1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * fs/kernfs/dir.c - kernfs directory implementation
4 *
5 * Copyright (c) 2001-3 Patrick Mochel
6 * Copyright (c) 2007 SUSE Linux Products GmbH
7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
8 */
9
10 #include <linux/sched.h>
11 #include <linux/fs.h>
12 #include <linux/namei.h>
13 #include <linux/idr.h>
14 #include <linux/slab.h>
15 #include <linux/security.h>
16 #include <linux/hash.h>
17
18 #include "kernfs-internal.h"
19
20 DEFINE_MUTEX(kernfs_mutex);
21 static DEFINE_SPINLOCK(kernfs_rename_lock); /* kn->parent and ->name */
22 static char kernfs_pr_cont_buf[PATH_MAX]; /* protected by rename_lock */
23 static DEFINE_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */
24
25 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
26
kernfs_active(struct kernfs_node * kn)27 static bool kernfs_active(struct kernfs_node *kn)
28 {
29 lockdep_assert_held(&kernfs_mutex);
30 return atomic_read(&kn->active) >= 0;
31 }
32
kernfs_lockdep(struct kernfs_node * kn)33 static bool kernfs_lockdep(struct kernfs_node *kn)
34 {
35 #ifdef CONFIG_DEBUG_LOCK_ALLOC
36 return kn->flags & KERNFS_LOCKDEP;
37 #else
38 return false;
39 #endif
40 }
41
kernfs_name_locked(struct kernfs_node * kn,char * buf,size_t buflen)42 static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
43 {
44 if (!kn)
45 return strlcpy(buf, "(null)", buflen);
46
47 return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
48 }
49
50 /* kernfs_node_depth - compute depth from @from to @to */
kernfs_depth(struct kernfs_node * from,struct kernfs_node * to)51 static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
52 {
53 size_t depth = 0;
54
55 while (to->parent && to != from) {
56 depth++;
57 to = to->parent;
58 }
59 return depth;
60 }
61
kernfs_common_ancestor(struct kernfs_node * a,struct kernfs_node * b)62 static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
63 struct kernfs_node *b)
64 {
65 size_t da, db;
66 struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
67
68 if (ra != rb)
69 return NULL;
70
71 da = kernfs_depth(ra->kn, a);
72 db = kernfs_depth(rb->kn, b);
73
74 while (da > db) {
75 a = a->parent;
76 da--;
77 }
78 while (db > da) {
79 b = b->parent;
80 db--;
81 }
82
83 /* worst case b and a will be the same at root */
84 while (b != a) {
85 b = b->parent;
86 a = a->parent;
87 }
88
89 return a;
90 }
91
92 /**
93 * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
94 * where kn_from is treated as root of the path.
95 * @kn_from: kernfs node which should be treated as root for the path
96 * @kn_to: kernfs node to which path is needed
97 * @buf: buffer to copy the path into
98 * @buflen: size of @buf
99 *
100 * We need to handle couple of scenarios here:
101 * [1] when @kn_from is an ancestor of @kn_to at some level
102 * kn_from: /n1/n2/n3
103 * kn_to: /n1/n2/n3/n4/n5
104 * result: /n4/n5
105 *
106 * [2] when @kn_from is on a different hierarchy and we need to find common
107 * ancestor between @kn_from and @kn_to.
108 * kn_from: /n1/n2/n3/n4
109 * kn_to: /n1/n2/n5
110 * result: /../../n5
111 * OR
112 * kn_from: /n1/n2/n3/n4/n5 [depth=5]
113 * kn_to: /n1/n2/n3 [depth=3]
114 * result: /../..
115 *
116 * [3] when @kn_to is NULL result will be "(null)"
117 *
118 * Returns the length of the full path. If the full length is equal to or
119 * greater than @buflen, @buf contains the truncated path with the trailing
120 * '\0'. On error, -errno is returned.
121 */
kernfs_path_from_node_locked(struct kernfs_node * kn_to,struct kernfs_node * kn_from,char * buf,size_t buflen)122 static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
123 struct kernfs_node *kn_from,
124 char *buf, size_t buflen)
125 {
126 struct kernfs_node *kn, *common;
127 const char parent_str[] = "/..";
128 size_t depth_from, depth_to, len = 0;
129 int i, j;
130
131 if (!kn_to)
132 return strlcpy(buf, "(null)", buflen);
133
134 if (!kn_from)
135 kn_from = kernfs_root(kn_to)->kn;
136
137 if (kn_from == kn_to)
138 return strlcpy(buf, "/", buflen);
139
140 if (!buf)
141 return -EINVAL;
142
143 common = kernfs_common_ancestor(kn_from, kn_to);
144 if (WARN_ON(!common))
145 return -EINVAL;
146
147 depth_to = kernfs_depth(common, kn_to);
148 depth_from = kernfs_depth(common, kn_from);
149
150 buf[0] = '\0';
151
152 for (i = 0; i < depth_from; i++)
153 len += strlcpy(buf + len, parent_str,
154 len < buflen ? buflen - len : 0);
155
156 /* Calculate how many bytes we need for the rest */
157 for (i = depth_to - 1; i >= 0; i--) {
158 for (kn = kn_to, j = 0; j < i; j++)
159 kn = kn->parent;
160 len += strlcpy(buf + len, "/",
161 len < buflen ? buflen - len : 0);
162 len += strlcpy(buf + len, kn->name,
163 len < buflen ? buflen - len : 0);
164 }
165
166 return len;
167 }
168
169 /**
170 * kernfs_name - obtain the name of a given node
171 * @kn: kernfs_node of interest
172 * @buf: buffer to copy @kn's name into
173 * @buflen: size of @buf
174 *
175 * Copies the name of @kn into @buf of @buflen bytes. The behavior is
176 * similar to strlcpy(). It returns the length of @kn's name and if @buf
177 * isn't long enough, it's filled upto @buflen-1 and nul terminated.
178 *
179 * Fills buffer with "(null)" if @kn is NULL.
180 *
181 * This function can be called from any context.
182 */
kernfs_name(struct kernfs_node * kn,char * buf,size_t buflen)183 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
184 {
185 unsigned long flags;
186 int ret;
187
188 spin_lock_irqsave(&kernfs_rename_lock, flags);
189 ret = kernfs_name_locked(kn, buf, buflen);
190 spin_unlock_irqrestore(&kernfs_rename_lock, flags);
191 return ret;
192 }
193
194 /**
195 * kernfs_path_from_node - build path of node @to relative to @from.
196 * @from: parent kernfs_node relative to which we need to build the path
197 * @to: kernfs_node of interest
198 * @buf: buffer to copy @to's path into
199 * @buflen: size of @buf
200 *
201 * Builds @to's path relative to @from in @buf. @from and @to must
202 * be on the same kernfs-root. If @from is not parent of @to, then a relative
203 * path (which includes '..'s) as needed to reach from @from to @to is
204 * returned.
205 *
206 * Returns the length of the full path. If the full length is equal to or
207 * greater than @buflen, @buf contains the truncated path with the trailing
208 * '\0'. On error, -errno is returned.
209 */
kernfs_path_from_node(struct kernfs_node * to,struct kernfs_node * from,char * buf,size_t buflen)210 int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
211 char *buf, size_t buflen)
212 {
213 unsigned long flags;
214 int ret;
215
216 spin_lock_irqsave(&kernfs_rename_lock, flags);
217 ret = kernfs_path_from_node_locked(to, from, buf, buflen);
218 spin_unlock_irqrestore(&kernfs_rename_lock, flags);
219 return ret;
220 }
221 EXPORT_SYMBOL_GPL(kernfs_path_from_node);
222
223 /**
224 * pr_cont_kernfs_name - pr_cont name of a kernfs_node
225 * @kn: kernfs_node of interest
226 *
227 * This function can be called from any context.
228 */
pr_cont_kernfs_name(struct kernfs_node * kn)229 void pr_cont_kernfs_name(struct kernfs_node *kn)
230 {
231 unsigned long flags;
232
233 spin_lock_irqsave(&kernfs_rename_lock, flags);
234
235 kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
236 pr_cont("%s", kernfs_pr_cont_buf);
237
238 spin_unlock_irqrestore(&kernfs_rename_lock, flags);
239 }
240
241 /**
242 * pr_cont_kernfs_path - pr_cont path of a kernfs_node
243 * @kn: kernfs_node of interest
244 *
245 * This function can be called from any context.
246 */
pr_cont_kernfs_path(struct kernfs_node * kn)247 void pr_cont_kernfs_path(struct kernfs_node *kn)
248 {
249 unsigned long flags;
250 int sz;
251
252 spin_lock_irqsave(&kernfs_rename_lock, flags);
253
254 sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
255 sizeof(kernfs_pr_cont_buf));
256 if (sz < 0) {
257 pr_cont("(error)");
258 goto out;
259 }
260
261 if (sz >= sizeof(kernfs_pr_cont_buf)) {
262 pr_cont("(name too long)");
263 goto out;
264 }
265
266 pr_cont("%s", kernfs_pr_cont_buf);
267
268 out:
269 spin_unlock_irqrestore(&kernfs_rename_lock, flags);
270 }
271
272 /**
273 * kernfs_get_parent - determine the parent node and pin it
274 * @kn: kernfs_node of interest
275 *
276 * Determines @kn's parent, pins and returns it. This function can be
277 * called from any context.
278 */
kernfs_get_parent(struct kernfs_node * kn)279 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
280 {
281 struct kernfs_node *parent;
282 unsigned long flags;
283
284 spin_lock_irqsave(&kernfs_rename_lock, flags);
285 parent = kn->parent;
286 kernfs_get(parent);
287 spin_unlock_irqrestore(&kernfs_rename_lock, flags);
288
289 return parent;
290 }
291
292 /**
293 * kernfs_name_hash
294 * @name: Null terminated string to hash
295 * @ns: Namespace tag to hash
296 *
297 * Returns 31 bit hash of ns + name (so it fits in an off_t )
298 */
kernfs_name_hash(const char * name,const void * ns)299 static unsigned int kernfs_name_hash(const char *name, const void *ns)
300 {
301 unsigned long hash = init_name_hash(ns);
302 unsigned int len = strlen(name);
303 while (len--)
304 hash = partial_name_hash(*name++, hash);
305 hash = end_name_hash(hash);
306 hash &= 0x7fffffffU;
307 /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
308 if (hash < 2)
309 hash += 2;
310 if (hash >= INT_MAX)
311 hash = INT_MAX - 1;
312 return hash;
313 }
314
kernfs_name_compare(unsigned int hash,const char * name,const void * ns,const struct kernfs_node * kn)315 static int kernfs_name_compare(unsigned int hash, const char *name,
316 const void *ns, const struct kernfs_node *kn)
317 {
318 if (hash < kn->hash)
319 return -1;
320 if (hash > kn->hash)
321 return 1;
322 if (ns < kn->ns)
323 return -1;
324 if (ns > kn->ns)
325 return 1;
326 return strcmp(name, kn->name);
327 }
328
kernfs_sd_compare(const struct kernfs_node * left,const struct kernfs_node * right)329 static int kernfs_sd_compare(const struct kernfs_node *left,
330 const struct kernfs_node *right)
331 {
332 return kernfs_name_compare(left->hash, left->name, left->ns, right);
333 }
334
335 /**
336 * kernfs_link_sibling - link kernfs_node into sibling rbtree
337 * @kn: kernfs_node of interest
338 *
339 * Link @kn into its sibling rbtree which starts from
340 * @kn->parent->dir.children.
341 *
342 * Locking:
343 * mutex_lock(kernfs_mutex)
344 *
345 * RETURNS:
346 * 0 on susccess -EEXIST on failure.
347 */
kernfs_link_sibling(struct kernfs_node * kn)348 static int kernfs_link_sibling(struct kernfs_node *kn)
349 {
350 struct rb_node **node = &kn->parent->dir.children.rb_node;
351 struct rb_node *parent = NULL;
352
353 while (*node) {
354 struct kernfs_node *pos;
355 int result;
356
357 pos = rb_to_kn(*node);
358 parent = *node;
359 result = kernfs_sd_compare(kn, pos);
360 if (result < 0)
361 node = &pos->rb.rb_left;
362 else if (result > 0)
363 node = &pos->rb.rb_right;
364 else
365 return -EEXIST;
366 }
367
368 /* add new node and rebalance the tree */
369 rb_link_node(&kn->rb, parent, node);
370 rb_insert_color(&kn->rb, &kn->parent->dir.children);
371
372 /* successfully added, account subdir number */
373 if (kernfs_type(kn) == KERNFS_DIR)
374 kn->parent->dir.subdirs++;
375
376 return 0;
377 }
378
379 /**
380 * kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree
381 * @kn: kernfs_node of interest
382 *
383 * Try to unlink @kn from its sibling rbtree which starts from
384 * kn->parent->dir.children. Returns %true if @kn was actually
385 * removed, %false if @kn wasn't on the rbtree.
386 *
387 * Locking:
388 * mutex_lock(kernfs_mutex)
389 */
kernfs_unlink_sibling(struct kernfs_node * kn)390 static bool kernfs_unlink_sibling(struct kernfs_node *kn)
391 {
392 if (RB_EMPTY_NODE(&kn->rb))
393 return false;
394
395 if (kernfs_type(kn) == KERNFS_DIR)
396 kn->parent->dir.subdirs--;
397
398 rb_erase(&kn->rb, &kn->parent->dir.children);
399 RB_CLEAR_NODE(&kn->rb);
400 return true;
401 }
402
403 /**
404 * kernfs_get_active - get an active reference to kernfs_node
405 * @kn: kernfs_node to get an active reference to
406 *
407 * Get an active reference of @kn. This function is noop if @kn
408 * is NULL.
409 *
410 * RETURNS:
411 * Pointer to @kn on success, NULL on failure.
412 */
kernfs_get_active(struct kernfs_node * kn)413 struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
414 {
415 if (unlikely(!kn))
416 return NULL;
417
418 if (!atomic_inc_unless_negative(&kn->active))
419 return NULL;
420
421 if (kernfs_lockdep(kn))
422 rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
423 return kn;
424 }
425
426 /**
427 * kernfs_put_active - put an active reference to kernfs_node
428 * @kn: kernfs_node to put an active reference to
429 *
430 * Put an active reference to @kn. This function is noop if @kn
431 * is NULL.
432 */
kernfs_put_active(struct kernfs_node * kn)433 void kernfs_put_active(struct kernfs_node *kn)
434 {
435 int v;
436
437 if (unlikely(!kn))
438 return;
439
440 if (kernfs_lockdep(kn))
441 rwsem_release(&kn->dep_map, 1, _RET_IP_);
442 v = atomic_dec_return(&kn->active);
443 if (likely(v != KN_DEACTIVATED_BIAS))
444 return;
445
446 wake_up_all(&kernfs_root(kn)->deactivate_waitq);
447 }
448
449 /**
450 * kernfs_drain - drain kernfs_node
451 * @kn: kernfs_node to drain
452 *
453 * Drain existing usages and nuke all existing mmaps of @kn. Mutiple
454 * removers may invoke this function concurrently on @kn and all will
455 * return after draining is complete.
456 */
kernfs_drain(struct kernfs_node * kn)457 static void kernfs_drain(struct kernfs_node *kn)
458 __releases(&kernfs_mutex) __acquires(&kernfs_mutex)
459 {
460 struct kernfs_root *root = kernfs_root(kn);
461
462 lockdep_assert_held(&kernfs_mutex);
463 WARN_ON_ONCE(kernfs_active(kn));
464
465 mutex_unlock(&kernfs_mutex);
466
467 if (kernfs_lockdep(kn)) {
468 rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
469 if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
470 lock_contended(&kn->dep_map, _RET_IP_);
471 }
472
473 /* but everyone should wait for draining */
474 wait_event(root->deactivate_waitq,
475 atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
476
477 if (kernfs_lockdep(kn)) {
478 lock_acquired(&kn->dep_map, _RET_IP_);
479 rwsem_release(&kn->dep_map, 1, _RET_IP_);
480 }
481
482 kernfs_drain_open_files(kn);
483
484 mutex_lock(&kernfs_mutex);
485 }
486
487 /**
488 * kernfs_get - get a reference count on a kernfs_node
489 * @kn: the target kernfs_node
490 */
kernfs_get(struct kernfs_node * kn)491 void kernfs_get(struct kernfs_node *kn)
492 {
493 if (kn) {
494 WARN_ON(!atomic_read(&kn->count));
495 atomic_inc(&kn->count);
496 }
497 }
498 EXPORT_SYMBOL_GPL(kernfs_get);
499
500 /**
501 * kernfs_put - put a reference count on a kernfs_node
502 * @kn: the target kernfs_node
503 *
504 * Put a reference count of @kn and destroy it if it reached zero.
505 */
kernfs_put(struct kernfs_node * kn)506 void kernfs_put(struct kernfs_node *kn)
507 {
508 struct kernfs_node *parent;
509 struct kernfs_root *root;
510
511 /*
512 * kernfs_node is freed with ->count 0, kernfs_find_and_get_node_by_ino
513 * depends on this to filter reused stale node
514 */
515 if (!kn || !atomic_dec_and_test(&kn->count))
516 return;
517 root = kernfs_root(kn);
518 repeat:
519 /*
520 * Moving/renaming is always done while holding reference.
521 * kn->parent won't change beneath us.
522 */
523 parent = kn->parent;
524
525 WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
526 "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
527 parent ? parent->name : "", kn->name, atomic_read(&kn->active));
528
529 if (kernfs_type(kn) == KERNFS_LINK)
530 kernfs_put(kn->symlink.target_kn);
531
532 kfree_const(kn->name);
533
534 if (kn->iattr) {
535 simple_xattrs_free(&kn->iattr->xattrs);
536 kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
537 }
538 spin_lock(&kernfs_idr_lock);
539 idr_remove(&root->ino_idr, kn->id.ino);
540 spin_unlock(&kernfs_idr_lock);
541 kmem_cache_free(kernfs_node_cache, kn);
542
543 kn = parent;
544 if (kn) {
545 if (atomic_dec_and_test(&kn->count))
546 goto repeat;
547 } else {
548 /* just released the root kn, free @root too */
549 idr_destroy(&root->ino_idr);
550 kfree(root);
551 }
552 }
553 EXPORT_SYMBOL_GPL(kernfs_put);
554
kernfs_dop_revalidate(struct dentry * dentry,unsigned int flags)555 static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
556 {
557 struct kernfs_node *kn;
558
559 if (flags & LOOKUP_RCU)
560 return -ECHILD;
561
562 /* Always perform fresh lookup for negatives */
563 if (d_really_is_negative(dentry))
564 goto out_bad_unlocked;
565
566 kn = kernfs_dentry_node(dentry);
567 mutex_lock(&kernfs_mutex);
568
569 /* The kernfs node has been deactivated */
570 if (!kernfs_active(kn))
571 goto out_bad;
572
573 /* The kernfs node has been moved? */
574 if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
575 goto out_bad;
576
577 /* The kernfs node has been renamed */
578 if (strcmp(dentry->d_name.name, kn->name) != 0)
579 goto out_bad;
580
581 /* The kernfs node has been moved to a different namespace */
582 if (kn->parent && kernfs_ns_enabled(kn->parent) &&
583 kernfs_info(dentry->d_sb)->ns != kn->ns)
584 goto out_bad;
585
586 mutex_unlock(&kernfs_mutex);
587 return 1;
588 out_bad:
589 mutex_unlock(&kernfs_mutex);
590 out_bad_unlocked:
591 return 0;
592 }
593
594 const struct dentry_operations kernfs_dops = {
595 .d_revalidate = kernfs_dop_revalidate,
596 };
597
598 /**
599 * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
600 * @dentry: the dentry in question
601 *
602 * Return the kernfs_node associated with @dentry. If @dentry is not a
603 * kernfs one, %NULL is returned.
604 *
605 * While the returned kernfs_node will stay accessible as long as @dentry
606 * is accessible, the returned node can be in any state and the caller is
607 * fully responsible for determining what's accessible.
608 */
kernfs_node_from_dentry(struct dentry * dentry)609 struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
610 {
611 if (dentry->d_sb->s_op == &kernfs_sops &&
612 !d_really_is_negative(dentry))
613 return kernfs_dentry_node(dentry);
614 return NULL;
615 }
616
__kernfs_new_node(struct kernfs_root * root,struct kernfs_node * parent,const char * name,umode_t mode,kuid_t uid,kgid_t gid,unsigned flags)617 static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
618 struct kernfs_node *parent,
619 const char *name, umode_t mode,
620 kuid_t uid, kgid_t gid,
621 unsigned flags)
622 {
623 struct kernfs_node *kn;
624 u32 gen;
625 int cursor;
626 int ret;
627
628 name = kstrdup_const(name, GFP_KERNEL);
629 if (!name)
630 return NULL;
631
632 kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);
633 if (!kn)
634 goto err_out1;
635
636 idr_preload(GFP_KERNEL);
637 spin_lock(&kernfs_idr_lock);
638 cursor = idr_get_cursor(&root->ino_idr);
639 ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
640 if (ret >= 0 && ret < cursor)
641 root->next_generation++;
642 gen = root->next_generation;
643 spin_unlock(&kernfs_idr_lock);
644 idr_preload_end();
645 if (ret < 0)
646 goto err_out2;
647 kn->id.ino = ret;
648 kn->id.generation = gen;
649
650 /*
651 * set ino first. This RELEASE is paired with atomic_inc_not_zero in
652 * kernfs_find_and_get_node_by_ino
653 */
654 atomic_set_release(&kn->count, 1);
655 atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
656 RB_CLEAR_NODE(&kn->rb);
657
658 kn->name = name;
659 kn->mode = mode;
660 kn->flags = flags;
661
662 if (!uid_eq(uid, GLOBAL_ROOT_UID) || !gid_eq(gid, GLOBAL_ROOT_GID)) {
663 struct iattr iattr = {
664 .ia_valid = ATTR_UID | ATTR_GID,
665 .ia_uid = uid,
666 .ia_gid = gid,
667 };
668
669 ret = __kernfs_setattr(kn, &iattr);
670 if (ret < 0)
671 goto err_out3;
672 }
673
674 if (parent) {
675 ret = security_kernfs_init_security(parent, kn);
676 if (ret)
677 goto err_out3;
678 }
679
680 return kn;
681
682 err_out3:
683 idr_remove(&root->ino_idr, kn->id.ino);
684 err_out2:
685 kmem_cache_free(kernfs_node_cache, kn);
686 err_out1:
687 kfree_const(name);
688 return NULL;
689 }
690
kernfs_new_node(struct kernfs_node * parent,const char * name,umode_t mode,kuid_t uid,kgid_t gid,unsigned flags)691 struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
692 const char *name, umode_t mode,
693 kuid_t uid, kgid_t gid,
694 unsigned flags)
695 {
696 struct kernfs_node *kn;
697
698 kn = __kernfs_new_node(kernfs_root(parent), parent,
699 name, mode, uid, gid, flags);
700 if (kn) {
701 kernfs_get(parent);
702 kn->parent = parent;
703 }
704 return kn;
705 }
706
707 /*
708 * kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
709 * @root: the kernfs root
710 * @ino: inode number
711 *
712 * RETURNS:
713 * NULL on failure. Return a kernfs node with reference counter incremented
714 */
kernfs_find_and_get_node_by_ino(struct kernfs_root * root,unsigned int ino)715 struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
716 unsigned int ino)
717 {
718 struct kernfs_node *kn;
719
720 rcu_read_lock();
721 kn = idr_find(&root->ino_idr, ino);
722 if (!kn)
723 goto out;
724
725 /*
726 * Since kernfs_node is freed in RCU, it's possible an old node for ino
727 * is freed, but reused before RCU grace period. But a freed node (see
728 * kernfs_put) or an incompletedly initialized node (see
729 * __kernfs_new_node) should have 'count' 0. We can use this fact to
730 * filter out such node.
731 */
732 if (!atomic_inc_not_zero(&kn->count)) {
733 kn = NULL;
734 goto out;
735 }
736
737 /*
738 * The node could be a new node or a reused node. If it's a new node,
739 * we are ok. If it's reused because of RCU (because of
740 * SLAB_TYPESAFE_BY_RCU), the __kernfs_new_node always sets its 'ino'
741 * before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
742 * hence we can use 'ino' to filter stale node.
743 */
744 if (kn->id.ino != ino)
745 goto out;
746 rcu_read_unlock();
747
748 return kn;
749 out:
750 rcu_read_unlock();
751 kernfs_put(kn);
752 return NULL;
753 }
754
755 /**
756 * kernfs_add_one - add kernfs_node to parent without warning
757 * @kn: kernfs_node to be added
758 *
759 * The caller must already have initialized @kn->parent. This
760 * function increments nlink of the parent's inode if @kn is a
761 * directory and link into the children list of the parent.
762 *
763 * RETURNS:
764 * 0 on success, -EEXIST if entry with the given name already
765 * exists.
766 */
kernfs_add_one(struct kernfs_node * kn)767 int kernfs_add_one(struct kernfs_node *kn)
768 {
769 struct kernfs_node *parent = kn->parent;
770 struct kernfs_iattrs *ps_iattr;
771 bool has_ns;
772 int ret;
773
774 mutex_lock(&kernfs_mutex);
775
776 ret = -EINVAL;
777 has_ns = kernfs_ns_enabled(parent);
778 if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
779 has_ns ? "required" : "invalid", parent->name, kn->name))
780 goto out_unlock;
781
782 if (kernfs_type(parent) != KERNFS_DIR)
783 goto out_unlock;
784
785 ret = -ENOENT;
786 if (parent->flags & KERNFS_EMPTY_DIR)
787 goto out_unlock;
788
789 if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
790 goto out_unlock;
791
792 kn->hash = kernfs_name_hash(kn->name, kn->ns);
793
794 ret = kernfs_link_sibling(kn);
795 if (ret)
796 goto out_unlock;
797
798 /* Update timestamps on the parent */
799 ps_iattr = parent->iattr;
800 if (ps_iattr) {
801 ktime_get_real_ts64(&ps_iattr->ia_ctime);
802 ps_iattr->ia_mtime = ps_iattr->ia_ctime;
803 }
804
805 mutex_unlock(&kernfs_mutex);
806
807 /*
808 * Activate the new node unless CREATE_DEACTIVATED is requested.
809 * If not activated here, the kernfs user is responsible for
810 * activating the node with kernfs_activate(). A node which hasn't
811 * been activated is not visible to userland and its removal won't
812 * trigger deactivation.
813 */
814 if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
815 kernfs_activate(kn);
816 return 0;
817
818 out_unlock:
819 mutex_unlock(&kernfs_mutex);
820 return ret;
821 }
822
823 /**
824 * kernfs_find_ns - find kernfs_node with the given name
825 * @parent: kernfs_node to search under
826 * @name: name to look for
827 * @ns: the namespace tag to use
828 *
829 * Look for kernfs_node with name @name under @parent. Returns pointer to
830 * the found kernfs_node on success, %NULL on failure.
831 */
kernfs_find_ns(struct kernfs_node * parent,const unsigned char * name,const void * ns)832 static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
833 const unsigned char *name,
834 const void *ns)
835 {
836 struct rb_node *node = parent->dir.children.rb_node;
837 bool has_ns = kernfs_ns_enabled(parent);
838 unsigned int hash;
839
840 lockdep_assert_held(&kernfs_mutex);
841
842 if (has_ns != (bool)ns) {
843 WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
844 has_ns ? "required" : "invalid", parent->name, name);
845 return NULL;
846 }
847
848 hash = kernfs_name_hash(name, ns);
849 while (node) {
850 struct kernfs_node *kn;
851 int result;
852
853 kn = rb_to_kn(node);
854 result = kernfs_name_compare(hash, name, ns, kn);
855 if (result < 0)
856 node = node->rb_left;
857 else if (result > 0)
858 node = node->rb_right;
859 else
860 return kn;
861 }
862 return NULL;
863 }
864
kernfs_walk_ns(struct kernfs_node * parent,const unsigned char * path,const void * ns)865 static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
866 const unsigned char *path,
867 const void *ns)
868 {
869 size_t len;
870 char *p, *name;
871
872 lockdep_assert_held(&kernfs_mutex);
873
874 /* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
875 spin_lock_irq(&kernfs_rename_lock);
876
877 len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
878
879 if (len >= sizeof(kernfs_pr_cont_buf)) {
880 spin_unlock_irq(&kernfs_rename_lock);
881 return NULL;
882 }
883
884 p = kernfs_pr_cont_buf;
885
886 while ((name = strsep(&p, "/")) && parent) {
887 if (*name == '\0')
888 continue;
889 parent = kernfs_find_ns(parent, name, ns);
890 }
891
892 spin_unlock_irq(&kernfs_rename_lock);
893
894 return parent;
895 }
896
897 /**
898 * kernfs_find_and_get_ns - find and get kernfs_node with the given name
899 * @parent: kernfs_node to search under
900 * @name: name to look for
901 * @ns: the namespace tag to use
902 *
903 * Look for kernfs_node with name @name under @parent and get a reference
904 * if found. This function may sleep and returns pointer to the found
905 * kernfs_node on success, %NULL on failure.
906 */
kernfs_find_and_get_ns(struct kernfs_node * parent,const char * name,const void * ns)907 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
908 const char *name, const void *ns)
909 {
910 struct kernfs_node *kn;
911
912 mutex_lock(&kernfs_mutex);
913 kn = kernfs_find_ns(parent, name, ns);
914 kernfs_get(kn);
915 mutex_unlock(&kernfs_mutex);
916
917 return kn;
918 }
919 EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
920
921 /**
922 * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
923 * @parent: kernfs_node to search under
924 * @path: path to look for
925 * @ns: the namespace tag to use
926 *
927 * Look for kernfs_node with path @path under @parent and get a reference
928 * if found. This function may sleep and returns pointer to the found
929 * kernfs_node on success, %NULL on failure.
930 */
kernfs_walk_and_get_ns(struct kernfs_node * parent,const char * path,const void * ns)931 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
932 const char *path, const void *ns)
933 {
934 struct kernfs_node *kn;
935
936 mutex_lock(&kernfs_mutex);
937 kn = kernfs_walk_ns(parent, path, ns);
938 kernfs_get(kn);
939 mutex_unlock(&kernfs_mutex);
940
941 return kn;
942 }
943
944 /**
945 * kernfs_create_root - create a new kernfs hierarchy
946 * @scops: optional syscall operations for the hierarchy
947 * @flags: KERNFS_ROOT_* flags
948 * @priv: opaque data associated with the new directory
949 *
950 * Returns the root of the new hierarchy on success, ERR_PTR() value on
951 * failure.
952 */
kernfs_create_root(struct kernfs_syscall_ops * scops,unsigned int flags,void * priv)953 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
954 unsigned int flags, void *priv)
955 {
956 struct kernfs_root *root;
957 struct kernfs_node *kn;
958
959 root = kzalloc(sizeof(*root), GFP_KERNEL);
960 if (!root)
961 return ERR_PTR(-ENOMEM);
962
963 idr_init(&root->ino_idr);
964 INIT_LIST_HEAD(&root->supers);
965 root->next_generation = 1;
966
967 kn = __kernfs_new_node(root, NULL, "", S_IFDIR | S_IRUGO | S_IXUGO,
968 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
969 KERNFS_DIR);
970 if (!kn) {
971 idr_destroy(&root->ino_idr);
972 kfree(root);
973 return ERR_PTR(-ENOMEM);
974 }
975
976 kn->priv = priv;
977 kn->dir.root = root;
978
979 root->syscall_ops = scops;
980 root->flags = flags;
981 root->kn = kn;
982 init_waitqueue_head(&root->deactivate_waitq);
983
984 if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
985 kernfs_activate(kn);
986
987 return root;
988 }
989
990 /**
991 * kernfs_destroy_root - destroy a kernfs hierarchy
992 * @root: root of the hierarchy to destroy
993 *
994 * Destroy the hierarchy anchored at @root by removing all existing
995 * directories and destroying @root.
996 */
kernfs_destroy_root(struct kernfs_root * root)997 void kernfs_destroy_root(struct kernfs_root *root)
998 {
999 kernfs_remove(root->kn); /* will also free @root */
1000 }
1001
1002 /**
1003 * kernfs_create_dir_ns - create a directory
1004 * @parent: parent in which to create a new directory
1005 * @name: name of the new directory
1006 * @mode: mode of the new directory
1007 * @uid: uid of the new directory
1008 * @gid: gid of the new directory
1009 * @priv: opaque data associated with the new directory
1010 * @ns: optional namespace tag of the directory
1011 *
1012 * Returns the created node on success, ERR_PTR() value on failure.
1013 */
kernfs_create_dir_ns(struct kernfs_node * parent,const char * name,umode_t mode,kuid_t uid,kgid_t gid,void * priv,const void * ns)1014 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
1015 const char *name, umode_t mode,
1016 kuid_t uid, kgid_t gid,
1017 void *priv, const void *ns)
1018 {
1019 struct kernfs_node *kn;
1020 int rc;
1021
1022 /* allocate */
1023 kn = kernfs_new_node(parent, name, mode | S_IFDIR,
1024 uid, gid, KERNFS_DIR);
1025 if (!kn)
1026 return ERR_PTR(-ENOMEM);
1027
1028 kn->dir.root = parent->dir.root;
1029 kn->ns = ns;
1030 kn->priv = priv;
1031
1032 /* link in */
1033 rc = kernfs_add_one(kn);
1034 if (!rc)
1035 return kn;
1036
1037 kernfs_put(kn);
1038 return ERR_PTR(rc);
1039 }
1040
1041 /**
1042 * kernfs_create_empty_dir - create an always empty directory
1043 * @parent: parent in which to create a new directory
1044 * @name: name of the new directory
1045 *
1046 * Returns the created node on success, ERR_PTR() value on failure.
1047 */
kernfs_create_empty_dir(struct kernfs_node * parent,const char * name)1048 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
1049 const char *name)
1050 {
1051 struct kernfs_node *kn;
1052 int rc;
1053
1054 /* allocate */
1055 kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR,
1056 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, KERNFS_DIR);
1057 if (!kn)
1058 return ERR_PTR(-ENOMEM);
1059
1060 kn->flags |= KERNFS_EMPTY_DIR;
1061 kn->dir.root = parent->dir.root;
1062 kn->ns = NULL;
1063 kn->priv = NULL;
1064
1065 /* link in */
1066 rc = kernfs_add_one(kn);
1067 if (!rc)
1068 return kn;
1069
1070 kernfs_put(kn);
1071 return ERR_PTR(rc);
1072 }
1073
kernfs_iop_lookup(struct inode * dir,struct dentry * dentry,unsigned int flags)1074 static struct dentry *kernfs_iop_lookup(struct inode *dir,
1075 struct dentry *dentry,
1076 unsigned int flags)
1077 {
1078 struct dentry *ret;
1079 struct kernfs_node *parent = dir->i_private;
1080 struct kernfs_node *kn;
1081 struct inode *inode;
1082 const void *ns = NULL;
1083
1084 mutex_lock(&kernfs_mutex);
1085
1086 if (kernfs_ns_enabled(parent))
1087 ns = kernfs_info(dir->i_sb)->ns;
1088
1089 kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
1090
1091 /* no such entry */
1092 if (!kn || !kernfs_active(kn)) {
1093 ret = NULL;
1094 goto out_unlock;
1095 }
1096
1097 /* attach dentry and inode */
1098 inode = kernfs_get_inode(dir->i_sb, kn);
1099 if (!inode) {
1100 ret = ERR_PTR(-ENOMEM);
1101 goto out_unlock;
1102 }
1103
1104 /* instantiate and hash dentry */
1105 ret = d_splice_alias(inode, dentry);
1106 out_unlock:
1107 mutex_unlock(&kernfs_mutex);
1108 return ret;
1109 }
1110
kernfs_iop_mkdir(struct inode * dir,struct dentry * dentry,umode_t mode)1111 static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
1112 umode_t mode)
1113 {
1114 struct kernfs_node *parent = dir->i_private;
1115 struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;
1116 int ret;
1117
1118 if (!scops || !scops->mkdir)
1119 return -EPERM;
1120
1121 if (!kernfs_get_active(parent))
1122 return -ENODEV;
1123
1124 ret = scops->mkdir(parent, dentry->d_name.name, mode);
1125
1126 kernfs_put_active(parent);
1127 return ret;
1128 }
1129
kernfs_iop_rmdir(struct inode * dir,struct dentry * dentry)1130 static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
1131 {
1132 struct kernfs_node *kn = kernfs_dentry_node(dentry);
1133 struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1134 int ret;
1135
1136 if (!scops || !scops->rmdir)
1137 return -EPERM;
1138
1139 if (!kernfs_get_active(kn))
1140 return -ENODEV;
1141
1142 ret = scops->rmdir(kn);
1143
1144 kernfs_put_active(kn);
1145 return ret;
1146 }
1147
kernfs_iop_rename(struct inode * old_dir,struct dentry * old_dentry,struct inode * new_dir,struct dentry * new_dentry,unsigned int flags)1148 static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
1149 struct inode *new_dir, struct dentry *new_dentry,
1150 unsigned int flags)
1151 {
1152 struct kernfs_node *kn = kernfs_dentry_node(old_dentry);
1153 struct kernfs_node *new_parent = new_dir->i_private;
1154 struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
1155 int ret;
1156
1157 if (flags)
1158 return -EINVAL;
1159
1160 if (!scops || !scops->rename)
1161 return -EPERM;
1162
1163 if (!kernfs_get_active(kn))
1164 return -ENODEV;
1165
1166 if (!kernfs_get_active(new_parent)) {
1167 kernfs_put_active(kn);
1168 return -ENODEV;
1169 }
1170
1171 ret = scops->rename(kn, new_parent, new_dentry->d_name.name);
1172
1173 kernfs_put_active(new_parent);
1174 kernfs_put_active(kn);
1175 return ret;
1176 }
1177
1178 const struct inode_operations kernfs_dir_iops = {
1179 .lookup = kernfs_iop_lookup,
1180 .permission = kernfs_iop_permission,
1181 .setattr = kernfs_iop_setattr,
1182 .getattr = kernfs_iop_getattr,
1183 .listxattr = kernfs_iop_listxattr,
1184
1185 .mkdir = kernfs_iop_mkdir,
1186 .rmdir = kernfs_iop_rmdir,
1187 .rename = kernfs_iop_rename,
1188 };
1189
kernfs_leftmost_descendant(struct kernfs_node * pos)1190 static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)
1191 {
1192 struct kernfs_node *last;
1193
1194 while (true) {
1195 struct rb_node *rbn;
1196
1197 last = pos;
1198
1199 if (kernfs_type(pos) != KERNFS_DIR)
1200 break;
1201
1202 rbn = rb_first(&pos->dir.children);
1203 if (!rbn)
1204 break;
1205
1206 pos = rb_to_kn(rbn);
1207 }
1208
1209 return last;
1210 }
1211
1212 /**
1213 * kernfs_next_descendant_post - find the next descendant for post-order walk
1214 * @pos: the current position (%NULL to initiate traversal)
1215 * @root: kernfs_node whose descendants to walk
1216 *
1217 * Find the next descendant to visit for post-order traversal of @root's
1218 * descendants. @root is included in the iteration and the last node to be
1219 * visited.
1220 */
kernfs_next_descendant_post(struct kernfs_node * pos,struct kernfs_node * root)1221 static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
1222 struct kernfs_node *root)
1223 {
1224 struct rb_node *rbn;
1225
1226 lockdep_assert_held(&kernfs_mutex);
1227
1228 /* if first iteration, visit leftmost descendant which may be root */
1229 if (!pos)
1230 return kernfs_leftmost_descendant(root);
1231
1232 /* if we visited @root, we're done */
1233 if (pos == root)
1234 return NULL;
1235
1236 /* if there's an unvisited sibling, visit its leftmost descendant */
1237 rbn = rb_next(&pos->rb);
1238 if (rbn)
1239 return kernfs_leftmost_descendant(rb_to_kn(rbn));
1240
1241 /* no sibling left, visit parent */
1242 return pos->parent;
1243 }
1244
1245 /**
1246 * kernfs_activate - activate a node which started deactivated
1247 * @kn: kernfs_node whose subtree is to be activated
1248 *
1249 * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
1250 * needs to be explicitly activated. A node which hasn't been activated
1251 * isn't visible to userland and deactivation is skipped during its
1252 * removal. This is useful to construct atomic init sequences where
1253 * creation of multiple nodes should either succeed or fail atomically.
1254 *
1255 * The caller is responsible for ensuring that this function is not called
1256 * after kernfs_remove*() is invoked on @kn.
1257 */
kernfs_activate(struct kernfs_node * kn)1258 void kernfs_activate(struct kernfs_node *kn)
1259 {
1260 struct kernfs_node *pos;
1261
1262 mutex_lock(&kernfs_mutex);
1263
1264 pos = NULL;
1265 while ((pos = kernfs_next_descendant_post(pos, kn))) {
1266 if (!pos || (pos->flags & KERNFS_ACTIVATED))
1267 continue;
1268
1269 WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
1270 WARN_ON_ONCE(atomic_read(&pos->active) != KN_DEACTIVATED_BIAS);
1271
1272 atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
1273 pos->flags |= KERNFS_ACTIVATED;
1274 }
1275
1276 mutex_unlock(&kernfs_mutex);
1277 }
1278
__kernfs_remove(struct kernfs_node * kn)1279 static void __kernfs_remove(struct kernfs_node *kn)
1280 {
1281 struct kernfs_node *pos;
1282
1283 lockdep_assert_held(&kernfs_mutex);
1284
1285 /*
1286 * Short-circuit if non-root @kn has already finished removal.
1287 * This is for kernfs_remove_self() which plays with active ref
1288 * after removal.
1289 */
1290 if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))
1291 return;
1292
1293 pr_debug("kernfs %s: removing\n", kn->name);
1294
1295 /* prevent any new usage under @kn by deactivating all nodes */
1296 pos = NULL;
1297 while ((pos = kernfs_next_descendant_post(pos, kn)))
1298 if (kernfs_active(pos))
1299 atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
1300
1301 /* deactivate and unlink the subtree node-by-node */
1302 do {
1303 pos = kernfs_leftmost_descendant(kn);
1304
1305 /*
1306 * kernfs_drain() drops kernfs_mutex temporarily and @pos's
1307 * base ref could have been put by someone else by the time
1308 * the function returns. Make sure it doesn't go away
1309 * underneath us.
1310 */
1311 kernfs_get(pos);
1312
1313 /*
1314 * Drain iff @kn was activated. This avoids draining and
1315 * its lockdep annotations for nodes which have never been
1316 * activated and allows embedding kernfs_remove() in create
1317 * error paths without worrying about draining.
1318 */
1319 if (kn->flags & KERNFS_ACTIVATED)
1320 kernfs_drain(pos);
1321 else
1322 WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
1323
1324 /*
1325 * kernfs_unlink_sibling() succeeds once per node. Use it
1326 * to decide who's responsible for cleanups.
1327 */
1328 if (!pos->parent || kernfs_unlink_sibling(pos)) {
1329 struct kernfs_iattrs *ps_iattr =
1330 pos->parent ? pos->parent->iattr : NULL;
1331
1332 /* update timestamps on the parent */
1333 if (ps_iattr) {
1334 ktime_get_real_ts64(&ps_iattr->ia_ctime);
1335 ps_iattr->ia_mtime = ps_iattr->ia_ctime;
1336 }
1337
1338 kernfs_put(pos);
1339 }
1340
1341 kernfs_put(pos);
1342 } while (pos != kn);
1343 }
1344
1345 /**
1346 * kernfs_remove - remove a kernfs_node recursively
1347 * @kn: the kernfs_node to remove
1348 *
1349 * Remove @kn along with all its subdirectories and files.
1350 */
kernfs_remove(struct kernfs_node * kn)1351 void kernfs_remove(struct kernfs_node *kn)
1352 {
1353 mutex_lock(&kernfs_mutex);
1354 __kernfs_remove(kn);
1355 mutex_unlock(&kernfs_mutex);
1356 }
1357
1358 /**
1359 * kernfs_break_active_protection - break out of active protection
1360 * @kn: the self kernfs_node
1361 *
1362 * The caller must be running off of a kernfs operation which is invoked
1363 * with an active reference - e.g. one of kernfs_ops. Each invocation of
1364 * this function must also be matched with an invocation of
1365 * kernfs_unbreak_active_protection().
1366 *
1367 * This function releases the active reference of @kn the caller is
1368 * holding. Once this function is called, @kn may be removed at any point
1369 * and the caller is solely responsible for ensuring that the objects it
1370 * dereferences are accessible.
1371 */
kernfs_break_active_protection(struct kernfs_node * kn)1372 void kernfs_break_active_protection(struct kernfs_node *kn)
1373 {
1374 /*
1375 * Take out ourself out of the active ref dependency chain. If
1376 * we're called without an active ref, lockdep will complain.
1377 */
1378 kernfs_put_active(kn);
1379 }
1380
1381 /**
1382 * kernfs_unbreak_active_protection - undo kernfs_break_active_protection()
1383 * @kn: the self kernfs_node
1384 *
1385 * If kernfs_break_active_protection() was called, this function must be
1386 * invoked before finishing the kernfs operation. Note that while this
1387 * function restores the active reference, it doesn't and can't actually
1388 * restore the active protection - @kn may already or be in the process of
1389 * being removed. Once kernfs_break_active_protection() is invoked, that
1390 * protection is irreversibly gone for the kernfs operation instance.
1391 *
1392 * While this function may be called at any point after
1393 * kernfs_break_active_protection() is invoked, its most useful location
1394 * would be right before the enclosing kernfs operation returns.
1395 */
kernfs_unbreak_active_protection(struct kernfs_node * kn)1396 void kernfs_unbreak_active_protection(struct kernfs_node *kn)
1397 {
1398 /*
1399 * @kn->active could be in any state; however, the increment we do
1400 * here will be undone as soon as the enclosing kernfs operation
1401 * finishes and this temporary bump can't break anything. If @kn
1402 * is alive, nothing changes. If @kn is being deactivated, the
1403 * soon-to-follow put will either finish deactivation or restore
1404 * deactivated state. If @kn is already removed, the temporary
1405 * bump is guaranteed to be gone before @kn is released.
1406 */
1407 atomic_inc(&kn->active);
1408 if (kernfs_lockdep(kn))
1409 rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
1410 }
1411
1412 /**
1413 * kernfs_remove_self - remove a kernfs_node from its own method
1414 * @kn: the self kernfs_node to remove
1415 *
1416 * The caller must be running off of a kernfs operation which is invoked
1417 * with an active reference - e.g. one of kernfs_ops. This can be used to
1418 * implement a file operation which deletes itself.
1419 *
1420 * For example, the "delete" file for a sysfs device directory can be
1421 * implemented by invoking kernfs_remove_self() on the "delete" file
1422 * itself. This function breaks the circular dependency of trying to
1423 * deactivate self while holding an active ref itself. It isn't necessary
1424 * to modify the usual removal path to use kernfs_remove_self(). The
1425 * "delete" implementation can simply invoke kernfs_remove_self() on self
1426 * before proceeding with the usual removal path. kernfs will ignore later
1427 * kernfs_remove() on self.
1428 *
1429 * kernfs_remove_self() can be called multiple times concurrently on the
1430 * same kernfs_node. Only the first one actually performs removal and
1431 * returns %true. All others will wait until the kernfs operation which
1432 * won self-removal finishes and return %false. Note that the losers wait
1433 * for the completion of not only the winning kernfs_remove_self() but also
1434 * the whole kernfs_ops which won the arbitration. This can be used to
1435 * guarantee, for example, all concurrent writes to a "delete" file to
1436 * finish only after the whole operation is complete.
1437 */
kernfs_remove_self(struct kernfs_node * kn)1438 bool kernfs_remove_self(struct kernfs_node *kn)
1439 {
1440 bool ret;
1441
1442 mutex_lock(&kernfs_mutex);
1443 kernfs_break_active_protection(kn);
1444
1445 /*
1446 * SUICIDAL is used to arbitrate among competing invocations. Only
1447 * the first one will actually perform removal. When the removal
1448 * is complete, SUICIDED is set and the active ref is restored
1449 * while holding kernfs_mutex. The ones which lost arbitration
1450 * waits for SUICDED && drained which can happen only after the
1451 * enclosing kernfs operation which executed the winning instance
1452 * of kernfs_remove_self() finished.
1453 */
1454 if (!(kn->flags & KERNFS_SUICIDAL)) {
1455 kn->flags |= KERNFS_SUICIDAL;
1456 __kernfs_remove(kn);
1457 kn->flags |= KERNFS_SUICIDED;
1458 ret = true;
1459 } else {
1460 wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
1461 DEFINE_WAIT(wait);
1462
1463 while (true) {
1464 prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
1465
1466 if ((kn->flags & KERNFS_SUICIDED) &&
1467 atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
1468 break;
1469
1470 mutex_unlock(&kernfs_mutex);
1471 schedule();
1472 mutex_lock(&kernfs_mutex);
1473 }
1474 finish_wait(waitq, &wait);
1475 WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
1476 ret = false;
1477 }
1478
1479 /*
1480 * This must be done while holding kernfs_mutex; otherwise, waiting
1481 * for SUICIDED && deactivated could finish prematurely.
1482 */
1483 kernfs_unbreak_active_protection(kn);
1484
1485 mutex_unlock(&kernfs_mutex);
1486 return ret;
1487 }
1488
1489 /**
1490 * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
1491 * @parent: parent of the target
1492 * @name: name of the kernfs_node to remove
1493 * @ns: namespace tag of the kernfs_node to remove
1494 *
1495 * Look for the kernfs_node with @name and @ns under @parent and remove it.
1496 * Returns 0 on success, -ENOENT if such entry doesn't exist.
1497 */
kernfs_remove_by_name_ns(struct kernfs_node * parent,const char * name,const void * ns)1498 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
1499 const void *ns)
1500 {
1501 struct kernfs_node *kn;
1502
1503 if (!parent) {
1504 WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
1505 name);
1506 return -ENOENT;
1507 }
1508
1509 mutex_lock(&kernfs_mutex);
1510
1511 kn = kernfs_find_ns(parent, name, ns);
1512 if (kn)
1513 __kernfs_remove(kn);
1514
1515 mutex_unlock(&kernfs_mutex);
1516
1517 if (kn)
1518 return 0;
1519 else
1520 return -ENOENT;
1521 }
1522
1523 /**
1524 * kernfs_rename_ns - move and rename a kernfs_node
1525 * @kn: target node
1526 * @new_parent: new parent to put @sd under
1527 * @new_name: new name
1528 * @new_ns: new namespace tag
1529 */
kernfs_rename_ns(struct kernfs_node * kn,struct kernfs_node * new_parent,const char * new_name,const void * new_ns)1530 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
1531 const char *new_name, const void *new_ns)
1532 {
1533 struct kernfs_node *old_parent;
1534 const char *old_name = NULL;
1535 int error;
1536
1537 /* can't move or rename root */
1538 if (!kn->parent)
1539 return -EINVAL;
1540
1541 mutex_lock(&kernfs_mutex);
1542
1543 error = -ENOENT;
1544 if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
1545 (new_parent->flags & KERNFS_EMPTY_DIR))
1546 goto out;
1547
1548 error = 0;
1549 if ((kn->parent == new_parent) && (kn->ns == new_ns) &&
1550 (strcmp(kn->name, new_name) == 0))
1551 goto out; /* nothing to rename */
1552
1553 error = -EEXIST;
1554 if (kernfs_find_ns(new_parent, new_name, new_ns))
1555 goto out;
1556
1557 /* rename kernfs_node */
1558 if (strcmp(kn->name, new_name) != 0) {
1559 error = -ENOMEM;
1560 new_name = kstrdup_const(new_name, GFP_KERNEL);
1561 if (!new_name)
1562 goto out;
1563 } else {
1564 new_name = NULL;
1565 }
1566
1567 /*
1568 * Move to the appropriate place in the appropriate directories rbtree.
1569 */
1570 kernfs_unlink_sibling(kn);
1571 kernfs_get(new_parent);
1572
1573 /* rename_lock protects ->parent and ->name accessors */
1574 spin_lock_irq(&kernfs_rename_lock);
1575
1576 old_parent = kn->parent;
1577 kn->parent = new_parent;
1578
1579 kn->ns = new_ns;
1580 if (new_name) {
1581 old_name = kn->name;
1582 kn->name = new_name;
1583 }
1584
1585 spin_unlock_irq(&kernfs_rename_lock);
1586
1587 kn->hash = kernfs_name_hash(kn->name, kn->ns);
1588 kernfs_link_sibling(kn);
1589
1590 kernfs_put(old_parent);
1591 kfree_const(old_name);
1592
1593 error = 0;
1594 out:
1595 mutex_unlock(&kernfs_mutex);
1596 return error;
1597 }
1598
1599 /* Relationship between s_mode and the DT_xxx types */
dt_type(struct kernfs_node * kn)1600 static inline unsigned char dt_type(struct kernfs_node *kn)
1601 {
1602 return (kn->mode >> 12) & 15;
1603 }
1604
kernfs_dir_fop_release(struct inode * inode,struct file * filp)1605 static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)
1606 {
1607 kernfs_put(filp->private_data);
1608 return 0;
1609 }
1610
kernfs_dir_pos(const void * ns,struct kernfs_node * parent,loff_t hash,struct kernfs_node * pos)1611 static struct kernfs_node *kernfs_dir_pos(const void *ns,
1612 struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
1613 {
1614 if (pos) {
1615 int valid = kernfs_active(pos) &&
1616 pos->parent == parent && hash == pos->hash;
1617 kernfs_put(pos);
1618 if (!valid)
1619 pos = NULL;
1620 }
1621 if (!pos && (hash > 1) && (hash < INT_MAX)) {
1622 struct rb_node *node = parent->dir.children.rb_node;
1623 while (node) {
1624 pos = rb_to_kn(node);
1625
1626 if (hash < pos->hash)
1627 node = node->rb_left;
1628 else if (hash > pos->hash)
1629 node = node->rb_right;
1630 else
1631 break;
1632 }
1633 }
1634 /* Skip over entries which are dying/dead or in the wrong namespace */
1635 while (pos && (!kernfs_active(pos) || pos->ns != ns)) {
1636 struct rb_node *node = rb_next(&pos->rb);
1637 if (!node)
1638 pos = NULL;
1639 else
1640 pos = rb_to_kn(node);
1641 }
1642 return pos;
1643 }
1644
kernfs_dir_next_pos(const void * ns,struct kernfs_node * parent,ino_t ino,struct kernfs_node * pos)1645 static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
1646 struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
1647 {
1648 pos = kernfs_dir_pos(ns, parent, ino, pos);
1649 if (pos) {
1650 do {
1651 struct rb_node *node = rb_next(&pos->rb);
1652 if (!node)
1653 pos = NULL;
1654 else
1655 pos = rb_to_kn(node);
1656 } while (pos && (!kernfs_active(pos) || pos->ns != ns));
1657 }
1658 return pos;
1659 }
1660
kernfs_fop_readdir(struct file * file,struct dir_context * ctx)1661 static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
1662 {
1663 struct dentry *dentry = file->f_path.dentry;
1664 struct kernfs_node *parent = kernfs_dentry_node(dentry);
1665 struct kernfs_node *pos = file->private_data;
1666 const void *ns = NULL;
1667
1668 if (!dir_emit_dots(file, ctx))
1669 return 0;
1670 mutex_lock(&kernfs_mutex);
1671
1672 if (kernfs_ns_enabled(parent))
1673 ns = kernfs_info(dentry->d_sb)->ns;
1674
1675 for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);
1676 pos;
1677 pos = kernfs_dir_next_pos(ns, parent, ctx->pos, pos)) {
1678 const char *name = pos->name;
1679 unsigned int type = dt_type(pos);
1680 int len = strlen(name);
1681 ino_t ino = pos->id.ino;
1682
1683 ctx->pos = pos->hash;
1684 file->private_data = pos;
1685 kernfs_get(pos);
1686
1687 mutex_unlock(&kernfs_mutex);
1688 if (!dir_emit(ctx, name, len, ino, type))
1689 return 0;
1690 mutex_lock(&kernfs_mutex);
1691 }
1692 mutex_unlock(&kernfs_mutex);
1693 file->private_data = NULL;
1694 ctx->pos = INT_MAX;
1695 return 0;
1696 }
1697
1698 const struct file_operations kernfs_dir_fops = {
1699 .read = generic_read_dir,
1700 .iterate_shared = kernfs_fop_readdir,
1701 .release = kernfs_dir_fop_release,
1702 .llseek = generic_file_llseek,
1703 };
1704