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