1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* -*- mode: c; c-basic-offset: 8; -*-
3 * vim: noexpandtab sw=8 ts=8 sts=0:
5 * symlink.c - operations for configfs symlinks.
8 * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
10 * configfs Copyright (C) 2005 Oracle. All rights reserved.
14 #include <linux/module.h>
15 #include <linux/namei.h>
16 #include <linux/slab.h>
18 #include <linux/configfs.h>
19 #include "configfs_internal.h"
21 /* Protects attachments of new symlinks */
22 DEFINE_MUTEX(configfs_symlink_mutex);
24 static int item_depth(struct config_item * item)
26 struct config_item * p = item;
28 do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
32 static int item_path_length(struct config_item * item)
34 struct config_item * p = item;
37 length += strlen(config_item_name(p)) + 1;
39 } while (p && !configfs_is_root(p));
43 static void fill_item_path(struct config_item * item, char * buffer, int length)
45 struct config_item * p;
48 for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
49 int cur = strlen(config_item_name(p));
51 /* back up enough to print this bus id with '/' */
53 memcpy(buffer + length, config_item_name(p), cur);
54 *(buffer + --length) = '/';
58 static int create_link(struct config_item *parent_item,
59 struct config_item *item,
60 struct dentry *dentry)
62 struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
63 struct configfs_symlink *sl;
67 if (!configfs_dirent_is_ready(target_sd))
70 sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
72 spin_lock(&configfs_dirent_lock);
73 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
74 spin_unlock(&configfs_dirent_lock);
78 sl->sl_target = config_item_get(item);
79 list_add(&sl->sl_list, &target_sd->s_links);
80 spin_unlock(&configfs_dirent_lock);
81 ret = configfs_create_link(sl, parent_item->ci_dentry,
84 spin_lock(&configfs_dirent_lock);
85 list_del_init(&sl->sl_list);
86 spin_unlock(&configfs_dirent_lock);
87 config_item_put(item);
97 static int get_target(const char *symname, struct path *path,
98 struct config_item **target, struct super_block *sb)
102 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
104 if (path->dentry->d_sb == sb) {
105 *target = configfs_get_config_item(path->dentry);
120 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
124 struct configfs_dirent *sd;
125 struct config_item *parent_item;
126 struct config_item *target_item = NULL;
127 const struct config_item_type *type;
129 sd = dentry->d_parent->d_fsdata;
131 * Fake invisibility if dir belongs to a group/default groups hierarchy
135 if (!configfs_dirent_is_ready(sd))
138 parent_item = configfs_get_config_item(dentry->d_parent);
139 type = parent_item->ci_type;
142 if (!type || !type->ct_item_ops ||
143 !type->ct_item_ops->allow_link)
147 * This is really sick. What they wanted was a hybrid of
148 * link(2) and symlink(2) - they wanted the target resolved
149 * at syscall time (as link(2) would've done), be a directory
150 * (which link(2) would've refused to do) *AND* be a deep
151 * fucking magic, making the target busy from rmdir POV.
152 * symlink(2) is nothing of that sort, and the locking it
153 * gets matches the normal symlink(2) semantics. Without
154 * attempts to resolve the target (which might very well
155 * not even exist yet) done prior to locking the parent
156 * directory. This perversion, OTOH, needs to resolve
157 * the target, which would lead to obvious deadlocks if
158 * attempted with any directories locked.
160 * Unfortunately, that garbage is userland ABI and we should've
161 * said "no" back in 2005. Too late now, so we get to
162 * play very ugly games with locking.
164 * Try *ANYTHING* of that sort in new code, and you will
165 * really regret it. Just ask yourself - what could a BOFH
166 * do to me and do I want to find it out first-hand?
168 * AV, a thoroughly annoyed bastard.
171 ret = get_target(symname, &path, &target_item, dentry->d_sb);
176 if (dentry->d_inode || d_unhashed(dentry))
179 ret = inode_permission(dir, MAY_WRITE | MAY_EXEC);
181 ret = type->ct_item_ops->allow_link(parent_item, target_item);
183 mutex_lock(&configfs_symlink_mutex);
184 ret = create_link(parent_item, target_item, dentry);
185 mutex_unlock(&configfs_symlink_mutex);
186 if (ret && type->ct_item_ops->drop_link)
187 type->ct_item_ops->drop_link(parent_item,
191 config_item_put(target_item);
195 config_item_put(parent_item);
201 int configfs_unlink(struct inode *dir, struct dentry *dentry)
203 struct configfs_dirent *sd = dentry->d_fsdata;
204 struct configfs_symlink *sl;
205 struct config_item *parent_item;
206 const struct config_item_type *type;
209 ret = -EPERM; /* What lack-of-symlink returns */
210 if (!(sd->s_type & CONFIGFS_ITEM_LINK))
215 parent_item = configfs_get_config_item(dentry->d_parent);
216 type = parent_item->ci_type;
218 spin_lock(&configfs_dirent_lock);
219 list_del_init(&sd->s_sibling);
220 spin_unlock(&configfs_dirent_lock);
221 configfs_drop_dentry(sd, dentry->d_parent);
226 * drop_link() must be called before
227 * list_del_init(&sl->sl_list), so that the order of
228 * drop_link(this, target) and drop_item(target) is preserved.
230 if (type && type->ct_item_ops &&
231 type->ct_item_ops->drop_link)
232 type->ct_item_ops->drop_link(parent_item,
235 spin_lock(&configfs_dirent_lock);
236 list_del_init(&sl->sl_list);
237 spin_unlock(&configfs_dirent_lock);
239 /* Put reference from create_link() */
240 config_item_put(sl->sl_target);
243 config_item_put(parent_item);
251 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
257 depth = item_depth(item);
258 size = item_path_length(target) + depth * 3 - 1;
260 return -ENAMETOOLONG;
262 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
264 for (s = path; depth--; s += 3)
267 fill_item_path(target, path, size);
268 pr_debug("%s: path = '%s'\n", __func__, path);
273 static int configfs_getlink(struct dentry *dentry, char * path)
275 struct config_item *item, *target_item;
278 item = configfs_get_config_item(dentry->d_parent);
282 target_item = configfs_get_config_item(dentry);
284 config_item_put(item);
288 down_read(&configfs_rename_sem);
289 error = configfs_get_target_path(item, target_item, path);
290 up_read(&configfs_rename_sem);
292 config_item_put(item);
293 config_item_put(target_item);
298 static const char *configfs_get_link(struct dentry *dentry,
300 struct delayed_call *done)
306 return ERR_PTR(-ECHILD);
308 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
310 return ERR_PTR(-ENOMEM);
312 error = configfs_getlink(dentry, body);
314 set_delayed_call(done, kfree_link, body);
319 return ERR_PTR(error);
322 const struct inode_operations configfs_symlink_inode_operations = {
323 .get_link = configfs_get_link,
324 .setattr = configfs_setattr,