fs/kernfs/mount.c

   1 /*
   2  * fs/kernfs/mount.c - kernfs mount implementation
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   7  *
   8  * This file is released under the GPLv2.
   9  */
  10
  11 #include <linux/fs.h>
  12 #include <linux/mount.h>
  13 #include <linux/init.h>
  14 #include <linux/magic.h>
  15 #include <linux/slab.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/namei.h>
  18 #include <linux/seq_file.h>
  19 #include <linux/exportfs.h>
  20
  21 #include "kernfs-internal.h"
  22
  23 struct kmem_cache *kernfs_node_cache;
  24
  25 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
  26 {
  27         struct kernfs_root *root = kernfs_info(sb)->root;
  28         struct kernfs_syscall_ops *scops = root->syscall_ops;
  29
  30         if (scops && scops->remount_fs)
  31                 return scops->remount_fs(root, flags, data);
  32         return 0;
  33 }
  34
  35 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  36 {
  37         struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
  38         struct kernfs_syscall_ops *scops = root->syscall_ops;
  39
  40         if (scops && scops->show_options)
  41                 return scops->show_options(sf, root);
  42         return 0;
  43 }
  44
  45 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
  46 {
  47         struct kernfs_node *node = kernfs_dentry_node(dentry);
  48         struct kernfs_root *root = kernfs_root(node);
  49         struct kernfs_syscall_ops *scops = root->syscall_ops;
  50
  51         if (scops && scops->show_path)
  52                 return scops->show_path(sf, node, root);
  53
  54         seq_dentry(sf, dentry, " \t\n\\");
  55         return 0;
  56 }
  57
  58 const struct super_operations kernfs_sops = {
  59         .statfs         = simple_statfs,
  60         .drop_inode     = generic_delete_inode,
  61         .evict_inode    = kernfs_evict_inode,
  62
  63         .remount_fs     = kernfs_sop_remount_fs,
  64         .show_options   = kernfs_sop_show_options,
  65         .show_path      = kernfs_sop_show_path,
  66 };
  67
  68 /*
  69  * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
  70  * number and generation
  71  */
  72 struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
  73         const union kernfs_node_id *id)
  74 {
  75         struct kernfs_node *kn;
  76
  77         kn = kernfs_find_and_get_node_by_ino(root, id->ino);
  78         if (!kn)
  79                 return NULL;
  80         if (kn->id.generation != id->generation) {
  81                 kernfs_put(kn);
  82                 return NULL;
  83         }
  84         return kn;
  85 }
  86
  87 static struct inode *kernfs_fh_get_inode(struct super_block *sb,
  88                 u64 ino, u32 generation)
  89 {
  90         struct kernfs_super_info *info = kernfs_info(sb);
  91         struct inode *inode;
  92         struct kernfs_node *kn;
  93
  94         if (ino == 0)
  95                 return ERR_PTR(-ESTALE);
  96
  97         kn = kernfs_find_and_get_node_by_ino(info->root, ino);
  98         if (!kn)
  99                 return ERR_PTR(-ESTALE);
 100         inode = kernfs_get_inode(sb, kn);
 101         kernfs_put(kn);
 102         if (!inode)
 103                 return ERR_PTR(-ESTALE);
 104
 105         if (generation && inode->i_generation != generation) {
 106                 /* we didn't find the right inode.. */
 107                 iput(inode);
 108                 return ERR_PTR(-ESTALE);
 109         }
 110         return inode;
 111 }
 112
 113 static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
 114                 int fh_len, int fh_type)
 115 {
 116         return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
 117                                     kernfs_fh_get_inode);
 118 }
 119
 120 static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
 121                 int fh_len, int fh_type)
 122 {
 123         return generic_fh_to_parent(sb, fid, fh_len, fh_type,
 124                                     kernfs_fh_get_inode);
 125 }
 126
 127 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
 128 {
 129         struct kernfs_node *kn = kernfs_dentry_node(child);
 130
 131         return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
 132 }
 133
 134 static const struct export_operations kernfs_export_ops = {
 135         .fh_to_dentry   = kernfs_fh_to_dentry,
 136         .fh_to_parent   = kernfs_fh_to_parent,
 137         .get_parent     = kernfs_get_parent_dentry,
 138 };
 139
 140 /**
 141  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
 142  * @sb: the super_block in question
 143  *
 144  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
 145  * %NULL is returned.
 146  */
 147 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 148 {
 149         if (sb->s_op == &kernfs_sops)
 150                 return kernfs_info(sb)->root;
 151         return NULL;
 152 }
 153
 154 /*
 155  * find the next ancestor in the path down to @child, where @parent was the
 156  * ancestor whose descendant we want to find.
 157  *
 158  * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
 159  * node.  If @parent is b, then we return the node for c.
 160  * Passing in d as @parent is not ok.
 161  */
 162 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
 163                                               struct kernfs_node *parent)
 164 {
 165         if (child == parent) {
 166                 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
 167                 return NULL;
 168         }
 169
 170         while (child->parent != parent) {
 171                 if (!child->parent)
 172                         return NULL;
 173                 child = child->parent;
 174         }
 175
 176         return child;
 177 }
 178
 179 /**
 180  * kernfs_node_dentry - get a dentry for the given kernfs_node
 181  * @kn: kernfs_node for which a dentry is needed
 182  * @sb: the kernfs super_block
 183  */
 184 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 185                                   struct super_block *sb)
 186 {
 187         struct dentry *dentry;
 188         struct kernfs_node *knparent = NULL;
 189
 190         BUG_ON(sb->s_op != &kernfs_sops);
 191
 192         dentry = dget(sb->s_root);
 193
 194         /* Check if this is the root kernfs_node */
 195         if (!kn->parent)
 196                 return dentry;
 197
 198         knparent = find_next_ancestor(kn, NULL);
 199         if (WARN_ON(!knparent))
 200                 return ERR_PTR(-EINVAL);
 201
 202         do {
 203                 struct dentry *dtmp;
 204                 struct kernfs_node *kntmp;
 205
 206                 if (kn == knparent)
 207                         return dentry;
 208                 kntmp = find_next_ancestor(kn, knparent);
 209                 if (WARN_ON(!kntmp))
 210                         return ERR_PTR(-EINVAL);
 211                 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
 212                                                strlen(kntmp->name));
 213                 dput(dentry);
 214                 if (IS_ERR(dtmp))
 215                         return dtmp;
 216                 knparent = kntmp;
 217                 dentry = dtmp;
 218         } while (true);
 219 }
 220
 221 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 222 {
 223         struct kernfs_super_info *info = kernfs_info(sb);
 224         struct inode *inode;
 225         struct dentry *root;
 226
 227         info->sb = sb;
 228         /* Userspace would break if executables or devices appear on sysfs */
 229         sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
 230         sb->s_blocksize = PAGE_SIZE;
 231         sb->s_blocksize_bits = PAGE_SHIFT;
 232         sb->s_magic = magic;
 233         sb->s_op = &kernfs_sops;
 234         sb->s_xattr = kernfs_xattr_handlers;
 235         if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
 236                 sb->s_export_op = &kernfs_export_ops;
 237         sb->s_time_gran = 1;
 238
 239         /* get root inode, initialize and unlock it */
 240         mutex_lock(&kernfs_mutex);
 241         inode = kernfs_get_inode(sb, info->root->kn);
 242         mutex_unlock(&kernfs_mutex);
 243         if (!inode) {
 244                 pr_debug("kernfs: could not get root inode\n");
 245                 return -ENOMEM;
 246         }
 247
 248         /* instantiate and link root dentry */
 249         root = d_make_root(inode);
 250         if (!root) {
 251                 pr_debug("%s: could not get root dentry!\n", __func__);
 252                 return -ENOMEM;
 253         }
 254         sb->s_root = root;
 255         sb->s_d_op = &kernfs_dops;
 256         return 0;
 257 }
 258
 259 static int kernfs_test_super(struct super_block *sb, void *data)
 260 {
 261         struct kernfs_super_info *sb_info = kernfs_info(sb);
 262         struct kernfs_super_info *info = data;
 263
 264         return sb_info->root == info->root && sb_info->ns == info->ns;
 265 }
 266
 267 static int kernfs_set_super(struct super_block *sb, void *data)
 268 {
 269         int error;
 270         error = set_anon_super(sb, data);
 271         if (!error)
 272                 sb->s_fs_info = data;
 273         return error;
 274 }
 275
 276 /**
 277  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 278  * @sb: super_block of interest
 279  *
 280  * Return the namespace tag associated with kernfs super_block @sb.
 281  */
 282 const void *kernfs_super_ns(struct super_block *sb)
 283 {
 284         struct kernfs_super_info *info = kernfs_info(sb);
 285
 286         return info->ns;
 287 }
 288
 289 /**
 290  * kernfs_mount_ns - kernfs mount helper
 291  * @fs_type: file_system_type of the fs being mounted
 292  * @flags: mount flags specified for the mount
 293  * @root: kernfs_root of the hierarchy being mounted
 294  * @magic: file system specific magic number
 295  * @new_sb_created: tell the caller if we allocated a new superblock
 296  * @ns: optional namespace tag of the mount
 297  *
 298  * This is to be called from each kernfs user's file_system_type->mount()
 299  * implementation, which should pass through the specified @fs_type and
 300  * @flags, and specify the hierarchy and namespace tag to mount via @root
 301  * and @ns, respectively.
 302  *
 303  * The return value can be passed to the vfs layer verbatim.
 304  */
 305 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 306                                 struct kernfs_root *root, unsigned long magic,
 307                                 bool *new_sb_created, const void *ns)
 308 {
 309         struct super_block *sb;
 310         struct kernfs_super_info *info;
 311         int error;
 312
 313         info = kzalloc(sizeof(*info), GFP_KERNEL);
 314         if (!info)
 315                 return ERR_PTR(-ENOMEM);
 316
 317         info->root = root;
 318         info->ns = ns;
 319
 320         sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
 321                          &init_user_ns, info);
 322         if (IS_ERR(sb) || sb->s_fs_info != info)
 323                 kfree(info);
 324         if (IS_ERR(sb))
 325                 return ERR_CAST(sb);
 326
 327         if (new_sb_created)
 328                 *new_sb_created = !sb->s_root;
 329
 330         if (!sb->s_root) {
 331                 struct kernfs_super_info *info = kernfs_info(sb);
 332
 333                 error = kernfs_fill_super(sb, magic);
 334                 if (error) {
 335                         deactivate_locked_super(sb);
 336                         return ERR_PTR(error);
 337                 }
 338                 sb->s_flags |= SB_ACTIVE;
 339
 340                 mutex_lock(&kernfs_mutex);
 341                 list_add(&info->node, &root->supers);
 342                 mutex_unlock(&kernfs_mutex);
 343         }
 344
 345         return dget(sb->s_root);
 346 }
 347
 348 /**
 349  * kernfs_kill_sb - kill_sb for kernfs
 350  * @sb: super_block being killed
 351  *
 352  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 353  * user needs extra cleanup, it can implement its own kill_sb() and call
 354  * this function at the end.
 355  */
 356 void kernfs_kill_sb(struct super_block *sb)
 357 {
 358         struct kernfs_super_info *info = kernfs_info(sb);
 359
 360         mutex_lock(&kernfs_mutex);
 361         list_del(&info->node);
 362         mutex_unlock(&kernfs_mutex);
 363
 364         /*
 365          * Remove the superblock from fs_supers/s_instances
 366          * so we can't find it, before freeing kernfs_super_info.
 367          */
 368         kill_anon_super(sb);
 369         kfree(info);
 370 }
 371
 372 /**
 373  * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 374  * @kernfs_root: the kernfs_root in question
 375  * @ns: the namespace tag
 376  *
 377  * Pin the superblock so the superblock won't be destroyed in subsequent
 378  * operations.  This can be used to block ->kill_sb() which may be useful
 379  * for kernfs users which dynamically manage superblocks.
 380  *
 381  * Returns NULL if there's no superblock associated to this kernfs_root, or
 382  * -EINVAL if the superblock is being freed.
 383  */
 384 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
 385 {
 386         struct kernfs_super_info *info;
 387         struct super_block *sb = NULL;
 388
 389         mutex_lock(&kernfs_mutex);
 390         list_for_each_entry(info, &root->supers, node) {
 391                 if (info->ns == ns) {
 392                         sb = info->sb;
 393                         if (!atomic_inc_not_zero(&info->sb->s_active))
 394                                 sb = ERR_PTR(-EINVAL);
 395                         break;
 396                 }
 397         }
 398         mutex_unlock(&kernfs_mutex);
 399         return sb;
 400 }
 401
 402 void __init kernfs_init(void)
 403 {
 404
 405         /*
 406          * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
 407          * can access the slab lock free. This could introduce stale nodes,
 408          * please see how kernfs_find_and_get_node_by_ino filters out stale
 409          * nodes.
 410          */
 411         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 412                                               sizeof(struct kernfs_node),
 413                                               0,
 414                                               SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
 415                                               NULL);
 416 }