fs/configfs/symlink.c

   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