fs/kernfs/mount.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * fs/kernfs/mount.c - kernfs mount implementation
   4  *
   5  * Copyright (c) 2001-3 Patrick Mochel
   6  * Copyright (c) 2007 SUSE Linux Products GmbH
   7  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   8  */
   9
  10 #include <linux/fs.h>
  11 #include <linux/mount.h>
  12 #include <linux/init.h>
  13 #include <linux/magic.h>
  14 #include <linux/slab.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/namei.h>
  17 #include <linux/seq_file.h>
  18 #include <linux/exportfs.h>
  19 #include <linux/uuid.h>
  20 #include <linux/statfs.h>
  21
  22 #include "kernfs-internal.h"
  23
  24 struct kmem_cache *kernfs_node_cache __ro_after_init;
  25 struct kmem_cache *kernfs_iattrs_cache __ro_after_init;
  26 struct kernfs_global_locks *kernfs_locks __ro_after_init;
  27
  28 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  29 {
  30         struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
  31         struct kernfs_syscall_ops *scops = root->syscall_ops;
  32
  33         if (scops && scops->show_options)
  34                 return scops->show_options(sf, root);
  35         return 0;
  36 }
  37
  38 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
  39 {
  40         struct kernfs_node *node = kernfs_dentry_node(dentry);
  41         struct kernfs_root *root = kernfs_root(node);
  42         struct kernfs_syscall_ops *scops = root->syscall_ops;
  43
  44         if (scops && scops->show_path)
  45                 return scops->show_path(sf, node, root);
  46
  47         seq_dentry(sf, dentry, " \t\n\\");
  48         return 0;
  49 }
  50
  51 static int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
  52 {
  53         simple_statfs(dentry, buf);
  54         buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
  55         return 0;
  56 }
  57
  58 const struct super_operations kernfs_sops = {
  59         .statfs         = kernfs_statfs,
  60         .drop_inode     = generic_delete_inode,
  61         .evict_inode    = kernfs_evict_inode,
  62
  63         .show_options   = kernfs_sop_show_options,
  64         .show_path      = kernfs_sop_show_path,
  65 };
  66
  67 static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
  68                             struct inode *parent)
  69 {
  70         struct kernfs_node *kn = inode->i_private;
  71
  72         if (*max_len < 2) {
  73                 *max_len = 2;
  74                 return FILEID_INVALID;
  75         }
  76
  77         *max_len = 2;
  78         *(u64 *)fh = kn->id;
  79         return FILEID_KERNFS;
  80 }
  81
  82 static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
  83                                             struct fid *fid, int fh_len,
  84                                             int fh_type, bool get_parent)
  85 {
  86         struct kernfs_super_info *info = kernfs_info(sb);
  87         struct kernfs_node *kn;
  88         struct inode *inode;
  89         u64 id;
  90
  91         if (fh_len < 2)
  92                 return NULL;
  93
  94         switch (fh_type) {
  95         case FILEID_KERNFS:
  96                 id = *(u64 *)fid;
  97                 break;
  98         case FILEID_INO32_GEN:
  99         case FILEID_INO32_GEN_PARENT:
 100                 /*
 101                  * blk_log_action() exposes "LOW32,HIGH32" pair without
 102                  * type and userland can call us with generic fid
 103                  * constructed from them.  Combine it back to ID.  See
 104                  * blk_log_action().
 105                  */
 106                 id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
 107                 break;
 108         default:
 109                 return NULL;
 110         }
 111
 112         kn = kernfs_find_and_get_node_by_id(info->root, id);
 113         if (!kn)
 114                 return ERR_PTR(-ESTALE);
 115
 116         if (get_parent) {
 117                 struct kernfs_node *parent;
 118
 119                 parent = kernfs_get_parent(kn);
 120                 kernfs_put(kn);
 121                 kn = parent;
 122                 if (!kn)
 123                         return ERR_PTR(-ESTALE);
 124         }
 125
 126         inode = kernfs_get_inode(sb, kn);
 127         kernfs_put(kn);
 128         return d_obtain_alias(inode);
 129 }
 130
 131 static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
 132                                           struct fid *fid, int fh_len,
 133                                           int fh_type)
 134 {
 135         return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
 136 }
 137
 138 static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
 139                                           struct fid *fid, int fh_len,
 140                                           int fh_type)
 141 {
 142         return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
 143 }
 144
 145 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
 146 {
 147         struct kernfs_node *kn = kernfs_dentry_node(child);
 148
 149         return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
 150 }
 151
 152 static const struct export_operations kernfs_export_ops = {
 153         .encode_fh      = kernfs_encode_fh,
 154         .fh_to_dentry   = kernfs_fh_to_dentry,
 155         .fh_to_parent   = kernfs_fh_to_parent,
 156         .get_parent     = kernfs_get_parent_dentry,
 157 };
 158
 159 /**
 160  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
 161  * @sb: the super_block in question
 162  *
 163  * Return: the kernfs_root associated with @sb.  If @sb is not a kernfs one,
 164  * %NULL is returned.
 165  */
 166 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 167 {
 168         if (sb->s_op == &kernfs_sops)
 169                 return kernfs_info(sb)->root;
 170         return NULL;
 171 }
 172
 173 /*
 174  * find the next ancestor in the path down to @child, where @parent was the
 175  * ancestor whose descendant we want to find.
 176  *
 177  * Say the path is /a/b/c/d.  @child is d, @parent is %NULL.  We return the root
 178  * node.  If @parent is b, then we return the node for c.
 179  * Passing in d as @parent is not ok.
 180  */
 181 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
 182                                               struct kernfs_node *parent)
 183 {
 184         if (child == parent) {
 185                 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
 186                 return NULL;
 187         }
 188
 189         while (child->parent != parent) {
 190                 if (!child->parent)
 191                         return NULL;
 192                 child = child->parent;
 193         }
 194
 195         return child;
 196 }
 197
 198 /**
 199  * kernfs_node_dentry - get a dentry for the given kernfs_node
 200  * @kn: kernfs_node for which a dentry is needed
 201  * @sb: the kernfs super_block
 202  *
 203  * Return: the dentry pointer
 204  */
 205 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 206                                   struct super_block *sb)
 207 {
 208         struct dentry *dentry;
 209         struct kernfs_node *knparent;
 210
 211         BUG_ON(sb->s_op != &kernfs_sops);
 212
 213         dentry = dget(sb->s_root);
 214
 215         /* Check if this is the root kernfs_node */
 216         if (!kn->parent)
 217                 return dentry;
 218
 219         knparent = find_next_ancestor(kn, NULL);
 220         if (WARN_ON(!knparent)) {
 221                 dput(dentry);
 222                 return ERR_PTR(-EINVAL);
 223         }
 224
 225         do {
 226                 struct dentry *dtmp;
 227                 struct kernfs_node *kntmp;
 228
 229                 if (kn == knparent)
 230                         return dentry;
 231                 kntmp = find_next_ancestor(kn, knparent);
 232                 if (WARN_ON(!kntmp)) {
 233                         dput(dentry);
 234                         return ERR_PTR(-EINVAL);
 235                 }
 236                 dtmp = lookup_positive_unlocked(kntmp->name, dentry,
 237                                                strlen(kntmp->name));
 238                 dput(dentry);
 239                 if (IS_ERR(dtmp))
 240                         return dtmp;
 241                 knparent = kntmp;
 242                 dentry = dtmp;
 243         } while (true);
 244 }
 245
 246 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
 247 {
 248         struct kernfs_super_info *info = kernfs_info(sb);
 249         struct kernfs_root *kf_root = kfc->root;
 250         struct inode *inode;
 251         struct dentry *root;
 252
 253         info->sb = sb;
 254         /* Userspace would break if executables or devices appear on sysfs */
 255         sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
 256         sb->s_blocksize = PAGE_SIZE;
 257         sb->s_blocksize_bits = PAGE_SHIFT;
 258         sb->s_magic = kfc->magic;
 259         sb->s_op = &kernfs_sops;
 260         sb->s_xattr = kernfs_xattr_handlers;
 261         if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
 262                 sb->s_export_op = &kernfs_export_ops;
 263         sb->s_time_gran = 1;
 264
 265         /* sysfs dentries and inodes don't require IO to create */
 266         sb->s_shrink->seeks = 0;
 267
 268         /* get root inode, initialize and unlock it */
 269         down_read(&kf_root->kernfs_rwsem);
 270         inode = kernfs_get_inode(sb, info->root->kn);
 271         up_read(&kf_root->kernfs_rwsem);
 272         if (!inode) {
 273                 pr_debug("kernfs: could not get root inode\n");
 274                 return -ENOMEM;
 275         }
 276
 277         /* instantiate and link root dentry */
 278         root = d_make_root(inode);
 279         if (!root) {
 280                 pr_debug("%s: could not get root dentry!\n", __func__);
 281                 return -ENOMEM;
 282         }
 283         sb->s_root = root;
 284         sb->s_d_op = &kernfs_dops;
 285         return 0;
 286 }
 287
 288 static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
 289 {
 290         struct kernfs_super_info *sb_info = kernfs_info(sb);
 291         struct kernfs_super_info *info = fc->s_fs_info;
 292
 293         return sb_info->root == info->root && sb_info->ns == info->ns;
 294 }
 295
 296 static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
 297 {
 298         struct kernfs_fs_context *kfc = fc->fs_private;
 299
 300         kfc->ns_tag = NULL;
 301         return set_anon_super_fc(sb, fc);
 302 }
 303
 304 /**
 305  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 306  * @sb: super_block of interest
 307  *
 308  * Return: the namespace tag associated with kernfs super_block @sb.
 309  */
 310 const void *kernfs_super_ns(struct super_block *sb)
 311 {
 312         struct kernfs_super_info *info = kernfs_info(sb);
 313
 314         return info->ns;
 315 }
 316
 317 /**
 318  * kernfs_get_tree - kernfs filesystem access/retrieval helper
 319  * @fc: The filesystem context.
 320  *
 321  * This is to be called from each kernfs user's fs_context->ops->get_tree()
 322  * implementation, which should set the specified ->@fs_type and ->@flags, and
 323  * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
 324  * respectively.
 325  *
 326  * Return: %0 on success, -errno on failure.
 327  */
 328 int kernfs_get_tree(struct fs_context *fc)
 329 {
 330         struct kernfs_fs_context *kfc = fc->fs_private;
 331         struct super_block *sb;
 332         struct kernfs_super_info *info;
 333         int error;
 334
 335         info = kzalloc(sizeof(*info), GFP_KERNEL);
 336         if (!info)
 337                 return -ENOMEM;
 338
 339         info->root = kfc->root;
 340         info->ns = kfc->ns_tag;
 341         INIT_LIST_HEAD(&info->node);
 342
 343         fc->s_fs_info = info;
 344         sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
 345         if (IS_ERR(sb))
 346                 return PTR_ERR(sb);
 347
 348         if (!sb->s_root) {
 349                 struct kernfs_super_info *info = kernfs_info(sb);
 350                 struct kernfs_root *root = kfc->root;
 351
 352                 kfc->new_sb_created = true;
 353
 354                 error = kernfs_fill_super(sb, kfc);
 355                 if (error) {
 356                         deactivate_locked_super(sb);
 357                         return error;
 358                 }
 359                 sb->s_flags |= SB_ACTIVE;
 360
 361                 uuid_t uuid;
 362                 uuid_gen(&uuid);
 363                 super_set_uuid(sb, uuid.b, sizeof(uuid));
 364
 365                 down_write(&root->kernfs_supers_rwsem);
 366                 list_add(&info->node, &info->root->supers);
 367                 up_write(&root->kernfs_supers_rwsem);
 368         }
 369
 370         fc->root = dget(sb->s_root);
 371         return 0;
 372 }
 373
 374 void kernfs_free_fs_context(struct fs_context *fc)
 375 {
 376         /* Note that we don't deal with kfc->ns_tag here. */
 377         kfree(fc->s_fs_info);
 378         fc->s_fs_info = NULL;
 379 }
 380
 381 /**
 382  * kernfs_kill_sb - kill_sb for kernfs
 383  * @sb: super_block being killed
 384  *
 385  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 386  * user needs extra cleanup, it can implement its own kill_sb() and call
 387  * this function at the end.
 388  */
 389 void kernfs_kill_sb(struct super_block *sb)
 390 {
 391         struct kernfs_super_info *info = kernfs_info(sb);
 392         struct kernfs_root *root = info->root;
 393
 394         down_write(&root->kernfs_supers_rwsem);
 395         list_del(&info->node);
 396         up_write(&root->kernfs_supers_rwsem);
 397
 398         /*
 399          * Remove the superblock from fs_supers/s_instances
 400          * so we can't find it, before freeing kernfs_super_info.
 401          */
 402         kill_anon_super(sb);
 403         kfree(info);
 404 }
 405
 406 static void __init kernfs_mutex_init(void)
 407 {
 408         int count;
 409
 410         for (count = 0; count < NR_KERNFS_LOCKS; count++)
 411                 mutex_init(&kernfs_locks->open_file_mutex[count]);
 412 }
 413
 414 static void __init kernfs_lock_init(void)
 415 {
 416         kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL);
 417         WARN_ON(!kernfs_locks);
 418
 419         kernfs_mutex_init();
 420 }
 421
 422 void __init kernfs_init(void)
 423 {
 424         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 425                                               sizeof(struct kernfs_node),
 426                                               0, SLAB_PANIC, NULL);
 427
 428         /* Creates slab cache for kernfs inode attributes */
 429         kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
 430                                               sizeof(struct kernfs_iattrs),
 431                                               0, SLAB_PANIC, NULL);
 432
 433         kernfs_lock_init();
 434 }