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1/* -*- mode: c; c-basic-offset: 8; -*-
2 * vim: noexpandtab sw=8 ts=8 sts=0:
3 *
4 * symlink.c - operations for configfs symlinks.
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public
8 * License as published by the Free Software Foundation; either
9 * version 2 of the License, or (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public
17 * License along with this program; if not, write to the
18 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 * Boston, MA 021110-1307, USA.
20 *
21 * Based on sysfs:
22 * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
23 *
24 * configfs Copyright (C) 2005 Oracle. All rights reserved.
25 */
26
27#include <linux/fs.h>
28#include <linux/module.h>
29#include <linux/namei.h>
30#include <linux/slab.h>
31
32#include <linux/configfs.h>
33#include "configfs_internal.h"
34
35/* Protects attachments of new symlinks */
36DEFINE_MUTEX(configfs_symlink_mutex);
37
38static int item_depth(struct config_item * item)
39{
40 struct config_item * p = item;
41 int depth = 0;
42 do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
43 return depth;
44}
45
46static int item_path_length(struct config_item * item)
47{
48 struct config_item * p = item;
49 int length = 1;
50 do {
51 length += strlen(config_item_name(p)) + 1;
52 p = p->ci_parent;
53 } while (p && !configfs_is_root(p));
54 return length;
55}
56
57static void fill_item_path(struct config_item * item, char * buffer, int length)
58{
59 struct config_item * p;
60
61 --length;
62 for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
63 int cur = strlen(config_item_name(p));
64
65 /* back up enough to print this bus id with '/' */
66 length -= cur;
67 strncpy(buffer + length,config_item_name(p),cur);
68 *(buffer + --length) = '/';
69 }
70}
71
72static int create_link(struct config_item *parent_item,
73 struct config_item *item,
74 struct dentry *dentry)
75{
76 struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
77 struct configfs_symlink *sl;
78 int ret;
79
80 ret = -ENOENT;
81 if (!configfs_dirent_is_ready(target_sd))
82 goto out;
83 ret = -ENOMEM;
84 sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
85 if (sl) {
86 sl->sl_target = config_item_get(item);
87 spin_lock(&configfs_dirent_lock);
88 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
89 spin_unlock(&configfs_dirent_lock);
90 config_item_put(item);
91 kfree(sl);
92 return -ENOENT;
93 }
94 list_add(&sl->sl_list, &target_sd->s_links);
95 spin_unlock(&configfs_dirent_lock);
96 ret = configfs_create_link(sl, parent_item->ci_dentry,
97 dentry);
98 if (ret) {
99 spin_lock(&configfs_dirent_lock);
100 list_del_init(&sl->sl_list);
101 spin_unlock(&configfs_dirent_lock);
102 config_item_put(item);
103 kfree(sl);
104 }
105 }
106
107out:
108 return ret;
109}
110
111
112static int get_target(const char *symname, struct path *path,
113 struct config_item **target)
114{
115 int ret;
116
117 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
118 if (!ret) {
119 if (path->dentry->d_sb == configfs_sb) {
120 *target = configfs_get_config_item(path->dentry);
121 if (!*target) {
122 ret = -ENOENT;
123 path_put(path);
124 }
125 } else {
126 ret = -EPERM;
127 path_put(path);
128 }
129 }
130
131 return ret;
132}
133
134
135int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
136{
137 int ret;
138 struct path path;
139 struct configfs_dirent *sd;
140 struct config_item *parent_item;
141 struct config_item *target_item = NULL;
142 struct config_item_type *type;
143
144 ret = -EPERM; /* What lack-of-symlink returns */
145 if (dentry->d_parent == configfs_sb->s_root)
146 goto out;
147
148 sd = dentry->d_parent->d_fsdata;
149 /*
150 * Fake invisibility if dir belongs to a group/default groups hierarchy
151 * being attached
152 */
153 ret = -ENOENT;
154 if (!configfs_dirent_is_ready(sd))
155 goto out;
156
157 parent_item = configfs_get_config_item(dentry->d_parent);
158 type = parent_item->ci_type;
159
160 ret = -EPERM;
161 if (!type || !type->ct_item_ops ||
162 !type->ct_item_ops->allow_link)
163 goto out_put;
164
165 ret = get_target(symname, &path, &target_item);
166 if (ret)
167 goto out_put;
168
169 ret = type->ct_item_ops->allow_link(parent_item, target_item);
170 if (!ret) {
171 mutex_lock(&configfs_symlink_mutex);
172 ret = create_link(parent_item, target_item, dentry);
173 mutex_unlock(&configfs_symlink_mutex);
174 if (ret && type->ct_item_ops->drop_link)
175 type->ct_item_ops->drop_link(parent_item,
176 target_item);
177 }
178
179 config_item_put(target_item);
180 path_put(&path);
181
182out_put:
183 config_item_put(parent_item);
184
185out:
186 return ret;
187}
188
189int configfs_unlink(struct inode *dir, struct dentry *dentry)
190{
191 struct configfs_dirent *sd = dentry->d_fsdata;
192 struct configfs_symlink *sl;
193 struct config_item *parent_item;
194 struct config_item_type *type;
195 int ret;
196
197 ret = -EPERM; /* What lack-of-symlink returns */
198 if (!(sd->s_type & CONFIGFS_ITEM_LINK))
199 goto out;
200
201 BUG_ON(dentry->d_parent == configfs_sb->s_root);
202
203 sl = sd->s_element;
204
205 parent_item = configfs_get_config_item(dentry->d_parent);
206 type = parent_item->ci_type;
207
208 spin_lock(&configfs_dirent_lock);
209 list_del_init(&sd->s_sibling);
210 spin_unlock(&configfs_dirent_lock);
211 configfs_drop_dentry(sd, dentry->d_parent);
212 dput(dentry);
213 configfs_put(sd);
214
215 /*
216 * drop_link() must be called before
217 * list_del_init(&sl->sl_list), so that the order of
218 * drop_link(this, target) and drop_item(target) is preserved.
219 */
220 if (type && type->ct_item_ops &&
221 type->ct_item_ops->drop_link)
222 type->ct_item_ops->drop_link(parent_item,
223 sl->sl_target);
224
225 spin_lock(&configfs_dirent_lock);
226 list_del_init(&sl->sl_list);
227 spin_unlock(&configfs_dirent_lock);
228
229 /* Put reference from create_link() */
230 config_item_put(sl->sl_target);
231 kfree(sl);
232
233 config_item_put(parent_item);
234
235 ret = 0;
236
237out:
238 return ret;
239}
240
241static int configfs_get_target_path(struct config_item * item, struct config_item * target,
242 char *path)
243{
244 char * s;
245 int depth, size;
246
247 depth = item_depth(item);
248 size = item_path_length(target) + depth * 3 - 1;
249 if (size > PATH_MAX)
250 return -ENAMETOOLONG;
251
252 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
253
254 for (s = path; depth--; s += 3)
255 strcpy(s,"../");
256
257 fill_item_path(target, path, size);
258 pr_debug("%s: path = '%s'\n", __func__, path);
259
260 return 0;
261}
262
263static int configfs_getlink(struct dentry *dentry, char * path)
264{
265 struct config_item *item, *target_item;
266 int error = 0;
267
268 item = configfs_get_config_item(dentry->d_parent);
269 if (!item)
270 return -EINVAL;
271
272 target_item = configfs_get_config_item(dentry);
273 if (!target_item) {
274 config_item_put(item);
275 return -EINVAL;
276 }
277
278 down_read(&configfs_rename_sem);
279 error = configfs_get_target_path(item, target_item, path);
280 up_read(&configfs_rename_sem);
281
282 config_item_put(item);
283 config_item_put(target_item);
284 return error;
285
286}
287
288static void *configfs_follow_link(struct dentry *dentry, struct nameidata *nd)
289{
290 int error = -ENOMEM;
291 unsigned long page = get_zeroed_page(GFP_KERNEL);
292
293 if (page) {
294 error = configfs_getlink(dentry, (char *)page);
295 if (!error) {
296 nd_set_link(nd, (char *)page);
297 return (void *)page;
298 }
299 }
300
301 nd_set_link(nd, ERR_PTR(error));
302 return NULL;
303}
304
305static void configfs_put_link(struct dentry *dentry, struct nameidata *nd,
306 void *cookie)
307{
308 if (cookie) {
309 unsigned long page = (unsigned long)cookie;
310 free_page(page);
311 }
312}
313
314const struct inode_operations configfs_symlink_inode_operations = {
315 .follow_link = configfs_follow_link,
316 .readlink = generic_readlink,
317 .put_link = configfs_put_link,
318 .setattr = configfs_setattr,
319};
320
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * symlink.c - operations for configfs symlinks.
4 *
5 * Based on sysfs:
6 * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
7 *
8 * configfs Copyright (C) 2005 Oracle. All rights reserved.
9 */
10
11#include <linux/fs.h>
12#include <linux/module.h>
13#include <linux/namei.h>
14#include <linux/slab.h>
15
16#include <linux/configfs.h>
17#include "configfs_internal.h"
18
19/* Protects attachments of new symlinks */
20DEFINE_MUTEX(configfs_symlink_mutex);
21
22static int item_depth(struct config_item * item)
23{
24 struct config_item * p = item;
25 int depth = 0;
26 do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
27 return depth;
28}
29
30static int item_path_length(struct config_item * item)
31{
32 struct config_item * p = item;
33 int length = 1;
34 do {
35 length += strlen(config_item_name(p)) + 1;
36 p = p->ci_parent;
37 } while (p && !configfs_is_root(p));
38 return length;
39}
40
41static void fill_item_path(struct config_item * item, char * buffer, int length)
42{
43 struct config_item * p;
44
45 --length;
46 for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
47 int cur = strlen(config_item_name(p));
48
49 /* back up enough to print this bus id with '/' */
50 length -= cur;
51 memcpy(buffer + length, config_item_name(p), cur);
52 *(buffer + --length) = '/';
53 }
54}
55
56static int configfs_get_target_path(struct config_item *item,
57 struct config_item *target, char *path)
58{
59 int depth, size;
60 char *s;
61
62 depth = item_depth(item);
63 size = item_path_length(target) + depth * 3 - 1;
64 if (size > PATH_MAX)
65 return -ENAMETOOLONG;
66
67 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
68
69 for (s = path; depth--; s += 3)
70 strcpy(s,"../");
71
72 fill_item_path(target, path, size);
73 pr_debug("%s: path = '%s'\n", __func__, path);
74 return 0;
75}
76
77static int create_link(struct config_item *parent_item,
78 struct config_item *item,
79 struct dentry *dentry)
80{
81 struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
82 char *body;
83 int ret;
84
85 if (!configfs_dirent_is_ready(target_sd))
86 return -ENOENT;
87
88 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
89 if (!body)
90 return -ENOMEM;
91
92 configfs_get(target_sd);
93 spin_lock(&configfs_dirent_lock);
94 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
95 spin_unlock(&configfs_dirent_lock);
96 configfs_put(target_sd);
97 kfree(body);
98 return -ENOENT;
99 }
100 target_sd->s_links++;
101 spin_unlock(&configfs_dirent_lock);
102 ret = configfs_get_target_path(parent_item, item, body);
103 if (!ret)
104 ret = configfs_create_link(target_sd, parent_item->ci_dentry,
105 dentry, body);
106 if (ret) {
107 spin_lock(&configfs_dirent_lock);
108 target_sd->s_links--;
109 spin_unlock(&configfs_dirent_lock);
110 configfs_put(target_sd);
111 kfree(body);
112 }
113 return ret;
114}
115
116
117static int get_target(const char *symname, struct path *path,
118 struct config_item **target, struct super_block *sb)
119{
120 int ret;
121
122 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
123 if (!ret) {
124 if (path->dentry->d_sb == sb) {
125 *target = configfs_get_config_item(path->dentry);
126 if (!*target) {
127 ret = -ENOENT;
128 path_put(path);
129 }
130 } else {
131 ret = -EPERM;
132 path_put(path);
133 }
134 }
135
136 return ret;
137}
138
139
140int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
141 struct dentry *dentry, const char *symname)
142{
143 int ret;
144 struct path path;
145 struct configfs_dirent *sd;
146 struct config_item *parent_item;
147 struct config_item *target_item = NULL;
148 const struct config_item_type *type;
149
150 sd = dentry->d_parent->d_fsdata;
151 /*
152 * Fake invisibility if dir belongs to a group/default groups hierarchy
153 * being attached
154 */
155 if (!configfs_dirent_is_ready(sd))
156 return -ENOENT;
157
158 parent_item = configfs_get_config_item(dentry->d_parent);
159 type = parent_item->ci_type;
160
161 ret = -EPERM;
162 if (!type || !type->ct_item_ops ||
163 !type->ct_item_ops->allow_link)
164 goto out_put;
165
166 /*
167 * This is really sick. What they wanted was a hybrid of
168 * link(2) and symlink(2) - they wanted the target resolved
169 * at syscall time (as link(2) would've done), be a directory
170 * (which link(2) would've refused to do) *AND* be a deep
171 * fucking magic, making the target busy from rmdir POV.
172 * symlink(2) is nothing of that sort, and the locking it
173 * gets matches the normal symlink(2) semantics. Without
174 * attempts to resolve the target (which might very well
175 * not even exist yet) done prior to locking the parent
176 * directory. This perversion, OTOH, needs to resolve
177 * the target, which would lead to obvious deadlocks if
178 * attempted with any directories locked.
179 *
180 * Unfortunately, that garbage is userland ABI and we should've
181 * said "no" back in 2005. Too late now, so we get to
182 * play very ugly games with locking.
183 *
184 * Try *ANYTHING* of that sort in new code, and you will
185 * really regret it. Just ask yourself - what could a BOFH
186 * do to me and do I want to find it out first-hand?
187 *
188 * AV, a thoroughly annoyed bastard.
189 */
190 inode_unlock(dir);
191 ret = get_target(symname, &path, &target_item, dentry->d_sb);
192 inode_lock(dir);
193 if (ret)
194 goto out_put;
195
196 if (dentry->d_inode || d_unhashed(dentry))
197 ret = -EEXIST;
198 else
199 ret = inode_permission(&init_user_ns, dir,
200 MAY_WRITE | MAY_EXEC);
201 if (!ret)
202 ret = type->ct_item_ops->allow_link(parent_item, target_item);
203 if (!ret) {
204 mutex_lock(&configfs_symlink_mutex);
205 ret = create_link(parent_item, target_item, dentry);
206 mutex_unlock(&configfs_symlink_mutex);
207 if (ret && type->ct_item_ops->drop_link)
208 type->ct_item_ops->drop_link(parent_item,
209 target_item);
210 }
211
212 config_item_put(target_item);
213 path_put(&path);
214
215out_put:
216 config_item_put(parent_item);
217 return ret;
218}
219
220int configfs_unlink(struct inode *dir, struct dentry *dentry)
221{
222 struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
223 struct config_item *parent_item;
224 const struct config_item_type *type;
225 int ret;
226
227 ret = -EPERM; /* What lack-of-symlink returns */
228 if (!(sd->s_type & CONFIGFS_ITEM_LINK))
229 goto out;
230
231 target_sd = sd->s_element;
232
233 parent_item = configfs_get_config_item(dentry->d_parent);
234 type = parent_item->ci_type;
235
236 spin_lock(&configfs_dirent_lock);
237 list_del_init(&sd->s_sibling);
238 spin_unlock(&configfs_dirent_lock);
239 configfs_drop_dentry(sd, dentry->d_parent);
240 dput(dentry);
241 configfs_put(sd);
242
243 /*
244 * drop_link() must be called before
245 * decrementing target's ->s_links, so that the order of
246 * drop_link(this, target) and drop_item(target) is preserved.
247 */
248 if (type && type->ct_item_ops &&
249 type->ct_item_ops->drop_link)
250 type->ct_item_ops->drop_link(parent_item,
251 target_sd->s_element);
252
253 spin_lock(&configfs_dirent_lock);
254 target_sd->s_links--;
255 spin_unlock(&configfs_dirent_lock);
256 configfs_put(target_sd);
257
258 config_item_put(parent_item);
259
260 ret = 0;
261
262out:
263 return ret;
264}
265
266const struct inode_operations configfs_symlink_inode_operations = {
267 .get_link = simple_get_link,
268 .setattr = configfs_setattr,
269};
270