1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * fs/sysfs/symlink.c - sysfs symlink implementation
4  *
5  * Copyright (c) 2001-3 Patrick Mochel
6  * Copyright (c) 2007 SUSE Linux Products GmbH
7  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8  *
9  * Please see Documentation/filesystems/sysfs.txt for more information.
10  */
11 
12 #include <linux/fs.h>
13 #include <linux/module.h>
14 #include <linux/kobject.h>
15 #include <linux/mutex.h>
16 #include <linux/security.h>
17 
18 #include "sysfs.h"
19 
sysfs_do_create_link_sd(struct kernfs_node * parent,struct kobject * target_kobj,const char * name,int warn)20 static int sysfs_do_create_link_sd(struct kernfs_node *parent,
21 				   struct kobject *target_kobj,
22 				   const char *name, int warn)
23 {
24 	struct kernfs_node *kn, *target = NULL;
25 
26 	BUG_ON(!name || !parent);
27 
28 	/*
29 	 * We don't own @target_kobj and it may be removed at any time.
30 	 * Synchronize using sysfs_symlink_target_lock.  See
31 	 * sysfs_remove_dir() for details.
32 	 */
33 	spin_lock(&sysfs_symlink_target_lock);
34 	if (target_kobj->sd) {
35 		target = target_kobj->sd;
36 		kernfs_get(target);
37 	}
38 	spin_unlock(&sysfs_symlink_target_lock);
39 
40 	if (!target)
41 		return -ENOENT;
42 
43 	kn = kernfs_create_link(parent, name, target);
44 	kernfs_put(target);
45 
46 	if (!IS_ERR(kn))
47 		return 0;
48 
49 	if (warn && PTR_ERR(kn) == -EEXIST)
50 		sysfs_warn_dup(parent, name);
51 	return PTR_ERR(kn);
52 }
53 
54 /**
55  *	sysfs_create_link_sd - create symlink to a given object.
56  *	@kn:		directory we're creating the link in.
57  *	@target:	object we're pointing to.
58  *	@name:		name of the symlink.
59  */
sysfs_create_link_sd(struct kernfs_node * kn,struct kobject * target,const char * name)60 int sysfs_create_link_sd(struct kernfs_node *kn, struct kobject *target,
61 			 const char *name)
62 {
63 	return sysfs_do_create_link_sd(kn, target, name, 1);
64 }
65 
sysfs_do_create_link(struct kobject * kobj,struct kobject * target,const char * name,int warn)66 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
67 				const char *name, int warn)
68 {
69 	struct kernfs_node *parent = NULL;
70 
71 	if (!kobj)
72 		parent = sysfs_root_kn;
73 	else
74 		parent = kobj->sd;
75 
76 	if (!parent)
77 		return -EFAULT;
78 
79 	return sysfs_do_create_link_sd(parent, target, name, warn);
80 }
81 
82 /**
83  *	sysfs_create_link - create symlink between two objects.
84  *	@kobj:	object whose directory we're creating the link in.
85  *	@target:	object we're pointing to.
86  *	@name:		name of the symlink.
87  */
sysfs_create_link(struct kobject * kobj,struct kobject * target,const char * name)88 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
89 		      const char *name)
90 {
91 	return sysfs_do_create_link(kobj, target, name, 1);
92 }
93 EXPORT_SYMBOL_GPL(sysfs_create_link);
94 
95 /**
96  *	sysfs_create_link_nowarn - create symlink between two objects.
97  *	@kobj:	object whose directory we're creating the link in.
98  *	@target:	object we're pointing to.
99  *	@name:		name of the symlink.
100  *
101  *	This function does the same as sysfs_create_link(), but it
102  *	doesn't warn if the link already exists.
103  */
sysfs_create_link_nowarn(struct kobject * kobj,struct kobject * target,const char * name)104 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
105 			     const char *name)
106 {
107 	return sysfs_do_create_link(kobj, target, name, 0);
108 }
109 EXPORT_SYMBOL_GPL(sysfs_create_link_nowarn);
110 
111 /**
112  *	sysfs_delete_link - remove symlink in object's directory.
113  *	@kobj:	object we're acting for.
114  *	@targ:	object we're pointing to.
115  *	@name:	name of the symlink to remove.
116  *
117  *	Unlike sysfs_remove_link sysfs_delete_link has enough information
118  *	to successfully delete symlinks in tagged directories.
119  */
sysfs_delete_link(struct kobject * kobj,struct kobject * targ,const char * name)120 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
121 			const char *name)
122 {
123 	const void *ns = NULL;
124 
125 	/*
126 	 * We don't own @target and it may be removed at any time.
127 	 * Synchronize using sysfs_symlink_target_lock.  See
128 	 * sysfs_remove_dir() for details.
129 	 */
130 	spin_lock(&sysfs_symlink_target_lock);
131 	if (targ->sd && kernfs_ns_enabled(kobj->sd))
132 		ns = targ->sd->ns;
133 	spin_unlock(&sysfs_symlink_target_lock);
134 	kernfs_remove_by_name_ns(kobj->sd, name, ns);
135 }
136 
137 /**
138  *	sysfs_remove_link - remove symlink in object's directory.
139  *	@kobj:	object we're acting for.
140  *	@name:	name of the symlink to remove.
141  */
sysfs_remove_link(struct kobject * kobj,const char * name)142 void sysfs_remove_link(struct kobject *kobj, const char *name)
143 {
144 	struct kernfs_node *parent = NULL;
145 
146 	if (!kobj)
147 		parent = sysfs_root_kn;
148 	else
149 		parent = kobj->sd;
150 
151 	kernfs_remove_by_name(parent, name);
152 }
153 EXPORT_SYMBOL_GPL(sysfs_remove_link);
154 
155 /**
156  *	sysfs_rename_link_ns - rename symlink in object's directory.
157  *	@kobj:	object we're acting for.
158  *	@targ:	object we're pointing to.
159  *	@old:	previous name of the symlink.
160  *	@new:	new name of the symlink.
161  *	@new_ns: new namespace of the symlink.
162  *
163  *	A helper function for the common rename symlink idiom.
164  */
sysfs_rename_link_ns(struct kobject * kobj,struct kobject * targ,const char * old,const char * new,const void * new_ns)165 int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ,
166 			 const char *old, const char *new, const void *new_ns)
167 {
168 	struct kernfs_node *parent, *kn = NULL;
169 	const void *old_ns = NULL;
170 	int result;
171 
172 	if (!kobj)
173 		parent = sysfs_root_kn;
174 	else
175 		parent = kobj->sd;
176 
177 	if (targ->sd)
178 		old_ns = targ->sd->ns;
179 
180 	result = -ENOENT;
181 	kn = kernfs_find_and_get_ns(parent, old, old_ns);
182 	if (!kn)
183 		goto out;
184 
185 	result = -EINVAL;
186 	if (kernfs_type(kn) != KERNFS_LINK)
187 		goto out;
188 	if (kn->symlink.target_kn->priv != targ)
189 		goto out;
190 
191 	result = kernfs_rename_ns(kn, parent, new, new_ns);
192 
193 out:
194 	kernfs_put(kn);
195 	return result;
196 }
197 EXPORT_SYMBOL_GPL(sysfs_rename_link_ns);
198