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: 4 * 5 * symlink.c - operations for configfs symlinks. 6 * 7 * Based on sysfs: 8 * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel 9 * 10 * configfs Copyright (C) 2005 Oracle. All rights reserved. 11 */ 12 13 #include <linux/fs.h> 14 #include <linux/module.h> 15 #include <linux/namei.h> 16 #include <linux/slab.h> 17 18 #include <linux/configfs.h> 19 #include "configfs_internal.h" 20 21 /* Protects attachments of new symlinks */ 22 DEFINE_MUTEX(configfs_symlink_mutex); 23 24 static int item_depth(struct config_item * item) 25 { 26 struct config_item * p = item; 27 int depth = 0; 28 do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p)); 29 return depth; 30 } 31 32 static int item_path_length(struct config_item * item) 33 { 34 struct config_item * p = item; 35 int length = 1; 36 do { 37 length += strlen(config_item_name(p)) + 1; 38 p = p->ci_parent; 39 } while (p && !configfs_is_root(p)); 40 return length; 41 } 42 43 static void fill_item_path(struct config_item * item, char * buffer, int length) 44 { 45 struct config_item * p; 46 47 --length; 48 for (p = item; p && !configfs_is_root(p); p = p->ci_parent) { 49 int cur = strlen(config_item_name(p)); 50 51 /* back up enough to print this bus id with '/' */ 52 length -= cur; 53 memcpy(buffer + length, config_item_name(p), cur); 54 *(buffer + --length) = '/'; 55 } 56 } 57 58 static int create_link(struct config_item *parent_item, 59 struct config_item *item, 60 struct dentry *dentry) 61 { 62 struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata; 63 struct configfs_symlink *sl; 64 int ret; 65 66 ret = -ENOENT; 67 if (!configfs_dirent_is_ready(target_sd)) 68 goto out; 69 ret = -ENOMEM; 70 sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL); 71 if (sl) { 72 spin_lock(&configfs_dirent_lock); 73 if (target_sd->s_type & CONFIGFS_USET_DROPPING) { 74 spin_unlock(&configfs_dirent_lock); 75 kfree(sl); 76 return -ENOENT; 77 } 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, 82 dentry); 83 if (ret) { 84 spin_lock(&configfs_dirent_lock); 85 list_del_init(&sl->sl_list); 86 spin_unlock(&configfs_dirent_lock); 87 config_item_put(item); 88 kfree(sl); 89 } 90 } 91 92 out: 93 return ret; 94 } 95 96 97 static int get_target(const char *symname, struct path *path, 98 struct config_item **target, struct super_block *sb) 99 { 100 int ret; 101 102 ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path); 103 if (!ret) { 104 if (path->dentry->d_sb == sb) { 105 *target = configfs_get_config_item(path->dentry); 106 if (!*target) { 107 ret = -ENOENT; 108 path_put(path); 109 } 110 } else { 111 ret = -EPERM; 112 path_put(path); 113 } 114 } 115 116 return ret; 117 } 118 119 120 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname) 121 { 122 int ret; 123 struct path path; 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; 128 129 sd = dentry->d_parent->d_fsdata; 130 /* 131 * Fake invisibility if dir belongs to a group/default groups hierarchy 132 * being attached 133 */ 134 ret = -ENOENT; 135 if (!configfs_dirent_is_ready(sd)) 136 goto out; 137 138 parent_item = configfs_get_config_item(dentry->d_parent); 139 type = parent_item->ci_type; 140 141 ret = -EPERM; 142 if (!type || !type->ct_item_ops || 143 !type->ct_item_ops->allow_link) 144 goto out_put; 145 146 ret = get_target(symname, &path, &target_item, dentry->d_sb); 147 if (ret) 148 goto out_put; 149 150 ret = type->ct_item_ops->allow_link(parent_item, target_item); 151 if (!ret) { 152 mutex_lock(&configfs_symlink_mutex); 153 ret = create_link(parent_item, target_item, dentry); 154 mutex_unlock(&configfs_symlink_mutex); 155 if (ret && type->ct_item_ops->drop_link) 156 type->ct_item_ops->drop_link(parent_item, 157 target_item); 158 } 159 160 config_item_put(target_item); 161 path_put(&path); 162 163 out_put: 164 config_item_put(parent_item); 165 166 out: 167 return ret; 168 } 169 170 int configfs_unlink(struct inode *dir, struct dentry *dentry) 171 { 172 struct configfs_dirent *sd = dentry->d_fsdata; 173 struct configfs_symlink *sl; 174 struct config_item *parent_item; 175 const struct config_item_type *type; 176 int ret; 177 178 ret = -EPERM; /* What lack-of-symlink returns */ 179 if (!(sd->s_type & CONFIGFS_ITEM_LINK)) 180 goto out; 181 182 sl = sd->s_element; 183 184 parent_item = configfs_get_config_item(dentry->d_parent); 185 type = parent_item->ci_type; 186 187 spin_lock(&configfs_dirent_lock); 188 list_del_init(&sd->s_sibling); 189 spin_unlock(&configfs_dirent_lock); 190 configfs_drop_dentry(sd, dentry->d_parent); 191 dput(dentry); 192 configfs_put(sd); 193 194 /* 195 * drop_link() must be called before 196 * list_del_init(&sl->sl_list), so that the order of 197 * drop_link(this, target) and drop_item(target) is preserved. 198 */ 199 if (type && type->ct_item_ops && 200 type->ct_item_ops->drop_link) 201 type->ct_item_ops->drop_link(parent_item, 202 sl->sl_target); 203 204 spin_lock(&configfs_dirent_lock); 205 list_del_init(&sl->sl_list); 206 spin_unlock(&configfs_dirent_lock); 207 208 /* Put reference from create_link() */ 209 config_item_put(sl->sl_target); 210 kfree(sl); 211 212 config_item_put(parent_item); 213 214 ret = 0; 215 216 out: 217 return ret; 218 } 219 220 static int configfs_get_target_path(struct config_item * item, struct config_item * target, 221 char *path) 222 { 223 char * s; 224 int depth, size; 225 226 depth = item_depth(item); 227 size = item_path_length(target) + depth * 3 - 1; 228 if (size > PATH_MAX) 229 return -ENAMETOOLONG; 230 231 pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size); 232 233 for (s = path; depth--; s += 3) 234 strcpy(s,"../"); 235 236 fill_item_path(target, path, size); 237 pr_debug("%s: path = '%s'\n", __func__, path); 238 239 return 0; 240 } 241 242 static int configfs_getlink(struct dentry *dentry, char * path) 243 { 244 struct config_item *item, *target_item; 245 int error = 0; 246 247 item = configfs_get_config_item(dentry->d_parent); 248 if (!item) 249 return -EINVAL; 250 251 target_item = configfs_get_config_item(dentry); 252 if (!target_item) { 253 config_item_put(item); 254 return -EINVAL; 255 } 256 257 down_read(&configfs_rename_sem); 258 error = configfs_get_target_path(item, target_item, path); 259 up_read(&configfs_rename_sem); 260 261 config_item_put(item); 262 config_item_put(target_item); 263 return error; 264 265 } 266 267 static const char *configfs_get_link(struct dentry *dentry, 268 struct inode *inode, 269 struct delayed_call *done) 270 { 271 char *body; 272 int error; 273 274 if (!dentry) 275 return ERR_PTR(-ECHILD); 276 277 body = kzalloc(PAGE_SIZE, GFP_KERNEL); 278 if (!body) 279 return ERR_PTR(-ENOMEM); 280 281 error = configfs_getlink(dentry, body); 282 if (!error) { 283 set_delayed_call(done, kfree_link, body); 284 return body; 285 } 286 287 kfree(body); 288 return ERR_PTR(error); 289 } 290 291 const struct inode_operations configfs_symlink_inode_operations = { 292 .get_link = configfs_get_link, 293 .setattr = configfs_setattr, 294 }; 295 296