fs/sysfs/symlink.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/sysfs/symlink.c - sysfs symlink implementation
   4  *
   5  * Copyright (c) 2001-3 Patrick Mochel
   6  * Copyright (c) 2007 SUSE Linux Products GmbH
   7  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   8  *
   9  * Please see Documentation/filesystems/sysfs.rst for more information.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/module.h>
  14 #include <linux/kobject.h>
  15 #include <linux/mutex.h>
  16 #include <linux/security.h>
  17
  18 #include "sysfs.h"
  19
  20 static int sysfs_do_create_link_sd(struct kernfs_node *parent,
  21                                    struct kobject *target_kobj,
  22                                    const char *name, int warn)
  23 {
  24         struct kernfs_node *kn, *target = NULL;
  25
  26         if (WARN_ON(!name || !parent))
  27                 return -EINVAL;
  28
  29         /*
  30          * We don't own @target_kobj and it may be removed at any time.
  31          * Synchronize using sysfs_symlink_target_lock.  See
  32          * sysfs_remove_dir() for details.
  33          */
  34         spin_lock(&sysfs_symlink_target_lock);
  35         if (target_kobj->sd) {
  36                 target = target_kobj->sd;
  37                 kernfs_get(target);
  38         }
  39         spin_unlock(&sysfs_symlink_target_lock);
  40
  41         if (!target)
  42                 return -ENOENT;
  43
  44         kn = kernfs_create_link(parent, name, target);
  45         kernfs_put(target);
  46
  47         if (!IS_ERR(kn))
  48                 return 0;
  49
  50         if (warn && PTR_ERR(kn) == -EEXIST)
  51                 sysfs_warn_dup(parent, name);
  52         return PTR_ERR(kn);
  53 }
  54
  55 /**
  56  *      sysfs_create_link_sd - create symlink to a given object.
  57  *      @kn:            directory we're creating the link in.
  58  *      @target:        object we're pointing to.
  59  *      @name:          name of the symlink.
  60  */
  61 int sysfs_create_link_sd(struct kernfs_node *kn, struct kobject *target,
  62                          const char *name)
  63 {
  64         return sysfs_do_create_link_sd(kn, target, name, 1);
  65 }
  66
  67 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
  68                                 const char *name, int warn)
  69 {
  70         struct kernfs_node *parent = NULL;
  71
  72         if (!kobj)
  73                 parent = sysfs_root_kn;
  74         else
  75                 parent = kobj->sd;
  76
  77         if (!parent)
  78                 return -EFAULT;
  79
  80         return sysfs_do_create_link_sd(parent, target, name, warn);
  81 }
  82
  83 /**
  84  *      sysfs_create_link - create symlink between two objects.
  85  *      @kobj:  object whose directory we're creating the link in.
  86  *      @target:        object we're pointing to.
  87  *      @name:          name of the symlink.
  88  */
  89 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
  90                       const char *name)
  91 {
  92         return sysfs_do_create_link(kobj, target, name, 1);
  93 }
  94 EXPORT_SYMBOL_GPL(sysfs_create_link);
  95
  96 /**
  97  *      sysfs_create_link_nowarn - create symlink between two objects.
  98  *      @kobj:  object whose directory we're creating the link in.
  99  *      @target:        object we're pointing to.
 100  *      @name:          name of the symlink.
 101  *
 102  *      This function does the same as sysfs_create_link(), but it
 103  *      doesn't warn if the link already exists.
 104  */
 105 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 106                              const char *name)
 107 {
 108         return sysfs_do_create_link(kobj, target, name, 0);
 109 }
 110 EXPORT_SYMBOL_GPL(sysfs_create_link_nowarn);
 111
 112 /**
 113  *      sysfs_delete_link - remove symlink in object's directory.
 114  *      @kobj:  object we're acting for.
 115  *      @targ:  object we're pointing to.
 116  *      @name:  name of the symlink to remove.
 117  *
 118  *      Unlike sysfs_remove_link sysfs_delete_link has enough information
 119  *      to successfully delete symlinks in tagged directories.
 120  */
 121 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 122                         const char *name)
 123 {
 124         const void *ns = NULL;
 125
 126         /*
 127          * We don't own @target and it may be removed at any time.
 128          * Synchronize using sysfs_symlink_target_lock.  See
 129          * sysfs_remove_dir() for details.
 130          */
 131         spin_lock(&sysfs_symlink_target_lock);
 132         if (targ->sd && kernfs_ns_enabled(kobj->sd))
 133                 ns = targ->sd->ns;
 134         spin_unlock(&sysfs_symlink_target_lock);
 135         kernfs_remove_by_name_ns(kobj->sd, name, ns);
 136 }
 137
 138 /**
 139  *      sysfs_remove_link - remove symlink in object's directory.
 140  *      @kobj:  object we're acting for.
 141  *      @name:  name of the symlink to remove.
 142  */
 143 void sysfs_remove_link(struct kobject *kobj, const char *name)
 144 {
 145         struct kernfs_node *parent = NULL;
 146
 147         if (!kobj)
 148                 parent = sysfs_root_kn;
 149         else
 150                 parent = kobj->sd;
 151
 152         kernfs_remove_by_name(parent, name);
 153 }
 154 EXPORT_SYMBOL_GPL(sysfs_remove_link);
 155
 156 /**
 157  *      sysfs_rename_link_ns - rename symlink in object's directory.
 158  *      @kobj:  object we're acting for.
 159  *      @targ:  object we're pointing to.
 160  *      @old:   previous name of the symlink.
 161  *      @new:   new name of the symlink.
 162  *      @new_ns: new namespace of the symlink.
 163  *
 164  *      A helper function for the common rename symlink idiom.
 165  */
 166 int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ,
 167                          const char *old, const char *new, const void *new_ns)
 168 {
 169         struct kernfs_node *parent, *kn = NULL;
 170         const void *old_ns = NULL;
 171         int result;
 172
 173         if (!kobj)
 174                 parent = sysfs_root_kn;
 175         else
 176                 parent = kobj->sd;
 177
 178         if (targ->sd)
 179                 old_ns = targ->sd->ns;
 180
 181         result = -ENOENT;
 182         kn = kernfs_find_and_get_ns(parent, old, old_ns);
 183         if (!kn)
 184                 goto out;
 185
 186         result = -EINVAL;
 187         if (kernfs_type(kn) != KERNFS_LINK)
 188                 goto out;
 189         if (kn->symlink.target_kn->priv != targ)
 190                 goto out;
 191
 192         result = kernfs_rename_ns(kn, parent, new, new_ns);
 193
 194 out:
 195         kernfs_put(kn);
 196         return result;
 197 }
 198 EXPORT_SYMBOL_GPL(sysfs_rename_link_ns);