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 configfs_get_target_path(struct config_item *item,
59 struct config_item *target, char *path)
64 depth = item_depth(item);
65 size = item_path_length(target) + depth * 3 - 1;
69 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
71 for (s = path; depth--; s += 3)
74 fill_item_path(target, path, size);
75 pr_debug("%s: path = '%s'\n", __func__, path);
79 static int create_link(struct config_item *parent_item,
80 struct config_item *item,
81 struct dentry *dentry)
83 struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
87 if (!configfs_dirent_is_ready(target_sd))
90 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
94 configfs_get(target_sd);
95 spin_lock(&configfs_dirent_lock);
96 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
97 spin_unlock(&configfs_dirent_lock);
98 configfs_put(target_sd);
102 target_sd->s_links++;
103 spin_unlock(&configfs_dirent_lock);
104 ret = configfs_get_target_path(parent_item, item, body);
106 ret = configfs_create_link(target_sd, parent_item->ci_dentry,
109 spin_lock(&configfs_dirent_lock);
110 target_sd->s_links--;
111 spin_unlock(&configfs_dirent_lock);
112 configfs_put(target_sd);
119 static int get_target(const char *symname, struct path *path,
120 struct config_item **target, struct super_block *sb)
124 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
126 if (path->dentry->d_sb == sb) {
127 *target = configfs_get_config_item(path->dentry);
142 int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
143 struct dentry *dentry, const char *symname)
147 struct configfs_dirent *sd;
148 struct config_item *parent_item;
149 struct config_item *target_item = NULL;
150 const struct config_item_type *type;
152 sd = dentry->d_parent->d_fsdata;
154 * Fake invisibility if dir belongs to a group/default groups hierarchy
157 if (!configfs_dirent_is_ready(sd))
160 parent_item = configfs_get_config_item(dentry->d_parent);
161 type = parent_item->ci_type;
164 if (!type || !type->ct_item_ops ||
165 !type->ct_item_ops->allow_link)
169 * This is really sick. What they wanted was a hybrid of
170 * link(2) and symlink(2) - they wanted the target resolved
171 * at syscall time (as link(2) would've done), be a directory
172 * (which link(2) would've refused to do) *AND* be a deep
173 * fucking magic, making the target busy from rmdir POV.
174 * symlink(2) is nothing of that sort, and the locking it
175 * gets matches the normal symlink(2) semantics. Without
176 * attempts to resolve the target (which might very well
177 * not even exist yet) done prior to locking the parent
178 * directory. This perversion, OTOH, needs to resolve
179 * the target, which would lead to obvious deadlocks if
180 * attempted with any directories locked.
182 * Unfortunately, that garbage is userland ABI and we should've
183 * said "no" back in 2005. Too late now, so we get to
184 * play very ugly games with locking.
186 * Try *ANYTHING* of that sort in new code, and you will
187 * really regret it. Just ask yourself - what could a BOFH
188 * do to me and do I want to find it out first-hand?
190 * AV, a thoroughly annoyed bastard.
193 ret = get_target(symname, &path, &target_item, dentry->d_sb);
198 if (dentry->d_inode || d_unhashed(dentry))
201 ret = inode_permission(&init_user_ns, dir,
202 MAY_WRITE | MAY_EXEC);
204 ret = type->ct_item_ops->allow_link(parent_item, target_item);
206 mutex_lock(&configfs_symlink_mutex);
207 ret = create_link(parent_item, target_item, dentry);
208 mutex_unlock(&configfs_symlink_mutex);
209 if (ret && type->ct_item_ops->drop_link)
210 type->ct_item_ops->drop_link(parent_item,
214 config_item_put(target_item);
218 config_item_put(parent_item);
222 int configfs_unlink(struct inode *dir, struct dentry *dentry)
224 struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
225 struct config_item *parent_item;
226 const struct config_item_type *type;
229 ret = -EPERM; /* What lack-of-symlink returns */
230 if (!(sd->s_type & CONFIGFS_ITEM_LINK))
233 target_sd = sd->s_element;
235 parent_item = configfs_get_config_item(dentry->d_parent);
236 type = parent_item->ci_type;
238 spin_lock(&configfs_dirent_lock);
239 list_del_init(&sd->s_sibling);
240 spin_unlock(&configfs_dirent_lock);
241 configfs_drop_dentry(sd, dentry->d_parent);
246 * drop_link() must be called before
247 * decrementing target's ->s_links, so that the order of
248 * drop_link(this, target) and drop_item(target) is preserved.
250 if (type && type->ct_item_ops &&
251 type->ct_item_ops->drop_link)
252 type->ct_item_ops->drop_link(parent_item,
253 target_sd->s_element);
255 spin_lock(&configfs_dirent_lock);
256 target_sd->s_links--;
257 spin_unlock(&configfs_dirent_lock);
258 configfs_put(target_sd);
260 config_item_put(parent_item);
268 const struct inode_operations configfs_symlink_inode_operations = {
269 .get_link = simple_get_link,
270 .setattr = configfs_setattr,