1 /* 2 * fs/sysfs/symlink.c - sysfs symlink implementation 3 * 4 * Copyright (c) 2001-3 Patrick Mochel 5 * Copyright (c) 2007 SUSE Linux Products GmbH 6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de> 7 * 8 * This file is released under the GPLv2. 9 * 10 * Please see Documentation/filesystems/sysfs.txt for more information. 11 */ 12 13 #include <linux/fs.h> 14 #include <linux/gfp.h> 15 #include <linux/mount.h> 16 #include <linux/module.h> 17 #include <linux/kobject.h> 18 #include <linux/namei.h> 19 #include <linux/mutex.h> 20 #include <linux/security.h> 21 22 #include "sysfs.h" 23 24 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target, 25 const char *name, int warn) 26 { 27 struct sysfs_dirent *parent_sd = NULL; 28 struct sysfs_dirent *target_sd = NULL; 29 struct sysfs_dirent *sd = NULL; 30 struct sysfs_addrm_cxt acxt; 31 enum kobj_ns_type ns_type; 32 int error; 33 34 BUG_ON(!name); 35 36 if (!kobj) 37 parent_sd = &sysfs_root; 38 else 39 parent_sd = kobj->sd; 40 41 error = -EFAULT; 42 if (!parent_sd) 43 goto out_put; 44 45 /* target->sd can go away beneath us but is protected with 46 * sysfs_assoc_lock. Fetch target_sd from it. 47 */ 48 spin_lock(&sysfs_assoc_lock); 49 if (target->sd) 50 target_sd = sysfs_get(target->sd); 51 spin_unlock(&sysfs_assoc_lock); 52 53 error = -ENOENT; 54 if (!target_sd) 55 goto out_put; 56 57 error = -ENOMEM; 58 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); 59 if (!sd) 60 goto out_put; 61 62 ns_type = sysfs_ns_type(parent_sd); 63 if (ns_type) 64 sd->s_ns = target->ktype->namespace(target); 65 sd->s_symlink.target_sd = target_sd; 66 target_sd = NULL; /* reference is now owned by the symlink */ 67 68 sysfs_addrm_start(&acxt, parent_sd); 69 /* Symlinks must be between directories with the same ns_type */ 70 if (!ns_type || 71 (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) { 72 if (warn) 73 error = sysfs_add_one(&acxt, sd); 74 else 75 error = __sysfs_add_one(&acxt, sd); 76 } else { 77 error = -EINVAL; 78 WARN(1, KERN_WARNING 79 "sysfs: symlink across ns_types %s/%s -> %s/%s\n", 80 parent_sd->s_name, 81 sd->s_name, 82 sd->s_symlink.target_sd->s_parent->s_name, 83 sd->s_symlink.target_sd->s_name); 84 } 85 sysfs_addrm_finish(&acxt); 86 87 if (error) 88 goto out_put; 89 90 return 0; 91 92 out_put: 93 sysfs_put(target_sd); 94 sysfs_put(sd); 95 return error; 96 } 97 98 /** 99 * sysfs_create_link - create symlink between two objects. 100 * @kobj: object whose directory we're creating the link in. 101 * @target: object we're pointing to. 102 * @name: name of the symlink. 103 */ 104 int sysfs_create_link(struct kobject *kobj, struct kobject *target, 105 const char *name) 106 { 107 return sysfs_do_create_link(kobj, target, name, 1); 108 } 109 110 /** 111 * sysfs_create_link_nowarn - create symlink between two objects. 112 * @kobj: object whose directory we're creating the link in. 113 * @target: object we're pointing to. 114 * @name: name of the symlink. 115 * 116 * This function does the same as sysf_create_link(), but it 117 * doesn't warn if the link already exists. 118 */ 119 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target, 120 const char *name) 121 { 122 return sysfs_do_create_link(kobj, target, name, 0); 123 } 124 125 /** 126 * sysfs_delete_link - remove symlink in object's directory. 127 * @kobj: object we're acting for. 128 * @targ: object we're pointing to. 129 * @name: name of the symlink to remove. 130 * 131 * Unlike sysfs_remove_link sysfs_delete_link has enough information 132 * to successfully delete symlinks in tagged directories. 133 */ 134 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ, 135 const char *name) 136 { 137 const void *ns = NULL; 138 spin_lock(&sysfs_assoc_lock); 139 if (targ->sd && sysfs_ns_type(kobj->sd)) 140 ns = targ->sd->s_ns; 141 spin_unlock(&sysfs_assoc_lock); 142 sysfs_hash_and_remove(kobj->sd, ns, name); 143 } 144 145 /** 146 * sysfs_remove_link - remove symlink in object's directory. 147 * @kobj: object we're acting for. 148 * @name: name of the symlink to remove. 149 */ 150 151 void sysfs_remove_link(struct kobject * kobj, const char * name) 152 { 153 struct sysfs_dirent *parent_sd = NULL; 154 155 if (!kobj) 156 parent_sd = &sysfs_root; 157 else 158 parent_sd = kobj->sd; 159 160 sysfs_hash_and_remove(parent_sd, NULL, name); 161 } 162 163 /** 164 * sysfs_rename_link - rename symlink in object's directory. 165 * @kobj: object we're acting for. 166 * @targ: object we're pointing to. 167 * @old: previous name of the symlink. 168 * @new: new name of the symlink. 169 * 170 * A helper function for the common rename symlink idiom. 171 */ 172 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ, 173 const char *old, const char *new) 174 { 175 struct sysfs_dirent *parent_sd, *sd = NULL; 176 const void *old_ns = NULL, *new_ns = NULL; 177 int result; 178 179 if (!kobj) 180 parent_sd = &sysfs_root; 181 else 182 parent_sd = kobj->sd; 183 184 if (targ->sd) 185 old_ns = targ->sd->s_ns; 186 187 result = -ENOENT; 188 sd = sysfs_get_dirent(parent_sd, old_ns, old); 189 if (!sd) 190 goto out; 191 192 result = -EINVAL; 193 if (sysfs_type(sd) != SYSFS_KOBJ_LINK) 194 goto out; 195 if (sd->s_symlink.target_sd->s_dir.kobj != targ) 196 goto out; 197 198 if (sysfs_ns_type(parent_sd)) 199 new_ns = targ->ktype->namespace(targ); 200 201 result = sysfs_rename(sd, parent_sd, new_ns, new); 202 203 out: 204 sysfs_put(sd); 205 return result; 206 } 207 208 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd, 209 struct sysfs_dirent *target_sd, char *path) 210 { 211 struct sysfs_dirent *base, *sd; 212 char *s = path; 213 int len = 0; 214 215 /* go up to the root, stop at the base */ 216 base = parent_sd; 217 while (base->s_parent) { 218 sd = target_sd->s_parent; 219 while (sd->s_parent && base != sd) 220 sd = sd->s_parent; 221 222 if (base == sd) 223 break; 224 225 strcpy(s, "../"); 226 s += 3; 227 base = base->s_parent; 228 } 229 230 /* determine end of target string for reverse fillup */ 231 sd = target_sd; 232 while (sd->s_parent && sd != base) { 233 len += strlen(sd->s_name) + 1; 234 sd = sd->s_parent; 235 } 236 237 /* check limits */ 238 if (len < 2) 239 return -EINVAL; 240 len--; 241 if ((s - path) + len > PATH_MAX) 242 return -ENAMETOOLONG; 243 244 /* reverse fillup of target string from target to base */ 245 sd = target_sd; 246 while (sd->s_parent && sd != base) { 247 int slen = strlen(sd->s_name); 248 249 len -= slen; 250 strncpy(s + len, sd->s_name, slen); 251 if (len) 252 s[--len] = '/'; 253 254 sd = sd->s_parent; 255 } 256 257 return 0; 258 } 259 260 static int sysfs_getlink(struct dentry *dentry, char * path) 261 { 262 struct sysfs_dirent *sd = dentry->d_fsdata; 263 struct sysfs_dirent *parent_sd = sd->s_parent; 264 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd; 265 int error; 266 267 mutex_lock(&sysfs_mutex); 268 error = sysfs_get_target_path(parent_sd, target_sd, path); 269 mutex_unlock(&sysfs_mutex); 270 271 return error; 272 } 273 274 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 275 { 276 int error = -ENOMEM; 277 unsigned long page = get_zeroed_page(GFP_KERNEL); 278 if (page) { 279 error = sysfs_getlink(dentry, (char *) page); 280 if (error < 0) 281 free_page((unsigned long)page); 282 } 283 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 284 return NULL; 285 } 286 287 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 288 { 289 char *page = nd_get_link(nd); 290 if (!IS_ERR(page)) 291 free_page((unsigned long)page); 292 } 293 294 const struct inode_operations sysfs_symlink_inode_operations = { 295 .setxattr = sysfs_setxattr, 296 .readlink = generic_readlink, 297 .follow_link = sysfs_follow_link, 298 .put_link = sysfs_put_link, 299 .setattr = sysfs_setattr, 300 .getattr = sysfs_getattr, 301 .permission = sysfs_permission, 302 }; 303 304 305 EXPORT_SYMBOL_GPL(sysfs_create_link); 306 EXPORT_SYMBOL_GPL(sysfs_remove_link); 307 EXPORT_SYMBOL_GPL(sysfs_rename_link); 308