1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  inode.c - part of debugfs, a tiny little debug file system
  4 *
  5 *  Copyright (C) 2004,2019 Greg Kroah-Hartman <greg@kroah.com>
  6 *  Copyright (C) 2004 IBM Inc.
  7 *  Copyright (C) 2019 Linux Foundation <gregkh@linuxfoundation.org>
  8 *
  9 *  debugfs is for people to use instead of /proc or /sys.
 10 *  See ./Documentation/core-api/kernel-api.rst for more details.
 11 */
 12
 13#define pr_fmt(fmt)	"debugfs: " fmt
 14
 15#include <linux/module.h>
 16#include <linux/fs.h>
 17#include <linux/mount.h>
 18#include <linux/pagemap.h>
 19#include <linux/init.h>
 20#include <linux/kobject.h>
 21#include <linux/namei.h>
 22#include <linux/debugfs.h>
 23#include <linux/fsnotify.h>
 24#include <linux/string.h>
 25#include <linux/seq_file.h>
 26#include <linux/parser.h>
 27#include <linux/magic.h>
 28#include <linux/slab.h>
 29#include <linux/security.h>
 30
 31#include "internal.h"
 32
 33#define DEBUGFS_DEFAULT_MODE	0700
 34
 35static struct vfsmount *debugfs_mount;
 36static int debugfs_mount_count;
 37static bool debugfs_registered;
 38static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS;
 39
 40/*
 41 * Don't allow access attributes to be changed whilst the kernel is locked down
 42 * so that we can use the file mode as part of a heuristic to determine whether
 43 * to lock down individual files.
 44 */
 45static int debugfs_setattr(struct user_namespace *mnt_userns,
 46			   struct dentry *dentry, struct iattr *ia)
 47{
 48	int ret;
 49
 50	if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) {
 51		ret = security_locked_down(LOCKDOWN_DEBUGFS);
 52		if (ret)
 53			return ret;
 54	}
 55	return simple_setattr(&init_user_ns, dentry, ia);
 56}
 57
 58static const struct inode_operations debugfs_file_inode_operations = {
 59	.setattr	= debugfs_setattr,
 60};
 61static const struct inode_operations debugfs_dir_inode_operations = {
 62	.lookup		= simple_lookup,
 63	.setattr	= debugfs_setattr,
 64};
 65static const struct inode_operations debugfs_symlink_inode_operations = {
 66	.get_link	= simple_get_link,
 67	.setattr	= debugfs_setattr,
 68};
 69
 70static struct inode *debugfs_get_inode(struct super_block *sb)
 71{
 72	struct inode *inode = new_inode(sb);
 73	if (inode) {
 74		inode->i_ino = get_next_ino();
 75		inode->i_atime = inode->i_mtime =
 76			inode->i_ctime = current_time(inode);
 77	}
 78	return inode;
 79}
 80
 81struct debugfs_mount_opts {
 82	kuid_t uid;
 83	kgid_t gid;
 84	umode_t mode;
 85	/* Opt_* bitfield. */
 86	unsigned int opts;
 87};
 88
 89enum {
 90	Opt_uid,
 91	Opt_gid,
 92	Opt_mode,
 93	Opt_err
 94};
 95
 96static const match_table_t tokens = {
 97	{Opt_uid, "uid=%u"},
 98	{Opt_gid, "gid=%u"},
 99	{Opt_mode, "mode=%o"},
100	{Opt_err, NULL}
101};
102
103struct debugfs_fs_info {
104	struct debugfs_mount_opts mount_opts;
105};
106
107static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
108{
109	substring_t args[MAX_OPT_ARGS];
110	int option;
111	int token;
112	kuid_t uid;
113	kgid_t gid;
114	char *p;
115
116	opts->opts = 0;
117	opts->mode = DEBUGFS_DEFAULT_MODE;
118
119	while ((p = strsep(&data, ",")) != NULL) {
120		if (!*p)
121			continue;
122
123		token = match_token(p, tokens, args);
124		switch (token) {
125		case Opt_uid:
126			if (match_int(&args[0], &option))
127				return -EINVAL;
128			uid = make_kuid(current_user_ns(), option);
129			if (!uid_valid(uid))
130				return -EINVAL;
131			opts->uid = uid;
132			break;
133		case Opt_gid:
134			if (match_int(&args[0], &option))
135				return -EINVAL;
136			gid = make_kgid(current_user_ns(), option);
137			if (!gid_valid(gid))
138				return -EINVAL;
139			opts->gid = gid;
140			break;
141		case Opt_mode:
142			if (match_octal(&args[0], &option))
143				return -EINVAL;
144			opts->mode = option & S_IALLUGO;
145			break;
146		/*
147		 * We might like to report bad mount options here;
148		 * but traditionally debugfs has ignored all mount options
149		 */
150		}
151
152		opts->opts |= BIT(token);
153	}
154
155	return 0;
156}
157
158static void _debugfs_apply_options(struct super_block *sb, bool remount)
159{
160	struct debugfs_fs_info *fsi = sb->s_fs_info;
161	struct inode *inode = d_inode(sb->s_root);
162	struct debugfs_mount_opts *opts = &fsi->mount_opts;
163
164	/*
165	 * On remount, only reset mode/uid/gid if they were provided as mount
166	 * options.
167	 */
168
169	if (!remount || opts->opts & BIT(Opt_mode)) {
170		inode->i_mode &= ~S_IALLUGO;
171		inode->i_mode |= opts->mode;
172	}
173
174	if (!remount || opts->opts & BIT(Opt_uid))
175		inode->i_uid = opts->uid;
176
177	if (!remount || opts->opts & BIT(Opt_gid))
178		inode->i_gid = opts->gid;
179}
180
181static void debugfs_apply_options(struct super_block *sb)
182{
183	_debugfs_apply_options(sb, false);
184}
185
186static void debugfs_apply_options_remount(struct super_block *sb)
187{
188	_debugfs_apply_options(sb, true);
189}
190
191static int debugfs_remount(struct super_block *sb, int *flags, char *data)
192{
193	int err;
194	struct debugfs_fs_info *fsi = sb->s_fs_info;
195
196	sync_filesystem(sb);
197	err = debugfs_parse_options(data, &fsi->mount_opts);
198	if (err)
199		goto fail;
200
201	debugfs_apply_options_remount(sb);
202
203fail:
204	return err;
205}
206
207static int debugfs_show_options(struct seq_file *m, struct dentry *root)
208{
209	struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
210	struct debugfs_mount_opts *opts = &fsi->mount_opts;
211
212	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
213		seq_printf(m, ",uid=%u",
214			   from_kuid_munged(&init_user_ns, opts->uid));
215	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
216		seq_printf(m, ",gid=%u",
217			   from_kgid_munged(&init_user_ns, opts->gid));
218	if (opts->mode != DEBUGFS_DEFAULT_MODE)
219		seq_printf(m, ",mode=%o", opts->mode);
220
221	return 0;
222}
223
224static void debugfs_free_inode(struct inode *inode)
225{
226	if (S_ISLNK(inode->i_mode))
227		kfree(inode->i_link);
228	free_inode_nonrcu(inode);
229}
230
231static const struct super_operations debugfs_super_operations = {
232	.statfs		= simple_statfs,
233	.remount_fs	= debugfs_remount,
234	.show_options	= debugfs_show_options,
235	.free_inode	= debugfs_free_inode,
236};
237
238static void debugfs_release_dentry(struct dentry *dentry)
239{
240	void *fsd = dentry->d_fsdata;
241
242	if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
243		kfree(dentry->d_fsdata);
244}
245
246static struct vfsmount *debugfs_automount(struct path *path)
247{
248	debugfs_automount_t f;
249	f = (debugfs_automount_t)path->dentry->d_fsdata;
250	return f(path->dentry, d_inode(path->dentry)->i_private);
251}
252
253static const struct dentry_operations debugfs_dops = {
254	.d_delete = always_delete_dentry,
255	.d_release = debugfs_release_dentry,
256	.d_automount = debugfs_automount,
257};
258
259static int debug_fill_super(struct super_block *sb, void *data, int silent)
260{
261	static const struct tree_descr debug_files[] = {{""}};
262	struct debugfs_fs_info *fsi;
263	int err;
264
265	fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
266	sb->s_fs_info = fsi;
267	if (!fsi) {
268		err = -ENOMEM;
269		goto fail;
270	}
271
272	err = debugfs_parse_options(data, &fsi->mount_opts);
273	if (err)
274		goto fail;
275
276	err  =  simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
277	if (err)
278		goto fail;
279
280	sb->s_op = &debugfs_super_operations;
281	sb->s_d_op = &debugfs_dops;
282
283	debugfs_apply_options(sb);
284
285	return 0;
286
287fail:
288	kfree(fsi);
289	sb->s_fs_info = NULL;
290	return err;
291}
292
293static struct dentry *debug_mount(struct file_system_type *fs_type,
294			int flags, const char *dev_name,
295			void *data)
296{
297	if (!(debugfs_allow & DEBUGFS_ALLOW_API))
298		return ERR_PTR(-EPERM);
299
300	return mount_single(fs_type, flags, data, debug_fill_super);
301}
302
303static struct file_system_type debug_fs_type = {
304	.owner =	THIS_MODULE,
305	.name =		"debugfs",
306	.mount =	debug_mount,
307	.kill_sb =	kill_litter_super,
308};
309MODULE_ALIAS_FS("debugfs");
310
311/**
312 * debugfs_lookup() - look up an existing debugfs file
313 * @name: a pointer to a string containing the name of the file to look up.
314 * @parent: a pointer to the parent dentry of the file.
315 *
316 * This function will return a pointer to a dentry if it succeeds.  If the file
317 * doesn't exist or an error occurs, %NULL will be returned.  The returned
318 * dentry must be passed to dput() when it is no longer needed.
319 *
320 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
321 * returned.
322 */
323struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
324{
325	struct dentry *dentry;
326
327	if (!debugfs_initialized() || IS_ERR_OR_NULL(name) || IS_ERR(parent))
328		return NULL;
329
330	if (!parent)
331		parent = debugfs_mount->mnt_root;
332
333	dentry = lookup_positive_unlocked(name, parent, strlen(name));
334	if (IS_ERR(dentry))
335		return NULL;
336	return dentry;
337}
338EXPORT_SYMBOL_GPL(debugfs_lookup);
339
340static struct dentry *start_creating(const char *name, struct dentry *parent)
341{
342	struct dentry *dentry;
343	int error;
344
345	if (!(debugfs_allow & DEBUGFS_ALLOW_API))
346		return ERR_PTR(-EPERM);
347
348	if (!debugfs_initialized())
349		return ERR_PTR(-ENOENT);
350
351	pr_debug("creating file '%s'\n", name);
352
353	if (IS_ERR(parent))
354		return parent;
355
356	error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
357			      &debugfs_mount_count);
358	if (error) {
359		pr_err("Unable to pin filesystem for file '%s'\n", name);
360		return ERR_PTR(error);
361	}
362
363	/* If the parent is not specified, we create it in the root.
364	 * We need the root dentry to do this, which is in the super
365	 * block. A pointer to that is in the struct vfsmount that we
366	 * have around.
367	 */
368	if (!parent)
369		parent = debugfs_mount->mnt_root;
370
371	inode_lock(d_inode(parent));
372	if (unlikely(IS_DEADDIR(d_inode(parent))))
373		dentry = ERR_PTR(-ENOENT);
374	else
375		dentry = lookup_one_len(name, parent, strlen(name));
376	if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
377		if (d_is_dir(dentry))
378			pr_err("Directory '%s' with parent '%s' already present!\n",
379			       name, parent->d_name.name);
380		else
381			pr_err("File '%s' in directory '%s' already present!\n",
382			       name, parent->d_name.name);
383		dput(dentry);
384		dentry = ERR_PTR(-EEXIST);
385	}
386
387	if (IS_ERR(dentry)) {
388		inode_unlock(d_inode(parent));
389		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
390	}
391
392	return dentry;
393}
394
395static struct dentry *failed_creating(struct dentry *dentry)
396{
397	inode_unlock(d_inode(dentry->d_parent));
398	dput(dentry);
399	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
400	return ERR_PTR(-ENOMEM);
401}
402
403static struct dentry *end_creating(struct dentry *dentry)
404{
405	inode_unlock(d_inode(dentry->d_parent));
406	return dentry;
407}
408
409static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
410				struct dentry *parent, void *data,
411				const struct file_operations *proxy_fops,
412				const struct file_operations *real_fops)
413{
414	struct dentry *dentry;
415	struct inode *inode;
416
417	if (!(mode & S_IFMT))
418		mode |= S_IFREG;
419	BUG_ON(!S_ISREG(mode));
420	dentry = start_creating(name, parent);
421
422	if (IS_ERR(dentry))
423		return dentry;
424
425	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
426		failed_creating(dentry);
427		return ERR_PTR(-EPERM);
428	}
429
430	inode = debugfs_get_inode(dentry->d_sb);
431	if (unlikely(!inode)) {
432		pr_err("out of free dentries, can not create file '%s'\n",
433		       name);
434		return failed_creating(dentry);
435	}
436
437	inode->i_mode = mode;
438	inode->i_private = data;
439
440	inode->i_op = &debugfs_file_inode_operations;
441	inode->i_fop = proxy_fops;
442	dentry->d_fsdata = (void *)((unsigned long)real_fops |
443				DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
444
445	d_instantiate(dentry, inode);
446	fsnotify_create(d_inode(dentry->d_parent), dentry);
447	return end_creating(dentry);
448}
449
450/**
451 * debugfs_create_file - create a file in the debugfs filesystem
452 * @name: a pointer to a string containing the name of the file to create.
453 * @mode: the permission that the file should have.
454 * @parent: a pointer to the parent dentry for this file.  This should be a
455 *          directory dentry if set.  If this parameter is NULL, then the
456 *          file will be created in the root of the debugfs filesystem.
457 * @data: a pointer to something that the caller will want to get to later
458 *        on.  The inode.i_private pointer will point to this value on
459 *        the open() call.
460 * @fops: a pointer to a struct file_operations that should be used for
461 *        this file.
462 *
463 * This is the basic "create a file" function for debugfs.  It allows for a
464 * wide range of flexibility in creating a file, or a directory (if you want
465 * to create a directory, the debugfs_create_dir() function is
466 * recommended to be used instead.)
467 *
468 * This function will return a pointer to a dentry if it succeeds.  This
469 * pointer must be passed to the debugfs_remove() function when the file is
470 * to be removed (no automatic cleanup happens if your module is unloaded,
471 * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
472 * returned.
473 *
474 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
475 * returned.
476 *
477 * NOTE: it's expected that most callers should _ignore_ the errors returned
478 * by this function. Other debugfs functions handle the fact that the "dentry"
479 * passed to them could be an error and they don't crash in that case.
480 * Drivers should generally work fine even if debugfs fails to init anyway.
481 */
482struct dentry *debugfs_create_file(const char *name, umode_t mode,
483				   struct dentry *parent, void *data,
484				   const struct file_operations *fops)
485{
486
487	return __debugfs_create_file(name, mode, parent, data,
488				fops ? &debugfs_full_proxy_file_operations :
489					&debugfs_noop_file_operations,
490				fops);
491}
492EXPORT_SYMBOL_GPL(debugfs_create_file);
493
494/**
495 * debugfs_create_file_unsafe - create a file in the debugfs filesystem
496 * @name: a pointer to a string containing the name of the file to create.
497 * @mode: the permission that the file should have.
498 * @parent: a pointer to the parent dentry for this file.  This should be a
499 *          directory dentry if set.  If this parameter is NULL, then the
500 *          file will be created in the root of the debugfs filesystem.
501 * @data: a pointer to something that the caller will want to get to later
502 *        on.  The inode.i_private pointer will point to this value on
503 *        the open() call.
504 * @fops: a pointer to a struct file_operations that should be used for
505 *        this file.
506 *
507 * debugfs_create_file_unsafe() is completely analogous to
508 * debugfs_create_file(), the only difference being that the fops
509 * handed it will not get protected against file removals by the
510 * debugfs core.
511 *
512 * It is your responsibility to protect your struct file_operation
513 * methods against file removals by means of debugfs_file_get()
514 * and debugfs_file_put(). ->open() is still protected by
515 * debugfs though.
516 *
517 * Any struct file_operations defined by means of
518 * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and
519 * thus, may be used here.
520 */
521struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
522				   struct dentry *parent, void *data,
523				   const struct file_operations *fops)
524{
525
526	return __debugfs_create_file(name, mode, parent, data,
527				fops ? &debugfs_open_proxy_file_operations :
528					&debugfs_noop_file_operations,
529				fops);
530}
531EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
532
533/**
534 * debugfs_create_file_size - create a file in the debugfs filesystem
535 * @name: a pointer to a string containing the name of the file to create.
536 * @mode: the permission that the file should have.
537 * @parent: a pointer to the parent dentry for this file.  This should be a
538 *          directory dentry if set.  If this parameter is NULL, then the
539 *          file will be created in the root of the debugfs filesystem.
540 * @data: a pointer to something that the caller will want to get to later
541 *        on.  The inode.i_private pointer will point to this value on
542 *        the open() call.
543 * @fops: a pointer to a struct file_operations that should be used for
544 *        this file.
545 * @file_size: initial file size
546 *
547 * This is the basic "create a file" function for debugfs.  It allows for a
548 * wide range of flexibility in creating a file, or a directory (if you want
549 * to create a directory, the debugfs_create_dir() function is
550 * recommended to be used instead.)
551 */
552void debugfs_create_file_size(const char *name, umode_t mode,
553			      struct dentry *parent, void *data,
554			      const struct file_operations *fops,
555			      loff_t file_size)
556{
557	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
558
559	if (!IS_ERR(de))
560		d_inode(de)->i_size = file_size;
561}
562EXPORT_SYMBOL_GPL(debugfs_create_file_size);
563
564/**
565 * debugfs_create_dir - create a directory in the debugfs filesystem
566 * @name: a pointer to a string containing the name of the directory to
567 *        create.
568 * @parent: a pointer to the parent dentry for this file.  This should be a
569 *          directory dentry if set.  If this parameter is NULL, then the
570 *          directory will be created in the root of the debugfs filesystem.
571 *
572 * This function creates a directory in debugfs with the given name.
573 *
574 * This function will return a pointer to a dentry if it succeeds.  This
575 * pointer must be passed to the debugfs_remove() function when the file is
576 * to be removed (no automatic cleanup happens if your module is unloaded,
577 * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
578 * returned.
579 *
580 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
581 * returned.
582 *
583 * NOTE: it's expected that most callers should _ignore_ the errors returned
584 * by this function. Other debugfs functions handle the fact that the "dentry"
585 * passed to them could be an error and they don't crash in that case.
586 * Drivers should generally work fine even if debugfs fails to init anyway.
587 */
588struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
589{
590	struct dentry *dentry = start_creating(name, parent);
591	struct inode *inode;
592
593	if (IS_ERR(dentry))
594		return dentry;
595
596	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
597		failed_creating(dentry);
598		return ERR_PTR(-EPERM);
599	}
600
601	inode = debugfs_get_inode(dentry->d_sb);
602	if (unlikely(!inode)) {
603		pr_err("out of free dentries, can not create directory '%s'\n",
604		       name);
605		return failed_creating(dentry);
606	}
607
608	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
609	inode->i_op = &debugfs_dir_inode_operations;
610	inode->i_fop = &simple_dir_operations;
611
612	/* directory inodes start off with i_nlink == 2 (for "." entry) */
613	inc_nlink(inode);
614	d_instantiate(dentry, inode);
615	inc_nlink(d_inode(dentry->d_parent));
616	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
617	return end_creating(dentry);
618}
619EXPORT_SYMBOL_GPL(debugfs_create_dir);
620
621/**
622 * debugfs_create_automount - create automount point in the debugfs filesystem
623 * @name: a pointer to a string containing the name of the file to create.
624 * @parent: a pointer to the parent dentry for this file.  This should be a
625 *          directory dentry if set.  If this parameter is NULL, then the
626 *          file will be created in the root of the debugfs filesystem.
627 * @f: function to be called when pathname resolution steps on that one.
628 * @data: opaque argument to pass to f().
629 *
630 * @f should return what ->d_automount() would.
631 */
632struct dentry *debugfs_create_automount(const char *name,
633					struct dentry *parent,
634					debugfs_automount_t f,
635					void *data)
636{
637	struct dentry *dentry = start_creating(name, parent);
638	struct inode *inode;
639
640	if (IS_ERR(dentry))
641		return dentry;
642
643	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
644		failed_creating(dentry);
645		return ERR_PTR(-EPERM);
646	}
647
648	inode = debugfs_get_inode(dentry->d_sb);
649	if (unlikely(!inode)) {
650		pr_err("out of free dentries, can not create automount '%s'\n",
651		       name);
652		return failed_creating(dentry);
653	}
654
655	make_empty_dir_inode(inode);
656	inode->i_flags |= S_AUTOMOUNT;
657	inode->i_private = data;
658	dentry->d_fsdata = (void *)f;
659	/* directory inodes start off with i_nlink == 2 (for "." entry) */
660	inc_nlink(inode);
661	d_instantiate(dentry, inode);
662	inc_nlink(d_inode(dentry->d_parent));
663	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
664	return end_creating(dentry);
665}
666EXPORT_SYMBOL(debugfs_create_automount);
667
668/**
669 * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
670 * @name: a pointer to a string containing the name of the symbolic link to
671 *        create.
672 * @parent: a pointer to the parent dentry for this symbolic link.  This
673 *          should be a directory dentry if set.  If this parameter is NULL,
674 *          then the symbolic link will be created in the root of the debugfs
675 *          filesystem.
676 * @target: a pointer to a string containing the path to the target of the
677 *          symbolic link.
678 *
679 * This function creates a symbolic link with the given name in debugfs that
680 * links to the given target path.
681 *
682 * This function will return a pointer to a dentry if it succeeds.  This
683 * pointer must be passed to the debugfs_remove() function when the symbolic
684 * link is to be removed (no automatic cleanup happens if your module is
685 * unloaded, you are responsible here.)  If an error occurs, ERR_PTR(-ERROR)
686 * will be returned.
687 *
688 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
689 * returned.
690 */
691struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
692				      const char *target)
693{
694	struct dentry *dentry;
695	struct inode *inode;
696	char *link = kstrdup(target, GFP_KERNEL);
697	if (!link)
698		return ERR_PTR(-ENOMEM);
699
700	dentry = start_creating(name, parent);
701	if (IS_ERR(dentry)) {
702		kfree(link);
703		return dentry;
704	}
705
706	inode = debugfs_get_inode(dentry->d_sb);
707	if (unlikely(!inode)) {
708		pr_err("out of free dentries, can not create symlink '%s'\n",
709		       name);
710		kfree(link);
711		return failed_creating(dentry);
712	}
713	inode->i_mode = S_IFLNK | S_IRWXUGO;
714	inode->i_op = &debugfs_symlink_inode_operations;
715	inode->i_link = link;
716	d_instantiate(dentry, inode);
717	return end_creating(dentry);
718}
719EXPORT_SYMBOL_GPL(debugfs_create_symlink);
720
721static void __debugfs_file_removed(struct dentry *dentry)
722{
723	struct debugfs_fsdata *fsd;
724
725	/*
726	 * Paired with the closing smp_mb() implied by a successful
727	 * cmpxchg() in debugfs_file_get(): either
728	 * debugfs_file_get() must see a dead dentry or we must see a
729	 * debugfs_fsdata instance at ->d_fsdata here (or both).
730	 */
731	smp_mb();
732	fsd = READ_ONCE(dentry->d_fsdata);
733	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
734		return;
735	if (!refcount_dec_and_test(&fsd->active_users))
736		wait_for_completion(&fsd->active_users_drained);
737}
738
739static void remove_one(struct dentry *victim)
740{
741        if (d_is_reg(victim))
742		__debugfs_file_removed(victim);
743	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
744}
745
746/**
747 * debugfs_remove - recursively removes a directory
748 * @dentry: a pointer to a the dentry of the directory to be removed.  If this
749 *          parameter is NULL or an error value, nothing will be done.
750 *
751 * This function recursively removes a directory tree in debugfs that
752 * was previously created with a call to another debugfs function
753 * (like debugfs_create_file() or variants thereof.)
754 *
755 * This function is required to be called in order for the file to be
756 * removed, no automatic cleanup of files will happen when a module is
757 * removed, you are responsible here.
758 */
759void debugfs_remove(struct dentry *dentry)
760{
761	if (IS_ERR_OR_NULL(dentry))
762		return;
763
764	simple_pin_fs(&debug_fs_type, &debugfs_mount, &debugfs_mount_count);
765	simple_recursive_removal(dentry, remove_one);
766	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
767}
768EXPORT_SYMBOL_GPL(debugfs_remove);
769
770/**
771 * debugfs_lookup_and_remove - lookup a directory or file and recursively remove it
772 * @name: a pointer to a string containing the name of the item to look up.
773 * @parent: a pointer to the parent dentry of the item.
774 *
775 * This is the equlivant of doing something like
776 * debugfs_remove(debugfs_lookup(..)) but with the proper reference counting
777 * handled for the directory being looked up.
778 */
779void debugfs_lookup_and_remove(const char *name, struct dentry *parent)
780{
781	struct dentry *dentry;
782
783	dentry = debugfs_lookup(name, parent);
784	if (!dentry)
785		return;
786
787	debugfs_remove(dentry);
788	dput(dentry);
789}
790EXPORT_SYMBOL_GPL(debugfs_lookup_and_remove);
791
792/**
793 * debugfs_rename - rename a file/directory in the debugfs filesystem
794 * @old_dir: a pointer to the parent dentry for the renamed object. This
795 *          should be a directory dentry.
796 * @old_dentry: dentry of an object to be renamed.
797 * @new_dir: a pointer to the parent dentry where the object should be
798 *          moved. This should be a directory dentry.
799 * @new_name: a pointer to a string containing the target name.
800 *
801 * This function renames a file/directory in debugfs.  The target must not
802 * exist for rename to succeed.
803 *
804 * This function will return a pointer to old_dentry (which is updated to
805 * reflect renaming) if it succeeds. If an error occurs, %NULL will be
806 * returned.
807 *
808 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
809 * returned.
810 */
811struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
812		struct dentry *new_dir, const char *new_name)
813{
814	int error;
815	struct dentry *dentry = NULL, *trap;
816	struct name_snapshot old_name;
817
818	if (IS_ERR(old_dir))
819		return old_dir;
820	if (IS_ERR(new_dir))
821		return new_dir;
822	if (IS_ERR_OR_NULL(old_dentry))
823		return old_dentry;
824
825	trap = lock_rename(new_dir, old_dir);
826	/* Source or destination directories don't exist? */
827	if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
828		goto exit;
829	/* Source does not exist, cyclic rename, or mountpoint? */
830	if (d_really_is_negative(old_dentry) || old_dentry == trap ||
831	    d_mountpoint(old_dentry))
832		goto exit;
833	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
834	/* Lookup failed, cyclic rename or target exists? */
835	if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
836		goto exit;
837
838	take_dentry_name_snapshot(&old_name, old_dentry);
839
840	error = simple_rename(&init_user_ns, d_inode(old_dir), old_dentry,
841			      d_inode(new_dir), dentry, 0);
842	if (error) {
843		release_dentry_name_snapshot(&old_name);
844		goto exit;
845	}
846	d_move(old_dentry, dentry);
847	fsnotify_move(d_inode(old_dir), d_inode(new_dir), &old_name.name,
848		d_is_dir(old_dentry),
849		NULL, old_dentry);
850	release_dentry_name_snapshot(&old_name);
851	unlock_rename(new_dir, old_dir);
852	dput(dentry);
853	return old_dentry;
854exit:
855	if (dentry && !IS_ERR(dentry))
856		dput(dentry);
857	unlock_rename(new_dir, old_dir);
858	if (IS_ERR(dentry))
859		return dentry;
860	return ERR_PTR(-EINVAL);
861}
862EXPORT_SYMBOL_GPL(debugfs_rename);
863
864/**
865 * debugfs_initialized - Tells whether debugfs has been registered
866 */
867bool debugfs_initialized(void)
868{
869	return debugfs_registered;
870}
871EXPORT_SYMBOL_GPL(debugfs_initialized);
872
873static int __init debugfs_kernel(char *str)
874{
875	if (str) {
876		if (!strcmp(str, "on"))
877			debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
878		else if (!strcmp(str, "no-mount"))
879			debugfs_allow = DEBUGFS_ALLOW_API;
880		else if (!strcmp(str, "off"))
881			debugfs_allow = 0;
882	}
883
884	return 0;
885}
886early_param("debugfs", debugfs_kernel);
887static int __init debugfs_init(void)
888{
889	int retval;
890
891	if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
892		return -EPERM;
893
894	retval = sysfs_create_mount_point(kernel_kobj, "debug");
895	if (retval)
896		return retval;
897
898	retval = register_filesystem(&debug_fs_type);
899	if (retval)
900		sysfs_remove_mount_point(kernel_kobj, "debug");
901	else
902		debugfs_registered = true;
903
904	return retval;
905}
906core_initcall(debugfs_init);