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 = NULL; 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_gen(&sb->s_uuid); 362 363 down_write(&root->kernfs_supers_rwsem); 364 list_add(&info->node, &info->root->supers); 365 up_write(&root->kernfs_supers_rwsem); 366 } 367 368 fc->root = dget(sb->s_root); 369 return 0; 370 } 371 372 void kernfs_free_fs_context(struct fs_context *fc) 373 { 374 /* Note that we don't deal with kfc->ns_tag here. */ 375 kfree(fc->s_fs_info); 376 fc->s_fs_info = NULL; 377 } 378 379 /** 380 * kernfs_kill_sb - kill_sb for kernfs 381 * @sb: super_block being killed 382 * 383 * This can be used directly for file_system_type->kill_sb(). If a kernfs 384 * user needs extra cleanup, it can implement its own kill_sb() and call 385 * this function at the end. 386 */ 387 void kernfs_kill_sb(struct super_block *sb) 388 { 389 struct kernfs_super_info *info = kernfs_info(sb); 390 struct kernfs_root *root = info->root; 391 392 down_write(&root->kernfs_supers_rwsem); 393 list_del(&info->node); 394 up_write(&root->kernfs_supers_rwsem); 395 396 /* 397 * Remove the superblock from fs_supers/s_instances 398 * so we can't find it, before freeing kernfs_super_info. 399 */ 400 kill_anon_super(sb); 401 kfree(info); 402 } 403 404 static void __init kernfs_mutex_init(void) 405 { 406 int count; 407 408 for (count = 0; count < NR_KERNFS_LOCKS; count++) 409 mutex_init(&kernfs_locks->open_file_mutex[count]); 410 } 411 412 static void __init kernfs_lock_init(void) 413 { 414 kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL); 415 WARN_ON(!kernfs_locks); 416 417 kernfs_mutex_init(); 418 } 419 420 void __init kernfs_init(void) 421 { 422 kernfs_node_cache = kmem_cache_create("kernfs_node_cache", 423 sizeof(struct kernfs_node), 424 0, SLAB_PANIC, NULL); 425 426 /* Creates slab cache for kernfs inode attributes */ 427 kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache", 428 sizeof(struct kernfs_iattrs), 429 0, SLAB_PANIC, NULL); 430 431 kernfs_lock_init(); 432 } 433