1/*
2 * fs/sysfs/symlink.c - sysfs symlink implementation
3 *
4 * Copyright (c) 2001-3 Patrick Mochel
5 * Copyright (c) 2007 SUSE Linux Products GmbH
6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
7 *
8 * This file is released under the GPLv2.
9 *
10 * Please see Documentation/filesystems/sysfs.txt for more information.
11 */
12
13#include <linux/fs.h>
14#include <linux/gfp.h>
15#include <linux/mount.h>
16#include <linux/module.h>
17#include <linux/kobject.h>
18#include <linux/namei.h>
19#include <linux/mutex.h>
20#include <linux/security.h>
21
22#include "sysfs.h"
23
24static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
25				const char *name, int warn)
26{
27	struct sysfs_dirent *parent_sd = NULL;
28	struct sysfs_dirent *target_sd = NULL;
29	struct sysfs_dirent *sd = NULL;
30	struct sysfs_addrm_cxt acxt;
31	enum kobj_ns_type ns_type;
32	int error;
33
34	BUG_ON(!name);
35
36	if (!kobj)
37		parent_sd = &sysfs_root;
38	else
39		parent_sd = kobj->sd;
40
41	error = -EFAULT;
42	if (!parent_sd)
43		goto out_put;
44
45	/* target->sd can go away beneath us but is protected with
46	 * sysfs_assoc_lock.  Fetch target_sd from it.
47	 */
48	spin_lock(&sysfs_assoc_lock);
49	if (target->sd)
50		target_sd = sysfs_get(target->sd);
51	spin_unlock(&sysfs_assoc_lock);
52
53	error = -ENOENT;
54	if (!target_sd)
55		goto out_put;
56
57	error = -ENOMEM;
58	sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
59	if (!sd)
60		goto out_put;
61
62	ns_type = sysfs_ns_type(parent_sd);
63	if (ns_type)
64		sd->s_ns = target->ktype->namespace(target);
65	sd->s_symlink.target_sd = target_sd;
66	target_sd = NULL;	/* reference is now owned by the symlink */
67
68	sysfs_addrm_start(&acxt, parent_sd);
69	/* Symlinks must be between directories with the same ns_type */
70	if (!ns_type ||
71	    (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) {
72		if (warn)
73			error = sysfs_add_one(&acxt, sd);
74		else
75			error = __sysfs_add_one(&acxt, sd);
76	} else {
77		error = -EINVAL;
78		WARN(1, KERN_WARNING
79			"sysfs: symlink across ns_types %s/%s -> %s/%s\n",
80			parent_sd->s_name,
81			sd->s_name,
82			sd->s_symlink.target_sd->s_parent->s_name,
83			sd->s_symlink.target_sd->s_name);
84	}
85	sysfs_addrm_finish(&acxt);
86
87	if (error)
88		goto out_put;
89
90	return 0;
91
92 out_put:
93	sysfs_put(target_sd);
94	sysfs_put(sd);
95	return error;
96}
97
98/**
99 *	sysfs_create_link - create symlink between two objects.
100 *	@kobj:	object whose directory we're creating the link in.
101 *	@target:	object we're pointing to.
102 *	@name:		name of the symlink.
103 */
104int sysfs_create_link(struct kobject *kobj, struct kobject *target,
105		      const char *name)
106{
107	return sysfs_do_create_link(kobj, target, name, 1);
108}
109
110/**
111 *	sysfs_create_link_nowarn - create symlink between two objects.
112 *	@kobj:	object whose directory we're creating the link in.
113 *	@target:	object we're pointing to.
114 *	@name:		name of the symlink.
115 *
116 *	This function does the same as sysf_create_link(), but it
117 *	doesn't warn if the link already exists.
118 */
119int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
120			     const char *name)
121{
122	return sysfs_do_create_link(kobj, target, name, 0);
123}
124
125/**
126 *	sysfs_delete_link - remove symlink in object's directory.
127 *	@kobj:	object we're acting for.
128 *	@targ:	object we're pointing to.
129 *	@name:	name of the symlink to remove.
130 *
131 *	Unlike sysfs_remove_link sysfs_delete_link has enough information
132 *	to successfully delete symlinks in tagged directories.
133 */
134void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
135			const char *name)
136{
137	const void *ns = NULL;
138	spin_lock(&sysfs_assoc_lock);
139	if (targ->sd && sysfs_ns_type(kobj->sd))
140		ns = targ->sd->s_ns;
141	spin_unlock(&sysfs_assoc_lock);
142	sysfs_hash_and_remove(kobj->sd, ns, name);
143}
144
145/**
146 *	sysfs_remove_link - remove symlink in object's directory.
147 *	@kobj:	object we're acting for.
148 *	@name:	name of the symlink to remove.
149 */
150
151void sysfs_remove_link(struct kobject * kobj, const char * name)
152{
153	struct sysfs_dirent *parent_sd = NULL;
154
155	if (!kobj)
156		parent_sd = &sysfs_root;
157	else
158		parent_sd = kobj->sd;
159
160	sysfs_hash_and_remove(parent_sd, NULL, name);
161}
162
163/**
164 *	sysfs_rename_link - rename symlink in object's directory.
165 *	@kobj:	object we're acting for.
166 *	@targ:	object we're pointing to.
167 *	@old:	previous name of the symlink.
168 *	@new:	new name of the symlink.
169 *
170 *	A helper function for the common rename symlink idiom.
171 */
172int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
173			const char *old, const char *new)
174{
175	struct sysfs_dirent *parent_sd, *sd = NULL;
176	const void *old_ns = NULL, *new_ns = NULL;
177	int result;
178
179	if (!kobj)
180		parent_sd = &sysfs_root;
181	else
182		parent_sd = kobj->sd;
183
184	if (targ->sd)
185		old_ns = targ->sd->s_ns;
186
187	result = -ENOENT;
188	sd = sysfs_get_dirent(parent_sd, old_ns, old);
189	if (!sd)
190		goto out;
191
192	result = -EINVAL;
193	if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
194		goto out;
195	if (sd->s_symlink.target_sd->s_dir.kobj != targ)
196		goto out;
197
198	if (sysfs_ns_type(parent_sd))
199		new_ns = targ->ktype->namespace(targ);
200
201	result = sysfs_rename(sd, parent_sd, new_ns, new);
202
203out:
204	sysfs_put(sd);
205	return result;
206}
207
208static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
209				 struct sysfs_dirent *target_sd, char *path)
210{
211	struct sysfs_dirent *base, *sd;
212	char *s = path;
213	int len = 0;
214
215	/* go up to the root, stop at the base */
216	base = parent_sd;
217	while (base->s_parent) {
218		sd = target_sd->s_parent;
219		while (sd->s_parent && base != sd)
220			sd = sd->s_parent;
221
222		if (base == sd)
223			break;
224
225		strcpy(s, "../");
226		s += 3;
227		base = base->s_parent;
228	}
229
230	/* determine end of target string for reverse fillup */
231	sd = target_sd;
232	while (sd->s_parent && sd != base) {
233		len += strlen(sd->s_name) + 1;
234		sd = sd->s_parent;
235	}
236
237	/* check limits */
238	if (len < 2)
239		return -EINVAL;
240	len--;
241	if ((s - path) + len > PATH_MAX)
242		return -ENAMETOOLONG;
243
244	/* reverse fillup of target string from target to base */
245	sd = target_sd;
246	while (sd->s_parent && sd != base) {
247		int slen = strlen(sd->s_name);
248
249		len -= slen;
250		strncpy(s + len, sd->s_name, slen);
251		if (len)
252			s[--len] = '/';
253
254		sd = sd->s_parent;
255	}
256
257	return 0;
258}
259
260static int sysfs_getlink(struct dentry *dentry, char * path)
261{
262	struct sysfs_dirent *sd = dentry->d_fsdata;
263	struct sysfs_dirent *parent_sd = sd->s_parent;
264	struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
265	int error;
266
267	mutex_lock(&sysfs_mutex);
268	error = sysfs_get_target_path(parent_sd, target_sd, path);
269	mutex_unlock(&sysfs_mutex);
270
271	return error;
272}
273
274static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
275{
276	int error = -ENOMEM;
277	unsigned long page = get_zeroed_page(GFP_KERNEL);
278	if (page) {
279		error = sysfs_getlink(dentry, (char *) page);
280		if (error < 0)
281			free_page((unsigned long)page);
282	}
283	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
284	return NULL;
285}
286
287static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
288{
289	char *page = nd_get_link(nd);
290	if (!IS_ERR(page))
291		free_page((unsigned long)page);
292}
293
294const struct inode_operations sysfs_symlink_inode_operations = {
295	.setxattr	= sysfs_setxattr,
296	.readlink	= generic_readlink,
297	.follow_link	= sysfs_follow_link,
298	.put_link	= sysfs_put_link,
299	.setattr	= sysfs_setattr,
300	.getattr	= sysfs_getattr,
301	.permission	= sysfs_permission,
302};
303
304
305EXPORT_SYMBOL_GPL(sysfs_create_link);
306EXPORT_SYMBOL_GPL(sysfs_remove_link);
307EXPORT_SYMBOL_GPL(sysfs_rename_link);
308