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 */
36 DEFINE_MUTEX(configfs_symlink_mutex);
37
item_depth(struct config_item * item)38 static 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
item_path_length(struct config_item * item)46 static 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
fill_item_path(struct config_item * item,char * buffer,int length)57 static 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 memcpy(buffer + length, config_item_name(p), cur);
68 *(buffer + --length) = '/';
69 }
70 }
71
create_link(struct config_item * parent_item,struct config_item * item,struct dentry * dentry)72 static 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 spin_lock(&configfs_dirent_lock);
87 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
88 spin_unlock(&configfs_dirent_lock);
89 kfree(sl);
90 return -ENOENT;
91 }
92 sl->sl_target = config_item_get(item);
93 list_add(&sl->sl_list, &target_sd->s_links);
94 spin_unlock(&configfs_dirent_lock);
95 ret = configfs_create_link(sl, parent_item->ci_dentry,
96 dentry);
97 if (ret) {
98 spin_lock(&configfs_dirent_lock);
99 list_del_init(&sl->sl_list);
100 spin_unlock(&configfs_dirent_lock);
101 config_item_put(item);
102 kfree(sl);
103 }
104 }
105
106 out:
107 return ret;
108 }
109
110
get_target(const char * symname,struct path * path,struct config_item ** target,struct super_block * sb)111 static int get_target(const char *symname, struct path *path,
112 struct config_item **target, struct super_block *sb)
113 {
114 int ret;
115
116 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
117 if (!ret) {
118 if (path->dentry->d_sb == sb) {
119 *target = configfs_get_config_item(path->dentry);
120 if (!*target) {
121 ret = -ENOENT;
122 path_put(path);
123 }
124 } else {
125 ret = -EPERM;
126 path_put(path);
127 }
128 }
129
130 return ret;
131 }
132
133
configfs_symlink(struct inode * dir,struct dentry * dentry,const char * symname)134 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
135 {
136 int ret;
137 struct path path;
138 struct configfs_dirent *sd;
139 struct config_item *parent_item;
140 struct config_item *target_item = NULL;
141 const struct config_item_type *type;
142
143 sd = dentry->d_parent->d_fsdata;
144 /*
145 * Fake invisibility if dir belongs to a group/default groups hierarchy
146 * being attached
147 */
148 ret = -ENOENT;
149 if (!configfs_dirent_is_ready(sd))
150 goto out;
151
152 parent_item = configfs_get_config_item(dentry->d_parent);
153 type = parent_item->ci_type;
154
155 ret = -EPERM;
156 if (!type || !type->ct_item_ops ||
157 !type->ct_item_ops->allow_link)
158 goto out_put;
159
160 /*
161 * This is really sick. What they wanted was a hybrid of
162 * link(2) and symlink(2) - they wanted the target resolved
163 * at syscall time (as link(2) would've done), be a directory
164 * (which link(2) would've refused to do) *AND* be a deep
165 * fucking magic, making the target busy from rmdir POV.
166 * symlink(2) is nothing of that sort, and the locking it
167 * gets matches the normal symlink(2) semantics. Without
168 * attempts to resolve the target (which might very well
169 * not even exist yet) done prior to locking the parent
170 * directory. This perversion, OTOH, needs to resolve
171 * the target, which would lead to obvious deadlocks if
172 * attempted with any directories locked.
173 *
174 * Unfortunately, that garbage is userland ABI and we should've
175 * said "no" back in 2005. Too late now, so we get to
176 * play very ugly games with locking.
177 *
178 * Try *ANYTHING* of that sort in new code, and you will
179 * really regret it. Just ask yourself - what could a BOFH
180 * do to me and do I want to find it out first-hand?
181 *
182 * AV, a thoroughly annoyed bastard.
183 */
184 inode_unlock(dir);
185 ret = get_target(symname, &path, &target_item, dentry->d_sb);
186 inode_lock(dir);
187 if (ret)
188 goto out_put;
189
190 if (dentry->d_inode || d_unhashed(dentry))
191 ret = -EEXIST;
192 else
193 ret = inode_permission(dir, MAY_WRITE | MAY_EXEC);
194 if (!ret)
195 ret = type->ct_item_ops->allow_link(parent_item, target_item);
196 if (!ret) {
197 mutex_lock(&configfs_symlink_mutex);
198 ret = create_link(parent_item, target_item, dentry);
199 mutex_unlock(&configfs_symlink_mutex);
200 if (ret && type->ct_item_ops->drop_link)
201 type->ct_item_ops->drop_link(parent_item,
202 target_item);
203 }
204
205 config_item_put(target_item);
206 path_put(&path);
207
208 out_put:
209 config_item_put(parent_item);
210
211 out:
212 return ret;
213 }
214
configfs_unlink(struct inode * dir,struct dentry * dentry)215 int configfs_unlink(struct inode *dir, struct dentry *dentry)
216 {
217 struct configfs_dirent *sd = dentry->d_fsdata;
218 struct configfs_symlink *sl;
219 struct config_item *parent_item;
220 const struct config_item_type *type;
221 int ret;
222
223 ret = -EPERM; /* What lack-of-symlink returns */
224 if (!(sd->s_type & CONFIGFS_ITEM_LINK))
225 goto out;
226
227 sl = sd->s_element;
228
229 parent_item = configfs_get_config_item(dentry->d_parent);
230 type = parent_item->ci_type;
231
232 spin_lock(&configfs_dirent_lock);
233 list_del_init(&sd->s_sibling);
234 spin_unlock(&configfs_dirent_lock);
235 configfs_drop_dentry(sd, dentry->d_parent);
236 dput(dentry);
237 configfs_put(sd);
238
239 /*
240 * drop_link() must be called before
241 * list_del_init(&sl->sl_list), so that the order of
242 * drop_link(this, target) and drop_item(target) is preserved.
243 */
244 if (type && type->ct_item_ops &&
245 type->ct_item_ops->drop_link)
246 type->ct_item_ops->drop_link(parent_item,
247 sl->sl_target);
248
249 spin_lock(&configfs_dirent_lock);
250 list_del_init(&sl->sl_list);
251 spin_unlock(&configfs_dirent_lock);
252
253 /* Put reference from create_link() */
254 config_item_put(sl->sl_target);
255 kfree(sl);
256
257 config_item_put(parent_item);
258
259 ret = 0;
260
261 out:
262 return ret;
263 }
264
configfs_get_target_path(struct config_item * item,struct config_item * target,char * path)265 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
266 char *path)
267 {
268 char * s;
269 int depth, size;
270
271 depth = item_depth(item);
272 size = item_path_length(target) + depth * 3 - 1;
273 if (size > PATH_MAX)
274 return -ENAMETOOLONG;
275
276 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
277
278 for (s = path; depth--; s += 3)
279 strcpy(s,"../");
280
281 fill_item_path(target, path, size);
282 pr_debug("%s: path = '%s'\n", __func__, path);
283
284 return 0;
285 }
286
configfs_getlink(struct dentry * dentry,char * path)287 static int configfs_getlink(struct dentry *dentry, char * path)
288 {
289 struct config_item *item, *target_item;
290 int error = 0;
291
292 item = configfs_get_config_item(dentry->d_parent);
293 if (!item)
294 return -EINVAL;
295
296 target_item = configfs_get_config_item(dentry);
297 if (!target_item) {
298 config_item_put(item);
299 return -EINVAL;
300 }
301
302 down_read(&configfs_rename_sem);
303 error = configfs_get_target_path(item, target_item, path);
304 up_read(&configfs_rename_sem);
305
306 config_item_put(item);
307 config_item_put(target_item);
308 return error;
309
310 }
311
configfs_get_link(struct dentry * dentry,struct inode * inode,struct delayed_call * done)312 static const char *configfs_get_link(struct dentry *dentry,
313 struct inode *inode,
314 struct delayed_call *done)
315 {
316 char *body;
317 int error;
318
319 if (!dentry)
320 return ERR_PTR(-ECHILD);
321
322 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
323 if (!body)
324 return ERR_PTR(-ENOMEM);
325
326 error = configfs_getlink(dentry, body);
327 if (!error) {
328 set_delayed_call(done, kfree_link, body);
329 return body;
330 }
331
332 kfree(body);
333 return ERR_PTR(error);
334 }
335
336 const struct inode_operations configfs_symlink_inode_operations = {
337 .get_link = configfs_get_link,
338 .setattr = configfs_setattr,
339 };
340
341