fs/sysfs/symlink.c

   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_sd(struct sysfs_dirent *parent_sd,
  25                                    struct kobject *target,
  26                                    const char *name, int warn)
  27 {
  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 || !parent_sd);
  35
  36         /* target->sd can go away beneath us but is protected with
  37          * sysfs_assoc_lock.  Fetch target_sd from it.
  38          */
  39         spin_lock(&sysfs_assoc_lock);
  40         if (target->sd)
  41                 target_sd = sysfs_get(target->sd);
  42         spin_unlock(&sysfs_assoc_lock);
  43
  44         error = -ENOENT;
  45         if (!target_sd)
  46                 goto out_put;
  47
  48         error = -ENOMEM;
  49         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  50         if (!sd)
  51                 goto out_put;
  52
  53         ns_type = sysfs_ns_type(parent_sd);
  54         if (ns_type)
  55                 sd->s_ns = target->ktype->namespace(target);
  56         sd->s_symlink.target_sd = target_sd;
  57         target_sd = NULL;       /* reference is now owned by the symlink */
  58
  59         sysfs_addrm_start(&acxt, parent_sd);
  60         /* Symlinks must be between directories with the same ns_type */
  61         if (!ns_type ||
  62             (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) {
  63                 if (warn)
  64                         error = sysfs_add_one(&acxt, sd);
  65                 else
  66                         error = __sysfs_add_one(&acxt, sd);
  67         } else {
  68                 error = -EINVAL;
  69                 WARN(1, KERN_WARNING
  70                         "sysfs: symlink across ns_types %s/%s -> %s/%s\n",
  71                         parent_sd->s_name,
  72                         sd->s_name,
  73                         sd->s_symlink.target_sd->s_parent->s_name,
  74                         sd->s_symlink.target_sd->s_name);
  75         }
  76         sysfs_addrm_finish(&acxt);
  77
  78         if (error)
  79                 goto out_put;
  80
  81         return 0;
  82
  83  out_put:
  84         sysfs_put(target_sd);
  85         sysfs_put(sd);
  86         return error;
  87 }
  88
  89 /**
  90  *      sysfs_create_link_sd - create symlink to a given object.
  91  *      @sd:            directory we're creating the link in.
  92  *      @target:        object we're pointing to.
  93  *      @name:          name of the symlink.
  94  */
  95 int sysfs_create_link_sd(struct sysfs_dirent *sd, struct kobject *target,
  96                          const char *name)
  97 {
  98         return sysfs_do_create_link_sd(sd, target, name, 1);
  99 }
 100
 101 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
 102                                 const char *name, int warn)
 103 {
 104         struct sysfs_dirent *parent_sd = NULL;
 105
 106         if (!kobj)
 107                 parent_sd = &sysfs_root;
 108         else
 109                 parent_sd = kobj->sd;
 110
 111         if (!parent_sd)
 112                 return -EFAULT;
 113
 114         return sysfs_do_create_link_sd(parent_sd, target, name, warn);
 115 }
 116
 117 /**
 118  *      sysfs_create_link - create symlink between two objects.
 119  *      @kobj:  object whose directory we're creating the link in.
 120  *      @target:        object we're pointing to.
 121  *      @name:          name of the symlink.
 122  */
 123 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
 124                       const char *name)
 125 {
 126         return sysfs_do_create_link(kobj, target, name, 1);
 127 }
 128 EXPORT_SYMBOL_GPL(sysfs_create_link);
 129
 130 /**
 131  *      sysfs_create_link_nowarn - create symlink between two objects.
 132  *      @kobj:  object whose directory we're creating the link in.
 133  *      @target:        object we're pointing to.
 134  *      @name:          name of the symlink.
 135  *
 136  *      This function does the same as sysfs_create_link(), but it
 137  *      doesn't warn if the link already exists.
 138  */
 139 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 140                              const char *name)
 141 {
 142         return sysfs_do_create_link(kobj, target, name, 0);
 143 }
 144
 145 /**
 146  *      sysfs_delete_link - remove symlink in object's directory.
 147  *      @kobj:  object we're acting for.
 148  *      @targ:  object we're pointing to.
 149  *      @name:  name of the symlink to remove.
 150  *
 151  *      Unlike sysfs_remove_link sysfs_delete_link has enough information
 152  *      to successfully delete symlinks in tagged directories.
 153  */
 154 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 155                         const char *name)
 156 {
 157         const void *ns = NULL;
 158         spin_lock(&sysfs_assoc_lock);
 159         if (targ->sd && sysfs_ns_type(kobj->sd))
 160                 ns = targ->sd->s_ns;
 161         spin_unlock(&sysfs_assoc_lock);
 162         sysfs_hash_and_remove(kobj->sd, ns, name);
 163 }
 164
 165 /**
 166  *      sysfs_remove_link - remove symlink in object's directory.
 167  *      @kobj:  object we're acting for.
 168  *      @name:  name of the symlink to remove.
 169  */
 170 void sysfs_remove_link(struct kobject *kobj, const char *name)
 171 {
 172         struct sysfs_dirent *parent_sd = NULL;
 173
 174         if (!kobj)
 175                 parent_sd = &sysfs_root;
 176         else
 177                 parent_sd = kobj->sd;
 178
 179         sysfs_hash_and_remove(parent_sd, NULL, name);
 180 }
 181 EXPORT_SYMBOL_GPL(sysfs_remove_link);
 182
 183 /**
 184  *      sysfs_rename_link - rename symlink in object's directory.
 185  *      @kobj:  object we're acting for.
 186  *      @targ:  object we're pointing to.
 187  *      @old:   previous name of the symlink.
 188  *      @new:   new name of the symlink.
 189  *
 190  *      A helper function for the common rename symlink idiom.
 191  */
 192 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
 193                         const char *old, const char *new)
 194 {
 195         struct sysfs_dirent *parent_sd, *sd = NULL;
 196         const void *old_ns = NULL, *new_ns = NULL;
 197         int result;
 198
 199         if (!kobj)
 200                 parent_sd = &sysfs_root;
 201         else
 202                 parent_sd = kobj->sd;
 203
 204         if (targ->sd)
 205                 old_ns = targ->sd->s_ns;
 206
 207         result = -ENOENT;
 208         sd = sysfs_get_dirent(parent_sd, old_ns, old);
 209         if (!sd)
 210                 goto out;
 211
 212         result = -EINVAL;
 213         if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
 214                 goto out;
 215         if (sd->s_symlink.target_sd->s_dir.kobj != targ)
 216                 goto out;
 217
 218         if (sysfs_ns_type(parent_sd))
 219                 new_ns = targ->ktype->namespace(targ);
 220
 221         result = sysfs_rename(sd, parent_sd, new_ns, new);
 222
 223 out:
 224         sysfs_put(sd);
 225         return result;
 226 }
 227 EXPORT_SYMBOL_GPL(sysfs_rename_link);
 228
 229 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 230                                  struct sysfs_dirent *target_sd, char *path)
 231 {
 232         struct sysfs_dirent *base, *sd;
 233         char *s = path;
 234         int len = 0;
 235
 236         /* go up to the root, stop at the base */
 237         base = parent_sd;
 238         while (base->s_parent) {
 239                 sd = target_sd->s_parent;
 240                 while (sd->s_parent && base != sd)
 241                         sd = sd->s_parent;
 242
 243                 if (base == sd)
 244                         break;
 245
 246                 strcpy(s, "../");
 247                 s += 3;
 248                 base = base->s_parent;
 249         }
 250
 251         /* determine end of target string for reverse fillup */
 252         sd = target_sd;
 253         while (sd->s_parent && sd != base) {
 254                 len += strlen(sd->s_name) + 1;
 255                 sd = sd->s_parent;
 256         }
 257
 258         /* check limits */
 259         if (len < 2)
 260                 return -EINVAL;
 261         len--;
 262         if ((s - path) + len > PATH_MAX)
 263                 return -ENAMETOOLONG;
 264
 265         /* reverse fillup of target string from target to base */
 266         sd = target_sd;
 267         while (sd->s_parent && sd != base) {
 268                 int slen = strlen(sd->s_name);
 269
 270                 len -= slen;
 271                 strncpy(s + len, sd->s_name, slen);
 272                 if (len)
 273                         s[--len] = '/';
 274
 275                 sd = sd->s_parent;
 276         }
 277
 278         return 0;
 279 }
 280
 281 static int sysfs_getlink(struct dentry *dentry, char *path)
 282 {
 283         struct sysfs_dirent *sd = dentry->d_fsdata;
 284         struct sysfs_dirent *parent_sd = sd->s_parent;
 285         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 286         int error;
 287
 288         mutex_lock(&sysfs_mutex);
 289         error = sysfs_get_target_path(parent_sd, target_sd, path);
 290         mutex_unlock(&sysfs_mutex);
 291
 292         return error;
 293 }
 294
 295 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 296 {
 297         int error = -ENOMEM;
 298         unsigned long page = get_zeroed_page(GFP_KERNEL);
 299         if (page) {
 300                 error = sysfs_getlink(dentry, (char *) page);
 301                 if (error < 0)
 302                         free_page((unsigned long)page);
 303         }
 304         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 305         return NULL;
 306 }
 307
 308 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd,
 309                            void *cookie)
 310 {
 311         char *page = nd_get_link(nd);
 312         if (!IS_ERR(page))
 313                 free_page((unsigned long)page);
 314 }
 315
 316 const struct inode_operations sysfs_symlink_inode_operations = {
 317         .setxattr       = sysfs_setxattr,
 318         .readlink       = generic_readlink,
 319         .follow_link    = sysfs_follow_link,
 320         .put_link       = sysfs_put_link,
 321         .setattr        = sysfs_setattr,
 322         .getattr        = sysfs_getattr,
 323         .permission     = sysfs_permission,
 324 };