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
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