = parent->i_ino; 376 fid->i32.parent_gen = parent->i_generation; 377 len = 4; 378 type = FILEID_INO32_GEN_PARENT; 379 } 380 *max_len = len; 381 return type; 382 } 383 384 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid, 385 int *max_len, struct inode *parent) 386 { 387 const struct export_operations *nop = inode->i_sb->s_export_op; 388 389 if (nop && nop->encode_fh) 390 return nop->encode_fh(inode, fid->raw, max_len, parent); 391 392 return export_encode_fh(inode, fid, max_len, parent); 393 } 394 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh); 395 396 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, 397 int connectable) 398 { 399 int error; 400 struct dentry *p = NULL; 401 struct inode *inode = dentry->d_inode, *parent = NULL; 402 403 if (connectable && !S_ISDIR(inode->i_mode)) { 404 p = dget_parent(dentry); 405 /* 406 * note that while p might've ceased to be our parent already, 407 * it's still pinned by and still positive. 408 */ 409 parent = p->d_inode; 410 } 411 412 error = exportfs_encode_inode_fh(inode, fid, max_len, parent); 413 dput(p); 414 415 return error; 416 } 417 EXPORT_SYMBOL_GPL(exportfs_encode_fh); 418 419 struct dentry * 420 exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, 421 int fileid_type, 422 int (*acceptable)(void *, struct dentry *), 423 void *context) 424 { 425 const struct export_operations *nop = mnt->mnt_sb->s_export_op; 426 struct dentry *result, *alias; 427 char nbuf[NAME_MAX+1]; 428 int err; 429 430 /* 431 * Try to get any dentry for the given file handle from the filesystem. 432 */ 433 if (!nop || !nop->fh_to_dentry) 434 return ERR_PTR(-ESTALE); 435 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type); 436 if (IS_ERR_OR_NULL(result)) 437 return result; 438 439 /* 440 * If no acceptance criteria was specified by caller, a disconnected 441 * dentry is also accepatable. Callers may use this mode to query if 442 * file handle is stale or to get a reference to an inode without 443 * risking the high overhead caused by directory reconnect. 444 */ 445 if (!acceptable) 446 return result; 447 448 if (d_is_dir(result)) { 449 /* 450 * This request is for a directory. 451 * 452 * On the positive side there is only one dentry for each 453 * directory inode. On the negative side this implies that we 454 * to ensure our dentry is connected all the way up to the 455 * filesystem root. 456 */ 457 if (result->d_flags & DCACHE_DISCONNECTED) { 458 err = reconnect_path(mnt, result, nbuf); 459 if (err) 460 goto err_result; 461 } 462 463 if (!acceptable(context, result)) { 464 err = -EACCES; 465 goto err_result; 466 } 467 468 return result; 469 } else { 470 /* 471 * It's not a directory. Life is a little more complicated. 472 */ 473 struct dentry *target_dir, *nresult; 474 475 /* 476 * See if either the dentry we just got from the filesystem 477 * or any alias for it is acceptable. This is always true 478 * if this filesystem is exported without the subtreecheck 479 * option. If the filesystem is exported with the subtree 480 * check option there's a fair chance we need to look at 481 * the parent directory in the file handle and make sure 482 * it's connected to the filesystem root. 483 */ 484 alias = find_acceptable_alias(result, acceptable, context); 485 if (alias) 486 return alias; 487 488 /* 489 * Try to extract a dentry for the parent directory from the 490 * file handle. If this fails we'll have to give up. 491 */ 492 err = -ESTALE; 493 if (!nop->fh_to_parent) 494 goto err_result; 495 496 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid, 497 fh_len, fileid_type); 498 if (!target_dir) 499 goto err_result; 500 err = PTR_ERR(target_dir); 501 if (IS_ERR(target_dir)) 502 goto err_result; 503 504 /* 505 * And as usual we need to make sure the parent directory is 506 * connected to the filesystem root. The VFS really doesn't 507 * like disconnected directories.. 508 */ 509 err = reconnect_path(mnt, target_dir, nbuf); 510 if (err) { 511 dput(target_dir); 512 goto err_result; 513 } 514 515 /* 516 * Now that we've got both a well-connected parent and a 517 * dentry for the inode we're after, make sure that our 518 * inode is actually connected to the parent. 519 */ 520 err = exportfs_get_name(mnt, target_dir, nbuf, result); 521 if (err) { 522 dput(target_dir); 523 goto err_result; 524 } 525 526 inode_lock(target_dir->d_inode); 527 nresult = lookup_one(mnt_user_ns(mnt), nbuf, 528 target_dir, strlen(nbuf)); 529 if (!IS_ERR(nresult)) { 530 if (unlikely(nresult->d_inode != result->d_inode)) { 531 dput(nresult); 532 nresult = ERR_PTR(-ESTALE); 533 } 534 } 535 inode_unlock(target_dir->d_inode); 536 /* 537 * At this point we are done with the parent, but it's pinned 538 * by the child dentry anyway. 539 */ 540 dput(target_dir); 541 542 if (IS_ERR(nresult)) { 543 err = PTR_ERR(nresult); 544 goto err_result; 545 } 546 dput(result); 547 result = nresult; 548 549 /* 550 * And finally make sure the dentry is actually acceptable 551 * to NFSD. 552 */ 553 alias = find_acceptable_alias(result, acceptable, context); 554 if (!alias) { 555 err = -EACCES; 556 goto err_result; 557 } 558 559 return alias; 560 } 561 562 err_result: 563 dput(result); 564 return ERR_PTR(err); 565 } 566 EXPORT_SYMBOL_GPL(exportfs_decode_fh_raw); 567 568 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, 569 int fh_len, int fileid_type, 570 int (*acceptable)(void *, struct dentry *), 571 void *context) 572 { 573 struct dentry *ret; 574 575 ret = exportfs_decode_fh_raw(mnt, fid, fh_len, fileid_type, 576 acceptable, context); 577 if (IS_ERR_OR_NULL(ret)) { 578 if (ret == ERR_PTR(-ENOMEM)) 579 return ret; 580 return ERR_PTR(-ESTALE); 581 } 582 return ret; 583 } 584 EXPORT_SYMBOL_GPL(exportfs_decode_fh); 585 586 MODULE_LICENSE("GPL"); 587